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[Display omitted] • Arc magmatic suite represented by charnockites and their variants and gabbros. • Mesoarchean magmatism and high grade metamorphism. • Evidence for onset of plate tectonics in the Mesoarchean. • Coorg block as part of the Ur supercontinent assembly. The Coorg Block in southern India is one of the oldest crustal fragments on the globe and is composed of Mesoarchean magmatic suites, dominantly charnockites, gabbros and their variants that were metamorphosed under granulite facies conditions. Here we investigate a suite of charnockites, metagabbros and amphibolite from this block by undertaking detailed field studies, petrological and geochemical analysis, and zircon and monazite isotope geochronology. Phase equilibria modeling using pseudosection computations shows ultrahigh-temperature metamorphic conditions yielding a P-T range of 10–11 kbar at 1000 °C for the charnockite assemblage and 8–9 kbar at 950 °C for the metagabbro. Geochemistry indicates that the felsic and mafic rocks are sub-alkaline and represent a tholeiitic magma series. The rocks were derived possibly through fractionation of a reduced primary magma in a Mesoarchean subduction-related setting. Zircon grains from the charnockites and gabbros show magmatic textures, with LREE depletion and HREE enrichment, negative La, Pr, Nd, Eu and positive Ce, Sm, Gd anomalies, and Th/U ratios consistent with magmatic crystallization. We present zircon and monazite U–Pb data from a comprehensive suite of samples that indicate timing of peak of magmatic emplacement for both the charnockite and gabbroic suites occurred at ∼ 3.15 Ga, closely followed by metamorphism at ∼ 3.0 Ga. The presence of magmatic xenocrysts of up to ∼ 3.5 Ga in some of these rocks suggest older crustal components in the basement. Zircon Lu–Hf analyses suggest that the amphibolite and gabbro were mostly derived from depleted mantle sources whereas the charnockite suite involved both juvenile and reworked Paleoarchean components. The tectonic setting of these felsic and mafic magmatic rock suites correlates with a Mesoarchean subduction system, complementing recent models on the emergence of modern-style plate tectonics in the early Earth. We correlate the Mesoarchean arc magmatic suites in the Coorg Block to the building blocks of the core of the Earth's oldest supercontinent Ur, with the surrounding Neoarchean granulite blocks and their equivalents in other cratonic fragments to the 'expanded Ur'. [ABSTRACT FROM AUTHOR]

[Display omitted] • The 'bar codes' of Paleoproterozoic LIP event from the Coorg Block revealed. • Zircon and baddeleyite ages from gabbroic dykes converging at 2.2 Ga mark a rift-related mafic magmatic event. • This event correlates with the attempted rifting in the Neoarchean supercontinent Kenorland. The Coorg Block in southern Peninsular India is one of the oldest crustal blocks on Earth that preserves the evidence for continental crust formation during the Paleo-Mesoarchean through subduction-related arc magmatism, followed by granulite facies metamorphism in the Mesoarchean. In this study, we report for the first time, the 'bar codes' of a major Paleoproterozoic Large Igneous Province in the Coorg Block through the finding of mafic dyke swarms. The gabbroic dykes from the Coorg Block, dominantly composed of plagioclase-pyroxene assemblage, show a restricted range in SiO 2 values of 50.04–51.27 wt.%, and exhibit a sub-alkaline tholeiitic nature. These rocks show relatively flat LREE and constant HREE patterns and lack obvious Eu anomalies. Trace element modeling suggests that the dyke swarm was fed from a melt that originated at a shallow mantle level in the spinel stability field. Zircon grains are rare in the gabbro samples and those separated from two samples yielded 207Pb/206Pb weighted mean dates of 2214 ± 12 Ma and 2221 ± 7 Ma. The grains show magmatic features with depleted LREE and enriched HREE and positive Ce and negative Eu anomalies. Baddeleyite grains were dated from five gabbro samples which yielded 207Pb/206Pb weighted mean ages ranging between 2217 ± 7 Ma and 2228 ± 10 Ma. The combined data show a clear age peak at ca. 2.2 Ga. The mafic dykes in the Coorg Block show geochemical similarities with ca. 2.2 Ga mafic dyke swarms in different regions of the Dharwar and other cratons in Peninsular India and elsewhere on the globe. The data also support the inference that the global mafic magmatism at ca. 2.2 Ga was linked with intracontinental rifting of the Archean cratons through mantle upwelling or plume activity. We correlate the mafic dyke swarms in the Coorg Block with attempted rifting of the Neoarchean supercontinent Kenorland. [ABSTRACT FROM AUTHOR]

