Evolution from Oceanic Subduction to Continental Collision: a Case Study from the Northern Tibetan Plateau Based on Geochemical and Geochronological Data
Evolution from Oceanic Subduction to Continental Collision: a Case Study from the Northern Tibetan Plateau Based on Geochemical and Geochronological Data
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DOI：
10.1093/petrology/egi080
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发表时间：
2006-03
影响因子：
3.9
通讯作者：
Shuguang Song;Lifei Zhang;Y. Niu;L. Su;B. Song;Dunyi Liu
中科院分区：
文献类型：
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作者：
Shuguang Song;Lifei Zhang;Y. Niu;L. Su;B. Song;Dunyi Liu
锆石U-Pb敏感高分辨离子探针测年结果显示，两带榴辉岩原岩组成与洋中脊玄武岩（MORB）或洋岛玄武岩（OIB）大致相似，变质年龄（480 ~ 440ma，北祁连加权平均年龄为4664 6Ma，北柴达木加权平均年龄为4577ma）重叠。柴达木北缘UHP带泥质片麻岩中含硅质锆石的峰值变质年龄为4236ma，比榴辉岩形成年龄小40Myr，逆变质年龄为403 9Ma。这些资料，结合区域关系，使我们可以推断，这两个平行带可能代表了一个从大洋俯冲到大陆碰撞，再到大陆逆冲，最后再到发掘的演化序列。祁连-柴达木克拉通可能是罗迪尼亚超大陆的一个残片，其北缘被动，洋相岩石圈扩张，在约423Ma时俯冲至华北克拉通之下，深bb10100km，在约403Ma时（泥质片麻岩锆石边缘年龄）被发掘。
Two apparently distinct, sub-parallel, paleo-subduction zones can be recognized along the northern margin of the Tibetan Plateau: the North Qilian Suture Zone (oceanic-type) with ophiolitic melanges and high-pressure eclogites and blueschists in the north, and the North Qaidam Belt (continental-type) in the south, an ultrahighpressure (UHP) metamorphic terrane comprising pelitic and granitic gneisses, eclogites and garnet peridotites. Eclogites from both belts have protoliths broadly similar to mid-ocean ridge basalts (MORB) or oceanic island basalts (OIB) in composition with overlapping metamorphic ages (480–440Ma, with weighted mean ages of 464 6Ma for North Qilian and 457 7Ma for North Qaidam), determined by zircon U–Pb sensitive high-resolution ion microprobe dating. Coesite-bearing zircon grains in pelitic gneisses from the North Qaidam UHP Belt yield a peak metamorphic age of 423 6Ma, 40Myr younger than the age of eclogite formation, and a retrograde age of 403 9Ma. These data, combined with regional relationships, allow us to infer that these two parallel belts may represent an evolutionary sequence from oceanic subduction to continental collision, and continental underthrusting, to final exhumation. The Qilian–Qaidam Craton was probably a fragment of the Rodinia supercontinent with a passive margin and extended oceanic lithosphere in the north, which was subducted beneath the North China Craton to depths >100 km at c. 423Ma and exhumed at c. 403Ma (zircon rim ages in pelitic gneiss).