Search

The mainly S-type Donkerhuk batholith intruded the accretionary prism in the Pan-African Damara Belt of Namibia. The batholith is elongate parallel to the regional SW–NE structural grain and the Okahandja Lineament Zone, which forms the accretionary prism backstop and the magma feeder zone. Over 5000 km 3 of granitic magmas were emplaced as thousands of sheets, over perhaps 20 myr, with sheet orientations determined by the regional stress field and wall-rock anisotropies. Some of the magma source rocks are inferred to have been cordierite-bearing, suggesting an upper pressure limit of 600 MPa (6 kbar). Calculated phase relations suggest magma emplacement at 450 MPa (4.5 kbar), corroborated by pseudosection modelling of the phase assemblage in a migmatitic wall rock. The magmas were initially highly H 2 O-undersaturated and at around 850°C, indicating fluid-absent conditions in the source rocks. This suggests intraplating of mantle magmas to provide heat and that the granitic magmas ascended only to the mid crust. The late-tectonic emplacement in a fore-arc shares similarities with younger and similarly large batholiths such as the Cretaceous Kodiak batholith in Alaska, but the internal architecture and age structure of the batholiths differ markedly, suggesting that different processes can trigger voluminous near-trench plutonism. Supplementary material: A Microsoft Excel spreadsheet, in xlsx format, showing the analytical data relevant to this paper, is available at https://doi.org/10.6084/m9.figshare.c.3470880

The Andean orogenic cycle and its subduction-related magmatism along the southwestern margin of South America began during the early Jurassic after an accretionary history throughout Paleozoic times. The Chilean and Argentinian Frontal Andes batholiths, together with the Coastal Batholith, represent most of the pre-Andean orogenic cycle plutonism. However, how late Paleozoic–Triassic magmatism occurred along this margin and its transition to the Andean orogenic cycle still remains unclear. Here we present a geodynamic model using all the available published Lu–Hf and oxygen isotopic data ranging from latitudes 28° to 40°S, together with 5 new Hf–O data and U–Pb zircon ages from the Chilean Frontal Andes. Data indicate that subduction began at least in the latest early Carboniferous and was continuous throughout the late Paleozoic–Triassic period. Isotopic and geochronological results show a continuous magmatic trend, from high δ 18 O values (continental) to mantle-like signatures, as the rocks get younger. Between latest early Carboniferous and earliest middle Permian, magmas formed in a subduction-related arc during the Gondwanide Orogeny. Later, throughout middle Permian to Triassic, magmatism occurred in a slab rollback extensional setting, triggered by low subducting plate velocities while Pangea was essentially in a static reference mode. There is no evidence for cessation of subduction during the Triassic and its renovation in the early Jurassic as previous work suggested. Therefore, we propose that Andean subduction has been a continuous tectonic process since Paleozoic times, whose initial geodynamic evolution was directly related to the Gondwanide Orogeny as part of the Pangea Assembly. Slab rollback, as well as shallowing and steepening of the subduction angle were among the triggers for the change in the type of magmatism observed among these rocks.

The eastern part of the Caucasus orogen, termed the Georgian segment, is mainly underlain by highly deformed Lower-Middle Jurassic shales, sandstones, and volcaniclastic rocks, and cut by numerous intrusive bodies of various compositions. All units contain a variety of mineral deposit types and their surrounding zones of hydrothermal alteration. Detailed geological and metallogenic research, after 30 years stagnation, has led to important new information regarding the evolution of this region. Three main stages of magmatic activity are now clearly distinguished. The oldest magmatism comprises early Jurassic events, related to extensional tectonism, with volcanism and subvolcanic plutonism that ranged from rhyolitic, through dacitic and andesitic, and to basaltic. Additional extensional processes (in Bajocian times) were characterized by intrusion of a gabbro and diorite dike system into slightly older late Early Jurassicearly Middle Jurassic formations. The final magmatic event was associated with Middle Jurassic folding and uplift during which multiphase diorite plutons were emplaced. Intense hydrothermal activity related to this latest magmatism was responisble for important polymetallic mineralization including more than 100 historically recognized outcropping occurrences. A detailed study of 11of the more significant of these occurrences has indicated anomalous concentrations of base metals as well as gold, thorium, yttrium, cobalt, cadmium, and bismuth. In addition, several new and potentially significant mineral occurrences were discovered, including two designated here as Gelia and Lechuri.

There is a nearly continuous record of magmatism through the Late Cretaceous–early Paleogene in Idaho and adjacent areas of Oregon and Montana, including the various phases of the Idaho batholith. We suggest that much of this magmatic record, however, has been obscured by subsequent tectonic deformation, erosion, and magmatic disruption and cannibalization, the latter of which can be tracked by zircon inheritance. Specifically, a mid-Cretaceous magmatic arc was significantly deformed by the western Idaho shear zone and intruded by the 83–67 Ma Atlanta peraluminous suite of the Idaho batholith. The northern part of the Atlanta peraluminous suite was, in turn, intruded by the 65–55 Ma Bitterroot lobe of the Idaho batholith. Consequently, the present age distribution of magmatism is strongly biased toward the youngest phases of plutonism; much of the older phases were destroyed by tectonic, magmatic, and erosional processes. The destruction of granitic batholiths may characterize Cordilleran-style orogens worldwide, which can lead to significant underestimates of magmatic fluxes.

Five late Pleistocene lava domes with a combined eruptive volume of ∼40 km 3 distributed over an area of ∼2000 km 2 represent the waning stages of the 10–1 Ma ignimbrite flare-up in the Altiplano Puna Volcanic Complex (APVC) of the Central Andes. Zircon crystal face (on unsectioned rims) and interior (on sectioned crystals) ages (U-Th and U-Pb, respectively) for a total of 252 crystals indicate remarkably consistent zircon crystallization histories: the youngest zircon surface ages (ca. 104–83 ka) are near 40 Ar/ 39 Ar eruption ages from sanidine and biotite (ca. 120–87 ka), but a significant population of surface ages predates eruption, ranging to secular equilibrium (with U-Pb interior ages to 3.5 Ma). The essentially continuous zircon crystallization history implies protracted magma presence, which agrees with temporally invariant Ti-in-zircon model temperatures, backed by the homogeneity of indirectly temperature-dependent compositional parameters. Zircon age spectra modeled using a finite-difference thermal and mass-balance model for open-system magma evolution indicate protracted zircon production in the magma reservoirs that require time-integrated recharge rates of ∼1 × 10 −3 km 3 /yr, corresponding to high intrusive to extrusive ratios of 75: 1. This rate is below the ∼5 × 10 −3 km 3 /yr threshold proposed in the literature for incubating the supereruptions defining the flare-up. When accounting for the shorter durations of high versus low recharge episodes over the ∼10 m.y. lifetime of the APVC flare-up, the contributions to composite batholith formation in the shallow crust of the APVC remained broadly constant during peaks and lulls in eruptive activity. This connotes that eruptive fluxes are a poor measure for intrusive fluxes. A corollary of this interpretation is that commonly applied intrusive to extrusive ratios will severely underestimate pluton formation rates during periods of low eruptive flux.

This work deals with the origin and evolution of the magmatic rocks in the area north of the Patos Lineament in the Borborema Province (BP). This northeastern segment of NE Brazil is composed of at least six different tectonic blocks with ages varying from late-Archaean to late-Palaeoproterozoic. Archaean rocks cover ca. 5% of the region. They were emplaced over a period of 700 Ma, with at least seven events of magma generation, at 3.41, 3.36, 3.25, 3.18, 3.12, 3.03, and 2.69 Ga. The rocks are subalkaline to slightly alkaline, with affinity to I- and M-type magmas; they follow trondhjemitic or potassium calc-alkaline differentiation trends. They have epsilon Nd(t) of +1.4 to −4.2 and negative anomalies for Ta–Nb, P and Ti, consistent with a convergent tectonic setting. Both subducted oceanic crust and upper mantle (depleted or metasomatised) served as sources of the magmas. After a time lapse of about 350 m y., large-scale emplacement of Paleoproterozoic units took place. These rocks cover about 50% of the region. Their geochemistry indicates juvenile magmatism with a minor contribution from crustal sources. These rocks also exhibit potassic calc-alkaline differentiation trends, again akin to I- and M-type magmas, and show negative anomalies for Ta–Nb, Ti and P. Depleted and metasomatised mantle, resulting from interaction with adakitic or trondhjemitic melts in a subduction zone setting, is interpreted to be the main source of the magmas, predominanting over crustal recycling. U–Pb ages indicate generation of plutonic rocks at 2.24–2.22 Ga (in some places at about 2.4–2.3 Ga) and 2.13–2.11 Ga, and andesitic volcanism at 2.15 Ga. Isotopic evidence indicates juvenile magmatism (epsilon Nd(t) of +2.9 to −2.9). After a time lapse of about 200 m y. a period of within-plate magmatic activity followed, with acidic volcanism (1.79 Ga) in Oros, granitic plutonism (1.74 Ga) in the Serido region, anorthosites (1.70 Ga) and A-type granites (1.6 Ga) in the Transverse Zone (TZ). Early Neoproterozoic volcanism at 1091 Ma, and A-type plutonism, from 920 to 775 Ma, mark the intracontinental magmatism in the TZ. In the Serido Domain, the Late Neoproterozoic registers several events of plutonism, at 600–593, 575–560, 548–533, 528–510, 495–450 Ma. These rocks cover ca. 15% of the area, while Neoproterozoic supracrustal rocks cover ca. 30%. The most important magmatic event is that at 575 Ma, consistent with the peak of widespread transpression and synchronous high temperature metamorphism. The Neoproterozoic rocks are mostly K-enriched alkaline or transitional to calc-alkaline. Inherited Archaean and Palaeoproterozoic zircons and Nd model ages, as well as moderate to strongly negative (−21 to −9) epsilon Nd, and persistent negative anomalies for Ta–Nb, Ti and P indicate significant crustal contributions in their genesis. While a convergent setting (subduction zone) could explain the Archaean and Palaeoproterozoic units, this is not so for the Neoproterozoic rocks which mimic the geochemical and isotopic features of the older sources. In the study area, the peak of juvenile accretion (mantle derived magmas) took place in the Archaean (3.4–2.7 Ga) and Palaeproterozoic (2.4–2.11 Ga), whereas crustal recycling predominated in the Neoproterozoic.

