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Granulites from the Narryer Terrane in the northern Yilgarn Craton, Australia, record evidence for high to ultrahigh thermal gradients during the Meso–Neoarchean. U–Pb zircon ages reflect a complex history of high‐grade, prolonged and poly‐phase metamorphism, with evidence for several thermal pulses at ca. 2745–2725, ca. 2690–2660, and ca. 2650–2610 Ma. Forward phase equilibrium modeling on rocks with varying bulk compositions and mineral assemblages suggests that peak temperatures reached 880–920°C at pressures of 5.5–6 kbar at ca. 2690–2665 Ma, followed by near‐isobaric cooling. These new P–T results also indicate that these rocks experienced some of the hottest thermal gradient regimes in the metamorphic record (≥150°C/kbar). Based on P–T models, U–Pb ages, and geochemical constraints, our data suggest that the geodynamic setting for the formation of this unusual thermal regime is ultimately tied to cratonization of the Yilgarn Craton. Previous models have inferred that ultrahigh thermal gradients and coeval large‐scale anatexis in the Narryer Terrane were primarily generated by mantle‐driven processes, despite most of the lithological, isotopic, and geochemical observations being at odds with the expected geological expression of large‐scale mantle upwelling. We re‐evaluate the mechanisms for high‐grade metamorphism in the Narryer terrane and propose that long‐lived high crustal temperatures between ca. 2690 Ma and 2610 Ma were instead facilitated by elevated radiogenic heat production in thickened, highly differentiated ancient crust. Mantle‐derived magma input and new crustal addition may not be the only drivers for high‐ to ultrahigh‐temperature metamorphism and stabilization of ancient crustal blocks. [ABSTRACT FROM AUTHOR]

Apatite provides a powerful means to determine the Sr isotopic composition (87Sr/86Sr) of ancient crust as it contains enough Sr to be measured accurately and precisely while typically having little post‐crystallisation radiogenic ingrowth due to its low Rb. Although utilising LG‐SIMS is beneficial for small‐volume targets, for example, inclusions, it is technically challenging to measure Sr isotopes in apatite with good accuracy and precision by SIMS, mainly due to molecular isobars interfering on Sr isotopes that have not previously been thoroughly assessed. This study evaluates all theoretically possible interferences affecting Sr isotope analysis of apatite by SIMS and develops a principle protocol for analysis and data processing that can be applied across a wide range of Sr concentration, even lower than 100 µg g−1. With careful control of the peak shape and applying precise mass centring at an intermediate mass resolution (ca. 4500), only interferences from the apatite matrix‐produced Ca dimers and 40Ca31P16O (present as a low mass tail) were found to be significant for the low trace element reference apatite used in this study, both of which can be precisely measured and corrected for. Despite this comprehensive approach, the Ca2 correction remained inadequate, possibly due to as yet unidentified doubly charged molecules interfering at the reference mass 82 peak (40Ca42Ca). While this can be reduced by employing an energy offset of at least −25 eV, precision significantly worsens in low Sr apatite (ca. 0.0024 in 1SE compared with ca. 0.0010 without offset for < 100 Sr µg g−1 apatite). Use of an empirical correction for the residual mass 82 interference is therefore preferred to an energy offset analytical approach, especially for low Sr apatite. Lastly, a slightly positive offset (ca. +0.0007) of unknown origin in 87Sr/86Sr was consistently observed across sessions with different analytical conditions, which may also be empirically corrected. The final corrected 87Sr/86Sr of the reference materials show good accuracy and precision with repeatability from ca. 0.0010 to 0.0002 in 1SE obtained for Sr contents from < 100 to 1500 µg g−1. [ABSTRACT FROM AUTHOR]

