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The δ18О values of carbonates and silicates (Ol, Phl, Mt) of calcite carbonatites, phoscorites, ijolites, and turjaites of the Kovdor pluton have been studied for the first time to elucidate the role of processes of contamination, retrograde exchange, and high-temperature fractionation in a magmatic system. It is established that no processes of crustal contamination are registered in the isotopic characteristics of silicates and that the δ18О values of olivine, phlogopite, and magnetite are lower relative to the compositions typical of equilibrium with mantle peridotite. At the same time, the carbonates show a complementary enrichment in the 18О isotope relative to the composition of derivative mantle melts. The estimated closure temperature of the O isotopic composition of olivine and the cooling rates of rocks do not support a hypothesis on retrograde isotope exchange. A redistribution of O isotopes between silicate and carbonate constituents of melts in the magmatic system before the origination of the Kovdor pluton and its cooling is suggested. According to the O isotope data, the carbonate constituent at that moment could strongly be dominant (in 1.5–4.5 times) over the silicate one. [ABSTRACT FROM AUTHOR]

The early Cambrian Takab iron ore deposit is situated in the northern part of the Sanandaj-Sirjan zone, western Iran. It consists of banded, nodular and disseminated magnetite hosted in folded micaschists. Trace element and Fe and O isotopic experiments reveal various hydrothermal precipitation environments under reduced to slightly oxidizing conditions. Disseminated magnetite has high Ti (945–1940 ppm) positively correlated with Mg + Al + Si, and heavy Fe (+0.76 to +1.86‰) and O (+1.0 to +4.07‰) isotopic compositions that support a magmatic/high-T hydrothermal origin. Banded magnetite has low Ti (15−200 ppm), V (≤100 ppm), Si and Mg (mostly ≤300 ppm) and variable Al. The ∂56Fe values vary from −0.2‰ to +1.12‰ but most values also support a magmatic/high-T hydrothermal origin. However, variable ∂18O (−2.52 to +1.22‰) values provide evidence of re-equilibration with lower-T fluid at ~200–300 °C. Nodular magnetite shows high Mn (≤1%), and mostly negative ∂56Fe values (average, −0.3‰) indicative of precipitation from an isotopically light hydrothermal fluid. Re-equilibration with carbonated rocks/fluids likely results in a negative Ce anomaly and higher ∂18O (average, +6.30‰). The Takab iron ore deposit has, thus, experienced a complex hydrothermal history. [ABSTRACT FROM AUTHOR]

• The 1.89 Ga Frere granular Fe formation was deposited on a redox stratified shelf. • Trend in whole-rock and magnetite δ 56Fe data tracks changes in sea level. • The δ 56Fe of iron formations are a robust tracer for Paleoproterozoic ocean circulation. • (Ce/Ce*) PAAS holds a primary seawater signature in spite of terrestrial input. • Primary δ 18O values of minerals were overprinted by diagenesis. The Paleoproterozoic (ca.1.89 Ga) Frere Formation is a ca. 300-m-thick sedimentary succession of five stacked, Fe- and silicate-rich shallowing upwards cycles or parasequences that were deposited during marine transgression. Deposition in an oxygen-stratified water column is supported by the occurrence of magnetite-rich mudstones (anoxic and distal) beneath shallower, hematite- and chert-rich grainstones (suboxic and proximal). Minor (LREE/HREE) PAAS depletion and positive Ce anomalies in grainstones support this interpretation. Sequence stratigraphic relationships suggest that the Frere Formation accumulated on an unrimmed continental shelf associated with coastal upwelling of Fe. Large variations in oxygen isotope ratios (δ 18O) of magnetite (–0.6 ‰ ≤ δ 18O ≤ +2.8 ‰, n = 12) and quartz (+8.8 ‰ ≤ δ 18O ≤ +20.1 ‰, n = 11) from lithofacies composing the Frere Formation indicate that pristine δ 18O of minerals were overprinted by diagenesis. Highly variable δ 18O values calculated at 200 °C in equilibrium with quartz (–3.0 to + 8.3 ‰) and magnetite (+8.0 to + 12.7 ‰) suggest that fluids with heterogeneous δ 18O evolved through oxygen isotope exchange between minerals and porewater in accumulating sediment during diagenesis. The Fe isotope ratios (δ 56Fe) of bulk rock (–0.50 ‰ ≤ δ 56Fe ≤ +1.55 ‰, n = 20) and magnetite separates (–0.09 ‰ ≤ δ 56Fe ≤ +2.06 ‰, n = 11) from deeper anoxic and shallow suboxic paleoenvironments define a decreasing trend through stratigraphically stacked parasequences. The high δ 56Fe values of magnetite (+0.7 ‰ to + 2.06 ‰) characterizing the base of the Frere Formation is interpreted to reflect equilibrium isotopic fractionation between dissolved Fe2+ aq and freshly precipitated Fe-(oxyhydr)oxide (Fe(OH) 3) resulting from sluggish recharge of Fe2+ aq from deeper shelf environments. These high δ 56Fe values of magnetite from shallow paleoenvironments may also reflect microbial dissimilatory Fe reduction at the seafloor. As sea level rose, continued deepening and encroachment of a well-mixed water mass increased the oxidation of Fe2+ aq , which ultimately increased the influence of kinetic isotopic fractionation between Fe2+ aq and Fe(OH) 3. Such a process produced δ 56Fe compositions of magnetite that gradually decrease through the stratigraphic thickness of the Frere Formation (+2‰ to −0.1 ‰). Thus, Fe isotopic data framed in a sequence stratigraphic context provides greater insight into water column processes on Fe-rich, oxygen stratified Paleoproterozoic and Mesoproterozoic shelves, as well as geologically younger restricted basins with a redox gradient. [ABSTRACT FROM AUTHOR]

The relationship between plutonic and volcanic components of magmatic plumbing systems continues to be a question of intense debate. The Oki-Dōzen Islands, Sea of Japan, preserve outcrops of temporally associated plutonic, hypabyssal, and volcanic rocks. Post-intrusion uplift juxtaposed Miocene syenites in inferred faulted contact with volcanic trachytes that are cut by rhyolite hypabyssal dikes. This provides a window deep into the timing and origins of magma storage architecture and dynamics. Zircon is ubiquitous in all samples; our aim is to determine what its age and composition can reveal about the plutonic-volcanic connection. Here we show magma source characteristics are recorded in zircon Hf isotopes; source composition and assimilation of heterogeneous hydrothermally altered crust in zircon O isotopes; and extensive fractional crystallization in zircon trace elements. Combined with new U-Th-Pb SHRIMP zircon ages, 6.4–5.7 Ma, compositional data show pluton formation was by protracted amalgamation of discrete magma pulses. The rhyolite dike preserves an evolved fraction segregated from these discrete magmas. Synchronous with plutonism was a volcanic eruption of trachyte magma derived from the same source, which may have stalled at a relatively shallow depth prior to eruption. Stalling occurred at least above the amphibole stability zone because amphibole-compatible Sc and Ti were not depleted in the trachyte melt resulting in elevated values of these in volcanic compared to plutonic zircon. Identifying smaller episodic magma pulses in a larger magmatic complex places constraints on potential magma fluxes and eruptible volumes. High-flux, large volume, plume-related ocean island magmatic systems may have extensive vertically distributed multi-stage magmatic reservoirs and subduction-related systems transcrustal magma reservoirs. By contrast, Oki-Dōzen was a low-flux system with incremental pluton growth and small- to moderate-scale eruptions. [ABSTRACT FROM AUTHOR]

The early Cambrian Takab iron ore deposit is situated in the northern part of the Sanandaj-Sirjan zone, western Iran. It consists of banded, nodular and disseminated magnetite hosted in folded micaschists. Trace element and Fe and O isotopic experiments reveal various hydrothermal precipitation environments under reduced to slightly oxidizing conditions. Disseminated magnetite has high Ti (945–1940 ppm) positively correlated with Mg + Al + Si, and heavy Fe (+0.76 to +1.86‰) and O (+1.0 to +4.07‰) isotopic compositions that support a magmatic/high-T hydrothermal origin. Banded magnetite has low Ti (15−200 ppm), V (≤100 ppm), Si and Mg (mostly ≤300 ppm) and variable Al. The ∂56Fe values vary from −0.2‰ to +1.12‰ but most values also support a magmatic/high-T hydrothermal origin. However, variable ∂18O (−2.52 to +1.22‰) values provide evidence of re-equilibration with lower-T fluid at ~200–300 °C. Nodular magnetite shows high Mn (≤1%), and mostly negative ∂56Fe values (average, −0.3‰) indicative of precipitation from an isotopically light hydrothermal fluid. Re-equilibration with carbonated rocks/fluids likely results in a negative Ce anomaly and higher ∂18O (average, +6.30‰). The Takab iron ore deposit has, thus, experienced a complex hydrothermal history.

Key message: Isotope variation (δ18O) in wood suggests new insights on growth rhythms in trees growing in tropical forest with extremely high precipitation, without seasonal droughts or flooding. It is well known that growth-limiting factors such as seasonal droughts can induce periodicities in woody tissue formation of tropical trees. In regions without seasonal droughts or flooding but sufficient water for photosynthesis (ever-wet tropical forests), rhythmic growth has been previously reported; however, triggering factors remain little explored. Our objective was to establish tree-ring frequency and probable growing season by analysis of the intra-annual variability of isotopic ratios in cellulose (δ18Ocellulose and δ13Ccellulose) and relationships with environmental variables in two tree species (Humiriastrum procerum and Virola dixonii) growing in an ever-wet tropical forest (Choco region of Colombia, precipitation 7200 mm year−1, mean annual temperature 25.9 °C), located close to the Pacific Ocean at ca 3° 57′ 12.54″ N–76° 59′ 27.96″ W. Here, we report annual rhythmic growth evidenced by radiocarbon analysis, leaf phenology, dendrometer records, and stable-isotope variation in cellulose. All evidence points to the probable growing season occurring during the least rainy months for both species. While intra-annual δ18Ocellulose values follow a rhythmic variation, δ13Ccellulose variations show a less clear pattern, probably due to deciduity and remobilization of non-structural carbon stored in previous growing stages. Furthermore, δ18Ocellulose covary with relative humidity, vapor pressure deficit, short-wave solar radiation, and temperature during the least rainy months. In contrast, δ13Ccellulose values were not significantly correlated with environmental variables. Our results show that stable-isotope variations in tree rings, even under ever-wet conditions, are valuable for understanding drivers of tropical tree growth in such conditions. [ABSTRACT FROM AUTHOR]

The world-class Shimensi tungsten (W)-polymetallic deposit is located in Jiangnan Orogen, with an estimated reserve of 742.5 kt WO3 @ 0.195% W, 403.6 kt Cu and 28 kt Mo. In this paper, the trace elements and Pb-O isotopes of scheelite (the main ore mineral) are presented to study the ore-forming material source and ore-forming fluid evolution. The results show that the REE distribution in scheelite is mainly controlled by the substitution mechanism of 3Ca2+ = 2REE3+ + □Ca (where □Ca is the Ca-site vacancy). Oxygen isotope data indicate that the scheelite mineralization occurred under high-temperature oxygen isotope equilibrium conditions, and that the ore-forming fluid has a magmatic–hydrothermal origin. The variation in scheelite Eu anomalies and the wide range of scheelite Y/Ho ratio indicate that the ore-forming fluid evolves from reducing to oxidizing, and the early-stage and late-stage ore-forming fluid may have been relatively rich in F− and HCO3−, respectively. The significant Mo decrease in scheelite from the early to late stage that are opposite to the influence of fO2 variation may have resulted from the crystallization of molybdenite and Mo-rich scheelite. Lead isotopes of the ore minerals of scheelite, wolframite, molybdenite and chalcopyrite can be divided into three groups, similar to these of feldspars in different granites. Both the Mesozoic porphyritic and fine-grained biotite granites have Pb isotope ratios similar to the ores, which suggests that the former two are the main ore material source.