Here we report a new study of a gabbroic suite and its associated dioritic and monzogranitic plutons situated in the Yangtze continental interior, the unique continental core in South China, by means of integrated U–Pb dating and Hf isotope analysis of zircon and whole rock Sr–Nd isotope and elemental geochemistry. These intrusive suites are parts of a large batholith (∼970 km2) known as the Neoproterozoic Huangling intrusive complex, which is emplaced in the Archean to Paleoproterozoic high-grade terrain. The gabbro and diorite are dated at 812 ± 3 Ma and 816 ± 6 Ma, respectively, whereas the monzogranite is dated at 801 ± 6 Ma. Trace element geochemistry of magmatic clinopyroxene, peritectic hornblende and petrography of the gabbro suggest that the mafic suite formed by anhydrous melt that had undergone the early stages of crystalline fractionation of plagioclase, clinopyroxene and/or garnet. Zircon Hf isotope and whole-rock Sr–Nd isotopic and elemental compositions infer that the gabbro was sourced by slightly enriched lithospheric mantle modified by previous subduction; the diorite is likely to have been derived from ∼850 Ma igneous rocks by anatexis and admixing variably with mantle-derived melt, whereas the monzogranite was dominantly sourced by the crystalline basement rocks. It is thus suggested that the associated igneous suites formed in a rift-related setting, and underplating of mantle-derived melt and mantle input had played a significant role during the magmatism. This plutonism event is synchronous with the initial deposition of widespread rift-basins in South China, which was succeeded by huge volumes of mid-late Neoproterozoic to Paleozoic sedimentary successions. These findings hence attest that the magmatism took place in a within-plate environment and a consecutively rift-related event was likely initiated at ∼850 Ma. In the interior of the Yangtze block, which is also widely recorded along its northern, western and northeastern margins and in the Cathaysia block.

New U-(Th)/Pb geochronology and geochemical analyses of plutonic bodies in the Hindu Kush range, NW Pakistan, provide insight on the crustal growth and tectonic evolution of the southern Eurasian margin. These new data outline a protracted magmatic history that spans the Cambrian to the Neogene (ca. 538 to 23 Ma) and record a variety of petrogenetic associations variably influenced by within plate, volcanic arc, and collision tectonic environments. The Kafiristan pluton (538 ± 4 to 487 ± 3 Ma) yields geochemical signatures consistent with extensional plutonism and rifting of the Hindu Kush terrane from Gondwana. The Tirich Mir (127 ± 1 to 123 ± 1 Ma) and Buni-Zom (110 ± 1 to 104 ± 1 Ma) plutons have geochemical signatures that can be attributed to a subduction related continental volcanic arc system that developed along the southern margin of Eurasia in the Mesozoic. The Garam Chasma pluton, the youngest body in the study area (27.3 ± 0.5 to 22.8 ± 0.4 Ma), yields a geochemical signature consistent with widespread anatexis during crustal thickening related to the development of the Himalaya. The present geochemical and geochronological analysis from the Hindu Kush have produced important new constraints on the timing of tectonic events and variable tectonic settings along the south Eurasian margin before and after the continued India–Asia collision.

Integrated geochemical, isotopic, and geochronological constraints from Jurassic plutonic rocks of the Central Cordillera in Colombia were used to determine the tectonic setting and long-term tectonomagmatic evolution of the Northern Andes. We examined three plutonic units with compositions that vary from diorite to granite and with U-Pb zircon crystallization ages from 165 Ma to 129 Ma. These units are interpreted as subduction-related magmas, as indicated by their K 2 O, Na 2 O contents, light to heavy rare earth element (LREE/HREE) ratios, and Pb isotope signatures. The Nd and Hf isotope compositions of these magmatic events become more juvenile (radiogenic) with time. This compositional record suggests an arc maturity trend in which partial melting of basaltic and peridotitic sources becomes more significant than radiogenic subducted sediments or the ancient continental crust. Global-scale tectonic reconstructions suggest that Late Jurassic to Early Cretaceous subduction of the Farallon oceanic plate under the Andean continental margin became highly oblique. The consequence was a reduction of the fusible sedimentary budget commonly incorporated during subduction into the mantle, leaving a more refractory mantle with a more primitive compositional signature, and a major decrease in magmatic activity in the Early Cretaceous. In addition, the magmatic evolution recorded in the North Andean Jurassic arc shows that long-term source evolution and regional-scale plate-tectonic processes also play an important role in the compositional evolution and volumes of magmatic products in convergent settings.

Geological mapping and zircon U–Pb/Hf isotope data from 35 samples from the central Tanzania Craton and surrounding orogenic belts to the south and east allow a revised model of Precambrian crustal evolution of this part of East Africa. The geochronology of two studied segments of the craton shows them to be essentially the same, suggesting that they form a contiguous crustal section dominated by granitoid plutons. The oldest orthogneisses are dated at ca. 2820 Ma (Dodoma Suite) and the youngest alkaline syenite plutons at ca. 2610 Ma (Singida Suite). Plutonism was interrupted by a period of deposition of volcano-sedimentary rocks metamorphosed to greenschist facies, directly dated by a pyroclastic metavolcanic rock which gave an age of ca. 2725 Ma. This is supported by detrital zircons from psammitic metasedimentary rocks, which indicate a maximum depositional age of ca. 2740 Ma, with additional detrital sources 2820 and 2940 Ma. Thus, 200 Ma of episodic magmatism in this part of the Tanzania Craton was punctuated by a period of uplift, exhumation, erosion and clastic sedimentation/volcanism, followed by burial and renewed granitic to syenitic magmatism. In eastern Tanzania (Handeni block), in the heart of the East African Orogen, all the dated orthogneisses and charnockites (apart from those of the overthrust Neoproterozoic granulite nappes), have Neoarchaean protolith ages within a narrow range between 2710 and 2630 Ma, identical to (but more restricted than) the ages of the Singida Suite. They show evidence of Ediacaran “Pan-African” isotopic disturbance, but this is poorly defined. In contrast, granulite samples from the Wami Complex nappe were dated at ca. 605 and ca. 675 Ma, coeval with previous dates of the “Eastern Granulites” of eastern Tanzania and granulite nappes of adjacent NE Mozambique. To the south of the Tanzania Craton, samples of orthogneiss from the northern part of the Lupa area were dated at ca. 2730 Ma and clearly belong to the Tanzania Craton. However, granitoid samples from the southern part of the Lupa “block” have Palaeoproterozoic (Ubendian) intrusive ages of ca. 1920 Ma. Outcrops further south, at the northern tip of Lake Malawi, mark the SE continuation of the Ubendian belt, albeit with slightly younger ages of igneous rocks (ca. 1870–1900 Ma) which provide a link with the Ponte Messuli Complex, along strike to the SE in northern Mozambique. In SW Tanzania, rocks from the Mgazini area gave Ubendian protolith ages of ca. 1980–1800 Ma, but these rocks underwent Late Mesoproterozoic high-grade metamorphism between 1015 and 1040 Ma. One granitoid gave a crystallisation age of ca. 1080 Ma correlating with known Mesoproterozoic crust to the east in SE Tanzania and NE Mozambique. However, while the crust in the Mgazini area was clearly one of original Ubendian age, reworked and intruded by granitoids at ca. 1 Ga, the crust of SE Tanzania is a mixed Mesoproterozoic terrane and a continuation from NE Mozambique. Hence the Mgazini area lies at the edge of the Ubendian belt which was re-worked during the Mesoproterozoic orogen (South Irumide belt), providing a further constraint on the distribution of ca. 1 Ga crust in SE Africa. Hf data from near-concordant analyses of detrital zircons from a sample from the Tanzania Craton lie along a Pb-loss trajectory (Lu/Hf = 0), extending back to ∼3.9 Ga. This probably represents the initial depleted mantle extraction event of the cratonic core. Furthermore, the Hf data from all igneous samples, regardless of age, from the entire study area (including the Neoproterozoic granulite nappes) show a shallow evolution trend (Lu/Hf = 0.028) extending back to the same mantle extraction age. This implies the entire Tanzanian crust sampled in this study represents over 3.5 billion years of crustal reworking from a single crustal reservoir and that the innermost core of the Tanzanian Craton that was subsequently reworked was composed of a very depleted, mafic source with a very high Lu/Hf ratio. Our study helps to define the architecture of the Tanzanian Craton and its evolution from a single age-source in the early Eoarchaean.