To further our knowledge of ore genesis in one of Australia's preeminent ore districts, we have completed a comprehensive geochemical study of ore-related porphyritic intrusions from the Archaean Kanowna Belle and Sunrise Dam gold deposits (both >10 Moz), Eastern Goldfields, Western Australia. Zircon samples (including samples from the newly developed Velvet mine) with ages ranging from 2.8 to 2.2 Ga, were investigated for O-OH isotopic signatures, trace element abundance, and U-Th-Pb compositions to elucidate the nature of the magmatic source and ore-related fluid. These intrusions have similarly high Sr/Y and La/Yb ratios to adakites from the Aleutian and Cook Islands, but lower Mg# values and higher K2O contents, suggesting they were derived from partial melts in a thickened crust. The modern analogs are post-collisional, high-Sr/Y granitoid porphyries in southern Tibet. Magmatic zircons have intermediate δ18O values (+5‰ to +6.3‰), and estimated magmatic crystallization temperatures (Ti-in-zircon) in between 660–760 °C. They are interpreted as having crystallized from positive δ18O magmas during water-fluxed melting of juvenile lower crust. Hydrothermal fluid modified zircons are texturally indistinguishable from magmatic zircons, but their trace element, OH, and isotopic compositions are distinct. The involvement of hydrothermal fluid in zircon growth is evidenced by a negative correlation between OH content and δ18O. In addition, the studied hydrothermal fluid modified zircons are characterized by high La contents, flat rare earth element patterns, weak Ce anomalies, and high Eu/Eu* ratios, suggesting they were related to a high-temperature, Zr-saturated, high-Eu, Cl-rich, and low-pH hydrothermal fluid. Such fluids are common in eastern Yilgarn gold camps. [ABSTRACT FROM AUTHOR]

The Sanjiang Orogen in the Southeastern Qinghai–Tibet Plateau is an ideal region to investigate the geodynamic processes related to the evolution of the Paleo-Tethys Ocean. New zircon SHRIMP U–Pb age data, whole-rock major and trace elements, and zircon Hf–O isotopic data of granodiorites and the associated dioritic enclaves from Baimaxueshan pluton in the eastern margin of the Qamdo–Simao Terrane provide key evidence for the subduction products of the Paleo-Tethyan oceanic lithosphere. Zircon U–Pb ages indicate that the dioritic enclaves and their host granodiorites were synchronously emplaced at ~255 Ma. The host granodiorites are normal calc-alkaline I-type granitoids, and characterized by uniform zircon ε Hf (t) values (−6.7 to +1.5), a wide-ranging δ 18 O values (6.1 to 9.3‰), and negative whole-rock ε Nd (t) values (−7.3 to −5.8). We suggest that these rocks were derived from the partial melting of ancient mafic lower crust with varying contributions from mantle-derived components. The dioritic enclave samples yield ε Hf (t) values (−4.7 to +2.1) and δ 18 O (5.8 to 8.3‰), which are similar to those of the host granitoids. They most likely originated from magma mixing between mantle-derived and crust-derived melts at or close to the Moho. The similar emplacement age but distinct whole-rock ε Nd (t) values between the Lancangjiang arc-related andesites and granodiorites and Baimaxueshan pluton preclude the possibility that they were generated by the same magmatic source. However, the consistent emplacement ages and whole-rock εNd(t) values of the Jinshajiang subduction-related granites and Baimaxueshan granitoids suggested that they were both generated by the westward subduction of the Jinshajiang PaleoTethyan oceanic lithosphere. [ABSTRACT FROM AUTHOR]

Precision and accuracy in SIMS zircon geochronology strongly depend on the method of determination of the interelement ion ratios (e.g., 206Pb/238U) from the measured secondary ion ratios (206Pb+/238U+). Six possible U-Pb calibrations (Pb/U-UO2/U, Pb/U-UO/U, Pb/U-UO2/UO, Pb/UO-UO2/U, Pb/UO-UO/U, Pb/UO-UO2 UO) based on simple power law relationships, and Pb/ UO2-related one- and two- (a power law) dimensional ones were compared using data acquired on the 91500 zircon reference material from one hundred measurement sessions, to determine the most statistically reliable scheme. Taking advantage of U oxide species (UO and UO2) over atomic U, due to their similar energy distribution to Pb and higher intensities, the data calibrated with Pb/UO-UO2/UO showed the smallest mean uncertainties and dispersions, and provided the best-fit calibration curve consistently. Although it was demonstrated with Temora 2 that the unknown zircon age was not changed significantly by different calibrations, its precision could be improved using the Pb/UO-UO2/UO calibration in zircon geochronology. [ABSTRACT FROM AUTHOR]

