Search results for "AMOR"
showing 10 items of 1531 documents
Metamorphic P–T paths for the Archean Caozhuang supracrustal sequence, eastern Hebei Province, North China Craton: Implications for a sagduction regi…
2020
Abstract Archean supracrustal rocks of amphibolite-facies occur as enclaves within granitoids gneiss domes and belts between domes, representing collision or sagduction regimes. In order to distinguish between tectonic regimes using metamorphic patterns, systematic data on metamorphic evolution and zircon age dating are presented for the Caozhuang supracrustal sequence of eastern Hebei Province, China, which occurs as enclaves in gneisses. A garnet biotite gneiss records a P–T path involving pre-peak isobaric heating to peak conditions at 780–800 °C and 10–11 kbar (medium-P/T type), followed by decompression to 5–6 kbar. Two Mg/Al-rich schists from the same locality show low P/T conditions …
Two orogenic events separated by 2.6Ga mafic dykes in the Central Zone, Limpopo Belt, southern Africa
2017
Abstract The Limpopo Belt of southern Africa is a typical early Precambrian orogen that experienced two high-grade metamorphic events which are a key for understanding its tectonic evolution. There has been a long-standing debate on whether the Neoarchean (c. 2.65 Ga) or the Palaeoproterozoic (c. 2.0 Ga) tectono-thermal event records continental collision. The clear field relationship between deformed mafic dykes and the surrounding rocks is a powerful tool to help reconstructing the deformation history. Mafic dykes intruded the 3.3–3.1 Ga Sand River Gneiss Suite in the Central Zone of the Limpopo Belt near Musina, South Africa, and were classified in the past into older Causeway dykes and …
Zircon ages, geochemistry and Nd isotopic systematics for the Palaeoproterozoic 2.3–1.8 Ga Kuilyu Complex, East Kyrgyzstan – The oldest continental b…
2017
Abstract Precambrian microcontinents represent key tectonic units in the accretionary collages of the western Central Asian Orogenic Belt (CAOB), and their geological history is reasonably well established since the Mesoproterozoic but remains weakly constrained for older epochs due to a scarcity of exposed Palaeoproterozoic and Archaean rocks. Early Precambrian rocks were previously reported from several metamorphic complexes in the Kyrgyz Tianshan orogenic belt, mainly based on multigrain conventional zircon dating, but the present study only confirmed such rocks at one site, namely in the Kuilyu Complex of eastern Kyrgyzstan. New single grain SHRIMP II zircon ages, geochemical data, and …
Extensive magmatism and metamorphism at ca. 3.2 Ga in the eastern Kaapvaal Craton
2020
Abstract The timing of the emergence of modern-style plate tectonics on Earth is of fundamental importance in understanding the thermal and compositional history of the planet. Although the magmatism and metamorphism in the eastern Kaapvaal Craton was thought by some as geological records for mid-Archean subduction at 3.2 Ga, their petrogenesis was fiercely debated. To reveal the nature of the 3.2 Ga magmatism and metamorphism in the eastern Kaapvaal Craton, here we provide a comprehensive zircon and monazite U-Pb geochronological investigation, coupled with in situ trace element and Hf-O isotopic analyses, for the magmatic and metamorphic rocks from the Barberton granitoid-greenstone terra…
U-Pb monazite ages from the Pakistan Himalaya record pre-Himalayan Ordovician orogeny and Permian continental breakup
2018
The Greater Himalayan Sequence in India and Nepal records crustal thickening processes that took place during and following the onset of India-Asia collision (ca. 54–50 Ma). These resulted in late Eocene–early Miocene kyanite- and sillimanite-grade regional metamorphism, and Oligocene–Miocene crustal anatexis, which formed migmatites and leucogranites. We present new U-Pb monazite data for kyanite- and sillimanite-grade gneisses of the Neoproterozoic to Cambrian Tanawal Formation in the Pakistan Himalaya, which have metamorphic ages of 482.4 ± 7.9 Ma and 464.5 ± 4.0 Ma, respectively. These ages, together with along-strike equivalent rocks in the Lesser Himalaya of India and Nepal, help to d…
Reply to J. Berger's comment on the article “Discovery of metamorphic microdiamonds from the parautochthonous units of the Variscan French Massif” by…
2015
International audience
Middle to Late Ordovician arc system in the Kyrgyz Middle Tianshan: From arc-continent collision to subsequent evolution of a Palaeozoic continental …
2016
New geological, geochronological and isotopic data reveal a previously unknown arc system that evolved south of the Kyrgyz Middle Tianshan (MTS) microcontinent during the Middle and Late Ordovician, 467-444 Ma ago. The two fragments of this magmatic arc are located within the Bozbutau Mountains and the northern Atbashi Range, and a marginal part of the arc, with mixed volcanic and sedimentary rocks, extends north to the Semizsai metamorphic unit of the southern Chatkal Range. A continental basement of the arc, indicated by predominantly felsic volcanic rocks in Bozbutau and Atbashi, is supported by whole-rock Nd- and Hf-in-zircon isotopic data. epsilon(Nd(t)) of + 0.9 to -2.6 and epsilon(Hf…
Pressure-temperature evolution during two granulite-facies metamorphic events (2.62 and 2.02 Ga) in rocks from the Central Zone of the Limpopo Belt, …
2018
Abstract The Central Zone of the Limpopo Belt in southern Africa is a classical example of a polymetamorphic terrane that experienced three metamorphic events at 3.22 Ga (M1), 2.66–2.61 Ga (M2) and 2.02 (M3). However, the geodynamic significance of these events is controversial as their P-T evolution was poorly constrained. We present new petrological and geochronological data for the M2 and M3 events. The Neoarchean M2 event is well-preserved in samples from a newly discovered enclave of supracrustal and magmatic rocks in the 2.612 Ga Bulai pluton that shielded the enclave against a Paleoproterozoic M3 overprint, which is dominant in rocks exposed outside the pluton. P-T pseudosection mode…
Age and provenance constraints on seismically-determined crustal layers beneath the Paleozoic southern Central Asian Orogen, Inner Mongolia, China
2016
Abstract We present 110 ages and 51 in-situ δ18O values for zircon xenocrysts from a post-99 Ma intraplate basaltic rock suite hosted in a subduction–accretion complex of the southern Central Asian Orogenic Belt in order to constrain a seismic profile across the Paleozoic Southern Orogen of Inner Mongolia and the northern margin of the North China Craton. Two zircon populations are recognized, namely a Phanerozoic group of 70 zircons comprising granitoid-derived (ca. 431–99 Ma; n = 31; peak at 256 Ma), meta-granitoid-derived (ca. 449–113 Ma; n = 24; peak at 251 Ma) and gabbro-derived (436–242 Ma; n = 15; peaks at 264 and 244 Ma) grains. Each textural type is characterized by a distinct zirc…
Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: an integrated geodynamic and petrological modelling approach
2017
The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India–Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure–temperature–time (P–T–t) path has been derived from thermomechanical simulations tailored for E…