Agawa gold prospect, located in Yamaguchi Prefecture, southwestern Japan, is a small prospect, where placer gold has been explored and mined since the 17th century. We investigated the prospect to clarify the genesis of the deposit based on the geology, hydrothermal alteration, geochronology, and ore mineralogy. The main mineralized zone of the prospect has a horizontal and vertical extensions of 500 m and 100 m, respectively, and a width of less than 100 m. Gold mineralization in the prospect occurs as dissemination and stockwork veinlets in the intensely sericitized rocks at the apical part of the Agawa dioritic porphyry intrusion at 86.5–88.5 Ma. Mineralization is typified by at least three stages – an early stage characterized by the occurrence of pyrrhotite and native gold; a middle stage by chalcopyrite; and a late stage by pyrite–bornite. Mineral assemblage and fluid inclusion microthermometry estimation suggest a trend of decreasing temperatures from 400°C to 160°C at a constant sulfur fugacity. The mineralizing fluids formed by the mixing of a hypogene fluid of possibly magmatic origin with an external lower-temperature and lower-salinity fluid. The mixing process decreased the temperature and salinity of the fluid, resulting in the precipitation of sulfides, native gold and Bi–Te alloys and sulfosalts. The magnetite-series signature of the Agawa porphyry and related molybdenite-bearing mineralization indicate that the plutonism of the San-in granitoids belt extends to the westernmost end of the Honshu Island. The compiled geochronology and distribution of the metallic deposits in the southwestern Japan arc show that transition from ilmenite-series to magnetite-series plutonism started earlier in the west, and shifted eastwards with time during the period from Late Cretaceous to Paleogene.

Beneath volcanoes are magmas that never erupt but that become frozen into feldspar- and quartz-rich rocks broadly called granite. Where the crystallized magmas form bodies with distinctive textures, they are grouped into named units—plutons. The rate (pace) at which magmas accumulate into plutons is fundamental to understanding both how room is made for the magmas and how unerupted and erupted magmas are connected. Dating plutonic rocks suggests that plutons accumulate slowly. Although the pace of magma accumulation does not preclude direct connections between plutons and small volcanic eruptions, it appears to be far too slow to support connections between most plutons and supereruptions.

In this contribution, we present field-based evidence that in the Mary Kathleen Domain from the Eastern Fold Belt of the Mount Isa Inlier the 1790–1750 Ma metasediments of the Leichhardt Superbasin were sheared and folded between 1750 and 1710 Ma. The Mary Kathleen Domain consists of a series of anastomosing high and low strain domains intruded syn- to late-tectonically by a series of 1740–1710 Ma felsic and mafic plutons and dykes. The timing relationships in the high strain domains are unclear due to mylonitisation and transposition but in the lower strain domains are well-preserved. The earliest deformation, D1, consists of a series of low angle truncation surfaces and shear zones that are folded around large scale N-S trending upright folds during D2. The D2 folds were refolded during D3 along NW to EW trending fold axes. An undeformed granitic pluton from the Mt Godkin area dated at ~1710 Ma that crosscuts the D2-D3 folds and the youngest detrital zircon population of ~1750 Ma constrains the timing of D1-D3 deformation between 1750 and 1710 Ma. Later, N-S (D4) and N-E (D5) trending brittle-ductile shears are interpreted to indicate a late Isan Orogeny overprint. The occurrence of contemporaneous folding in the Western Fold Belt suggests that between 1750 and 1710 Ma the eastern margin of the North Australia Craton was experiencing a significant deformation event that can be correlated with similarly aged deformation events from other parts of the North Australia Craton, from South Australia Craton and from East Antarctica. Following the assembly of most of the Nuna Supercontinent by 1.8 Ga, we postulate that the 1750–1710 Ma deformation and plutonism observed in Mount Isa Inlier is part of a series of worldwide orogenic events that contributed to the final configuration of the Nuna Supercontinent.

The Xolapa Complex (XC) is a high-grade metamorphic belt exposed along the southern margin of the North American plate in Mexico. Its evolution includes an episode of widespread anatexis related to crustal thickening and subsequent uplift to upper crustal levels, which culminated in the Paleocene. On the basis of field and petrographic work, this study integrates a petrological modelling approach with LA-ICP-MS U–Pb zircon and monazite geochronology to elucidate the tectonothermal evolution of this metamorphic belt. The study area in central XC includes a suite of alternating migmatitic paragneiss and garnet-bearing mafic schist. Petrological evidence and phase equilibria calculations demonstrate that a staurolite–kyanite grade metamorphism occurred at ~640–670 °C and 8–9 kbar before extensive migmatization took place. Differential anatexis of fertile and refractory layers occurred progressively via biotite and amphibole dehydration-melting reactions, and continued during peak metamorphism at granulite-facies conditions of ~800–820 °C and ~5–7 kbar. According to Ti-in-zircon thermometry, melt generation/mobilization progressed during cooling until crystallize at ~700 °C. The age of prograde metamorphism was likely recorded by monazite cores that give mid- to Late Cretaceous ages. Cooling and melt crystallization could be constrained by leucosome zircon dated at 61.8±0.6 Ma. Both zircon and low-Y monazite from whole rock and melanosome portions, respectively, are consistent with an episode of growth around 60.9±0.5 Ma. Monazite, however, would have continued its crystallization process for a period of ca. 10 Ma. Thin zircon and high-Y monazite rims show ages between ~34–25 Ma and are interpreted to reflect a stage of reheating by magmatic advection related to large Oligocene plutonism in the region. Age and nature of central XC basement show good correlation with other Early-Cretaceous volcano-sedimentary basins of central and southern Mexico. A period of crustal thickening would have buried the sequence at depths of ~30 km, causing Barrovian-type metamorphism during mid- to Late Cretaceous time and eventually, anatexis that evolved at granulite-facies conditions during orogenic collapse in the Paleocene (≥62 Ma). The time span from leucosome crystallization to late-stage reheating in central XC would imply a protracted high-temperature evolution indicating a middle- to upper-crustal residence time of at least ca. 30 Ma.

Garnet is a prominent recorder of metamorphic processes and plays a pivotal role in deciphering the pressure-temperature evolution of metamorphic rocks. However, the potential of regional metamorphic garnet for laser ablation U–Pb dating remains unexplored, as variable and low U ( We applied LA-ICP-MS U–Pb dating to garnet and zircon, monazite, and xenotime from The Straits Schist, western Connecticut, USA, to constrain the timing of garnet growth within the overall Acadian-age metamorphic history recorded by this unit. We assessed the effects of U-rich inclusions on garnet U–Pb data using high-resolution microbeam sampling, grain size analysis, and calculations assessing how inclusion size and abundance affect U concentrations measured in garnet. When analysing garnet, our results demonstrate that by scrutinizing the time-resolved U-signal, U-rich inclusions can be identified and effectively removed during data evaluation. If U-rich inclusions are unaccounted for, ‘garnet’ analyses have elevated U contents compared to pure garnet and in a Tera-Wasserburg diagram, data points are shifted to the left, right, or along the garnet regression line, for inclusions older, younger or of the same age as the garnet, respectively. Garnet from two metapelitic samples yielded lower intercept ages of 409 ± 10 Ma and 406 ± 15 Ma, and a combined U–Pb age of 406.1 ± 8.3 Ma. Metamorphic zircon yielded age clusters at 446.2 ± 4.2 Ma, 413.3 ± 3.0 Ma, and 382.9 ± 2.8 Ma, monazite ages range between 390 and 355 Ma, and xenotime yielded 370.1 ± 5.6 Ma. The ∼446 Ma age peak is attributed to detrital zircon formed during the waning stages of the Taconian orogeny. Early Acadian metamorphism is recorded by garnet and ∼413 Ma zircon, whereas monazite and zircon ages of 390 to 383 Ma, coincide with peak metamorphic conditions. Early Carboniferous monazite and xenotime ages could reflect the incursion of fluids into The Straits Schist during Neo-Acadian metamorphism, coeval plutonism in New England, or breakdown of garnet during regional exhumation.

