Metamorphic P鈥?i>T paths of the Zanhuang amphibolites and metapelites: constraints on the tectonic evolution of the Paleoproterozoic Trans-North China Orogen

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• 作者：Ling-Ling Xiao (1) xiaolingl05@mails.gucas.ac.cn
  Chun-Ming Wu (1) wucm@gucas.ac.cn
  Guo-Chun Zhao (2) gzhao@hkucc.hku.hk
  Jing-Hui Guo (3) jhguo@mail.igcas.ac.cn
  Liu-Dong Ren (4) ldren@cags.net.cn
• 关键词：Amphibolite &#8211 ; Metamorphic P− ; T path &#8211 ; Metapelite &#8211 ; North China Craton &#8211 ; Zanhuang complex
• 刊名：International Journal of Earth Sciences
• 出版时间：June 2011
• 出版年：2011
• 期刊代码：54_0016-7835
• 类别：ear
• 卷：100
• 期：4
• 页码：717-739
• 数据来源：sp

摘要

Garnet-bearing metapelites and amphibolites are exposed in the south and middle parts of the Zanhuang complex, which is located in the central segment of the nearly NS-striking Trans-North China Orogen. These rocks preserve three metamorphic mineral assemblages forming at the prograde, peak and post-peak decompression stages. The prograde metamorphic stage (M₁) is represented by mineral inclusions within garnet porphyroblasts, the peak metamorphic stage (M₂) is represented by garnet rims and matrix minerals, whereas the retrograde stage (M₃) is represented by amphibole + plagioclase symplectite rimming garnet porphyroblasts in the amphibolites and biotite + plagioclase symplectite rimming garnet porphyroblasts in the metapelites. All garnet porphyroblasts in the metapelites preserve prograde chemical zoning except for the ubiquitous, quite narrow zones from the underwent post-peak decompression. It has been determined through thermobarometric computation that the metamorphic conditions are 650–710掳C at 8.2−9.2 kbar for the M₁ (inclusion) assemblages, >810掳C at >12.5 kbar for the metamorphic peak M₂ (matrix) assemblages, and 660–680掳C at 4.4–4.5 kbar for the retrograde M₃ (symplectite) assemblages. These rocks are thus determined to have undergone metamorphism with clockwise P–T paths involving nearly isothermal decompression (ITD) segments, which is inferred to be related to the amalgamation of the Eastern and Western Blocks to form the coherent basement of the North China Craton along the Trans-North China Orogen in the late Paleoproterozoic (1.88–1.85 Ga).