We present >500 zircon δ18O and Lu-Hf isotope analyses on previously dated zircons to explore the interplay between spatial and temporal magmatic signals in Zealandia Cordillera. Our data cover ~8500 km² of middle and lower crust in the Median Batholith (Fiordland segment of Zealandia Cordillera) where Mesozoic arc magmatism along the paleo-Pacific margin of Gondwana was focused along an ~100 km wide, arc-parallel zone. Our data reveal three spatially distinct isotope domains that we term the eastern, central, and western isotope domains. These domains parallel the Mesozoic arc-axis, and their boundaries are defined by major crustal-scale faults that were reactivated as ductile shear zones during the Early Cretaceous. The western isotope domain has homogenous, mantle-like δ18O (Zrn) values of 5.8 ± 0.3‰ (2 St.dev.) and initial εHf (Zrn) values of +4.2 ± 1.0 (2 St.dev.). The eastern isotope domain is defined by isotopically low and homogenous δ18O (Zrn) values of 3.9 ± 0.2‰ and initial εHf values of +7.8 ± 0.6. The central isotope domain is characterized by transitional isotope values that display a strong E-W gradient with δ18O (Zrn) values rising from 4.6 to 5.9‰ and initial εHf values decreasing from +5.5 to +3.7. We find that the isotope architecture of the Median Batholith was in place before the initiation of Mesozoic arc magmatism and pre-dates Early Cretaceous contractional deformation and transpression. Our data show that Mesozoic pluton chemistry was controlled in part by long-lived, spatially distinct isotope domains that extend from the crust through to the upper mantle. Isotope differences between these domains are the result of the crustal architecture (an underthrusted low-δ18O source terrane) and a transient event beginning at ca. 129 Ma that primarily involved a depleted-mantle component contaminated by recycled trench sediments (10-20%). When data showing the temporal and spatial patterns of magmatism are integrated, we observe a pattern of decreasing crustal recycling of the low-δ18O source over time, which ultimately culminated in a mantlecontrolled flare-up. Our data demonstrate that spatial and temporal signals are intimately linked, and when evaluated together they provide important insights into the crustal architecture and the role of both stable and transient arc magmatic trends in Cordilleran batholiths. [ABSTRACT FROM AUTHOR]

Volcanism in the Azores is generally accepted to result from the decompression melting in the upper mantle associated with the Azorean plume. Basalts on the island of São Miguel have been previously recognised as having δ18O values lower than MORB with different authors ascribing this low-δ18O signature to either a component within the plume itself or as the result of assimilation of crustal materials at shallow level. Here we assess these contrasting models by using a suite of samples that are both geographically and temporally spread. We find that while low-δ18O mafic magmas (reaching 4.98 ‰) do occur on São Miguel, they are spatially restricted to the Picos fissure system, between the central volcanoes of Sete Cidades and Fogo. Basalts of similar age from outside this restricted region return δ18O values that are similar to MORB. This spatial constraint argues that the source of the observed low-δ18O signature is within the crust rather than a component of the plume. Previous studies on mafic to intermediate rocks of the Picos fissure system have identified the assimilation of broadly syenitic lithologies, which were found as co-erupted lithic clasts at the Fogo volcano and may have δ18O values as low as 2.6 ‰. However, trace element geochemistry indicates that these lithologies have not been assimilated within our low-δ18O samples, a more likely assimilant is altered oceanic crust or mafic lavas within the island edifice. • Multi-mineral O isotopic study of basalts from the island of São Miguel • Some basalts have low-δ18O while the majority are MORB-like. • Low-δ18O magmas are primarily found within the Picos fissure system. • Similar aged basalts at Sete Cidades volcano c. 10 km W have normal-δ18O. • We suggest crustal assimilation causes the low-δ18O values of Picos basalts. [ABSTRACT FROM AUTHOR]

Abstract We present the first zircon‐based U‐Pb geochronology, trace element concentrations, and O and Hf isotope compositions for Snæfell, an off‐rift volcano in eastern Iceland. These data provide constraints on the longevity and petrogenetic conditions of the Snæfell magmatic system. U‐Pb zircon ages range from 545 ± 59 to 266 ± 16 ka (2SE), but differences between grain core and mantle ages within each sample reveal zircon residence times of 100–200 kyr—far longer than observed at other Neovolcanic systems in Iceland. Zircon δ18O is restricted to ∼3.5–4‰, and zircon εHf ranges ∼+13 to ∼+17, which is substantially more radiogenic than Snæfell basalts. This combined O and Hf isotopic perspective suggests rhyolite petrogenesis at Snæfell can be attributed to fractional crystallization of mantle‐derived basaltic magmas with limited influence of pre‐existing crustal material. Trace element evidence further characterizes the magmatic source material: Sc/Yb

We present the first zircon‐based U‐Pb geochronology, trace element concentrations, and O and Hf isotope compositions for Snæfell, an off‐rift volcano in eastern Iceland. These data provide constraints on the longevity and petrogenetic conditions of the Snæfell magmatic system. U‐Pb zircon ages range from 545 ± 59 to 266 ± 16 ka (2SE), but differences between grain core and mantle ages within each sample reveal zircon residence times of 100–200 kyr—far longer than observed at other Neovolcanic systems in Iceland. Zircon δ18O is restricted to ∼3.5–4‰, and zircon εHf ranges ∼+13 to ∼+17, which is substantially more radiogenic than Snæfell basalts. This combined O and Hf isotopic perspective suggests rhyolite petrogenesis at Snæfell can be attributed to fractional crystallization of mantle‐derived basaltic magmas with limited influence of pre‐existing crustal material. Trace element evidence further characterizes the magmatic source material: Sc/Yb <∼0.01 suggests an amphibole‐free petrogenetic environment, and Ti concentrations in zircon <5 ppm suggest a cool, near‐solidus, crystallization environment for the majority of the zircon's pre‐eruptive history, with elevated Ti in zircon surfaces suggesting a late thermal perturbation, perhaps a mafic input that remobilized (to the point of eruption triggering) near‐solidus magmas. These zircon‐based conclusions are broadly consistent with previous interpretations of rhyolite petrogenesis conditions at Snæfell but provide a multi‐faceted perspective with more detailed resolution of source materials, magma generating processes, system longevity, and pre‐eruptive conditions. Key Points: First zircon‐based constraints on longevity and petrogenetic processes associated with production of rhyolites at Snæfell volcano, IcelandZircon crystallization and residence occurs on timescales up to ∼200 kyr at Snæfell—much longer than at other studied Neovolcanic centersHf and O isotopes in zircon reveal petrogenesis dominated by fractional crystallization of mantle melts with minor crustal assimilation [ABSTRACT FROM AUTHOR]

A new natural zircon reference material SA01 is introduced for U‐Pb geochronology as well as O and Hf isotope geochemistry by microbeam techniques. The zircon megacryst is homogeneous with respect to U‐Pb, O and Hf isotopes based on a large number of measurements by laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS). Chemical abrasion isotope dilution thermal ionisation mass spectrometry (CA‐ID‐TIMS) U‐Pb isotopic analyses produced a mean 206Pb/238U age of 535.08 ± 0.32 Ma (2s, n = 10). Results of SIMS and LA‐ICP‐MS analyses on individual shards are consistent with the TIMS ages within uncertainty. The δ18O value determined by laser fluorination is 6.16 ± 0.26‰ (2s, n = 14), and the mean 176Hf/177Hf ratio determined by solution MC‐ICP‐MS is 0.282293 ± 0.000007 (2s, n = 30), which are in good agreement with the statistical mean of microbeam analyses. The megacryst is characterised by significant localised variations in Th/U ratio (0.328–4.269) and Li isotopic ratio (−5.5 to +7.9‰); the latter makes it unsuitable as a lithium isotope reference material. [ABSTRACT FROM AUTHOR]

This study investigates the prospectivity for porphyry Cu mineralisation of the early Paleozoic Loch Lilly-Kars Belt, which follows the southern margin of the Paleoproterozoic Broken Hill (Willyama) Inlier in western New South Wales, Australia. The belt is thought to have resulted from the 515–510 Ma collision of a volcanic passive margin and an intra-oceanic island arc above a west-dipping subduction zone, with subsequent post-collisional magmatism. To identify fertility signals of selected magmatic intrusive rocks, we combined whole-rock analyses with in-situ zircon trace-element and isotopic measurements. Data reveal that both Cambrian (ca 496 Ma) and Devonian (ca 393 Ma) intrusive suites are present in the Loch Lilly-Kars Belt. Cambrian dioritic rocks are largely non-fertile for porphyry Cu mineralisation, whereas Devonian monzodiorites and monzonitic porphyries carry strong fertility signals that include high whole-rock Sr/Y (>35) and V/Sc (>10) values, associated with the occurrence of equant, stubby zircons showing relatively constant Eu/Eu* values without any significant Eu anomalies. Although only few samples were analysed and more intensive exploration is required, the results of this study indicate significant potential for porphyry Cu mineralisation in this poorly known belt. [ABSTRACT FROM AUTHOR]

We carried out a coordinated mineralogical and isotopic study of a Wark-Lovering (WL) rim on a Ca,Al-rich inclusion (CAI) from the reduced CV3 chondrite Vigarano. The outermost edge of the CAI mantle is mineralogically and texturally distinct compared to the underlying mantle that is composed of coarse, zoned melilite (Åk ∼10-60) grains. The mantle edge contains fine-grained gehlenite with hibonite and rare grossite that likely formed by rapid crystallization from a melt enriched in Ca and Al. These gehlenite and hibonite layers are surrounded by successive layers of spinel, zoned melilite (Åk ∼0-10), zoned diopside that grades outwards from Al,Ti-rich to Al,Ti-poor, and forsteritic olivine intergrown with diopside. These layered textures are indicative of sequential condensation of spinel, melilite, diopside, and forsterite onto hibonite. Anorthite occurs as a discontinuous layer that corrodes adjacent melilite and Al-diopside, and appears to have replaced them, probably even later than the forsterite layer formation. Based on these observations, we conclude that the WL rim formation was initiated by flash melting and extensive evaporation of the original inclusion edge, followed by subsequent gas-solid reactions under highly dynamic conditions. All the WL rim minerals are 16O-rich (Δ17O = ∼−23‰), indicating their formation in an 16O-rich nebular reservoir. Our Al-Mg measurements of hibonite, spinel, and diopside from the WL rim, as well as spinel and Al,Ti-diopside in the core, define a single, well-correlated isochron with an inferred initial 26Al/27Al ratio of (4.94 ± 0.12) × 10−5. This indicates that the WL rim formed shortly after the host CAI. In contrast, the lack of 26Mg excesses in the WL rim anorthite suggest its later formation or later isotopic disturbance in the solar nebula, after 26Al had decayed. [ABSTRACT FROM AUTHOR]