The Cassiterita Orthogneiss is the oldest pluton so far found within the Mineiro belt. In situ zircon U-Pb ages constrain the crystallization of the Cassiterita Orthogneiss to between 2472 ± 11 and 2414 ± 29 Ma. Zircon overgrowths are dated at 2024 ± 54 Ma, which matches the timing of the regional metamorphic overprint in the main belt. One metatonalite dike yields a zircon U-Pb age of 2156 ± 17 Ma, while a single inherited core is concordant at 2426 ± 17 Ma. The studied rocks exhibit low to medium grade metamorphism, and show tonalitic and granodioritic composition akin to TTG suites (tonalite-trondhjemite-granodiorite). The trace element patterns suggest that partial melting and fractional crystallization operated in the genesis. The La/Yb N , Yb N , Sr/Y, Nb/Ta and Zr/Sm values point to a garnet amphibolite residue. The positive e Nd(t) (+5.2 to +1.3) and low 87 Sr/ 86 Sr i (0.700–0.702) isotopic signatures suggest a LREE- and/or LILE LILE-enriched MORB mantle source. The zircon e Hf(t) parameters (-8.0 to +2.9) of the studied samples indicate some crustal assimilation during magma genesis. The chemical and isotopic signatures of the Cassiterita Orthogneiss are similar to nearby (ca. 2.35 Ga) TTG plutons, interpreted as cogenetic. This peculiar plutonism (from 2.47 to 2.35 Ga) marks the earliest stage of a long-lived accretionary regime (2.47–2.00 Ga) that built the Mineiro belt. This earliest orogenic event is roughly coeval with the (chemical) sedimentary infill of the passive basin (Minas Supergroup), previously dated at ca. 2.42 Ga. The age matches suggest a geodynamic link between the oceanic arc magmatism and penecontemporaneous basin infill in the continental margin. Early Paleoproterozoic TTG plutons such as the Cassiterita Orthogneiss have been related to the earliest accretionary processes that developed away from continental margins, where roughly coeval dike swarms and A-type plutons are emplaced along with the onset of passive basins. We explore the potential association and temporal interplay between convergent and intraplate settings and other major changes beyond the Archean-Paleoproterozoic Transition.

The Northern Andean Block is the result of complex tectonic interaction between the Farallon-Nazca, South American, and Caribbean Plates. Abundant late Cenozoic volcanism (and associated hypabyssal porphyritic plutonism), beginning in the mid- to late Miocene, is the result of subduction-related mantle-derived magmatic activity, superimposed upon a compositionally varied and structurally complex basement during the late stages of the Northern Andean orogeny. Tectonic consolidation and subduction of the segmented Nazca Plate during the late Miocene-Pliocene led to conformation of the modern-day Colombian segment of the Northern Andean Volcanic Zone. The Colombian arc segment represents the northernmost expression of subduction-related volcanism within South America’s Andean Cordillera.

This paper describes a detailed petrographic and isotopic study of hypabyssal sheets of quartz-syenite that represent the ultimate differentiation product of the oceanite alkaline magmatic reservoir of the Piton des Neiges stratovolcano (Réunion Island). Clay minerals of the corrensite to chlorite series crystallized during the late-magmatic activity, with quartz, carbonates and accessory minerals from juvenile fluids filling the primary porosity of the quartz-syenite. It is proposed that a double chemical transfer occurred at the end of the crystallization process: degassing of the exsolved CO2-rich and SiO2-rich fluid from the magmatic chamber through the porous quartz-syenite and diffusion of Al, Fe and Mg from the intruded basalts affected by the juvenile fluids towards the primary porosity of the quartz-syenite, feeding the crystallization of late-magmatic clays in the residual primary pores after quartz and carbonate deposition. This process may be generalized to alkaline plutonism, as well as to the primitive crusts of terrestrial planets, and may be the first source of clays in early planets.

New whole-rock lead (Pb) isotope analyses are presented in this study for granitoid orthogneisses from the Southwest Grenville Province in Ontario and Western Quebec. These data are used to test the location of a cryptic Archean-Proterozoic suture proposed on the basis of neodymium (Nd) isotope mapping. Immediately south of the inferred suture boundary, Pb isotope results show a crustal component derived solely from a juvenile Paleoproterozoic mantle source. These data are distinctly different from the reworked Archean craton to the northwest and strongly support the boundary derived from Nd isotope data. Pb signatures in the Paleoproterozoic crust suggest a southerly increase in magmatic reworking due to intensive plutonism during the late Paleoproterozoic and early Mesoproterozoic periods. The accretion of a juvenile arc to the Archean margin during the Penokean event (ca. 1.85 Ga) would have triggered subduction-zone reversal and the development of a long-lived ensialic arc on the composite margin. This was expressed as a 1.75 Ga Killarnian magmatic event and subsequent early Mesoproterozoic magmatism. This tectonic model for the Southwest Grenville Province shows that its crustal evolution is consistent with the Paleoproterozoic Makkovik-Ketilidian Orogen of Labrador and Southern Greenland. Hence, the application of whole-rock Pb isotope data in conjunction with Nd model ages provides data useful for mapping the extent of crustal terranes of differing age, which is essential for modeling the tectonic evolution of complex ancient accretionary orogens.

The Central Andes is a key global location to study the enigmatic relation between volcanism and plutonism because it has been the site of large ignimbrite- forming eruptions during the past several million years and currently hosts the world's largest zone of silicic partial melt in the form of the Altiplano- Puna Magma (or Mush) Body (APMB) and the Southern Puna Magma Body (SPMB). In this themed issue, results from the recently completed PLUTONS project are synthesized. This project focused an interdisciplinary study on two regions of large-scale surface uplift that have been found to represent ongoing movement of magmatic fluids in the middle to upper crust. The locations are Uturuncu in Bolivia near the center of the APMB and Lazufre on the Chile-Argentina border, on the edge of the SPMB. These studies use a suite of geological, geochemical, geophysical (seismology, gravity, surface deformation, and electromagnetic methods), petrological, and geomorphological techniques with numerical modeling to infer the subsurface distribution, quantity, and movements of magmatic fluids, as well as the past history of eruptions. Both Uturuncu and Lazufre show separate geophysical anomalies in the upper, middle, and lower crust (e.g., low seismic velocity, low resistivity, etc.) indicating multiple distinct reservoirs of magma and/or hydrothermal fluids with different physical properties. The characteristics of the geophysical anomalies differ somewhat depending on the technique used-reflecting the different sensitivity of each method to subsurface melt (or fluid) of different compositions, connectivity, and volatile content and highlight the need for integrated, multidisciplinary studies. While the PLUTONS project has led to significant progress, many unresolved issues remain and new questions have been raised.

Chrome chlorites are usually found as secondary phases formed by hydrothermal alteration of chromite deposits and associated mafic/ultramafic rocks. Here, we report the 40Ar/39Ar age of chrome chlorites separated from the Luobusa massive chromitites which have undergone secondary alteration by CO2-rich hydrothermal fluids. The dating results reveal that the intermediate heating steps (from 4 to 10) of sample L7 generate an age plateau of 29.88 &plusmn, 0.42 Ma (MSWD = 0.12, plateau 39Ar = 74.6%), and the plateau data points define a concordant inverse isochron age of 30.15 &plusmn, 1.05 Ma (MSWD = 0.08, initial 40Ar/36Ar = 295.8 &plusmn, 9.7). The Ar release pattern shows no evidence of later degassing or inherited radiogenic component indicated by an atmospheric intercept, thus representing the age of the hydrothermal activity. Based on the agreement of this hydrothermal age with the ~30 Ma adakitic plutons exposed in nearby regions (the Zedong area, tens of kilometers west Luobusa) and the extensive late Oligocene plutonism distributed along the southeastern Gangdese magmatic belt, it is suggested that the hydrothermal fluids are likely related to the ~30 Ma magmatism. The hydrothermal fluid circulation could be launched either by remote plutons (such as the Sangri granodiorite, the nearest ~30 Ma pluton west Luobusa) or by a similar coeval pluton in the local Luobusa area (inferred, not found or reported so far). Our results provide important clues for when the listwanites in Luobusa were formed.

The Ndembera metavolcanic rocks represent a continuum of compositions ranging from intermediate to more siliceous calc-alkaline trachyandesites-dacites-trachytes-rhyolites which have been intruded by largely metaluminous, calc-alkaline I-type granites in the Palaeoproterozoic Usagaran Belt of southwestern Tanzania. SHRIMP U–Pb zircon age data show that the Ndembera metavolcanic rocks were extruded at 1871 ± 30 Ma, an event that was largely coeval with the emplacement of cross-cutting microcline-biotite rich granites at 1896 ± 29 Ma. Despite some compositional differences, both the granites and metavolcanic rocks share similar geochemical features including very coherent REE patterns characterized by enrichment of the LREE relative to the HREE (La/YbCN = 13.6–32.8 (average = 23.9) for metavolcanic rocks and La/YbCN = 10.8–38.2 (average = 21.8) for granites), negative Eu anomalies (Eu/Eu* = 0.45–1.01 (average = 0.83) for volcanic rocks and Eu/Eu* = 0.48–0.70 (average = 0.60) for granites), negative Ta, Ti and Nb anomalies (Nb/Lapm = 0.14–0.29 (average = 0.20 for volcanic rocks and Nb/Lapm = 0.01–0.37 (average = 0.16) for granites). The metavolcanic rocks have ɛNd (1871 Ma) values of −0.03 to −4.89 and TDM ages of 2243–2714 which are broadly similar to those of the granites (ɛNd (1896 Ma) values of −3.56 to −4.59 and TDM ages of 2469–2646 Ma). The geochemical similarities between the Ndembera volcanic rocks and granites, coupled with their similar emplacement age, suggest that the two rock suites were derived by the same processes in the same tectonic setting from an isotopically similar source. These geochemical features coupled with the paucity of mafic rocks suggest the derivation of the pluto-volcanic suite by crustal anatexis of basic meta-igneous rocks mixed with a minor metasedimentary component in an intra-continental setting. The more siliceous compositions in the suite may have formed by subsequent fractionation involving hornblende, plagioclase, biotite, titanite and apatite as indicated by the negative correlation between SiO2 and MgO, Fe2O3, Al2O3, CaO, TiO2 and P2O5, low Sr contents and negative Eu and Ti anomalies. The ∼1.87 Ga coeval felsic volcanic and granitic magmatic event documented in the Ndembera Group is also a feature of the nearby Ubendian belt to the west pointing to a Palaeoproterozoic regional thermal event that occurred in southwestern and western Tanzania.

