Granulites record the tectonic evolution from collisional thickening to extensional thinning of the Tongbai orogen in central China
Granulites record the tectonic evolution from collisional thickening to extensional thinning of the Tongbai orogen in central China
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麻粒岩记录了中国中部桐柏造山带从碰撞增厚到伸展减薄的构造演化
DOI：
10.1111/jmg.12522
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发表时间：
2020
影响因子：
3.4
通讯作者：
Zheng Yong-Fei
中科院分区：
文献类型：
--
作者：
Zhang Qiang-Qiang;Gao Xiao-Ying;Zheng Yong-Fei
对桐柏麻粒岩进行了岩石学和地球化学的综合研究。研究结果揭示了会聚板块边界岩石圈从碰撞增厚到伸展减薄的构造演化过程。岩石学观察、锆石U-Pb定年和假剖面计算表明，麻粒岩经历了四个变质阶段，分为两个变质旋回。第一个循环发生在490-450 Ma，涉及785-815°C和10-14 kbar的高磷（HP）变质作用（M1），随后减压加热至840-880°C和8-9 kbar，进行中压麻粒岩相变质作用（M2），石榴石地幔中金红石+蓝晶石+钾长石包裹体的出现表明了高压。第二个周期发生在C。在890-980°C和9-11 kbar下持续加热至超高温（UHT）变质（M3），随后减压冷却至740-880°C和7-9 kbar（M4），直到405 Ma。高压变质作用与秦岭造山带的超高压榴辉岩相变质作用是同步的，表明其与寒武纪大陆碰撞作用有关。超高温变质作用发生在减压条件下，表明碰撞增厚的造山岩石圈变薄。因此，桐柏造山带在碰撞造山作用下先增厚后减薄，可能是造山根下沉的结果。这种构造演化在碰撞造山带中可能是普遍的，即大陆碰撞过程中的挤压转变为大陆裂陷过程中的伸展。
A combined study of petrology and geochemistry was carried out for granulites from the Tongbai orogen in central China. The results reveal the tectonic evolution from collisional thickening to extensional thinning of the lithosphere at the convergent plate boundary. Petrographic observations, zircon U–Pb dating, and pseudosection calculations indicate that the granulites underwent four metamorphic stages, which are categorized into two cycles. The first cycle occurred at 490–450 Ma and involves high‐P (HP) metamorphism (M1) at 785–815°C and 10–14 kbar followed by decompressional heating to 840–880°C and 8–9 kbar for medium‐pressure granulite facies metamorphism (M2), defining a clockwise P–T path. The high pressure is indicated by the occurrence of inclusions of rutile+kyanite+K‐feldspar in the garnet mantle. The second cycle occurred at c. 440 Ma and shows an anticlockwise P–T path with continuous heating to ultrahigh‐temperature (UHT) metamorphism (M3) at 890–980°C and 9–11 kbar, followed by decompressional cooling to 740–880°C and 7–9 kbar (M4) till 405 Ma. The HP metamorphism is synchronous with the ultrahigh‐pressure eclogite facies metamorphism in the Qinling orogen, indicating its relevance to the continental collision in the Cambrian. The UHT metamorphism took place at reduced pressures, indicating thinning of the collision‐thickened orogenic lithosphere. Therefore, the Tongbai orogen was initially thickened by the collisional orogeny and then thinned, possibly as a result of foundering of the orogenic root. Such tectonic evolution may be common in collisional orogens where compression during continental collision switched to extension during continental rifting.