Current understanding of the fate of subducted material (and related fluids) in the deep Earth can be improved by combining major and trace element geochemistry with stable isotopic compositions of mantle rocks or minerals. Limited isotopic fractionation during high temperature processes means that significant deviations from mantle-like isotope ratios in mantle rocks probably result from recycling of surficial material. To determine the effects and origins of mantle metasomatic fluids/melts, new δ15N and δ18O data have been collected for thirteen mantle xenoliths – harzburgites, wehrlites, lherzolites, and MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) rocks – from the Bultfontein kimberlite (Kimberley, South Africa), which show varying degrees of metasomatism. The δ18O values of olivine and orthopyroxene in phlogopite-free harzburgites match the mantle composition (δ18O olivine = +5.2 ± 0.3‰; δ18O orthopyroxene = +5.7 ± 0.3‰; 2 s.d.), consistent with previous inferences that harzburgites were formed by interaction with ancient silica-rich melts unrelated to subduction processes. Wehrlite samples display mineral compositional characteristics (e.g., low La/Zr in clinopyroxene) resembling those of other products of kimberlite melt metasomatism, such as PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks. The inferred interaction with kimberlite melts may be responsible for O isotopic disequilibrium between clinopyroxene and olivine (Δ18O = +0.2‰) in the wehrlites of this study. In contrast with broadly mantle-like δ18O values, the δ15N value of phlogopite in a wehrlite sample (+5.9‰) differs from the mantle composition (δ15N = −5 ± 2‰). This unusual N isotopic composition in kimberlite-related mantle products might indicate that a recycled crustal component occurred in the source of the Kimberley kimberlites, or was assimilated during interaction with the lithospheric mantle. Similar major and trace element characteristics in clinopyroxene from phlogopite-lherzolite and MARID samples suggest metasomatism by fluids of similar composition. Lherzolite and MARID clinopyroxene δ18O values (as low as +4.4‰) extend below those reported in mantle peridotites (i.e. δ18O clinopyroxene = +5.6 ± 0.3‰; 2 s.d.), and strong negative correlations are found between mineral δ18O values and major element compositions (e.g., Na 2 O contents in clinopyroxene). Furthermore, phlogopite δ15N values (+4 to +7‰) in the studied lherzolite and MARID samples are higher than mantle values. Combined, the low δ18O-high δ15N isotopic signatures of MARID and lherzolite samples suggest progressive mantle metasomatism by a melt containing a recycled oceanic crust (eclogitic) component. This study demonstrates that progressive enrichment of the subcontinental lithospheric mantle may be inextricably linked to plate tectonics via recycling of subducted crustal material into the deep mantle. [ABSTRACT FROM AUTHOR]

High-K granitoids are among the most abundant rock types in many Archean cratons. Late Neoarchean monzogranitic to syenogranitic gneisses with high-K affinities are widely distributed in the Anshan, Suizhong, Qinhuangdao, and Aolaishan areas on the northeastern margin of the North China Craton (NCC). In this contribution, we present an integrated study of zircon U–Pb–Hf–O isotopic compositions and whole-rock elemental compositions of amphibolites and trondhjemitic and monzo–syenogranitic gneisses of the Jinzhou area in the metamorphic basement of eastern Hebei–western Liaoning, with the aim of constraining their petrogenesis and geodynamic setting. Emplacement ages of the amphibolites and trondhjemitic–monzogranitic gneisses are 2543 ± 27, 2532 ± 19, and 2513 ± 7 Ma, respectively. The amphibolites are tholeiitic in composition with SiO 2 contents of 49.7–50.8 wt%, variable degrees of light rare-earth-element (LREE) enrichment and high-field-strength element (HFSE) depletion, and high zircon εHf(t) values of +2.6 to +6.3, suggesting a depleted lithospheric mantle origin. The major- and trace-element compositions of the trondhjemitic gneisses are similar to those of the low-pressure tonalite–trondhjemite–granodiorite (TTG) suite. The zircon Hf (εHf(t) = +1.6 to +3.9) and O (δ18O = +3.76‰ to +5.73‰) isotopic compositions of the trondhjemitic gneisses indicate a juvenile basaltic source at the base of a thickened magmatic arc. The monzogranitic gneisses differ from their TTG counterparts in that they have lower SiO 2 and higher MgO, K 2 O, and incompatible-element (especially Ba, Th, Sr, P, and LREE) contents. They also have slightly evolved zircon εHf(t) values (+0.6 to +3.8) and higher δ18O values (+4.69‰ to +6.13‰). These features suggest that the monzogranitic gneisses represent sanukitoid-type rocks, with a mantle source modified by crust-derived melts. The weakly deformed syenogranitic gneisses are characterized by high SiO 2 and K 2 O, and very low MgO, Cr, and Ni contents, suggesting that they were formed by partial melting of local TTG rocks. Our results, together with those of previous investigations, suggest that the 2554–2513 Ma low- to high-K magmatism in the Jinzhou area most likely originated in an arc–back-arc tectonic setting on the northern margin of the NCC. The large volumes of high-K granitoids in eastern Hebei–western Liaoning are related to extensive mantle–crust interactions and crustal reworking in such a setting. Unlabelled Image • 2543 Ma amphibolites originated from a mantle wedge slightly metasomatized by slab-derived fluids. • 2532 Ma Trondhjemitic gneisses originated from a juvenile basaltic source at the base of a thickened magmatic arc. • 2513 Ma monzogranitic gneisses originated from an enriched mantle metasomatized by sediment-derived melts. • Ca. 2.55–2.49 Ga low- to high-K magmatism in the Jinzhou area were most likely formed in an arc-back-arc tectonic setting. [ABSTRACT FROM AUTHOR]

The Chamuhan Granite is located in the eastern part of the Central Asian Orogen where it crops out as an elongated, NE-trending composite monzogranite. The pluton consists of two phases with a fine – grained monzogranite (G2) at depth in sharp contact with a medium – grained monzogranite (G1) above. The medium-grained monzogranite can be subdivided into G1a and G1b based on the degree of metasomatism affecting it, with the G1b being more altered. Tungsten–molybdenum mineralisation is hosted by quartz (−fluorite) veins or forms disseminated sulfides in G1a, indicating a genetic association between the monzogranite and ore. Magmatic zircons from G1a yield a weighted mean age of 144 ± 2 Ma, and hydrothermal zircons from G1a yield a weighted mean age of 143 ± 1 Ma, indicating that the hydrothermal zircons are very close in age to the medium-grained monzogranite. Monazite grains yield U – Pb isotope ages of 138 ± 3 Ma for G1a, 137 ± 1 Ma for G1b, and 139 ± 2 Ma for the fine-grained monzogranite (G2) phase. These dates are the same within analytical error, and are coeval with the molybdenite Re – Os weighted mean age of 140 ± 2 Ma, indicating that the monazite and molybdenite were deposited during hydrothermal alteration. The Chamuhan Granite is geochemically a metaluminous to slightly peraluminous high – K calc-alkaline granite, and is especially characterised by its REE tetrad pattern and a huge Eu depletion that are accompanied by a non – "Charge-and Radius-Controlled" (CHARAC) trace element behaviour. This and the O-isotopic data from the granite phases are indicative of a highly differentiated magma that interacted strongly with a co–existing fluid emanating from the magma during the late stage of its crystallisation. The interaction between the magma and related hydrothermal fluid resulted in the enrichment of W–Mo(–Nb–Ta–Th–U–Hf–Rb–Y). All the studied granitic rocks have homogeneous initial isotope values with positive εNd(t) values of 0.1–3, and T DM2 dates between 924 and 691 Ma. This is consistent with granites derived from a pre-existing juvenile crust derived from a depleted mantle during the Neoproterozoic. The molybdenite in the Chamuhan W – Mo deposit has a narrow δ34S VCDT range of 0.1–1.6‰ characteristic of a magmatic origin, and the Pb isotopic compositions with 206Pb/204Pb ratios between 18.298 and 18.882, 207Pb/204Pb ratios between 15.494 and 15.538 and 208Pb/204Pb ratios between 38.046 and 38.206, are similar to the calculated initial Pb isotopic ratios of the Chamuhan Granite. We thus suggest that there is an intimate relationship between the Chamuhan Granite and mineralisation, and that the mineralising process is related to a post-collisional extensional event following the formation of an over-thickened continental crust and during closure of the Mongol-Okhotsk and Paleo-Pacific oceanic plates. • The Chamuhan Granite is a highly fractionated granite with REE tetrad effect. • The interaction between magma and fluid resulted in the enrichment of W and Mo. • The Nd – Hf isotope data indicate the granite was sourced from a juvenile crust. [ABSTRACT FROM AUTHOR]

Primitive (high-Cr, Ni), high-Mg andesites (HMA) at convergent plate margins are considered primary, mantle-derived melts, and are not part of the classical tholeiitic or so-called calc-alkaline igneous differentiation series. Their genesis is often considered the product of melting of lower crustal sequences or the subducting slab, though their genesis is far from being understood. Alternatively, they may represent differentiated rocks from boninitic precursors. Here we present isotope and geochemical data for a rare suite of high-Mg andesites that were preserved as decimetre-sized boulders in molasse-type sedimentary rocks of the Oligocene-Miocene Gonfolite Lombarda (Como Formation; Italy), as part of the post-orogenic alpine sedimentary succession. The HMA have moderate to high MgO (1.9–6.4 wt%), high Al 2 O 3 (16.3–18.8 wt%), along with high Cr (30–306 ppm) and Ni (13–92 ppm), and moderate Yb (1.2–2.5 ppm) and Y (12–26 ppm) abundances, matching those of primitive HMA. These HMA are LILE- and LREE-enriched and most samples have negligible negative Eu anomalies. Primitive mantle-normalized compositions show depletions in Nb, Ta, P, Ti and Y. Most samples have unradiogenic Nd (εNd: −6.2 to −7.8) and radiogenic 87Sr/86Sr isotope compositions (0.708 to 0.710), elevated δ18O values (+7.6 ‰ to +9.5 ‰) and radiogenic Pb isotope compositions, with a pronounced variation in 207Pb/204Pb and 208Pb/204Pb at rather constant 206Pb/204Pb. Initial εHf isotope values range from −0.4 to −2.3, some of which deviate from the Hf Nd crust-mantle isotope array. One sample is unevolved (87Sr/86Sr: 0.708; εNd: −3.3, εHf: +1.8, δ18O: 8.5 ‰) whereas another sample is strongly evolved (87Sr/86Sr: 0.720; εNd: −9.3, εHf: −5.8, δ18O: 9.3 ‰); the latter probably representing a crustal melt. The remaining samples have intermediate compositions (87Sr/86Sr: 0.709–0.713; εNd: −6.2 to −8.5, εHf: −0.4 to −4.3, δ18O: 7.6–10.6 ‰) that either result from limited AFC processes or represent source heterogeneities. The sum of these features cannot be the result of a simple slab or mantle wedge melting process. To account for the observed geochemical signatures of the high-Mg andesites, a three-stage model is suggested that invokes melting of slab-derived sediment diapirs, followed by melt-rock-reaction in the mantle wedge and subsequent crustal assimilation-fractional crystallization (AFC). The diapirs that rise into the mantle wedge are composed of subducted wet, Alpine sediments. Hydrous dacitic (siliceous) partial melts derived from them react with the ambient mantle wedge and cause the formation of boninitic melts with elevated MgO, Ni and Cr; the archetype features of primitive high-Mg andesites. Subsequent interaction with the overlying arc crust is evidenced by crustal xenoliths, which may account for some isotope features of the rock suite. We consider this scenario most plausible because it is relatively simple, and explain most if not all geochemical features, based on modelling and experimental evidence. • High-Mg andesites are an important component in active collision zones. • Radiogenic and stable isotope data reveal a role for a sediment diapir. • Geochemical data imply limited involvement of melts and fluids but some AFC. [ABSTRACT FROM AUTHOR]

