Late-Paleozoic emplacement and Meso-Cenozoic reactivation of the southern Kazakhstan granitoid basement

International audienceThe Ili-Balkhash Basin in southeastern Kazakhstan is located at the junction of the actively deforming mountain ranges of western Junggar and the Tien Shan, and is therefore part of the southwestern Central Asian Orogenic Belt. The basement of the Ili-Balkhash area consists of an assemblage of mainly Precambrian microcontinental fragments, magmatic arcs and accretionary complexes. Eight magmatic basement samples (granitoids and tuffs) from the Ili-Balkhash area were dated with zircon U-Pb LA-ICP-MS and yield Carboniferous to late Permian (~ 350-260 Ma) crystallization ages. These ages are interpreted as reflecting the transition from subduction to (post-) collisional magmatism, related to the closure of the Junggar-Balkhash Ocean during the Carboniferous – early Permian and hence, to the final late Paleozoic accretion history of the ancestral Central Asian Orogenic Belt. Apatite fission track (AFT) dating of 14 basement samples (gneiss, granitoids and volcanic tuffs) mainly provides Cretaceous cooling ages. Thermal history modeling based on the AFT data reveals that several intracontinental tectonic reactivation episodes affected the studied basement during the late Mesozoic and Cenozoic. Late Mesozoic reactivation and associated basement exhumation is interpreted as distant effects of the Cimmerian collisions at the southern Eurasian margin and possibly of the Mongol-Okhotsk Orogeny in SE Siberia during the Jurassic – Cretaceous. Following tectonic stability during the Palaeogene, inherited basement structures were reactivated during the Neogene (constrained by Miocene AFT ages of ~ 17–10 Ma). This late Cenozoic reactivation is interpreted as the far-field response of the India-Eurasia collision and reflects the onset of modern mountain building and denudation in southeast Kazakhstan, which seems to be at least partially controlled by the inherited basement architecture

Influence of source materials and fractionating assemblage on magmatism along the Aegean Arc, and implications for crustal growth

Volcanic products from Methana, Santorini and Nisyros show mineralogical and geochemical characteristics that can be linked to their differentiation at different crustal levels, and varying sources of subducted sediments. The products from Methana, in the western part of the arc, where the overriding plate is thicker, are affected by amphibole fractionation and crustal contamination. Santorini volcano, in the central part of the arc, is located on an extensively thinned section of the overriding plate; it shows high Y-contents, a-typical for average continental crust. Crustal contamination is minor, similar to Nisyros volcano. Products of the latter, easternmost volcanic centre have been variably affected by amphibole fractionation. Its sub-arc magma source is different from the central and western part of the arc, reflecting sedimentary input from the Nile. Amphibole fractionation, caused by crystallization at greater depths, seems necessary to lower Y-contents and yield volcanic products that resemble average continental crust in this respect. In detail, however, none of the magmatic products of the Aegean Arc displays MREE–HREE patterns or levels of compatible elements that are an exact match for average continental crust. Garnet stability and mixing processes appear crucial to obtain the REE and compatible element characteristics of continental crust

Accretion of peri-Gondwanan terranes to Asia: distant tectonic effects on the Central Asian Orogenic Belt revealed by thermochronometry of the Talas-Fergana region, Kyrgyz Tien Shan

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Source to sink study of the Jurassic to Paleogene sedimentary record of the Kyrgyz Tien Shan reveal tectonic and climatic signals from the evolving Asian continent

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