Apatite fission track thermochronology on the Kyrgyz Tien Shan basement revealed a polyphased thermal history of the study-area. We interpret the Mesozoic and Cenozoic cooling-events as periods of tectonic reactivation. [ABSTRACT FROM AUTHOR]

Apatite is a useful geochronological tool due to its common occurrence and incorporation of a variety of radioactive parent isotopes during crystallisation. However, an understanding of the geological conditions recorded by each of these isotopic systems in apatite is necessary for their effective application to geological problems. In this study, U–Pb, Sm–Nd, and Lu–Hf dates for apatite grains from samples of ∼ 3.0 Ga TTG gneisses in the Akia terrane of the North Atlantic Craton (south-western Greenland) were obtained in order to better understand the conditions under which isotopic re-equilibration in apatite is achieved. This isotopic data records at least two thermotectonic events subsequent to the initial magmatic crystallisation of these rocks. Whereas the Lu–Hf and Sm–Nd isotopic systems in these apatites record a regional high temperature metamorphic event at ∼2.7 Ga, the U–Pb system records a milder thermal event at ∼ 1.7 Ga. This decoupling of the U–Pb from the Sm–Nd and Lu–Hf systems in apatite reflects a difference in closure temperature. The regional thermal effects of the ∼ 1.7 Ga Nagssugtoqidian orogeny in adjacent parts of the North Atlantic Craton resulted in partial to complete reequilibration of the U–Pb systems in apatite across the Akia terrane but were insufficient to cause open system behaviour of Sm–Nd or Lu–Hf. The indistinguishable apatite Sm–Nd and Lu–Hf ages produced in each analysed sample suggest that these systems are similarly susceptible to isotopic re-equilibration. The older ages produced by the Sm–Nd and Lu–Hf systems relative to U–Pb in apatite demonstrate that the former are more robust and thus more likely to faithfully record high temperature events than the U–Pb system. [ABSTRACT FROM AUTHOR]

The Phanerozoic tectonic evolution of the Chuya-Kurai zone was studied by means of zircon U/Pb-dating, apatite fission track (AFT) and apatite (U-Th)/He (AHe) thermochronology performed on basement rocks. Our results suggest that multiple magmatic episodes during the Paleozoic, related to the accretion-collision tectonics in Central Asia, affected our study area. Mesozoic and Cenozoic basement cooling events are interpreted as periods of tectonic reactivation. A new tectonic model for Late Cenozoic evolution of the Chuya-Kurai zone is proposed. [ABSTRACT FROM AUTHOR]