Fluid flow along crustal plate boundary-scale serpentinite shear zones may provide insights into element transfer at one of Earth's most important but least accessible lithological boundaries: the slab-mantle wedge plate interface. For ∼55 km in the Southern Alps of New Zealand, a 10 to 100s m wide block-in-matrix serpentinite mélange shear zone – the Livingstone Fault – separates the harzburgitic base of the Dun Mountain Ophiolite Belt from arc-derived metasedimentary and minor metabasaltic rocks. Transects across the shear zone reveal systematic chemical and isotopic changes over several hundred meters, from harzburgite (<1 wt% H 2 O, 87Sr/86Sr = 0.7031–0.7045, δ 18 O = ∼ + 5.3 ‰) to massive and then foliated mélange serpentinite (up to 13.7 wt% H 2 O, 87Sr/86Sr = 0.7084, δ 18 O = + 7.8 ‰). These changes require hydration of peridotite by fluids derived from, or that interacted with, the metasediment-dominated wallrock (87Sr/86Sr = 0.7073–0.7093, δ 18 O ≥ + 9.6 ‰). Tremolite-veined serpentinite and metasomatized greyschist blocks (87Sr/86Sr = 0.7063–0.7071; δ 18 O = + 8.7) within the serpentinite mélange also require ultramafic- and metasediment–derived element mixing. Halogens (Br and I) were enriched in serpentinized ultramafic rocks. By analogy with the crustal Livingstone Fault, the slab-mantle plate interface may have a strongly anisotropic basal serpentinite mélange shear zone that grades into a thicker zone of massive and variably serpentinized peridotite with a progressively decreasing "slab" element and isotope signature. Permeability in subduction-related shear zones is predicted to be mainly parallel to the slab but channelized fluid mobility across the Livingstone Fault was aided by transient fracturing. Oxidation of harzburgite during serpentinization appears to have been accompanied by mobilization of Si, Ca, Mg, Sr, Br, I, Ga, Mo, Ta, W, V and Y. As many of these elements occur in the sources of arc magmas, serpentinization may play an important role in mobilizing them. The Livingstone Fault lithologies and their element and isotope transfer records means this shear zone may represent a field-accessible analogue for the shallow slab-mantle plate interface. • Crustal plate-boundary serpentinite shear zone analogue for slab-mantle interface. • Harzburgite is separated from metasediments by a serpentinite shear zone melange. • Transects across fault show systematic element and Sr, O isotope redistribution. [ABSTRACT FROM AUTHOR]

Geochemical and isotopic (carbon and oxygen) compositions of Paleoproterozoic carbonate rocks of the Bemil and Lagoa Seca quarries – Gandarela Formation – Quadrilátero Ferrífero – Brazil, were determined. Few samples (12 out of 69) show relatively higher REE contents that are associated with strongly positive correlation with the immobile elements including Al, Ni, Th, Cr, Sc and Y coupled with a negative correlation between ΣREE and CaO, suggesting that the observed variations in the ΣREE values in these samples were controlled mainly by the input of terrigenous materials. The Eu and Ce anomalies (normalized by the PAAS) of the analyzed samples vary from 1.1 to 2.13 and 0.79 to 1.03, respectively for Bemil quarry samples and 0.74 to 2.7 and 0.32 to 0.99, respectively, for samples from the Lagoa Seca quarry. In the present study, Al 2 O 3 content do not show significant correlation with Eu/Eu* (correlation coefficient r = 0.23). Hence the positive europium anomalies in these samples seem to have not been influenced by the amount of terrigenous materials in them. Y/Ho ratios range from 27 to 93 for Bemil quarry samples and 24 to 132 for samples from the Lagoa Seca quarry. Some samples have Y/Ho ratio more or less similar to chondritic values (∼28). High REE contents, non-seawater-like REE patterns, the large abundance of certain trace elements such as Sc, Th and Hf, high (La/Yb) sn ratios and low Y/Ho ratios collectively suggest that few samples were mainly influenced by the incorporation of terrigenous materials. Most of the studied samples (38 out of 69) of the Bemil and Lagoa Seca quarries have δ18O (VPDB) values lower than −12‰, corresponding to carbonates that underwent changes by post-depositional processes. The δ13C values (0.69‰ to −4.46‰ and 0.07‰ to −6.18‰) of the majority of the analyzed samples, both of the Bemil quarry and the Lagoa Seca quarry, are similar to those marine carbonates of the same age (∼2.42 Ga). Samples that have δ13C values around −4‰ are likely to result from decarbonation reactions. Two samples (LS11 and LS12) may record glacial periods. • The samples analyzed reveal possible contamination by terrigenous materials. • Most of the samples exhibit seawater-like REE patterns. • Most of the samples from Bemil and Lagoa Seca quarries present δ13C ranging from −2.95 to +0.67, and can be correlated with carbonates of the same age in other parts of the world. [ABSTRACT FROM AUTHOR]

Abstract The late Neoproterozoic São Rafael pluton, located in the Seridó Belt of the Borborema geologic province, northeastern Brazil, is an unfoliated, metaluminous, epidote-bearing, high-K calc-alkalic granitoid. Three facies are present in its northern lobe: (i) a dominant massive granite to quartz monzonite porphyritic facies containing microcline phenocrysts, (ii) subordinate fine-grained facies, similar to the porphyritic facies except lacking amphibole, that crop out as inselbergs ("Serras"), and (iii) rare pillows of microgranular mafic enclaves (MMEs) that are present within the porphyritic facies. Chemical analyses include 19 bulk-rock data, and 33 microprobe data of epidote and amphibole. Beginning with bulk chemistry and postulated mineral compositions, an iterative procedure of solving matrices characterizes a rock sample. Derived information includes: (i) identifying what minerals are present, (ii) their relative abundances, and (iii) their chemical compositions, even for minerals (such as biotite or amphibole) with complexly variable compositions. Calculated mineral compositions are compatible with microprobe data. The matrix solutions further indicate alternative mineral assemblages, and the compositions of "phantom" minerals that could have existed in the magma source, although absent in the pluton. They establish that olivine, but not clinopyroxene, was a possible phantom mineral and that MMEs are of unrelated magmatic origin. According to matrix analysis, amphibole in an outer zone of the porphyritic facies is solely of neoformed origin, whereas amphibole in an inner zone of the porphyritic facies is of mixed origin—partly neoformed and partly residual (i.e., xenocrystic) "patchy" amphibole derived from MMEs. A qualified geothermometer provides T solidus = 730 ± 6 °C for the outer subfacies, and a qualified geobarometer provides P = 0.78 ± 0.06 kbar. Amphibole in MMEs crystallized at depth, at P~3.3 kbar. Corroded epidote attests to the pressure-sensitive instability of that mineral during rapid ascent decompression. Cathodoluminescence reveals complexly structured zircons with magmatic overgrowths and inherited cores. 207Pb/206Pb ages of inherited components cluster at ~2.0 Ga and ~2.4 Ga, these ages being prominent in the local basement. Oscillatory-zoned magmatic components yield a concordia upper intercept age of 580 ± 9 Ma, interpreted as the age of igneous crystallization. Values of δ18O in zircon are only slightly higher than δ18O in mantle-like zircon. At 0.58 Ga, ε Hf in magmatic zircon was notably unradiogenic (−22 to −26), indicating a magma source in old continental crust as adduced by ages of inherited zircon. A U-Pb titanite date is around 0.55 Ga. For the Rb-Sr and Sm-Nd whole-rock systems, isotopic inheritance from the magma protolith is so extreme and variable that isochrons are actually "scatterchrons" that provide no useable age information. Rb-Sr cooling ages of biotite are 498 ± 1 Ma. Most Sm-Nd depleted mantle ages lie in the range of 2.6 ± 0.13 Ga. São Rafael magma was "unregenerate," not isotopically homogenized when emplaced. Highlights • An unusual epidote-bearing granitoid in the Borborema Province, NE Brazil • Chemical data, and U-Pb, Lu-Hf, Rb-Sr, Sm-Nd, and O isotope data • Matrix calculations of constituent minerals, their abundances and compositions • Matrix analysis of "phantom" mineral assemblages that subsequently had disappeared • A profound degree of isotopic inheritance pertaining to radiogenic isotope systems [ABSTRACT FROM AUTHOR]

Abstract Along the proto-Pacific margin of Gondwana, from Venezuela to northeastern Patagonia, the Early–Middle Ordovician Famatinian orogeny was the first orogenic event following assembly of the supercontinent. Previous isotope studies of the igneous and (meta-)sedimentary rocks of southwestern Gondwana yield ambiguous implications for the role of juvenile mantle addition during the early crustal growth at the supercontinental margin. To interpret the geological and tectonic evolution of the orogen and the magma sources in different episodes we look at evidence from a large area of southern South America, including the 700 × 600 km type sector of the orogen in the Sierras Pampeanas (27°–33°S), the Precordillera, and northeastern Patagonia. Previous geological, geochemical and geochronological results are reviewed together with new U—Pb SHRIMP crystallization ages, 177Hf/176Hf and 18O/16O data for dated zircon, and whole-rock Sr and Nd isotope compositions. Four geological domains are recognized in the Sierras Pampeanas (Western, Central, Eastern and Foreland Famatinian domains). Magmatism is mostly restricted to the interval 463 ± 4 to 486 ± 7 Ma, with the most intense period of emplacement between 468 and 472 Ma constituting a magmatic flare-up. Granitoid emplacement in both northeastern Patagonia and the Cordon de Lila (Puna Altiplano, Chile) was effectively synchronous with that in the Sierras Pampeanas, defining a continuous belt. Combined geochemical and isotopic data (whole-rock Sr, Nd; Hf, O in zircon) indicate that the source of calcic metaluminous suites is the subcontinental lithosphere – both mantle and mafic lower crust – with variable contamination by the Early Paleozoic metasedimentary country rocks. The lithospheric mantle involved is assumed to underlie the outcropping 1330–1030 Ma age basement of the Western Domain, which exhibits tectonic characteristics of active continental margin in the north and oceanic arc-back arc in the south. The latter sector is the potential source of some minor Famatinian igneous rocks with less evolved isotopic compositions, although a restricted asthenospheric addition cannot be discarded in this case. Minor peraluminous granites are spatially associated with the metaluminous sequence, but major highly-peraluminous batholiths occur on the eastern flank of the Central Domain. Field relations and geochemical/isotopic evidence indicate that the most obvious source of these crustal melts was the very thick post-early Cambrian metasedimentary sequence comprising the host country rocks. Episodic tectono-magmatic evolution of the Famatinian magmatic belt in two overlapping stages is invoked to explain different characteristics in the four recognized domains in the type sector: • ca. 474–486? Ma, roll-back stage. This is a mainly extensional interval involving asthenospheric upwelling and thinning of the subcontinental mantle; full development of the marine ensialic basins and early emplacement of both metaluminous granites and highly-peraluminous batholiths in the Central and Eastern Famatinian domains. Trondhjemite plutons with an adakitic signature were emplaced in the Foreland Domain • ca. 468–472 Ma, slab break-off stage. Steepening of the oceanic slab and arc migration to the southwest ended with slab break-off due to subduction of continental crust during continental collision with the Precordillera terrane. This stage produced voluminous metaluminous magmatism at the western edge of the Central Domain (the flare-up episode), K-bentonites in the Precordillera, leucogranites in the Western Domain and scattered metaluminous and peraluminous plutons in all Famatinian domains. Both slab roll-back and break-off stages developed during a high-T regime typical of hot orogens. Although asthenospheric mantle was a necessary heat source for lithospheric melting, its material contribution to the growth of Early Paleozoic crust was apparently very minor. Recycling of Mesoproterozoic lithosphere, including the subcontinental mantle, coupled with crustal melting of Early Paleozoic metasedimentary sequences, accounts for most Famatinian magmatism. Comparable results from the Central Andes and East Antarctica confirm that the early stages of the Terra Australis orogen in SW Gondwana were dominated by lithospheric reworking processes. [ABSTRACT FROM AUTHOR]