The geological and metallogenic history of the Singhbhum Craton of eastern India is marked by several episodes of volcanism, plutonism, sedimentation and mineralization spanning from Paleoarchean to Mesoproterozoic in a dynamic tectonic milieu. Distinct signatures of this Archean-Proterozoic geodynamic process are preserved in discrete crustal provinces that constitute the Singhbhum Craton. Here we report new major, trace and PGE geochemical data from the ~ 3.4 Ga Iron Ore Group (IOG) volcanic rocks of the Jamda-Koira basin, a part of the BIF-bearing volcano-sedimentary sequences of the Noamundi-Jamda-Koira iron ore basin in the western part of Singhbhum Granite (SBG), and ~ 2.25 Ga metavolcanic rocks of Malangtoli. The IOG and Malangtoli volcanic rocks are porphyritic basalts and despite belonging to different ages, they exhibit similar mineralogical composition marked by clinopyroxene, plagioclase (present as both phenocryst and groundmass), opaques and volcanic glass (restricted to groundmass). The igneous mineralogy of these rocks has been overprinted by greenschist to lower amphibolite grade of metamorphism. The Malangtoli samples show low and high MgO compositional varieties. Immobile trace element compositions classify the IOG samples as andesite having a calc-alkaline composition, whereas the Malangtoli rocks correspond to basalt and andesite displaying a tholeiitic to calc-alkaline trend. The IOG basalts show low to moderate PGE contents marked by 26.23–68.35 ppb of ΣPGE, whereas the Malangtoli basalts display a moderate to high concentration of PGE (ΣPGE = 43.01–190.43 ppb). The studied samples have relatively enriched ΣPPGE ranging from 24.1–63.3 ppb (IOG) and 34–227.3 ppb (Malangtoli) against 2.2–4.1 ppb and 1.9–8.9 ppb ΣIPGE contents respectively. PPGE/IPGE ratios for IOG and Malangtoli samples range from 7.7–17.6 and 4.8–59.9. HFSE, REE and PGE compositions suggest a low degree (

A complex array of faulted arc rocks and variably metamorphosed forearc accretionary complex rocks form a mappable arc–forearc boundary in southern Alaska known as the Border Ranges fault (BRF). We use detrital U–Pb zircon dating of metasedimentary rocks within the Knik River terrane in the western Chugach Mountains to show that a belt of Early Cretaceous amphibolite-facies metamorphic rocks along the BRF was formed when older mélange rocks of the Chugach accretionary complex were reworked in a sinistral-oblique thrust reactivation of the BRF during a period of forearc plutonism. The metamorphic subterrane of the Knik River terrane has a maximum depositional age (MDA) of 156.5 ± 1.5 Ma and a detrital zircon age spectrum that is indistinguishable from the Potter Creek assemblage of the Chugach accretionary complex, supporting correlation of these units. These ages contrast strongly with new and existing data that show Triassic to earliest Jurassic detrital zircon ages from metamorphic screens in the plutonic subterrane of the Knik River terrane, a fragmented Early Jurassic plutonic assemblage generally interpreted as the basement of the Peninsular terrane. Based on these findings, we propose the following new terminology for the Knik River terrane: (1) “Carpenter Creek metamorphic complex” for the Early Cretaceous “metamorphic subterrane”, (2) “western Chugach trondhjemite suite” for the Early Cretaceous forearc plutons within the belt, (3) “Friday Creek assemblage” for a transitional mélange unit that contains blocks of the Carpenter Creek complex in a chert–argillite matrix, and (4) “Knik River metamorphic complex” in reference to metamorphic rocks engulfed by Early Jurassic plutons of the Peninsular terrane that represent the roots of the Talkeetna arc. The correlation of the Carpenter Creek metamorphic complex with the Chugach mélange indicates that the trace of the BRF lies ∼1–5 km north of the map trace shown on geologic maps, although, like other segments of the BRF, this boundary is blurred by local complexities within the BRF system. Ductile deformation of the mélange is sufficiently intense that few vestiges of its original mélange fabric exist, suggesting the scarcity of rocks described as mélange in the cores of many orogens may result from misidentification of rocks that have been intensely overprinted by younger, ductile deformation.

For more than 25 yr, the Mazatzal orogeny has been a central component of virtually all tectonic models involving the Proterozoic rocks of the southwestern United States. Recent recognition that some sedimentary sequences and some major structures are Mesoproterozoic rather than Paleoproterozoic has led to new questions about the nature, even the existence, of the Mazatzal orogeny. This study aims to clarify the relationship between Mazatzal (ca. 1.65 Ga) and Picuris (ca. 1.45 Ga) orogenic activity. New U-Pb geochronology of variably deformed igneous and metasedimentary rocks constrains several periods of deformation at ca. 1.68 Ga, 1.66 Ga, and 1.49–1.45 Ga in the Four Peaks area of central Arizona. Detrital zircon analyses and field relationships indicate the deposition of a rhyolite-sandstone-shale assemblage at ca. 1.660 Ga with renewed deposition at 1.502–1.490 Ga and a significant disconformity, but no recognized angular unconformity, between these episodes. Three populations of monazite growth at 1.484 ± 0.003 Ga, 1.467 ± 0.004 Ga, and 1.457 ± 0.005 Ga indicate prolonged Mesoproterozoic metamorphism. The ca. 1.485 Ga population is associated with the formation of the Four Peaks syncline during Mesoproterozoic orogenesis and subsequent amphibolite-facies contact metamorphism. Rocks in the Four Peaks area record polyphase deformation, sedimentation, and plutonism from the Paleoproterozoic to Mesoproterozoic. Hf-isotopic data suggest the involvement of older, nonjuvenile crust. In this area, effects of the Mazatzal (ca. 1.65 Ga) and Picuris orogenies (ca. 1.49–1.45 Ga) are entwined and involved sedimentation, deformation, pluton emplacement, and pluton-enhanced metamorphism.

The Gravina belt consists of Upper Jurassic through Lower Cretaceous marine clastic strata and mafic-intermediate volcanic rocks that occur along the western flank of the Coast Mountains in southeast Alaska and coastal British Columbia. This report presents U-Pb ages and Hf isotope determinations of detrital zircons that have been recovered from samples collected from various stratigraphic levels and from along the length of the belt. The results support previous interpretations that strata in the western portion of the Gravina belt accumulated along the inboard margin of the Alexander-Wrangellia terrane and in a back-arc position with respect to the western Coast Mountains batholith. Our results are also consistent with previous suggestions that eastern strata accumulated along the western margin of the inboard Stikine, Yukon-Tanana, and Taku terranes and in a fore-arc position with respect to the eastern Coast Mountains batholith. The history of juxtaposition of western and eastern assemblages is obscured by subsequent plutonism, deformation, and metamorphism within the Coast Mountains orogen, but may have occurred along an Early Cretaceous sinistral transform system. Our results are inconsistent with models in which an east-facing subduction zone existed along the inboard margin of the Alexander-Wrangellia terrane during Late Jurassic-Early Cretaceous time.

The Karagwe-Ankole belt forms part of a complex system of orogenic belts in Central-East Africa that record the amalgamation of Archaean and/or Paleoproterozoic continental kernels in the Proterozoic. The actual timing of tectonic processes, including initial basin formation and subsequent deformation, is only poorly constrained so that the geodynamic significance of the Karagwe-Ankole belt within the broader system of Proterozoic orogens in Central-East Africa is not well understood. This paper presents U–Pb ages of detrital zircons constraining the age of sediments of the eastern parts of the Karagwe-Ankole fold belt overlying the western Tanzania Craton and 39Ar–40Ar muscovite ages from mylonites and phyllonites associated with the main phase of subsequent shortening and fold-and-thrust tectonics (D2). 39Ar–40Ar muscovite ages from the main detachment between Archaean basement gneisses and imbricated cover rocks of the Kagera Supergroup in the eastern, frontal parts of the Karagwe-Ankole Belt constrain the timing of the main fabric forming event and thrusting (D2) to 1326 ± 10 Ma. This age is at the young end of the age range for the main phase of granite plutonism and mafic dyke emplacement that have previously been related to crustal extension and associated intracontinental rifting. If correct and representative for the main phase of deformation in the rest of the Karagwe-Ankole belt, the ages may rather point to a collisional event between the Congo and Tanzania Cratons west of the Karagwe-Ankole belt in Mesoproterozoic times, indicating a closer correlation with rocks of the Kibara Belt (sensu stricto) to the immediate south. U–Pb detrital zircon ages for the older Muyaga and overlying Bukoba Group of the Kagera Supergroup confirm the Paleoproterozoic timing of sedimentation from ca. 1780 Ma, but before ca. 1568 Ma. The presence of a distinct group of ca. 1750–1790 Ma zircons in the Bukoba Group indicate uplift, erosion and subsequent reworking of sediments and volcanic units contained in the Lower Muyaga Group to the west. The ages also suggest a correlation between the Bwezigoro Group of SW Uganda and the Bukoba Group indicating the presence of a far more extensive Paleoproterozoic and/or Early Mesoproterozoic foreland basin overlying the western margin of the Archaean Tanzania Craton and Paleoproterozoic Uganda Block.