High-performance countercurrent chromatography (HPCCC) with electrospray light-scattering detection was applied for the first time to isolate a spirostanol and a novel furostanol saponin from Liriope platyphylla. Due to the large differences in KD values between the two compounds, a two-step HPCCC method was applied in this study. The primary HPCCC employed methylene chloride/methanol/isopropanol/water (9:6:1:4 v/v, 4 mL/min, normal-phase mode) conditions to yield a spirostanol saponin ( 1). After the primary HPCCC run, the solute retained in the stationary phase (SP extract) in HPCCC column was recovered and subjected to the second HPCCC on the n-hexane/ n-butanol/water system (1:9:10 v/v, 5 mL/min, reversed-phase mode) to yield a novel furostanol saponin ( 2). The isolated spirostanol saponin was determined to be 25( S)-ruscogenin 1- O-β- d-glucopyranosyl (1→2)-[β- d-xylopyranosyl (1→3)]-β- d-fucopyranoside (spicatoside A), and the novel furostanol saponin was elucidated to be 26- O-β- d-glucopyranosyl-25( S)-furost-5(6)-ene-1β-3β-22α-26-tetraol-1- O-β- d-glucopyranosyl (1→2)-[β- d-xylopyranosyl-(1→3)]-β- d-fucopyranoside (spicatoside D). [ABSTRACT FROM AUTHOR]

The Permo-Triassic granites of the New England Orogen, eastern Australia, were emplaced into a volcanic arc complex accreted to the eastern Gondwana margin in the Late Devonian or Early Carboniferous. Zircon U–Pb dating shows that the S-type Hillgrove (∼297 Ma) and Bundarra (∼287 Ma) Supersuites predated intrusion of the I-type Moonbi Supersuite (∼250 Ma) by up to 50 Ma. The high δ 18 O zrn of the S-type granites (10.0–11.5‰), and range of U–Pb ages (∼370–300 Ma) and δ 18 O zrn (∼5–10‰) of their inherited zircon cores, show that their source rocks were predominantly weathered Carboniferous volcaniclastics, the youngest deposited < 25 Ma before the granites were emplaced. In contrast, the lower δ 18 O zrn (6.9–7.8‰) and lack of inheritance in the I-type granites is consistent with a zircon poor, more juvenile source, probably a mafic igneous underplate mixed with a small amount of volcanogenic and/or oceanic sediment. Despite the differences in source materials, the εHf( t ) values of all granites, both S- and I-type, are similar (+5.0 ± 0.5 cf. +5.9 ± 0.5), consistent with both the mafic and sedimentary components in the granite sources being relatively young and similar in Hf isotopic composition at the time of granite genesis. In young, isotopically juvenile orogens, the O isotopic composition of well-dated igneous and inherited zircon can be a much more sensitive indicator of petrogenetic processes than the zircon Hf isotopic compositions alone. [ABSTRACT FROM AUTHOR]

Abstract: Early Permian (Cisuralian) S-type monzogranites of the Bundarra Supersuite, New England Orogen (NEO), eastern Australia, have chemical and isotopic compositions indicative of their being derived from young, weathered, volcanogenic sedimentary source rocks. High δ18Ozrn values of zircon precipitated from the melt phase of the magma (ca. 11.5‰) confirm that the previously measured high granite whole-rock values (δ18OWR) are a primary magmatic feature. Abundant inherited detrital zircon cores with a range of dates (360–300Ma) and distinctly lower δ18Ozrn values (ca. 5–10‰) were derived from mostly young (Carboniferous) volcanogenic source rocks that became less primitive and more isotopically diverse with time. The age difference between the youngest inherited zircon population and the earliest zircon growth during magma genesis is about 15Ma. An arc-related volcanogenic sedimentary pile built up over about 50Ma was weathered, buried, and partially melted, producing voluminous peraluminous magmas within no more than ca. 15Ma of the youngest source sediment being deposited. The time interval between the initiation of melting and post-emplacement magma crystallization was about 5Ma. The S-type Bundarra Supersuite in the NEO is a rare case in which the entire geologic cycle has been captured by zircon. Recognizing this is uniquely possible because of the relatively simple populations of inherited and newly-grown zircon, and their distinctive oxygen isotopic compositions. [Copyright &y& Elsevier]