The rare earth element (REE) tetrad effect includes a large, strongly negative Eu anomaly, and appears in highly evolved, fractionated granite and/or A-type granite, which it is sometimes interpreted as evidence of fluid-rock interaction. Magnesium is a fluid-mobile element, and its isotopes show very little fractionation during igneous processes. In order to understand the formational processes that cause the REE tetrad effect in granitic magmas and the role of fluid-rock interaction in producing REE tetrad patterns, this study analyzed magnesium and oxygen isotope compositions along with REE patterns in three Cretaceous granites from the Okcheon belt, Korea. Samples exhibited a linear correlation between magnesium isotopic values (δ26Mg) and SiO2, MgO, TiO2, initial 87Sr/86Sr, 143Nd/144Nd values. Oxygen isotope values also showed some correlation with SiO2, TiO2, δ26Mg, initial 87Sr/86Sr, and 143Nd/144Nd values. Our data indicate that the three granites should be evolved from source magma derived from isotopically heterogeneous source materials within the crust. In addition, the relationship between initial 143Nd/144Nd and δ26Mg values strongly suggests that the REE tetrad effect may develop before the granitic magma evolved from crustal source material rather than during late stage of magma differentiation or hydrothermal alteration. [ABSTRACT FROM AUTHOR]

Changes in stable chromium isotopes (denoted as δ53Cr) in ancient carbonate sediments are increasingly used to reconstruct the oxygenation history in Earth’s atmosphere and oceans through time. As a significant proportion of marine carbonate older than the Cambrian is microbially-mediated, the utility of δ53Cr values in ancient carbonates hinges on whether these sediments accurately capture the isotope composition of their environment. We report Cr concentrations (Cr) and δ53Cr values of modern marginal marine and non-marine microbial carbonates. These data are supported by stable C and O isotope compositions, as well as rare earth elements and yttrium (REY) concentrations. In addition, we present data on ancient analogs from Precambrian strata. Microbial carbonates from Marion Lake (Australia, δ53Cr ≈ 0.99‰) and Mono Lake (USA, ≈0.78‰) display significantly higher δ53Cr values compared with ancient microbialites from the Andrée Land Group in Greenland (720 Ma, ≈0.36‰) and the Bitter Springs Formation in Australia (800 Ma, ≈−0.12‰). The δ53Cr values are homogenous within microbialite specimens and within individual study sites. This indicates that biological parameters, such as vital effects, causing highly variable δ53Cr values in skeletal carbonates, do not induce variability in δ53Cr values in microbialites. Together with stable C and O isotope compositions and REY patterns, δ53Cr values in microbialites seem to be driven by environmental parameters such as background lithology and salinity. In support, our Cr and δ53Cr results of ancient microbial carbonates agree well with data of abiotically precipitated carbonates of the Proterozoic. If detrital contamination is carefully assessed, microbialites have the potential to record the δ53Cr values of the waters from which they precipitated. However, it remains unclear if these δ53Cr values record (paleo-) redox conditions or rather result from other physico-chemical parameters.

Rodingite is produced by Ca-rich fluid metasomatism of mafic igneous rocks in oceanic lithosphere. Despite its importance for the composition of subduction zone magmas, its formation mechanism still remains obscure. To address this issue, we investigated the major-trace element and Mg–O–Sr–Nd isotope compositions of rodingites in serpentinites from the Xigaze ophiolite, southern Tibet. Coexisting gabbros and rodingites show consistently depleted Sr Nd isotope compositions, suggesting their formation in a mid-ocean ridge setting. The rodingites exhibit variable δ26Mg values from −0.61‰ to −0.14‰, with an average of −0.37‰ ± 0.28‰ (n = 19; 2 SD), mostly lower than those of −0.26‰ to −0.13‰ for the protolith gabbros. Compared to the relatively homogeneous δ18O values of 6.1‰–6.7‰ for the gabbros, the rodingites show highly variable δ18O values from 3.8‰ to 9.4‰. The rodingites can be subdivided into two groups based on mineral assemblages and formation conditions. Group I rodingite is prehnite-dominated and hydrogarnet-free, formed at temperatures of 200–300 °C, and has higher δ18O values of 8.1‰ ± 1.4‰ (n = 15) and δ26Mg values of −0.32‰ ± 0.19‰ (n = 12). Group II rodingite consists mainly of hydrogarnet and clinopyroxene, formed at temperatures of 300–400 °C, and has lower δ18O values of 5.4‰ ± 2.5‰ (n = 7) and δ26Mg values of −0.44‰ ± 0.35‰ (n = 7). Modeling of the fluid–rock interactions between the protolith gabbro and fluid was undertaken using the Mg O isotope compositions of the serpentinizing fluid inferred from the associated serpentinites. Based on the modeling results, we propose that the metasomatism of gabbros by Ca-rich, low-δ26Mg fluids produced during serpentinization would result in the Mg O isotope compositions of the rodingites. Such rodingites with low δ26Mg values would generate the geochemical heterogeneity in the mantle wedge overlying the subducting oceanic lithosphere and eventually give rise to Ca-rich, low-δ26Mg basaltic magmas. The results indicate that low δ26Mg values of basaltic rocks cannot be unambiguously ascribed to carbonated mantle sources. • The Xigaze rodingites show low δ26Mg and variable δ18O values. • The rodingites were formed through metasomatism of gabbros by serpentinizing fluids under seafloor. • The subduction of rodingites in subduction zones can greatly affect mantle Mg isotopic composition. [ABSTRACT FROM AUTHOR]

Oxygen, magnesium, and silicon isotopic compositions in the mineralogically complex, ultrarefractory (UR) calcium-aluminum-rich inclusion (CAI) E101.1 from the reduced CV3 chondrite Efremovka confirm that E101.1 is a compound CAI composed of several lithological units that were once individual CAIs, free-floating in the solar protoplanetary disk. Each precursor unit was found to have had its own thermal history prior to being captured and incorporated into the partially molten host CAI. Four major lithological units can be distinguished on the basis of their isotopic compositions. (1) Al-diopside-rich sinuous fragments, hereafter sinuous pyroxene, are 16 O-rich (Δ 17 O ≤ −20‰) and have light Mg and Si isotopic compositions with mass fractionation down to −3.5‰/amu for both isotopic systems. We attribute these peculiar isotopic compositions to kinetic effects during condensation out of thermal equilibrium. (2) Spinel clusters are 16 O-rich (Δ 17 O ∼ −22‰) and have Mg isotope systematics consistent with extensive equilibration with the host melt. This includes (i) δ 25 Mg values varying between + 2.6‰ and + 6.5‰ close to the typical value of host melilite at ∼+5‰, and (ii) evidence for exchange of radiogenic 26 Mg with adjacent melilite as indicated by Al/Mg systematics. The spinel clusters may represent fine-grained spinel-rich proto-CAIs captured, partially melted, and recrystallized in the host melt. Al/Mg systematics indicate that both the sinuous pyroxene fragments and spinel clusters probably had canonical or near-canonical 26 Al contents before partial equilibration. (3) The main CAI host (Δ 17 O ≤ −2‰) had a complex thermal history partially obscured by subsequent capture and assimilation events. Its formation, referred to as the “cryptic” stage, could have resulted from the partial melting and crystallization of a 16 O-rich precursor that underwent 16 O-depletion and a massive evaporation event characteristic of F and FUN CAIs (Fractionated with Unknown Nuclear effects). Alternatively, a 16 O-rich UR precursor may have coagulated with a 16 O-poor FUN CAI having 48 Ca anomalies, as indicated by perovskite, before subsequent extensive melting. The Al/Mg systematics (2.4 × 10 −5  ≤  ( 26 Al / 27 Al ) 0 ′  ≤ 5.4 × 10 −5 , where ( 26 Al / 27 Al ) 0 ′ is a model initial 26 Al/ 27 Al ratio per analysis spot) are best understood if the FUN component was 26 Al-poor, as are many FUN CAIs. (4) A complete Wark-Lovering rim (WLR) surrounds E101.1. Its Mg and Si isotopic compositions indicate that it formed by interaction of the evaporated interior CAI with an unfractionated 16 O-rich condensate component. Heterogeneities in 26 Al content in WLR spinels (3.7 × 10 −5  ≤  ( 26 Al / 27 Al ) 0 ′  ≤ 5.7 × 10 −5 ) suggest that the previously reported age difference of as much as 300,000 years between interior CAIs and their WLRs may be an artifact resulting from Mg isotopic perturbations, possibly by solid state diffusion or mixing between the interior and condensate components. The isotopic systematics of E101.1 imply that 16 O-rich and 16 O-poor reservoirs co-existed in the earliest solar protoplanetary disk and that igneous CAIs experienced a 16 O-depletion in an early high temperature stage. The coagulation of various lithological units in E101.1 and their partial assimilation supports models of CAI growth by competing fragmentation and coagulation in a partially molten state. Our results suggest that chemical and isotopic heterogeneities of unclear origin in regular CAIs may result from such a complex aggregation history masked by subsequent melting and recrystallization. [ABSTRACT FROM AUTHOR]

A detailed study of the Sr- and O- isotopic composition of minerals in the Upper Group 2 (UG2) unit of the eastern Bushveld Complex revealed significant variations in the pegmatoidal footwall pyroxenite and the UG2 chromitite layer itself. Initial 87 Sr/ 86 Sr ratios (Sr i ) of interstitial plagioclase in the footwall rocks are significantly higher than in adjacent rocks of the Critical Zone. The δ 18 O values of plagioclase-pyroxene and plagioclase-chromite mineral pairs in footwall pyroxenite and chromitite are consistent with oxygen isotope exchange from crystallization temperatures down to 700 °C and 800 °C, respectively, whereas in other parts of the UG2, plagioclase and pyroxene δ 18 O values are consistent with O isotope equilibration at liquidus crystallization temperatures of approximately 1150 °C. We propose that the higher initial 87 Sr/ 86 Sr of plagioclase in the UG2 chromitite and the footwall pyroxenite reflects infiltration of fluid derived from dehydrating country rocks beneath the Bushveld Complex. Fluids could have been introduced either late or during chromitite crystallization. The chromitite layer and its pegmatoidal footwall could have acted as barriers to entrap late stage crustal fluids. Alternatively, reaction of fluids with the chromite-bearing crystallizing mush layer would induce hydration melting of pyroxene and plagioclase supplying Cr and Al to the melt, thus invoking further chromite formation. This dissolution-reaction releases Cr from pyroxene, which along with pre-existing disseminated chromite could refine the chromitite layers. The pegmatoidal UG2 footwall constitutes the reaction front-line of this process, which recrystallized to a coarse-grained rock upon cooling. This study emphasizes the role of crustal fluids and late- and post-magmatic processes in layered intrusions taking place at subsolidus temperatures, whereby isotopic and chemical compositions may be significantly changed. [ABSTRACT FROM AUTHOR]