The Eastern Desert of Egypt is well known as a gold-mining district since ancient times. Gold mineralization is closely associated with the granitic rocks in such way that the mineralization is either hosted by or occurs immediately adjacent to the granite intrusions. Granitic rocks accompanying gold mineralization in the Eastern Desert can be grouped into three categories i.e. syn-late tectonic calc-alkaline granites, calc-alkaline to mildly alkaline granites of the transitional stage and post-tectonic alkaline granites. Tectonically, gold mineralization is linked with the tectonothermal stages that were operative during the evolution of the Arabian–Nubian Shield (ANS). During the primitive stages of the island-arc formation, pre-orogenic gold mineralization (auriferous exhalites) was formed by hot brines accompanying submarine volcanic activity. No role for the granite is observed in this stage. Syn-orogenic gold mineralization (i.e. gold hosted in altered ophiolitic serpentinites along thrust faults and in sutures, quartz veins hosted in the metavolcano-sedimentary assemblage and/or the I-type granitic rocks surrounding them) connected with the collision and accretion stage is characterized by emplacement of calc-alkaline (I-type) older granite batholiths. Shear fractures reflected in brittle–ductile shear zones and amphibolite-green schist facies regional metamorphism were broadly contemporaneous with this intense compressional tectonic regime. Available fluid inclusion microthermometry and isotopic studies reveal that both metamorphic and magmatic fluids related to the syn-late tectonic calc-alkaline granites were operative. A further indication for the role of the granites is indicated by the presence of some concentrations of Antimony, Bismuth, Molybdenum, Tungsten, Rubidium, Beryllium, Tin, Yttrium, Ytterbium, Tantalum and Niobium in some auriferous quartz veins in the Egyptian gold mines. In the cratonal development of the (ANS), the land underwent a transitional stage between the major subduction-related calc-alkaline magmatic activity and the subsequent post-tectonic plutonism represented by the alkaline granites. This transitional stage is dominated by the eruption of Dokhan volcanics and deposition of molass-type Hammamat sediments. At ~ 590–530 Ma, the Arabian–Nubian Shield was deformed by post-accretionary structures, in the form of N-trending shortening zones such as the Hamisana shear zone and NW-trending strike-slip faults such as the Najd fault system. The regional NNW–SSE directed extension opened spaces that were progressively sealed with different magmatic phases including among them a considerable proportion of rocks referred to as “younger granites” in the Egyptian literature. Late-orogenic gold mineralization connected with the transitional stage is represented principally by the gold-bearing quartz veins traversing Hammamat molasse sediments, quartz veins traversing syn-extensional younger granites and generally quartz veins in ductile to brittle shears related to the Najd fault system and within Hamisana shear zone and its splays. By the end of Pan African orogeny until the Tertiary, the basement was intermittently intruded by a number of sub-alkaline to per alkaline granite bodies that host Mo, Sn, W, Nb–Ta and U mineralization in the Eastern Desert of Egypt. Anorogenic gold mineralization connected with post-orogenic granites is represented by small amounts of the element in disseminations, stockworks and quartz veins of Sn–W–Ta–U mineralization. The present review shows that gold mineralization in Egypt is an expression of two major cycles with distinct magmatic and tectonic characteristics, and the two cycles were separated by a transitional stage. The emplacement of granites in the compressional cycle played an important role in metamorphosing the country rocks by producing the heat energy required for the regional metamorphism and the providing of the magmatic fluids. The H 2 O–CO 2 fluids enriched in volatiles were released at the greenschist–amphibolite facies transition at 450°–500 °C and mixed with the I-type calc-alkaline granite related fluids and both moved down a temperature gradient away from the amphibolite-green schist transition at depth to a lower temperature regime in the upper levels where it is deposited in brittle–ductile shear zones. With the extensional cycle, the syn-extensional granite intrusions acted as heat engine in such way that the heat of the granite drove the convective cells to circulate through the auriferous host-granite contacts, leaching gold and other elements and depositing it in structurally favorable sites. In addition, the contrasts in competency between the granites with brittle deformational characteristics and the surrounding country rocks with a ductile response to stress, led to a generation of extensive fracture pattern within the more competent unit.

Ten localities, representing metasedimentary and igneous rocks from the northern part of the Paleoproterozoic Perapohja Belt, Fennoscandian Shield, were sampled for zircon U–Pb dating by LA-MC-ICP-MS and Sm–Nd analysis by TIMS. The results revealed two phases of granitic magmatism that took place at 1.99 Ga and 1.79–1.77 Ga. The former age (1989 ± 6 Ma) was given by the Kierovaara granite pluton representing the first example of felsic plutonism of this age in northern Finland, though A-type felsic volcanic rocks of the same age have previously been recognized. The strongly negative initial ɛnd values obtained for granitoids, ranging from −3.9 to −11.4, are compatible with the previous Sm–Nd data, indicating the presence of Archean basement in northern Finland at the time of granite emplacement. A garnet-whole rock Sm–Nd age of 1752 ± 14 Ma was measured for a mica gneiss, constraining the time of metamorphic cooling down to the closure temperature of garnet. Detrital zircon grains from quartzite samples belonging to the Jatulian Palokivalo Formation and a stratigraphically unassigned lithodemic unit, the Mellajoki Suite, yielded solely Archean zircon populations. In contrast, our sample from the Martimo Formation representing Kalevian sedimentation revealed a 66% Paleoproterozoic detrital zircon component with the youngest zircon grains showing an age of ca. 1.91 Ga. The new age data allow us to constrain the depositional time of this sedimentary unit between ca. 1.91 and 1.88 Ga, the latter being the time of the synorogenic plutonism. Our geochronological data coupled with recent data from other Karelian belts suggest that the depositional time period for rocks assigned to the Kaleva spans ca. 150 Ma and the simple division of these rocks into two non-coeval units, the Lower and Upper Kaleva, has become problematic.

s. For similar reasons the sessions dealing with Recent Advances in Exploration Geophysics attracted more than 70 papers. The rare interaction of Soviet and Australian geologists in these economic geology sessions would have been most interesting. Significant numbers of presentations concerned plate tectonics, which had gained acceptance over the previous decade. Precambrian geology and deep sea drilling also generated much interest and attracted numerous contributions. The largest audiences, approaching 300, were observed in sessions dealing with Circum–Pacific plutonism, exploration geophysics, uranium geology, mineral deposits, tectonics and Precambrian geology. Notably the Sydney IGC was the first following the formal establishment of the International Geological Correlation Programme (IGCP) in early 1973. Over the previous decade Australia had contributed significantly to this development (Harrington, 1994). Specialist Congress symposia sponsored by IGCP projects concerned: — Earliest Archaean tectonics and magmatism — Circum-Pacific plutonism — Tectonic aspects of ophiolites — Global correlation of epochs of folding — Correlation of kaolin genesis and age — Precambrian / Cambrian boundary problem

Dykes in the Strudengau area (SW Moldanubian Zone, Austria) can be mineralogically divided into lamprophyres (spessartites and kersantites) and felsic dykes (granite porphyries, granitic dykes and pegmatoid dykes). Geochemical analyses of 11 lamprophyres and 7 felsic dykes show evidence of fractional crystallization. The lamprophyres are characterized by metaluminous compositions, intermediate SiO2 contents and high amounts of MgO and K2O; these rocks have high Ba (800–3000 ppm) and Sr (250–1000 ppm) contents as well as an enrichment of large-ion lithophile elements over high field strength elements, typical for enriched mantle sources with variable modifications due to fractionation and crustal contamination. This geochemical signature has been reported from durbachites (biotite- and K feldspar-rich mela-syenites particularly characteristic of the Variscan orogen in Central Europe). For most major elements, calculated fractionation trends from crystallization experiments of durbachites give an excellent match with the data from the Strudengau dykes. This suggests that the lamprophyres and felsic dykes were both products of fractional crystallization and subsequent magma mixing of durbachitic and leucogranitic melts. Rb–Sr geochronological data on biotite from five undeformed kersantites and a locally deformed granite porphyry gave cooling ages of c. 334–318 Ma, indicating synchronous intrusion of the dykes with the nearby outcropping Weinsberger granite (part of the South Bohemian Batholith, c. 330–310 Ma). Oriented matrix biotite separated from the locally deformed granite porphyry gave an Rb–Sr age of c. 318 Ma, interpreted as a deformation age during extensional tectonics. We propose a large-scale extensional regime at c. 320 Ma in the Strudengau area, accompanied by plutonism of fractionated magmas of syncollisional mantle-derived sources, mixed with crustal components. This geodynamic setting is comparable to other areas in the Variscan belt documenting an orogenic wide extension by the end of the Carboniferous.

