Multi-phase Paleozoic magmatism in the North Qaidam ultrahigh-pressure metamorphic units, NW China: implications for transition from continental collision to extensional collapse
Multi-phase Paleozoic magmatism in the North Qaidam ultrahigh-pressure metamorphic units, NW China: implications for transition from continental collision to extensional collapse
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中国西北柴达木北超高压变质单元的多期古生代岩浆作用：对大陆碰撞向伸展塌陷转变的影响
DOI：
10.1080/00206814.2022.2051085
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发表时间：
2022-03
影响因子：
2.6
通讯作者：
Yu Qi
中科院分区：
文献类型：
--
作者：
Wentao Ji;Shengyao Yu;Yue Yue;Yinbiao Peng;Xiangyu Gao;Pei Lv;Chuanzhi Li;Xingzhou Jiang;Lintao Wang;Yu Qi
摘要柴北缘俯冲碰撞带是一条典型的阿尔卑斯型超高压变质带，是早古生代柴达木地块俯冲到欧龙布鲁克地块之下的产物，具有大洋俯冲、大陆俯冲、碰撞、折返直至碰撞后伸展塌陷的完整记录。本文通过对柴北缘超高压变质单元花岗岩类的系统岩石学、锆石U-Pb年代学、Hf同位素和全岩地球化学分析，确定了它们的成因，进一步揭示了大陆碰撞造山带的构造演化。锆石U-Pb测年得到的加权平均年龄分别为433 ± 2 Ma、351 ± 8 Ma、416 ± 4 Ma、389 ± 3 Ma和383 ± 1 Ma，后三个年龄的εHf（t）值分别为−2.4 ~ 3.3、−5.9 ~ 1.1和−3.3 ~ 2.4。根据野外关系、岩石学、年代学和地球化学结果，可将这些花岗岩类划分为三组。早群花岗闪长岩（~433 Ma）具有明显的埃达克岩化学特征：（1）高La/Yb和Sr/Y比值，低Y和HREE值，（2）高Al 2 O3，低Mg#、Cr和Ni值，具明显的Eu正异常。岩石学和地球化学特征表明，早群埃达克质花岗闪长岩可能来自加厚的镁铁质下地壳中的变基性岩的部分熔融。中群花岗岩（~416 Ma）与I型花岗岩类有密切关系，以高Na_2 O（>4.18 wt.%）为特征;低的A/CNK值可能是俯冲陆壳长英质片麻岩部分熔融的结果。晚群花岗岩（389 ~ 351 Ma）也是I型花岗岩，其成因为中元古界地壳部分熔融，并有少量地幔物质输入。通过对这些花岗岩类的综合研究，沿着区域地质背景和高压-超高压变质作用，提出了柴北缘超高压变质带从洋壳俯冲、陆壳俯冲、碰撞作用到伸展塌陷的四阶段演化过程。原特提斯洋最终闭合后，俯冲陆壳经历了高压-超高压榴辉岩相变质作用（460 ~ 430 Ma），下地壳增厚，产生埃达克岩和S型花岗岩。俯冲洋板（425 ~ 400 Ma）断裂后，负浮力的减少导致深俯冲陆壳折返，伴随着深熔和同碰撞I型花岗岩，代表着构造体制由挤压向伸展的转变。由于构造转换，幔源侵入体和碰撞后花岗岩类在400 ~ 350 Ma期间侵位。同时，岩浆岩（460 ~ 350 Ma）的La/Yb和Sr/Y比值明显降低，表明地壳厚度从同碰撞到后碰撞阶段逐渐减小。
ABSTRACT The North Qaidam subduction-collision zone is a typical Alpine-type ultra-high pressure (UHP) metamorphic zone due to the Early Palaeozoic subduction of the Qaidam Block beneath the Oulongbuluke Block, with an integrated record of oceanic subduction, continental subduction, collision, and exhumation to post-collisional extensional collapse. In this study, systemic petrology, zircon U-Pb geochronology, Hf isotopic data and whole-rock geochemical analyses have been carried out for granitoids in the North Qaidam UHP metamorphic units to determine their petrogenesis and further reveal the tectonic evolution of the continental collision orogen. Zircon U-Pb dating yields weighted mean ages of 433 ± 2 Ma, 351 ± 8 Ma, 416 ± 4 Ma, 389 ± 3 Ma and 383 ± 1 Ma, with the εHf(t) values of the latter three ages ranging from −2.4 to 3.3, −5.9 to 1.1 and −3.3 to 2.4, respectively. Based on field relationship, petrological, geochronological, and geochemical results, these granitoids could be divided three groups. The early group granodiorites (~433 Ma) show a marked chemical resemblance to adakites: (1) high La/Yb and Sr/Y ratios, with low Y and HREE values; (2) high Al2O3 and low Mg#, Cr, and Ni values with obvious positive Eu anomalies. Petrological and geochemical characters indicate that the early group adaktic granodiorites may be derived from partial melting of metabasite in a thickened mafic lower crust. The middle group granites (~416 Ma) have an affinity to I-type granitoids, characterized by high Na2O contents (>4.18 wt.%) and low A/CNK values, which were probably generated by partial melting of felsic gneiss of subducted continental crust. The late group granites (389 ~ 351 Ma) are also I-type granitoids, which were originated from partial melting of Mesoproterozoic crust, with minor mantle material input. According to a comprehensive study of these granitoids, along with regional geological background and HP-UHP metamorphism, a four-stage evolutionary process of the North Qaidam UHP metamorphic belt from oceanic subduction, continental subduction, collision to extensional collapse is proposed. After the final closure of the Proto-Tethys Ocean, the subducted continental crust experienced HP-UHP eclogite-faces metamorphism (460 ~ 430 Ma), and thickening of the lower crust lead to generation of adakites and S-type granites. Following break-off of the subducting oceanic slab (425 ~ 400 Ma), the reduction in negative buoyancy caused the exhumation of deeply subducted continental crust accompanied by associated anataxis and syn-collisional I-type granitoids, representing the transition in tectonic regime from compression to extension. Due to the tectonic transition, mantle-derived intrusions and post-collisional granitoids were emplaced during 400 ~ 350 Ma. Simultaneously, the pronounced decreasing in La/Yb and Sr/Y ratios of magmatic rocks (age of 460 ~ 350 Ma) suggested that the crustal thickness decreased gradually from syn-collisional to post-collisional stage.
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影响因子：
3.5
作者：
Jinxiang Li;K. Qin;Guangming Li;J. Richards;Junxing Zhao;Mingjian Cao
通讯作者：
Jinxiang Li;K. Qin;Guangming Li;J. Richards;Junxing Zhao;Mingjian Cao
影响因子：
3.9
作者：
Shuguang Song;Lifei Zhang;Y. Niu;L. Su;B. Song;Dunyi Liu
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影响因子：
4.9
作者：
Zhang Jianxin;Sun Deyou;Li Yunshuai;Gong Jianghua
通讯作者：
Gong Jianghua
影响因子：
3
作者：
Jingsui Yang;Cailai Wu;Jianxin Zhang;R. Shi;F. Meng;J. Wooden;Houng-Yi Yang
通讯作者：
Jingsui Yang;Cailai Wu;Jianxin Zhang;R. Shi;F. Meng;J. Wooden;Houng-Yi Yang
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影响因子：
6.1
作者：
Qishuai Huang;Xiaoran Zhang;Yahui Yue;Liyun Zhang
通讯作者：
Liyun Zhang