The Neoarchean-Paleoproterozoic boundary at 2.5 Ga is marked by fundamental changes in the composition of the mantle, crust and atmosphere-hydrosphere. These changes show that the evolution of Earth's deep interior and its exterior are linked, but the causes of the global transitions are cryptic. The isotopic signatures of detrital zircon enable the nature of felsic magma sources before and after 2.5 Ga to be compared, providing insight into the processes driving secular change. For this purpose, we present new oxygen and Hf isotope data from detrital zircon grains hosted by Paleoproterozoic metasedimentary rocks of the North Australian Craton, which record three magmatic events at 2.7 Ga, 2.5 Ga and 1.87 Ga. Scattered zircon ε Hf (+6 to −10) coupled with mantle-like δ 18 O at 2.7 Ga indicates both new crustal addition and the reworking of older materials. At 2.5 Ga, a wide range in zircon ε Hf (+7 to −12) and δ 18 O (5 to 7‰) reflects reworking of infracrustal and (subordinate) supracrustal components of various crustal residence age. The dominance of subchondritic zircon ε Hf suggests that depleted mantle inputs were limited. The ε Hf array contracts markedly (+3 to −8) at 1.87 Ga and is coupled with isotopically heavy oxygen (δ 18 O from 7 to 9.5‰), indicating a substantial contribution from clay-rich supracrustal sources. We attribute the contraction of the zircon ε Hf array at ca. 1.87 Ga to the melting of a range of Neoarchean crustal components, where the disparate Hf isotope signatures of these were partially homogenised by sedimentary processes. The shift in felsic magma sources after 2.5 Ga, from dominantly infracrustal to supracrustal, implies a change in the mechanical behaviour of the lithosphere, from soft to rigid. This may have contributed to the transition in the composition of the continents at the Neoarchean-Paleoproterozoic boundary. [ABSTRACT FROM AUTHOR]

In the central Erzgebirge within the Bohemian Massif, lenses of high pressure and ultrahigh pressure felsic granulites occur within meta-sedimentary and meta-igneous amphibolite-facies felsic rocks. In the felsic granulite, melt rich parts and restite form alternating layers, and were identified by petrology and bulk rock geochemistry. Mineral assemblages representing the peak P-T conditions were best preserved in melanocratic restite layers. In contrast, in the melt rich leucocratic layers, garnet and related HP minerals as kyanite are almost completely resorbed. Both layers display differences in accessory minerals: melanosomes have frequent and large monazite and Fe–Ti-minerals but lack xenotime and apatite; leucosomes have abundant apatite and xenotime while monazite is rare. Here we present a detailed petrographic study of zircon grains (abundance, size, morphology, inclusions) in granulite-facies and amphibolite-facies felsic gneisses, along with their oxygen and hafnium isotope compositions. Our data complement earlier U Pb ages and trace element data (REE, Y, Hf, U) on zircons from the same rocks (Tichomirowa et al., 2005). Our results show that the degree of melting determines the behaviour of zircon in different layers of the granulites and associated amphibolite-facies rocks. In restite layers of the granulite lenses, small, inherited, and resorbed zircon grains are preserved and new zircon formation is very limited. In contrast, new zircons abundantly grew in the melt rich leucocratic layers. In these layers, the new zircons (U Pb age, trace elements, Hf, O isotopes) best preserve the information on peak metamorphic conditions due to intense corrosion of other metamorphic minerals. The new zircons often contain inherited cores. Compared to cores, the new zircons and rims show similar or slightly lower Hf isotope values, slightly higher Hf model ages, and decreased oxygen isotope ratios. The isotope compositions (Hf, O) of new zircons indicate partial Hf isotope homogenization in the melt, and melt infiltration from an external source. New zircon was most likely formed by a peritectic reaction with melt above the wet solidus (peritectic zircon). Conversely, the amphibolite-facies host gneisses lack indications of significant melt production. Pre-metamorphic zircons experienced mainly solid-state recrystallization and variable Pb loss with only minor new zircon formation. However, subtle changes in cathodoluminescence pattern, in the Hf and O isotopes, and in the Lu/Hf, Yb/Hf ratios of zircons suggest that small volumes of melt were locally present. In difference to granulites, melt was internally produced. The detection of low degree melts (inferred from zircon geochemistry) is extremely important for the rheology because these amphibolite-facies rocks could act as large scale ductile shear zones. The new zircon data support a different P-T path for closely spaced amphibolite- and granulite-facies rocks. [ABSTRACT FROM AUTHOR]

In several Calcium–Aluminum-rich Inclusions (CAIs) from the CV3 chondrites Allende and Efremovka, representative of the most common igneous CAI types (type A, type B and Fractionated with Unknown Nuclear isotopic anomalies, FUN), the relationship between 16 O-excesses and TiO 2 content in pyroxene indicates that the latter commonly begins to crystallize with a near-terrestrial 16 O-poor composition and becomes 16 O-enriched during crystallization, reaching a near-solar composition. Mass balance calculations were performed to investigate the contribution of spinel to this 16 O-enrichment. It is found that a back-reaction of early-crystallized 16 O-rich spinel with a silicate partial melt having undergone a 16 O-depletion is consistent with the O isotopic evolution of CAI minerals during magmatic crystallization. Dissolution of spinel explains the O isotopic composition ( 16 O-excess and extent of mass fractionation) of pyroxene as well as that of primary anorthite/dmisteinbergite and possibly that of the last melilite crystallizing immediately before pyroxene. It requires that igneous CAIs behaved as closed-systems relative to oxygen from nebular gas during a significant fraction of their cooling history, contrary to the common assumption that CAI partial melts constantly equilibrated with gas. The mineralogical control on O isotopes in igneous CAIs is thus simply explained by a single 16 O-depletion during magmatic crystallization. This 16 O-depletion occurred in an early stage of the thermal history, after the crystallization of spinel, i.e. in the temperature range for melilite crystallization/partial melting and did not require multiple, complex or late isotope exchange. More experimental work is however required to deduce the protoplanetary disk conditions associated with this 16 O-depletion. [ABSTRACT FROM AUTHOR]

Early to mid Carboniferous I-type granites distributed in a broad meridional belt west of Sydney, southeastern Australia, represent the last phase of granite magmatism in the southern Lachlan Fold Belt. Rare inherited zircon in the granites, in combination with zircon precipitated from the melt phase of the magmas, provides direct evidence of the nature and age of the source rocks from which the granites were derived, and the isotopic compositions of those rocks. Most granites from the north and central parts of the belt, represented by the Wuuluman, Home Rule, Oberon and Lett plutons (334 ± 3, 328 ± 4, 339 ± 2 and 328 ± 2 Ma, respectively), are characterized by scarce inherited zircon dominantly of Siluro-Devonian age, consistent with all being derived from a common zircon-poor source rock of mid to late Devonian age. Based on the isotopic compositions of the igneous zircon rims, that source was relatively homogeneous and immature (δ 18 O zrn 6–7‰, εHf(t) 0–+4). Two samples of the Tarana pluton (331 ± 2 Ma), near the centre of the belt, show evidence for heterogeneity in that source and the presence of a more evolved component that is also more zircon rich. Together with the Lett pluton from the same geochemical suite, their zircon rim compositions define a mixing array between more and less evolved end members (δ 18 O zrn 5.5–9.5‰, εHf(t) -4–+4). Only in the southern Chapmans Creek pluton (327 ± 3 Ma) is there clear evidence that the source of the granite also contained a minor component with a similar older protolith to the LFB early Palaeozoic sediments that host most of the LFB pre-Carboniferous granites. Presence of that component, which overwhelmingly dominates the inheritance in the pre-Carboniferous granites, is also reflected in a slightly elevated whole rock initial 87 Sr/ 86 Sr (> 0.7050) and igneous δ 18 O zrn (ca. 7.5‰), but not in the igneous zircon εHf(t) (ca. +2). The amount of restitic zircon in granite is determined by not only the proportion of restite present but also the zircon contents of the various source rock components. The process of restite unmixing does not necessarily mean that more mafic, restite-rich granites will contain more inherited zircon. [ABSTRACT FROM AUTHOR]

It is well-established that lanthanide rare earth elements (REEs) have the potential to record the nature and source characteristics of their host magmas, in both whole-rock and their minerals. Accessory minerals that concentrate REEs are especially useful in crustal evolution studies, both for their elemental and isotopic information; the classic and unrivalled example being zircon. Approaches using a single radiogenic isotopic system, or one radiogenic and one stable isotope system (e.g., Hf and O) in one REE-bearing mineral (usually zircon) are common, but those involving multiple isotopes in several minerals remain scarce despite offering many advantages. Importantly, the latter approaches also allow comparing different techniques and provide evidence on whether isotopic systems were disturbed by secondary processes. This contribution documents several isotopic systems within the abundant accessory mineral of Caledonian high Ba-Sr granitoids from Northwest Scotland. We present a multi-isotope study of titanite, zircon and apatite from two localities (Strontian and Rogart), which were selected for their contrasting whole-rock isotopic signatures - the former deriving from a depleted mantle source, whereas the latter derived from a strongly enriched mantle source. New in-situ Sm-Nd in titanite and apatite and Hf in zircon isotope data are discussed and compared with in-situ oxygen isotope data previously published for the same samples. An internal consistency is observed for Nd isotopes in apatite and titanite. Nd isotopes values for both minerals strongly correlate with Hf isotopes in zircon. Isotopic data at the mineral scale confirm the Strontian and Rogart source characteristics previously defined from whole-rock isotope data, with the Rogart having a more enriched signature than the Strontian source along the "Caledonian Parental Magma Array"(CPMA). In contrast, a significant discrepancy exists between whole-rock and REE-mineral oxygen isotope data as the latter can be affected by post emplacement alteration and hence can be misinterpreted. Importantly, the contribution of sediments in the CPMA source(s) can be estimated from a diagram combining Sm-Nd isotopic signatures and (La/Sm) N in apatite and titanite. Overall, we demonstrate that detailed petrogenetic records are not only available in zircons but also in magmatic titanite and apatite, and we suggest that integrated multi-mineral approaches have potential to maximise constraints from in-situ mineral isotope geochemistry. [ABSTRACT FROM AUTHOR]

We investigated the mobility pattern of an Upper Palaeolithic woolly mammoth (Mammuthus primigenius) from the Kraków Spadzista site in southern Poland, one of the largest mammoth bone accumulations in Europe. We conducted in situ laser ablation (MC-) ICPMS Sr isotopic and trace element concentration measurements accompanied by spatially-resolved oxygen isotope measurements of dental enamel on a last upper molar tooth (M6). Our study documents excellent preservation of in vivo geochemical and isotopic records and reveals recurring changes in 87Sr/86Sr that oscillate between two endmembers and correlate with analogous variations in δ18O, as well as U and Sr concentrations. The observed periodicity corresponds to annual cycles of enamel mineralization as revealed by enamel histology and documents up to 11 years of woolly mammoths' life in a single dental plate. The high degree of correlation between the duration of enamel mineralization and the Sr and O isotopic records suggests that the mammoth migrated between two areas of distinct Sr isotopic composition as well as characteristic U and Sr concentrations, presumably forced by seasonal food availability. The mammoth grazed in southern Poland in winter time as indicated by lower δ18O values and likely moved 250–400 km northwards to the Polish midlands during summer. This migration pattern remained stable for at least 12–13 years of the animal's adult life as archived in this molar tooth. Our study documents a fixed mobility behaviour of an adult mammoth some 10,000 years before the Last Glacial Maximum. • Histology of woolly mammoth molar indicates enamel mineralization over 12–13 years. • High resolution Sr and O isotopes record repetitive, annual composition changes. • Woolly mammoth from Kraków-Spadzista site migrated seasonally for 250–400 km. [ABSTRACT FROM AUTHOR]

The oxygen (O) and neodymium (Nd) isotopic composition of monazite provides an ideal tracer of metamorphism and hydrothermal activity. Calibration of the matrix effect and monitoring of the external precision of monazite O−Nd isotopes with microbeam techniques, such as secondary ion mass spectrometry (SIMS) and laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICPMS), require well-characterized natural monazite standards for precise microbeam measurements. However, the limited number of standards available is impeding the application of monazite O−Nd isotopes. Here, we report on the RW-1 monazite as a potential new working reference material for microbeam analysis of O−Nd isotopes. Microbeam measurements by electron probe microanalysis (EPMA), SIMS, and LA-MC-ICPMS at 10−24 µm scales have confirmed that it is homogeneous in both elemental and O−Nd isotopic compositions. SIMS measurements yield δ18O values consistent, within errors, with those obtained by laser fluorination techniques. Precise analyses of Nd isotope by thermal ionization mass spectrometry (TIMS) are consistent with mean results of LA-MC-ICPMS analyses. We recommend δ18O = 6.30‱ ± 0.16‱ (2SD) and 143Nd/144Nd = 0.512282 ± 0.000011 (2SD) as being the reference values for the RW-1 monazite.