The Luanchuan granitoids in the East Qinling Orogen, Central China host multiple genetic types of Mo-W-Pb-Zn-Ag polymetallic deposits. Here we present results from systematic geochronological and geochemical investigations on apatite with a view to gain insights into the petrogenesis, metallogenesis and potential for mineral exploration. We analyzed 388 apatite grains from eight Late Mesozoic granitic plutons in the Luanchuan ore district. Apatite U–Pb geochronology yields 206Pb/238U mean ages in the range of 151.5–102.3 Ma, representing the crystallization ages. Through integrating our results with those from previous studies on the multi-stage magmatism (160–130 Ma; 111–108 Ma) and metallogeny (150–139 Ma; 138–135 Ma; 114 Ma), the newly obtained apatite ages can be correlated with coeval magmatic and metallogenetic events of this ore district. In comparison, except for the Nannihu pluton which is ca. 19 Ma younger than the corresponding zircon U–Pb ages, the other studied plutons show almost consistent apatite and zircon U–Pb ages within error ranges, suggesting rapid post magmatic cooling below ~450 °C in response to shallow emplacement. Apatite chemistry displays ΣREE concentrations in the range of 2379–15,925 ppm, characterized by rather high LREE concentrations, depleted to flat HREE profiles and distinctive negative Eu anomalies, suggesting crust-mantle mixing in the magma source prior to apatite crystallization, which incorporated different degrees of sediment melting and slab melting components triggered by the subducted Paleo-Pacific slab-derived fluids. In conjunction with element concentrations and ratios (e.g., Sr, Mn, Cl, Y, La/Y, Eu/Eu*, (Sm/Nd) N , (La/Sm) N , (Eu/Eu*) N , (Ce/Ce*) N , (La/Yb) N) in apatite, the Luanchuan granitoids are classified as moderately oxidized and mineralized I-type granites. We suggest that the Huangbeiling pluton and other igneous rocks in its vicinity likely have relatively higher potential for future W-Mo/Mo-W exploration, and that different degrees of magmatic differentiation might have generated the porphyry-skarn Mo–W deposit in the Yuku ore field. Moreover, our study also demonstrates that the apatite REE concentrations and ratios can be used as potential indicators for mineral exploration. Unlabelled Image • Late Mesozoic apatite ages related to coeval magmatic and metallogenic events. • Apatite chemical data used as indicators for mineral exploration. • Potential areas for mineral exploration identified in the Luanchuan ore district. [ABSTRACT FROM AUTHOR]

Abstract The accretion of the Avalon and Meguma terranes to the Laurentian margin was a major event in the development of the Appalachian orogen. The Minas Fault Zone delineates the boundary between these terranes. A strongly lineated and foliated granite intrusion (Kelly Brook pluton) exposed along the West River St. Mary's Fault intruded into Meguma Supergroup metasedimentary rocks. Well-developed C-S fabrics characterize the pluton with muscovite aligned in the S fabric, and a shallow (~10°) westerly plunging quartz stretching lineation. New U-Pb (zircon, LA-ICP-MS) geochronological data yield a crystallization age of 375.0 ± 4.6 Ma for the Kelly Brook pluton that is indistinguishable from other Late-Devonian intrusive rocks in the Meguma terrane. Petrographic data for muscovite indicate that it grew prior to deformation. A 100% plateau 40Ar/39Ar age of 369.0 ± 1.2 Ma on a single muscovite grain constrains the time of cooling of the granite to approximately 450 to 420 °C. Apatite grains also demonstrate pre- to syn -deformational fabrics and yield a U-Pb (LA-ICP-MS) age of 361.2 ± 5.6 Ma indicating the temperature of the granite was still above 350 °C at this time. Earliest Tournaisian fossils in the unconformably overlying Horton Group strata indicate that the granite was exposed by ca. 359 Ma. Exhumation rates of the Kelly Brook pluton and the Meguma terrane from approximately 9.5–13.3 km depth from ca. 375 Ma to surface exposure at ca. 359 Ma are 0.06 to 0.08 cm yr−1. Estimates for the Upper Devonian regional geothermal gradient in the northern Meguma terrane are high between 39.5 °C km−1 and 67.8 °C km−1, gradients that are common in extensional tectonic environments such as the Basin and Range province. An apatite fission-track age of 215 ± 14 Ma indicates Mesozoic reburial and reheating of the granite prior to opening of the Atlantic Ocean. Highlights • Geochronological and microstructural data record the Late-Devonian relationship between the Avalon and Meguma terranes • The Late-Devonian (ca. 375–359 Ma) geothermal gradient in the northern Meguma terrane was high • Age data coupled with a fabric analysis can elucidate the geothermal gradient and exhumation rates along terrane boundaries [ABSTRACT FROM AUTHOR]

