Abstract

Petrogeochemical and geochronological studies were conducted on the main varieties of granitoids from the Sedelga and Berezovsky batholiths in the eastern Bureya continental Massif of the Central Asian Fold Belt. SHRIMP-II U–Pb zircon dating of granitoids constrained the time of formation to the Late Triassic and Early Jurassic between 208 to 193 Ma. Our studies revealed that the batholiths contain peraluminous granitoids of high K calc-alkaline series clearly enriched in Rb, K, Th, U, and Pb and relatively depleted in Nb, Ta, Y, HREE, Sr, Ba, Ti, and P and belong to I-type granites. Synthesis of the U–Pb geochronological data indicates that magmatism of tectonic blocks constituting the Bureya Massif at 213–183 Ma was accompanied by the emplacement of granitoid rocks of the Khara Complex. Strike-slip tectonics as a reflection of oblique collision of continental blocks and transform movement might have been an important mechanism of granitoid derivation in the Bureya Massif. Strike-slip faults were likely to penetrate deep into the crust initiating the ascent of an asthenospheric diapir and its fluids into the higher crustal levels thus transferring the heat and triggering melting with appreciable concentrations of Th, U, Rb, Pb and losses of Sr, P, Ba, and Ti. The depletion in Nb, Ta, Ti, and P and the enrichment in Pb make these granitoids similar to those of subduction zones. Granitoids of the Khara Complex display subduction-related (associated with the preceding subduction) and within-plate (associated with an asthenospheric diapir and its fluids) geochemical features, which is characteristic of transform margin environments. The most likely settings for granitoid magmatism to occur throughout the eastern margin of the Bureya Massif in the Late Triassic and Early Jurassic were transform settings associated with asthenospheric diapirism following the cessation of subduction.

中文翻译：

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中亚造山带东布列亚大陆断块的哈拉复合体花岗岩：年龄和形成的地球动力学背景

摘要

对中亚褶皱带东部布列亚大陆地块的Sedelga和Berezovsky岩基中的主要类花岗岩进行了岩石地球化学和地质年代研究。花岗岩类的SHRIMP-II U–Pb锆石测年将208至193 Ma之间的三叠纪晚期和侏罗纪早期的形成时间限制了。我们的研究表明，岩床中含有高钾钙碱性系列的高铝花岗类花岗岩，明显富含Rb，K，Th，U和Pb，而相对贫乏Nb，Ta，Y，HREE，Sr，Ba，Ti和P，属于I型花岗岩。U–Pb年代学数据的综合表明，构成Bureya地块的构造块在213–183 Ma的岩浆活动伴随着Khara复杂体的花岗岩体的侵入。走向滑移构造学是大陆块倾斜碰撞和变换运动的反映，可能是Bureya地块中花岗岩类推导的重要机制。走滑断层很可能深入地壳，导致软流圈底辟的上升，其流体上升到较高的地壳水平，从而以明显的Th，U，Rb，Pb浓度和Sr的损失转移热量并触发融化， P，Ba和Ti。Nb，Ta，Ti和P的贫化和Pb的富集使这些类花岗岩与俯冲带相似。Khara Complex的花岗岩类具有俯冲相关的（与先前的俯冲相关）和板内（与软流圈的底辟及其流体）相关的地球化学特征，这是转换余量环境的特征。