In order to clarify the early history of Japan, particularly during the Early Paleozoic, pre-Devonian granitoids in the South Kitakami Belt (SKB), NE Japan were dated by U–Pb zircon age by laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS). Two samples of diorite/tonalite from the Nagasaka area (Shoboji Diorite) and two of mylonitic tonalite from the Isawa area (Isawagawa Tonalite) yielded late Cambrian ages (500–490 Ma) for the primary magmatism. These ages newly identify a ca. 500 Ma (late Cambrian) arc plutonism in central NE Japan, which has not been recognized previously and has the following geological significance. The Cambrian granitoids are the oldest felsic plutonic rocks in NE Japan, which are independent of the previously known ca. 450 Ma (latest Ordovician) Hikami Granite in SKB. The Cambrian granitoids are extremely small in size at present but likely had a much larger distribution primarily, at least 30 km wide and potentially up to 80 km wide in a cross-arc direction. Their southerly extension was recognized in the Hitachi area (ca. 200 km to the south) and in central Kyushu (ca. 1500 km to SW). They likely represent remnants of the same mature arc plutonic belt in Early Paleozoic Japan, which developed in western Panthalassan (paleo-Pacific) margin, as well as the Khanka block in Far East Russia. The extremely small size of the Cambrian granitoids at present can be best explained by intermittent, severe tectonic erosion since the Paleozoic. This Cambrian arc granitoid belt likely developed from Primorye possibly to eastern Cathaysia (South China) via Japan.

Sausar Fold Belt (SFB) in central India forms the southern part of the Central Indian Tectonic Zone (CITZ) – a crustal scale Proterozoic mobile belt dissecting the Indian craton, whose tectonothermal history and age is important for understanding the Proterozoic crustal history of the Indian craton. SFB comprises a gneissic basement (TBG: Tirodi Biotite Gneiss) overlain by a supracrustal sequence of quartzite–pelite–carbonate (SSG: Sausar Group). SSG and TBG are deformed and metamorphosed in greenschist to amphibolite facies. Two phases of granite intrusion are observed in the SSG – a syntectonic foliated granite and a post-tectonic massive granite, with clear structural relationship with the host rocks. Monazite chemical dating (U–Th–total Pb) of the foliated and massive granites yield Neoproterozoic (ca. 945–928 Ma) ages that contradict many earlier geochronological interpretations. Foliated granites and the immediately adjacent TBG show monazite grains with ca. 945 Ma mean age, interpreted as the timing of D2 deformation and amphibolite facies metamorphism of SSG. The post tectonic granites intruded these rocks around 928 Ma, and were largely undeformed. A terminal thermal overprint is found in some monazite grain rims at ca. 785 Ma age. The younger Sausar tectonothermal events have overprinted the adjacent high-grade granulites of Ramakona–Katangi Granulite (RKG) belt, and should not be considered as parts of the same tectonothermal event representing different depth sections only.

Newly discovered xenoliths within Pliocene and Quaternary intermediate volcanic rocks from southern Peru permit examination of lithospheric processes by which thick crust (60–70 km) and high average elevations (3–4 km) resulted within the Altiplano, the second most extensive orogenic plateau on Earth. The most common petrographic groups of xenoliths studied here are igneous or meta-igneous rocks with radiogenic isotopic ratios consistent with recent derivation from asthenospheric mantle ( 87 Sr/ 86 Sr = 0.704–0.709, 143 Nd/ 144 Nd = 0.5126–0.5129). A second group, consisting of felsic granulite xenoliths exhibiting more radiogenic compositions ( 87 Sr/ 86 Sr = 0.711–0.782, 143 Nd/ 144 Nd = 0.5121–0.5126), is interpreted as supracrustal rocks that underwent metamorphism at ~9 kbar (~30–35 km paleodepth, assuming a mean crustal density of 2.8 g/cm 3 ) and ~750 °C. These rocks are correlated with nonmetamorphosed rocks of the Mitu Group and assigned a Mesozoic (Upper Triassic or younger) age based on detrital zircon U-Pb ages. A felsic granulite Sm-Nd garnet whole-rock isochron of 42 ± 2 Ma demonstrates that garnet growth took place in Eocene time. Monazite grains associated with quenched anatectic melt networks in the same rocks yield ion microprobe U-Pb ages ranging from 3.2 ± 0.2 to 4.4 ± 0.3 Ma (2σ). These disparate geochronologic data sets are reconciled by a model wherein Mesozoic cover rocks were transferred to >30 km depth beneath the plateau in the Eocene and progressively heated until at least Pliocene time. Isothermal decompression and partial melting ensued as these rocks were entrained as xenoliths in volcanic host magmas and transported toward the surface. Mafic granulites and peridotites from the same xenolith suite comprise the basement of the metasedimentary sequence, exhibiting isotopic characteristics of Central Andean crust. Calculated equilibrium pressures for these basement rocks are >11 kbar, suggesting that the basement-cover interface lies beneath the northernmost Altiplano at ~30–40 km below the surface. Together, these results indicate that crustal thickening under the northernmost Altiplano started earlier than major latest Oligocene and Miocene uplift episodes affecting the region and was coeval with a flat slab–related regional episode of deformation. Total shortening must have been at least 20% more than previous estimates in order to satisfy the basement to cover depth constraints provided by the xenolith data. Sedimentary rocks at >30 km paleodepth require that Andean basement thrusts decapitated earlier Triassic normal faults, trapping Paleozoic and Mesozoic rocks below the main decollement. Magma loading from intense Cenozoic plutonism within the plateau probably played an additional role in transporting Mesozoic cover rocks to >30 km and thickening the crust beneath the northern Altiplano.

In order to better understand the interactions between plutonic activity and strain localization during metamorphic core complexes formation the Miocene granodioritic pluton of Serifos (Cyclades, Greece) is studied. This pluton (11.6-9.5 Ma) intruded the Cycladic Blueschists during thinning of the Aegean domain along a system of low-angle normal faults belonging to the south-dipping West Cycladic Detachment System (WCDS). Based on structural fieldwork, together with microstructural observations and anisotropy of magnetic susceptibility (AMS), we recognize a continuum of deformation from magmatic to brittle conditions within the magmatic body. This succession of deformation events is kinematically compatible with the development of the WCDS. The architecture of the pluton shows a marked asymmetry resulting from its interaction with the detachments. We propose a tectonic scenario for the emplacement of Serifos pluton and its subsequent cooling during the Aegean extension. (1) A first stage corresponds to the metamorphic core complex initiation and associated southwestward shearing along the Meghalo Livadhi detachment. (2) In a second stage the Serifos pluton has intruded the dome at shallow crustal level, piercing through the ductile/brittle Meghalo Livadhi detachment. Southwest-directed extensional deformation was contemporaneously transferred upward in the crust along the more localized Kavos Kiklopas detachment. (3) A third stage was marked by syn-magmatic extensional deformation and strain localization at the contact between the pluton and the host rocks resulting in narrow shear zones nucleation which (4) continued to develop after the pluton solidification.

The Mesozoic magmatic history of the North American margin records the evolution from a more segmented assemblage of parautochthonous and allochthonous terranes to the more cohesive northern Cordilleran orogenic belt. We characterize the setting of magmatism, tectonism, and epigenetic mineralization in the western Fortymile mining district, east-central Alaska, where parautochthonous and allochthonous Paleozoic tectonic assemblages are juxtaposed, using sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon geochronology, whole-rock geochemistry, and feldspar Pb isotopes of Mesozoic intrusions and spatially associated mineral prospects. New SHRIMP U-Pb zircon ages and published U-Pb and 40 Ar/ 39 Ar ages indicate four episodes of plutonism in the western Fortymile district: Late Triassic (216–208 Ma), Early Jurassic (199–181 Ma), mid-Cretaceous (112–94 Ma), and Late Cretaceous (70–66 Ma). All age groups have calc-alkalic arc compositions that became more evolved through time. Pb isotope compositions of feldspars from Late Triassic, Early Jurassic, and Late Cretaceous igneous rocks similarly became more radiogenic with time and are consistent with the magmas being mantle derived but extensively contaminated by upper crustal components with evolving Pb isotopic compositions. Feldspar Pb isotopes from mid-Cretaceous rocks have isotopic ratios that indicate magma derivation from upper crustal sources, probably thickened mid-Paleozoic basement. The origin of the mantle component in Late Cretaceous granitoids suggested by Pb isotopic ratios is uncertain, but we propose that it reflects asthenospheric upwelling following slab breakoff and sinking of an inactive inner subduction zone that delivered the previously accreted Wrangellia composite terrane to the North American continental margin, after the outer Farallon subduction zone was established. Epigenetic Pb-Zn-Ag ± Cu prospects in the western Fortymile district are spatially associated with splays of the northeast-trending Kechumstuk sinistral-normal fault zone and with ca. 68–66 Ma felsic intrusions and dikes. The similarity between Pb isotope compositions of feldspars from the Late Cretaceous igneous bodies and sulfides from the epithermal prospects suggests a Late Cretaceous age for most of the mineralization. Fluid flow along the faults undoubtedly played a major role in mineralization. We interpret displacement on the northeast-trending faults to be a far-field effect of dextral translation along Late Cretaceous plate-scale boundaries and faults that were roughly parallel to the subsequently developed Denali and Tintina fault systems, which currently bound the region.