This study introduces a new zircon reference material, LKZ-1, for the in situ U−Pb dating and O−Hf isotopic and trace element analyses. The secondary ion mass spectrometric analyses for this gem-quality single-crystal zircon yielded a weighted mean 206Pb/238U age of 572.6 ± 2.0 Ma (2σ, n = 22, MSWD = 0.90), with moderately high U concentrations (619 ± 21 ppm, 1 SD), restricted Th/U ratios (0.146 ± 0.002, 1 SD), and negligible common Pb content (206Pbc < 0.2%). A comparable 206Pb/238U age (570.0 ± 2.5 Ma, 2σ) was produced by the isotope dilution-thermal ionization mass spectrometry. The secondary ion mass spectrometric and laser ablation-assisted multiple collector inductively coupled plasma mass spectrometer analyses respectively showed that LKZ-1 had little variation in O (δ18OV-SMOW = 10.65 ± 0.14‰; laser fluorination value = 10.72 ± 0.02‰; 1 SD) and Hf (176Hf/177Hf = 0.281794 ± 0.000016, 1 SD) isotopic compositions. LKZ-1 was also fairly homogeneous in its chemical composition (RSD of laser ablation ICPMS data ≤ 10%), displaying a relatively uniform chondrite-normalized rare earth element pattern ((Lu/Gd)N = 31 ± 3, Eu/Eu* = 0.43 ± 0.17, Ce/Ce* = 44 ± 32; 1 SD). These consistencies suggest that the LKZ-1 zircon is a suitable working standard for geochronological and geochemical analyses.

It is well established that A-type granites enriched in high field strength elements, such as Zr, Nb and the REE, form in anorogenic tectonic settings. The sources of these elements and the processes controlling their unusual enrichment, however, are still debated. They are addressed here using neodymium and oxygen isotope analyses of samples from the 1.24 Ga Strange Lake pluton in the Paleoproterozoic Core Zone of Québec-Labrador, an A-type granitic body characterized by hyper-enrichment in the REE, Zr, and Nb. Age-corrected εNd values for bulk rock samples and sodic amphiboles (mainly arfvedsonite) from the pluton range from −0.6 to −5.7, and −0.3 to −5.3, respectively. The εNd values for the Napeu Kainiut quartz monzonite, which hosts the pluton, range from −4.8 to −8.1. The Sm/Nd ratios of the suite and the host quartz monzonite range from 0.0967 to 0.1659, large variations that can be explained by in situ fractionation of early LREE-minerals (Strange Lake), and late hydrothermal HREE remobilization. Oxygen isotope analyses of quartz of both Strange Lake and the host yielded δO values between +8.2 and +9.1, which are considerably higher than the mantle value of 5.7 ± 0.2‰. Bulk rock oxygen isotope analyses of biotite-gneisses in the vicinity of the Strange Lake pluton yielded δO values of 6.3, 8.6 and 9.6‰. The negative εNd values and positive δO values of the Strange Lake and Napeu Kainiut samples indicate that both magmas experienced considerable crustal contamination. The extent of this contamination was estimated, assuming that the contaminants were sedimentary-derived rocks from the underlying Archean Mistinibi (para-) gneiss complex, which is characterized by low εNd and high δO values. Mixing of 5-15% of a gneiss, having an εNd value of −15 and a δO value of +11, with a moderately enriched mantle source (εNd = +0.9, δO = +6.3) would produce values similar to those obtained for the Strange Lake granites. Based on analogies between the Nain Plutonic Suite and the Gardar alkaline igneous province (SW-Greenland), we conclude that the Strange Lake pluton and associated REE-mineralized anorogenic bodies formed from a combination of subduction-induced fertilization of the sublithospheric mantle, crustal extension and in situ magma evolution. [ABSTRACT FROM AUTHOR]

Monitoring injected CO 2 in CCS sites using oxygen isotopes of water has been demonstrated in field and laboratory experiments. Here, we examine natural CO 2 -rich springs in the Daylesford-Hepburn region, South East Australia, which show water 18 O depletion compared to local precipitation. Geochemical modelling shows that water-rock reactions are unlikely to have a significant effect on the observed δ 18 O values, which can only be explained by isotopic exchange with CO 2 . The water δ 18 O shift can be used for monitoring CO 2 impact on shallow groundwater aquifers, provided that there is sufficient CO 2 and distinction between water and CO 2 δ 18 O values exists. [ABSTRACT FROM AUTHOR]

The combination of U–Pb, Lu–Hf and O isotopic analyses in global zircon databases has recently been used to constrain continental crustal growth and evolution. To identify crust-forming events, these studies rely on the assumption that new crust is formed from depleted mantle sources. In contrast, this work suggests that post-collisional mafic magmas and their derivatives represent a non-negligible contribution to crustal growth, despite having zircons with “crust-like” Hf–O isotopic characteristics. We address this paradox and its implications for crustal evolution on the basis of a case study from the Variscan French Massif Central (FMC). The late stages of continental collisions are systematically marked by the emplacement of peculiar mafic magmas, rich in both compatible (Fe, Mg, Ni, Cr) and incompatible elements (K 2 O, HFSE, LREE) and displaying crust-like trace element patterns. This dual signature is best explained by melting of phlogopite- (and/or amphibole-) bearing peridotite, formed by contamination of the mantle by limited amounts (10–20%) of crustal material during continental subduction shortly preceding collision. Mass balance constraints show that in melts derived from such a hybrid source, 62–85% of the bulk mass is provided by the mantle component, whereas incompatible trace elements are dominantly crustal in origin. Thereby, post-collisional mafic magmas represent significant additions to the crust, whilst their zircons have “crustal” isotope signatures (e.g. − 2 < ε Hf t < − 9 and + 6.4 < δ O 18 < + 10 ‰ in the FMC). Because post-collisional mafic magmas are (i) ubiquitous since the late Archean; (ii) the parental magmas of voluminous granitoid suites; and (iii) selectively preserved in the geological record, zircons crystallized from such magmas (and any material derived from their differentiation or reworking) bias the crustal growth record of global zircon Hf–O isotopic datasets towards ancient crust formation and, specifically, may lead to an under-estimation of crustal growth rates since the late Archean. [ABSTRACT FROM AUTHOR]

Fluids are important for mass transfer at the slab–mantle interface in subduction zones. However, it is usually difficult to trace fluids from specific sources in a subducting slab, especially those derived from dehydration of serpentinite. Coesite-bearing whiteschist at Dora-Maira in the Western Alps is characterized by strong Mg enrichment relative to the country rocks, which requires infiltration of Mg-rich fluids into the supracrustal rock. In order to constrain the origin of such Mg-rich fluids, we have performed an integrated study of whole-rock Mg and O isotopes, zircon U–Pb ages and O isotopes for the whiteschist and related rocks. Zircons in the whiteschist show two groups of U–Pb ages at ∼262 Ma and ∼34 Ma, respectively, for relict and newly grown domains. The Permian U–Pb ages of relict magmatic domains are consistent with the protolith age of host metagranite, suggesting that their common protolith is the Permian granite. The Tertiary U–Pb ages occur in coesite-bearing metamorphic domains, consistent with the known age for ultrahigh-pressure metamorphism. The metamorphic domains have δ 18 O values of 5.8 – 6.8 ‰ , whereas the relict magmatic domains have high δ 18 O values of ∼ 10 ‰ . Such high δ 18 O values are also characteristic of the metagranite, indicating that the whiteschist protolith underwent metasomatism by metamorphic fluids with low δ 18 O value of ∼ 2 – 4 ‰ . The whiteschist mostly has whole-rock δ 26 Mg values of −0.07 to 0.72‰, considerably higher than country-rock δ 26 Mg values of −0.54 to − 0.11 ‰ . Thus, the metamorphic fluids are not only rich in Mg but also heavy in Mg isotopes. They were probably derived from the breakdown of Mg-rich hydrous minerals such as talc and antigorite in serpentinite at the slab–mantle interface in the subduction channel. Therefore, the dehydration of mantle wedge serpentinite during the subduction and exhumation of continental crust can provide the Mg-rich fluids responsible for the metasomatism of crustal rocks at subarc depths. [ABSTRACT FROM AUTHOR]

In this study we present U–Pb and Hf isotope data combined with O isotopes in zircon from Neoarchean granitoids and gneisses of the southern São Francisco craton in Brazil. The basement rocks record three distinct magmatic events: Rio das Velhas I (2920–2850 Ma), Rio das Velhas II (2800–2760 Ma) and Mamona (2750–2680 Ma). The three sampled metamorphic complexes (Bação, Bonfim and Belo Horizonte) have distinct ε Hf vs. time arrays, indicating that they grew as separate terranes. Paleoarchean crust is identified as a source which has been incorporated into younger magmatic rocks via melting and mixing with younger juvenile material, assimilation and/or source contamination processes. The continental crust in the southern São Francisco craton underwent a change in magmatic composition from medium- to high-K granitoids in the latest stages, indicating a progressive HFSE enrichment of the sources that underwent anatexis in the different stages and possibly shallowing of the melting depth. Oxygen isotope data shows a secular trend towards high δ 18 O (up to 7.79‰) indicating the involvement of metasediments in the petrogenesis of the high potassium granitoids during the Mamona event. In addition, low δ 18 O values (down to 2.50‰) throughout the Meso- and Neoarchean emphasize the importance of meteoritic fluids in intra-crustal magmatism. We used hafnium isotope modelling from a compilation of detrital zircon compositions to constrain crustal growth rates and geodynamics from 3.50 to 2.65 Ga. The modelling points to a change in geodynamic process in the southern São Francisco craton at 2.9 Ga, from a regime dominated by net crustal growth in the Paleoarchean to a Neoarchean regime marked by crustal reworking. The reworking processes account for the wide variety of granitoid magmatism and are attributed to the onset of continental collision. [ABSTRACT FROM AUTHOR]

The elongate Monteirópolis batholith (270 km 2 ) is composed of alkali feldspar granite to granodiorite, it is part of the Águas Belas–Canindé composite batholith and it intruded rocks of the Pernambuco–Alagoas Domain, northeastern Brazil. This batholith is bounded by the NNE–SSW-trending Jacaré dos Homens transpressional shear zone on its southwestern margin, and displays low-angle foliation, coeval to the development of a regional flat-lying foliation. Microgranular dioritic enclaves and amphibole-rich clots are abundant. The mineralogy of this pluton comprises biotite and amphibole as major accessory phases, and titanite and magmatic epidote as trace minerals. Major and trace element chemistry shows high SiO 2 , total alkalis, Ba and Sr, low Fe# and Nb contents, all of these conferring a high-K calc-alkaline character. The rocks are enriched in LREE and LILE and depleted in HFSE, and show fractionated chondrite-normalized REE patterns with Eu/Eu* = 0.67 to 1.25. Chondrite-normalized spidergrams show marked negative Nb–Ta and Ti anomalies, typical of subduction-related magmas. U–Pb SHRIMP zircon data yielded a crystallization age of 626 ± 4 Ma. Regional structures and U–Pb geochronological data for the Jacaré dos Homens transpressional shear zone suggest that shearing was initiated at ca. 640 Ma. Dilatational movements along this shear zone opened space for magma emplacement. The rocks in this batholith are characterized by slightly negative to slightly positive εNd values (− 0.78 to + 1.06), average Nd-model age of 1.0 Ga, low initial 87 Sr/ 86 Sr (626 Ma) values of 0.7050 to 0.7052, and low δ 18 O values (zircon) of + 5.00 to + 5.94‰ V-SMOW. A possible protolith, Tonian mantle-derived rocks in the lower continental crust, could have been partially melted by underplating of mantle-derived mafic magma during collision of the São Francisco Craton and the Pernambuco–Alagoas Domain during onset of the Brasiliano orogeny. [ABSTRACT FROM AUTHOR]

