Metamorphic P-T path and tectonic implications of pelitic granulites from the Daqingshan Complex of the Khondalite Belt, North China Craton

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• 作者：Jia Cai ; Fulai Liu ; Pinghua Liu ; Chaohui Liu ; Fang Wang ; Jianrong Shi
• 关键词：Pelitic granulite ; Phase equilibria modeling ; P&ndash ; T path ; The Khondalite Belt ; Western Block ; North China Craton
• 刊名：Precambrian Research
• 出版年：February, 2014
• 年：2014
• 卷：241
• 期：Complete
• 页码：161-184
• 全文大小：10851 K

文摘

Pelitic granulites are cropped out in the Daqingshan Complex of the Khondalite Belt, a Paleoproterozoic tectonic belt in the Western Block of the North China Craton. Petrological studies show that these granulites contain four distinct metamorphic assemblages. The core of a garnet porphyroblast, along with fine-grained inclusions of biotite + plagioclase + K-feldspar + quartz 卤 sillimanite 卤 ilmenite, defines the prograde metamorphic (M₁) stage. The peak (M₂) assemblage consists of garnet (mantle) + biotite + K-feldspar + plagioclase + quartz 卤 sillimanite 卤 orthopyroxene 卤 ilmenite 卤 magnetite 卤 rutile. Peak metamorphism was followed by a near-isothermal decompression (M₃) and the development of coronae of garnet + biotite + cordierite + plagioclase + quartz 卤 K-feldspar 卤 sillimanite 卤 spinel 卤 ilmenite 卤 magnetite (M₃) in the Crd-Grt-Bt gneisses during the following garnet breakdown reactions: garnet + sillimanite + melt 鈫?#xA0;cordierite + biotite + Fe-oxide and garnet + melt 鈫?#xA0;biotite + quartz + plagioclase. Retrograde cooling (M₄) assemblages are represented by biotite + muscovite + sillimanite + quartz + plagioclase + K-feldspar 卤 ilmenite. Quantitative phase equilibria modeling in the system Na₂O-CaO-K₂O-FeO-MgO-Al₂O₃-SiO₂-H₂O-TiO₂-Fe₂O₃ was applied to obtain P-T conditions of <780 掳C and <9 kbar for M₁, 840-880 掳C and 9-11 kbar for M₂, 800-870 掳C and 5.0-7.5 kbar for M₃, and <660 掳C and 4.1-6.9 kbar for M₄. The combination of the mineral assemblages, mineral compositions, and metamorphic reaction histories in the Daqingshan pelitic granulites defines a clockwise P-T path that involves periods of near-isothermal decompression and late cooling that followed the peak granulite-facies metamorphism. This result is consistent with the tectonic history of the Daqingshan Complex in the Khondalite Belt, which involved continent-continent subduction and collision followed by exhumation and cooling. This suggests a continent-continent collisional event between the Yinshan and Ordos blocks, which became amalgamated to form the Paleoproterozoic Khondalite Belt in the Western Block of the North China Craton.