We report the discovery of Archean (2980-2670 Ma) zircons from the Yilgarn Craton in Western Australia that record unusually low δ18O signatures (to -0.5‰). These zircons occur in cordierite-orthopyroxene granulites that retain the geochemical signature of intense premetamorphic hydrothermal alteration. We propose a model whereby the low-δ18O zircons crystallized within protoliths that record multiple stages of high-temperature interaction and hydrothermal exchange between shallow crustal material and 18O-depleted meteoric fluids, in a setting analogous to that of the Yellowstone caldera. Burial and subsequent granulitefacies metamorphism of this crust led to the crystallization of zircon, which acquired and preserved the extremely 18O-depleted signature of the whole rock. The apparent absence of strongly 18O depleted Archean zircons has been a puzzling feature of the global zircon record, but we suggest this is an artifact of poor preservation potential. Our findings suggest that long-lived, shallow crustal magmatic-hydrothermal systems similar to those operating in modern caldera complexes were also a feature of Archean Earth. [ABSTRACT FROM AUTHOR]

• First in-situ apatite U-Pb ages from pseudotachylytes. • The lower crust fails seismically during the early stages of continental collision. • Earthquakes create long-lived fluid pathways in the lower crust. Determining the precise age of fossil earthquakes is essential for understanding the tectonic setting in which they occurred. Pseudotachylytes are quenched frictional melts that occur along coseismic fractures and represent evidence of fossil earthquakes in the rock record. Here, we present the first in-situ apatite U-Pb ages for three samples from Lofoten in the northern Norwegian Caledonides, that occur within and adjacent to lower-crustal pseudotachylytes: a pristine pseudotachylyte, a mylonitized pseudotachylyte, and a mylonite that contains pseudotachylyte transposed into the shear plane. The apatite U-Pb ages are combined with cathodoluminescence and electron backscatter diffraction analysis to provide microstructural constraints on the interpretation of ages. Apatite shows evidence of either fragmentation and annealing, or dislocation creep in response to coseismic rupture. The results suggest that the short-lived thermal pulse generated by the earthquake is sufficient to reset the apatite U-Pb system. The age of 426 ± 19 Ma is interpreted to date lower-crustal seismicity during the early Caledonian orogeny. Later fluid-rock interaction along the same structures led to partial resetting of the apatite U-Pb systematics, indicating that seismic brittle failure of the lower continental crust occurs at the incipient stages of continental collision, and that the resulting structures are preferential pathways for later fluid flow in the otherwise impermeable anhydrous lower crust. [ABSTRACT FROM AUTHOR]

At convergent margins fluids liberated from subducting slabs metasomatise the overlying mantle wedge, enriching it in volatiles, incompatible elements and possibly ore-forming metals. Despite the genetic link between this process, the genesis of arc magmas, and formation of porphyry Cu–Au deposits, there is currently little understanding of the behaviour of chalcophile and siderophile elements during subduction-related mantle metasomatism. In this study, we report sulfur isotopic compositions and PGE concentrations of sulfides in a suite of garnet peridotites from the Western Gneiss Region of Norway, sampling mantle wedge from ∼100 to ∼250 km depth. Sulfides hosted in metasomatised samples have δ 34 S deviated from typical mantle values, ranging between −10.0 and +5.4‰, indicating derivation of sulfur from subducted crust. Sulfides in pervasively metasomatised samples have atypical PGE signatures, with strong enrichment in Os and Ru relative to Ir, whereas channelised fluid flow produced sulfides extremely enriched in Pd, up to 700 times the concentration found in non-metasomatised samples. These signatures are reconcilable with a high oxidation state of the metasomatising agents and demonstrate that subduction can recycle chalcophile and siderophile elements into and within the mantle, along with sulfur. We further show that because the solubility of Os and Ru in fluids is redox sensitive, and Pd is more soluble than the I-PGE, ratios such as Os/Ir, Ru/Ir plotted against Pd/Ir can be used to trace the metasomatic oxidation of mantle samples, mantle-derived magmas and porphyry Cu±Au deposits. This geochemical insight is used to show that Au-rich porphyry Cu deposits are derived from more oxidised mantle wedge than Au-poor porphyry deposits. [ABSTRACT FROM AUTHOR]