Magnesium and oxygen are critical elements in the solid Earth and hydrosphere. A better understanding of the combined behavior of Mg and O isotopes will refine their use as a tracer of geochemical processes and Earth evolution. In this study, the Mg-isotope compositions of garnet and omphacite separated from well-characterized xenolithic eclogites from the Roberts Victor kimberlite pipe (South Africa) have been measured by solution multi-collector ICP-MS. The reconstructed whole-rock δ 26 Mg values of Type I (metasomatized) eclogites range from − 0.61‰ to − 0.20‰ (Type IA) and from − 0.60‰ to − 0.30‰ (Type IB) (mean − 0.43‰ ± 0.12‰), while δ 26 Mg of Type IIA (fresh, least metasomatized) eclogites ranges from − 1.09‰ to − 0.17‰ (mean − 0.69‰ ± 0.41‰); a Type IIB (fresh, least metasomatized) has δ 26 Mg of − 0.37‰. Oxygen-isotope compositions of garnet were analyzed in situ by SIMS (CAMECA 1280) and cross-checked by laser fluorination. Garnets have δ 18 O of 6.53‰ to 9.08‰ in Type IA, 6.14‰ to 6.65‰ in Type IB, and 2.34‰ to 2.91‰ in Type IIB. The variation of δ 26 Mg and δ 18 O in Type IA and IB eclogites is consistent with the previously proposed model for the evolution of these samples, based on major and trace elements and radiogenic isotopes. In this model, the protoliths (Type II eclogites) were metasomatized by carbonatitic to kimberlitic melts/fluids to produce first Type IA eclogites and then Type IB. Metasomatism has changed the O-isotope compositions, but the Mg-isotope compositions of Type IA are mainly controlled by the protoliths; those of Type IB eclogites reflect mixing between the protoliths and the kimberlitic melt/fluid. The combination of a large range of δ 26 Mg and low δ 18 O in Type II eclogites cannot be explained easily by seawater alteration of oceanic crust, interaction of carbonate/silicate sediments with oceanic crust, or partial melting of mafic rocks. [ABSTRACT FROM AUTHOR]

Combined U-Pb-Hf-O isotopic analyses of zircons are useful probes to investigate the origin and temporal evolution of long-lived magma reservoirs feeding large eruptions. This study presents a complete dataset of zircon Hf-O isotopes of the latest five Toba eruptions in the Quaternary. The new isotopic data differ slightly within and between eruptive units, with the majority of zircons having ε Hf values between −8 to −5 and δ18O values between 6 and 6.8. These Hf-O isotopic compositions of zircons were considered to inherit from an enriched and slightly heterogenous magma source. Specifically, zircons of the Oldest Toba Tuff (OTT) have rather restricted and constant Hf-O isotopes, which may crystallize from a reservoir protractedly supplied from the same magma source. Zircons of the Middle Toba Tuff (MTT) have a large range of δ18O values varying from ~6 to 8, with low ε Hf values extending to −14, indicating shallow-level crustal contamination. The largely negative correlations between ε Hf and δ18O for zircons from the MTT are indicative of contamination of high-δ18O crustal materials, whereas those of the positive correlations for zircons from the Youngest Toba Tuff (YTT) imply contamination of hydrothermally altered low-δ18O crustal materials. It is important that the Hf-O isotopes of all the zircons do not record any single batch of magma that was derived from partial melting of depleted mantle peridotites, but are consistent with an enriched and heterogenous mantle source hybridized by the subducted sediments, followed by contamination of low-δ18O or high-δ18O materials during their ascent to the surface or storage in the shallow magma reservoirs. The increase of zircon δ18O values towards eruptions in both the MTT and YTT suggests that the two eruptions might be accompanied by roof collapse that added high-δ18O materials to the magma. Thus, assimilation of high-δ18O crustal materials could be a possible trigger for the MTT and YTT eruptions. • Toba volcanic rocks were derived from an isotopically enriched and heterogenous mantle source. • Hf-O isotopes of the MTT zircon crystals exhibit characteristics of shallow-level crustal contamination. • The YTT magma reservoir was contaminated by both high- and low-δ18O crustal materials. • Assimilation of high-δ18O materials by roof collapse could be a likely eruption trigger for the MTT and YTT eruptions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Magnetite can be used to trace metal and fluid sources in iron oxide copper gold (IOCG) deposits using O, Fe, and Ti stable isotope geochemistry. • This is the first work to explore Ti isotope geochemistry in a hydrothermal system and in a mineral deposit. • Magnetite from the Ernest Henry IOCG deposit in Queensland, Australia exhibits magmatic O isotope signatures, but non-magmatic Fe isotope signatures, suggesting that much of the Fe in the deposit was sourced from the leaching of crustal rocks by magmatic-hydrothermal fluids. • Ti isotope signatures indicate that Ti was mobilized during the mineralization of the copper ore resulting in Ti isotope compositions that are more fractionated than what has been observed in magmatic systems. Iron oxide copper gold (IOCG) deposits are globally important sources of Cu; however, their origins remain poorly understood with respect to the metal and fluid sources involved in their formation. In this work, we utilize integrated Fe, Ti, and O isotopic data for magnetite to trace major metal and fluid inputs for the Proterozoic-aged Ernest Henry IOCG deposit—the largest known IOCG deposit in the Cloncurry District, Queensland, Australia. Magnetite separates from ore stage and pre-ore biotite-magnetite (bt-mgt) and magnetite-actinolite (mgt-act) alteration assemblages from Ernest Henry were analyzed for their O, Fe, and Ti isotope abundances, reported as δ18O (VSMOW), δ56Fe (IRMM-14), and δ49Ti (OL-Ti). Select magnetite samples were also analyzed for 17O (reported as Δ'17O 0.5305) and range from −0.118 to −0.056 ‰—suggesting evaporitic input. The δ18O values from ore stage (+1.57 to +7.36 ‰), bt-mgt (+0.34 to +5.68 ‰), and mgt-act (+1.68 to +2.10 ‰) samples are consistent with a magmatic-hydrothermal origin for ore and pre-ore mineralizing fluids at Ernest Henry; non-magmatic δ18O values > c. 5 ‰ may be explained through localized carbonate wall rock assimilation. Despite this, δ56Fe values for ore stage (−0.50 to +0.33 ‰), bt-mgt (−0.65 to +0.38 ‰), and mgt-act (−0.26 to +0.30 ‰) magnetite are generally isotopically lighter than the accepted range (c. +0.06 to +0.49 ‰) for igneous and magmatic-hydrothermal magnetite and exhibit a relatively large range of c. 1 ‰, suggesting Fe source mixing within the deposit. Ore stage magnetite δ49Ti (−1.64 to + 3.79 ‰; avg: +1.49 ‰; 2σ = 2.63 ‰) compositions are generally higher and more variable than either the bt-mgt (-0.44 to + 1.49 ‰; avg: +0.62 ‰; 2σ = 1.13 ‰) or mgt-act (+0.27 to + 1.89 ‰; avg: +1.05 ‰; 2σ = 1.56 ‰) and suggest that Ti isotope fractionation occurred due to differential mobility in the fluid. The data are best explained by models invoking both magmatic and non-magmatic metal and fluid input. Fluid flow channeled between the footwall and hanging wall shear zones introduced non-magmatic Fe that may have been leached from local mafic units by magmatic-hydrothermal fluids, resulting in neoformed and regeneratively replaced magnetite with magmatic δ18O, but non-magmatic δ56Fe values during pre-ore alteration. These fluids may have mixed with Fe-poor evaporitic fluids prior to magnetite formation. Later magmatic Fe and O contributions during ore stage mineralization resulted in magnetite with variable δ56Fe and irresolvable δ18O overprinting. Ernest Henry is the first known example of an IOCG deposit with a major leached metal component identified through metal stable isotope geochemistry. [ABSTRACT FROM AUTHOR]

A major unanswered question in solar system formation is the origin of the oxygen isotopic dichotomy between the Sun and the planets. Individual Calcium–Aluminum-rich inclusions (CAIs) from CV chondrites exhibit almost the full isotopic range, but how their composition evolved is still unclear, which prevents robust astrochemical conclusions. A key issue is notably the yet unsolved origin of the 16 O-rich isotopic composition of pyroxene in type B CAIs. Here, I report an in-situ oxygen isotope study of the archetypal type B CAI USNM-3529-Z from Allende with emphasis on the isotopic composition of pyroxene and its isotopic and petrographic relationships with other major minerals. The O isotopic composition of pyroxene is correlated with indicators of magmatic growth, indicating that the pyroxene evolved from a 16 O-poor composition and became progressively enriched in 16 O during its crystallization, contrary to the long held assumption that pyroxene was initially 16 O-rich. This variation is well explained by isotopic exchange between a 16 O-poor partial melt having the isotopic composition of melilite and a 16 O-rich gas having the isotopic composition of spinel, during pyroxene crystallization. The isotopic evolution of 3529-Z is consistent with formation in an initially 16 O-rich environment where spinel and gehlenitic melilite crystallized, followed by a 16 O-depletion associated with melilite partial melting and recrystallization and finally a return to the initial 16 O-rich environment before pyroxene crystallization. This strongly suggests that the environment of CAI formation was globally 16 O-rich, with local 16 O-depletions systematically associated with high temperature events. The Al/Mg isotopic systematics of 3529-Z further indicates that this suite of isotopic changes occurred in the first 150 000 yr of the solar system, during the main CAI formation period. A new astrophysical setting is proposed, where the 16 O-depletion occurs in an optically thin surface layer of the disk and may have originated by evaporation of 16 O-poor interstellar dust or non-mass-dependant isotopic fractionation. [ABSTRACT FROM AUTHOR]

The robust nature of the mineral zircon, combined with our analytical ability to readily acquire in-situ uranium-lead (U-Pb), lutetium-hafnium (Lu-Hf) and oxygen (O) isotopic data, has resulted in a rapid rise in the use of zircon isotopic datasets for studying both the generation of continental crust and its growth through Earth history. In such studies there has been a strong focus on developing methods to determine the timing and/or proportion of juvenile magmatic addition to the continental crust. One widespread approach to determine the timing of crustal growth has been the construction or fitting of ‘reworking arrays’ to regional Hf isotopic datasets. Simple stochastic models are presented which highlight that in many cases apparent reworking arrays are much more likely to represent a process of on-going dilution and refertilisation of ancient crust, consistent with “Hot Zone” models of granitoid generation and the need to refertilise lower crustal reservoirs to maintain magmatism. A new compilation of magmatic rock zircon Lu-Hf and O isotope data is used to demonstrate that the use of mantle-like O isotope data as a screening tool for “meaningful” Hf model ages is also unlikely to be reliable, with independently constrained data indicating that as few as 14% of Hf model ages provide a meaningful indicator of the timing of crustal growth. The limitations of Hf model ages are discussed with regard to existing approaches for continental growth and we demonstrate that popular inverse modelling approaches suffer from a bias created by both the use of model ages and numerical artefacts. In an effort to address some of the limitations within existing models, we develop stochastic models based on joint calibration of multiple datasets which allow for more unique solutions. [ABSTRACT FROM AUTHOR]