Lu Hf geochronology is a powerful method to constrain the temporal evolution of geological systems. Traditional application of this dating method requires time-consuming chemical separation of the parent (176Lu) and daughter (176Hf) isotopes that is commonly accompanied by loss of textural context of the analysed minerals. In contrast, In-situ (laser-ablation based) Lu Hf geochronology offers a number of advantages including rapid analysis with high spatial resolution, as well as control on textural relationships of the analysed mineral. However, laser-ablation based Lu Hf geochronology has been hindered by isobaric interferences of 176Yb and 176Lu on 176Hf that have effectively masked reliable determination of 176Lu and 176Hf. We present a methodology that resolves these interferences using LA-ICP-MS/MS (laser ablation tandem inductively coupled mass spectrometry) and NH 3 gas to separate Hf from Lu. Both Lu, Yb, and Hf react with NH 3 to form a variety of product ions. By measuring high order reaction products (e.g. Hf(NH)(NH 2)(NH 3) 3 +), we demonstrate that 176Hf can be measured interference-free from 176Lu and 176Yb with sufficient sensitivity to yield useful geochronological age data. The novel in-situ Lu Hf technique has been successfully applied to a variety of Palaeozoic and Precambrian-aged garnet, apatite and xenotime samples, including published reference materials. The resulting age uncertainties are as low as ~0.5% (95% conf. interval). The technique has the potential to obtain spatially-resolved Lu Hf ages in garnet-bearing samples that would be difficult to obtain by conventional techniques. The method also offers the opportunity for rapid "campaign style" geochronology in complex terrains that record poly-metamorphic histories. In apatite, the expected higher closure temperature of the Lu Hf system compared to the commonly used U Pb system allows high-temperature thermal history reconstructions. In addition, Lu Hf dating of apatite allows dating of samples with low U and high common Pb (e.g. mafic and low-grade metamorphic rocks and ore deposits). Furthermore, apatite tends to incorporate little to no common Hf, allowing single grain ages to be calculated, which opens new doors for detrital provenance studies. In situ Lu Hf dating of xenotime offers an additional avenue to U Pb dating, and may be particularly beneficial to dating of rare earth element ore deposits that often have complex temporal records of development. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ordovician to Triassic maximum depositional ages are determined from Sibumasu in NW Thailand. • 1200–900 Ma, 650–500 Ma and 2500–2460 Ma populations are present in all 8 NW Thai detrital samples. • Hf signatures change provenance from Gondwana in Ordovician-Permian to Indosinian in Triassic. • Our comparison with published detrital data is inconsistent with composite Sibumasu models. The evolution of the Sibumasu Terrane forms a principal component in the history of the Tethys Oceans with the northward movement of Gondwana-derived terranes creating the Asian continent that we recognise today. While there are various reconstructions for the palaeoposition of the Sibumasu Terrane during the Proterozoic and Paleozoic, the terrane is commonly placed outboard of the northwest Australian margin in the Gondwanan supercontinent. In this study, U–Pb and Lu–Hf isotopic information has been collected from detrital zircons of Paleozoic and Mesozoic sedimentary rocks obtained from the Sibumasu Terrane in northwest Thailand. This is the first zircon Hf analysis from these sedimentary sequences. These new data are statistically and visually compared with data from Sibumasu, Indochina, Sukhothai, West Burma and Tethyan Himalayas terranes along with the terranes of China, India and Western Australia. Our detrital data are consistent with other published data indicating consistent sources across the Sibumasu Terrane, inconsistent with composite terrane reconstructions. However, temporally, the detrital ages change from older Paleozoic sedimentary sequences (sourcing zircons from Neoproterozoic and older "Gondwanan" sources) to latest Permian-Triassic sedimentary units with Indosinian zircon sources. This change is consistently reflected in this study through both the U–Pb ages and Hf signatures with Proterozoic age peaks characteristic of Gondwana and younger Indosinian sources being consistent with granitoids emplaced through the amalgamation of Thailand. The temporal changes in the isotopic systems reflect the movement of the Sibumasu Terrane from the northwest Australian margin of Gondwana to its collision with the terranes of present-day Asia. [ABSTRACT FROM AUTHOR]