ABSTRACT

Permo-Carboniferous felsic magmatic rocks are widely exposed on the northern half of the south-eastern Central Asian Orogenic Belt. However, their origin and spatiotemporal distribution are unknown. Herein, zircon U-Pb-Hf isotopic data, major and trace element compositions of the whole-rock, and Sr-Nd isotopic data derived for felsic volcanic rocks and granites of the Chaganaobao and Baiyinaobao areas in central Inner Mongolia are combined with the data from previous studies. The integration of these results reveals that the Uliastai Continental Margin, Erenhot-Hegenshan Ophiolite Belt, and Northern Orogenic Belt have coeval magmatic lull or trough at c. 307 Ma, which overlap with the closure timing of the Hegenshan Ocean. The Latest Carboniferous−Early Permian (c. 303−295 Ma) felsic volcanic rocks in the Chaganaobao area of the Uliastai Continental Margin comprise dacite, trachydacite, and rhyolite, while demonstrating positive whole-rock ε_Nd(t) (+2.9 to +4.7) and zircon ε_Hf(t) values (+7.65 to +13.78). Early Permian granites of the Baiyinaobao area located within the Northern Orogenic Belt show positive ε_Hf(t) values (+ 2.70 to +11.33) and low TFe₂O₃ + MgO + TiO₂ contents. The geochemical composition reveals that those felsic magmatic rocks mainly originate from the partial melting of juvenile crustal components with subordinate input of mantle-derived melts. Those c. 305−275 Ma felsic magmatic rocks from the north of the south-eastern Central Asian Orogenic Belt exhibit affinities of post-collision type granites in geochemical nature. Therefore, the flare-up of the Early Permian magmatism surrounding the Erenhot-Hegenshan Ophiolite Belt could be related to the extension after the final closure of the Hegenshan Ocean.

摘要

二叠纪-石炭纪长英质岩浆岩广泛出露在中亚造山带东南部的北半部。然而，它们的起源和时空分布是未知的。本文将内蒙古中部察干澳堡和白音澳堡地区长英质火山岩和花岗岩的锆石U-Pb-Hf同位素数据、全岩主量和微量元素组成、Sr-Nd同位素数据与数据结合起来。从以前的研究。这些结果的综合表明，乌利亚斯泰大陆边缘、二连浩特-鹤根山蛇绿岩带和北部造山带在c.有同期的岩浆停滞或低谷。307 Ma，与鹤根山洋闭合时间重叠。最新石炭纪-早二叠纪（c._Nd (t) (+2.9 至 +4.7) 和锆石 ε _Hf (t) 值（+7.65 至 +13.78）。位于北部造山带内的白依脑堡地区早二叠世花岗岩具有正的ε _Hf (t) 值（+ 2.70 至+11.33）和低 TFe ₂ O ₃ + MgO + TiO ₂内容。地球化学成分表明，这些长英质岩浆岩主要来源于幼年地壳成分的部分熔融，其次是幔源熔体的输入。那些c。中亚造山带东南部北部的 305～275 Ma 长英质岩浆岩在地球化学性质上表现出与后碰撞型花岗岩的亲和性。因此，二连浩特-鹤根山蛇绿岩带周围早二叠世岩浆活动的爆发可能与鹤根山洋最终闭合后的延伸有关。