During the late Archaean, exotic juvenile continental (TTG) terranes assembled into stable cratons leading to continental emergence and deposition of shallow-marine sedimentary sequences. This period of cratonisation coincided with crustal reworking and maturation driving the production of granites sensu stricto on most cratons, and may mark a final transition to mobile-lid tectonics. We investigate the relative timing of continental assembly, stabilization, emergence, and maturation, during the formation of the North Atlantic Craton (NAC) in West Greenland from its constituent terranes, using geochemical data from zircon and monazite extracted from its oldest mature metasedimentary unit, the Storø quartzite. Zircons form two U-Pb age groups: (i) an older > 2820 Ma group with juvenile (elevated) ϵ Hf(t) and δ 18 O , derived from weathering surrounding Mesoarchaean terranes; and (ii) a younger < 2700 Ma group with less radiogenic (lower) ϵ Hf(t) and elevated δ 18 O that record post-burial metamorphism peaking ca. 2620 Ma. The quartzite protolith has a maximum depositional age of ca. 2830 Ma, and was deposited after final TTG formation but prior to granite magmatism at ca. 2715 Ma, during which time terranes had sufficiently assembled, stabilized, and emerged to form a common watershed. Cratons form via lateral accretion which requires strong continental lithosphere, for which one agent is crustal reworking and maturation. However, for the NAC, terrane assembly and emergence commenced prior to granite formation, and crustal reworking may be a response to lithospheric thickening. Cratonisation involves a series of complex, intertwined processes operating over 100's of millions of years, which together lead to the development of thick, stable, continental lithosphere. Studies of ancient mature metasediments such as the Storø quartzite can help build timelines for these processes to ultimately better understand their choreography and co-dependencies, that together produced Earth's enduring cratons. • Oldest mature sediment documents formation of North Atlantic Craton (NAC). • Storø quartzite derived from proximal Mesoarchaean TTG terranes. • Deposited between 2830–2715 Ma when terranes formed common watershed. • Initial NAC assembly and stabilization onset before crustal maturation. • Assembly of NAC complex, intertwined process operating over 100's Ma. [ABSTRACT FROM AUTHOR]

