Metamorphic P–T–t evolution of mafic HP granulites in the northeastern segment of the Tarim Craton (Dunhuang block): Evidence for early Paleozoic continental subduction
Metamorphic P–T–t evolution of mafic HP granulites in the northeastern segment of the Tarim Craton (Dunhuang block): Evidence for early Paleozoic continental subduction
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DOI：
10.1016/j.lithos.2014.02.020
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发表时间：
2014-05
期刊：
影响因子：
3.5
通讯作者：
Zhenyu He;Zeming Zhang;K. Zong;H. Xiang;R. Klemd
中科院分区：
文献类型：
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作者：
Zhenyu He;Zeming Zhang;K. Zong;H. Xiang;R. Klemd
敦煌地块位于塔里木盆地东北部，北接中亚造山带，南接阿尔金-祁连造山带。研究表明，敦煌地块早古生代高压镁铁质麻粒岩经历了四期变质作用：角闪岩相（M1）、峰值高压麻粒岩相（M2）和两个晚期角闪岩相退变质作用。根据相平衡模型，四个变质阶段的P-T条件分别为720-750 °C和11-13 kbar，760-800 °C和14-16 kbar，690-720 °C和8-8.5 kbar，< 6 kbar和< 640 °C。峰期麻粒岩相变质作用的特点是地温梯度低，约为1000 ℃。16 °C/km。锆石U-Pb定年结果表明，高压麻粒岩相变质作用发生于约1000年。431 Ma和早期退变质角闪岩相叠加在约。403 Ma.因此，研究的基性岩在这里揭示了顺时针P-T-t路径，包括埋藏加热之前的峰麻粒岩相变质和随后的减压冷却与隆升速率约。0.8 km/Ma。这与高压变质岩的大陆亲缘性相结合，表明敦煌地块在早古生代曾经历过碰撞造山作用。
The Dunhuang block, which constitutes the northeastern segment of the Tarim Craton, is located between the Central Asian Orogenic Belt (CAOB) to the north and the Altyn–Qilian Orogenic Belt to the south. The present study reveals that the early Paleozoic HP mafic granulites from the Dunhuang block underwent four stages of metamorphism: prograde amphibolite-facies (M1), peak high-pressure (HP) granulite-facies (M2) and two late stages of amphibolite-facies retrograde metamorphism. Based on phase equilibrium modeling, P–T conditions of the four stages of metamorphism are estimated at 720–750 °C and 11–13 kbar, 760–800 °C and 14–16 kbar, 690–720 °C and 8–8.5 kbar, and at < 6 kbar and < 640 °C respectively. Peak granulite-facies metamorphism is characterized by a low geothermal gradient of ca. 16 °C/km. Zircon U–Pb dating shows that the HP granulite-facies metamorphism occurred at ca. 431 Ma and the early retrograde amphibolite-facies overprint at ca. 403 Ma. Thus the investigated mafic rocks here reveal a clockwise P–T–t path involving burial heating before peak granulite-facies metamorphism and subsequent decompression–cooling with an uplift rate of ca. 0.8 km/Ma. This, together with a continental affinity of the HP metamorphic rocks, indicates that the Dunhuang block experienced a collisional orogenesis during the early Paleozoic.