The Algodoes metavolcano-sedimentary sequence is located at the northern margin of the Archean/Paleoproterozoic Troia Massif, northern Borborema Province (NE Brazil). It represents a well-preserved Paleoproterozoic greenstone-like sequence affected by two major plutonic events. The early plutonism, represented by the Cipo orthogneisses, mainly comprises biotite-bearing metatonalites, which share similar geochemical signatures with Archean tonalite-trondjhemite-granodiorite (TTG). For these rocks, we report U–Pb (LA-ICPMS) zircon ages of 2189 ± 14 Ma and 2180 ± 15 Ma. A subsequent plutonic magmatism occurred at ∼2150–2130 Ma and is mainly represented by hornblende-bearing dioritic to tonalitic orthogneisses of the Madalena Suite and Sao Jose da Macaoca Complex. Geochemical data indicate that these dioritic/tonalitic orthogneisses have adakitic characteristics and strongly suggest mantle-related magmas. A ( sensu stricto ) granite plutonism (Serra da Palha orthogneisses) also intruded the Algodoes sequence and yielded U–Pb (LA-ICPMS) zircon age of 2150 ± 16 Ma. These granitic orthogneisses show high-K content, A-type characteristics and probably derived from partial melting of a crustal (tonalitic) source. We suggest that the early ∼2190–2160 Ma TTG plutons probably developed in intra-oceanic arc setting, whereas the following ∼2150–2130 Ma adakitic plutons and A-type granitic magmatism developed in response to arc-continent collision.

The actual study deals with the temporal and geochemical evolution of the arc magmatism and the Cu–Mo–Au mineralization in the Neo-Tethyan belt of the Arasbaran region in northwestern Iran. The magmatic activity in this section of the Neo-Tethyan belt periodically occurred from Upper Cretaceous to Quaternary. The Cretaceous magmatic rocks are calc-alkaline to tholeiitic in nature without any mineralization in the Arasbaran region. Cenozoic magmatism begins with alkaline (shoshonitic) volcanism at an early stage and is followed by alkaline to calc-alkaline plutonism. No significant mineralization is associated with the early stage alkaline magmatism and the most porphyry and epithermal mineralizations are related to the late stage adakite-like, calc-alkaline magmatism. The subsequent, post-collisional alkaline magmatism follows in the Plio-Quaternary. Magmatism and the related mineralization decrease in age from the north to the south, and the mineralization changes in time and space from a Cu–Mo to a Cu–Au association. Mineralization stages at the Arasbaran region consist of (a) Upper Oligocene to Lower Miocene (~ 20 Ma) Cu–Mo porphyry and intrusion mineralization, and (b) Upper Miocene (~ 10 Ma), Cu–Au porphyry and epithermal Cu–Au mineralization. Although the exact timing of the porphyry mineralization relative to the final collision is unclear, the presence of most porphyry and epithermal mineralizations in the Upper Oligocene to Upper Miocene, post-collisional, adakite-like intrusions, is related to crustal thickening and delamination of lower crust suggesting that they formed at a late stage of the Arasbaran magmatic arc evolution following a major volcanic stage in the Eocene. Mineralogical and geochemical characteristics of the mineralized porphyry bodies in Arasbaran region indicate that significant amounts of hornblende was fractionated prior to plagioclase crystallization as a consequence of high magmatic water contents. In contrast, the earlier, barren plagioclase-phyric magmas were relatively dry. Fertile plutonic suites in Arasbaran region may be recognized by their relatively late timing with respect to the voluminous Eocene volcanism. Widespread presence of hornblende phenocrysts, and major and trace element compositions with relatively high Sr/Y and La/Yb ratios, high Sr (> 400 ppm) and Nd (≥ 20 ppm) indicate a long-lived mature arc setting.

International audience; Granite pebbles from an Eocene or Oligocene conglomerate lying on a Ghomaride nappe of theInternal Zones of the Rif belt (Alboran domain, Morocco) have been dated by U/Pb on zircon at 281 Ma. Nogranite pluton being known in the Rif belt nor in the neighbouring Betic Cordillera, the origin of these calcalkalineKungurian (end of the Early Permian) granites is discussed. A provenance from a nearby unitpresently drowned in the Alboran sea is likely. Comparisons with other circum-Mediterranean domainsshow that this late plutonism characterizes an original domain in the Variscan orogen.

This paper shows an updated geological, petrographical-chemical and structural picture of the contact aureole of the 6.9 Ma Mt. Capanne monzogranitic pluton in western Elba Island (Tuscan Archipelago), that is one of the most known Tertiary intrusive bodies in Italy. Most of the foliated metamorphic rocks derived from a Mesozoic Ligurian-type ophiolitic succession (Punta Polveraia-Fetovaia Unit) and are in the horneblende to pyroxene hornfels facies with estimated Tpeak > 610°C (locally > 650°C). Local variations of the metamorphic zonation of the at least 150-200 m thick aureole are due to the different lithological, physical and structural (e.g., bedding, fracturing) nature of the original rocks, but also to hydrofracturing phenomena which occurred during the synmetamorphic upflow of the metasomatic hot fluids. The history of the emplacement and uplift of the Mt. Capanne pluton was defined through the metamorphic- structural evolution of its contact metamorphic aureole. The growth of the thermometamorphic minerals took place in several stages being both syn-kinematic with respect to the main ductile D folding event (connected to the plutonic intrusion) and static post-kinematic one. Ductile shear zones, characterized also by mylonites, were also active during recrystallization in a general shear-type regime (average value of W = 0.7) related to the vertical uplift of the pluton (pure shear) and lateral ductile flow of the covers (simple shear). The exhumation of the cooled pluton continued producing tangential cascade-type folding event (D), detachment faults, and later high-angle faulting in the host rocks. The role of Western Elba in the geological frame of the whole island since Late Miocene times is also outlined in the paper.

International audience; The Variscan middle crust of the eastern Pyrenees is represented by the Bélesta and Caramany gneissic units of the North Pyrenean Agly Massif. In this study, we date and reinterpret the orthogneisses and granites composing these units. We characterize a recurrent plutonic activity spanning all the Paleozoic in this part of the Pyrenean crust. The Bélesta unit (amphibolite facies) is mainly composed of sills of (Latest Ediacaran)–Earliest Cambrian (542 ± 4 and 540 ± 4 Ma) orthogneisses (70% of the series), almost unknown in the Pyrenees until now, and Latest Carboniferous–(Earliest Permian) (307 ± 3–298 ± 3 Ma time span) granites (15% of the series). These plutonic rocks were emplaced in probably Ediacaran aluminous pelites later transformed into paragneisses (15% of the series). The Caramany unit (granulite facies) is mainly composed of Precambrian aluminous paragneisses migmatized during the Latest Carboniferous–(Earliest Permian) (299 ± 4 Ma), sills of Earliest Cambrian (529 ± 5 Ma) orthogneisses and sills (about 30% of the series) of Late Carboniferous (308 ± 3–299 ± 3 Ma) opxbearing and opx-free granodiorites, grt-bearing leucogranites and norites. Among these last rocks, the Ansignan charnockite, forming a 800 m-thick laccolith near the base of the Caramany unit, and previously dated at 314 ± 6/7 Ma (Respaut, Lancelot, Neues Jahrbuch Miner Abh 147-1:21–34, 1983), is refined at 307 ± 3 Ma. Our results confirm the importance of the Late Carboniferous plutonism in deep levels of the Pyrenean crust, which largely resulted from recycling of older para- and orthoderived rocks of this crust. The emplacement of hundreds of metres in thickness of granites and other plutonic rocks in the Variscan Pyrenees occurred in a rather short time both as sills in these deep levels and as large plutons in shallower levels, a fact which necessarily had consequences on the HT–LP Carboniferous metamorphism.

The western Saldania belt in South Africa exposes a section through a fore-arc region that records deformation, sedimentation and plutonism in the late Neoproterozoic and Cambrian (>560 to

The early Paleozoic orogen of South China is possibly one of the few examples of intraplate orogeny in the world. It is characterized by an angular unconformity between post-Silurian cover and pre-Devonian strata and by the intensive and extensive early Paleozoic granitic plutonism. However, synchronous mafic–ultramafic rocks have not been well-studied, but they are crucial for understanding the nature and evolution of the orogen. In this paper, we present the first detailed LA-ICP-MS zircon U–Pb dating, major and trace element geochemical and Sr–Nd–Hf isotopic data for a Silurian gabbroic pluton (Dakang) and a coeval granitic pluton (Guiyang), that have recently been identified in central Fujian, in the southeastern part of the orogen. We assess the origin of these mafic and granitic rocks and their relationship to the evolution of the early Paleozoic orogen in South China. LA-ICP-MS zircon U–Pb dating shows that the Dakang and Guiyang plutons were emplaced at 441–438 Ma and 431 Ma, respectively. The Dakang pluton consists of gabbros and minor intermediate rocks (diorite, monzodiorite and monzonite). These rocks are all metaluminous and potassic, and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). They have initial 87Sr/86Sr of 0.7066–0.7098, eNd (T) of − 7.0 to − 3.3 and eHf (T) (in-situ zircon) of − 5.2 to − 4.4. Geochemical data suggest that the Dakang gabbroic magmas were derived by partial melting of previously subduction-modified lithospheric mantle in the spinel–garnet transition zone at a high temperature (~ 1300 °C). These primary magmas underwent fractionation crystallization of clinopyroxene and amphibole, forming the evolved gabbros and intermediate rocks. The Guiyang pluton consists of weakly peraluminous granites, which show low Ga/Al ratios (10,000*Ga/Al