• A new high-precision multicollection SIMS boron isotope technique. • Boron isotope measurements from a diverse suite of Icelandic lavas. • Boron isotopes in basalts correlate with indicators of mantle heterogeneity. • Boron elemental and isotope systematics detect recycled materials. • Enriched heterogeneities are consistent with devolatilization and rehydration. Enriched mantle heterogeneities are widely considered to be generated through subduction, but the connections between specific subducted materials and the chemical signatures of mantle heterogeneities are not clearly defined. Boron is strongly isotopically fractionated at the surface and traces slab devolatilization, making it a potent tracer of previously subducted and recycled materials. Here, we present high-precision SIMS boron concentrations and isotope ratios on a comprehensive suite of quenched basaltic glasses from all neovolcanic zones in Iceland, two rhyolite glasses, and a set of primitive melt inclusions from central Iceland. Boron isotope ratios (δ 11 B) in Icelandic basalts and melt inclusions range from −11.6‰ to −1.0‰, averaging −4.9‰, which is higher than mid-ocean ridge basalt (MORB; δ 11 B = − 7.1 ‰). Because the δ 11 B value of the Icelandic crust is low, the high δ 11 B compositions of the Icelandic lavas are not easily explained through crustal assimilation processes. Icelandic basalt glass and melt inclusion B/Ce and δ 11 B values correlate with trace element ratio indicators of the degree of mantle partial melting and mantle heterogeneity (e.g. Nb/Zr, La/Yb, Sm/Yb), which indicate that the boron systematics of basalts are controlled by mantle heterogeneity. Additionally, basalts with low B/Ce have high 206Pb/204Pb, further indicating mantle source control. These correlations can be used to deduce the boron systematics of the individual Icelandic mantle components. The enriched endmember within the Iceland mantle source has a high δ 11 B value and low B/Ce, consistent with the composition of "rehydrated" recycled oceanic crust. The depleted endmember comprises multiple distinct components with variable B/Ce, likely consisting of depleted MORB mantle and/or high 3He/4He mantle and two more minor depleted components that are consistent with recycled metasomatized mantle wedge and recycled slab gabbro. The compositions of these components place constraints on the devolatilization history of recycled oceanic crust. The high δ 11 B value and low B/Ce composition of the enriched component within the Iceland mantle source is inconsistent with a simple devolatilization process and suggests that the recycled oceanic crust component may have been isotopically overprinted by B-rich fluids derived from the underlying hydrated slab lithospheric mantle (i.e. "rehydration"). Further, the B/Ce and δ 11 B systematics of other OIBs can be used to constrain the devolatilization histories of recycled components on a global scale. Globally, most OIB B/Ce compositions suggest that recycled components have lost >99% of their boron, and their δ 11 B values suggest that rehydration may be a sporadic process, and not ubiquitous. [ABSTRACT FROM AUTHOR]

Our understanding of crust – mantle evolution and geodynamics of the early Earth has been hampered by the scarcity of Hadean to Eoarchean rocks and by the almost ubiquitous isotopic disturbance of the oldest rocks. Here we present in-situ zircon U-Pb ages, O-OH and Lu-Hf isotopes, as well as whole-rock Sr-Nd-Hf-Pb isotopes for the recently identified Eoarchean Aktash gneisses in the Tarim Craton, NW China. The new age data confirm that the Aktash gneisses were formed at least by ∼3.72 Ga and were affected by two metamorphic events at ∼3.56 and ∼2.0 Ga, respectively. Whole-rock isotopic data show that the Sr-Nd-Hf-Pb isotopic systematics have all been variously disturbed by ∼2.0 Ga regional granulite facies metamorphism, resulting in decoupling of Nd-Hf isotopic systematics that is, in some samples, similar to that observed in SW Greenland. The least disturbed sample (16ALT67), however, yielded chondritic to slightly sub-chondritic whole-rock ε Nd (−0.3) and ε Hf (−0.9). This is consistent with the in-situ magmatic zircon ε Hf (weighted mean −0.2 to −1.8) for most samples of the Aktash gneisses, suggesting a mafic source derived from chondritic mantle with a short crustal residence time. Our data thus provide no evidence for the presence of an Eoarchean depleted mantle or a Hadean enriched crust, implying that early Earth crust – mantle differentiation was either limited or balanced by large-scale crustal recycling. In-situ zircon O–OH data show that metamorphism and later alteration tend to decrease the zircon δ 18 O of the Aktash gneisses, and the weighed mean δ 18 O of pristine magmatic zircons (6.2–6.3‰) from the least disturbed samples indicate that the mafic source was mildly altered at low temperature by the early hydrosphere, facilitating partial melting and formation of some of the earliest preserved continental crust known on Earth. • Zircon Hf-O and whole-rock Sr-Nd-Hf-Pb isotopic data for the 3.72 Ga Aktash gneisses. • Whole-rock Nd-Hf isotopic decoupling resulted from granulite-facies metamorphism. • Primary isotopic data indicate an altered mafic source derived from chondritic mantle. • Filtered zircon Hf-O isotopic data suggest similar sources for other Eoarchean rocks. [ABSTRACT FROM AUTHOR]