Crystal fractionation of contaminated melts and re-melting of newly underplated basaltic crust generated Late Triassic andesitic and dioritic intrusions in the southern Yidun Terrane, SW China
Crystal fractionation of contaminated melts and re-melting of newly underplated basaltic crust generated Late Triassic andesitic and dioritic intrusions in the southern Yidun Terrane, SW China
复制标题
中国西南部义敦地体南部受污染熔体的晶体分异和新底侵玄武岩地壳的重熔产生了晚三叠世安山岩和闪长岩侵入体
DOI：
10.1016/j.lithos.2019.05.033
复制
发表时间：
2019-10
期刊：
影响因子：
3.5
通讯作者：
Lei-Luo Xu
中科院分区：
文献类型：
--
作者：
Xin-Song Wang;Xian-Wu Bi;You-Wei Chen;Li-Chuan Pan;Lei-Luo Xu
大陆弧中安山质和闪长质岩石的成因是激烈争论的，提出的模型包括板片熔融，幼年镁铁质下地壳熔融，镁铁质和长英质岩浆混合，以及经历MASH（熔融，同化，储存和均质化）过程的幔源熔体。争议来自于它们多成因的可能性和大块岩石同位素示踪剂的模糊性，更不用说岩浆演化的过程了。在这里，我们报告我们的调查在南部义敦地体（三叠纪大陆弧在中国西南部）的两个阶段的闪长质秀瓦库侵入体（第1和第2阶段），镁铁质微粒包体（MMEs）的第1阶段的侵入体，以及安山质红山侵入体的岩石成因。通过锆石U-Pb定年、原位锆石Hf-O同位素分析、岩石Sr-Nd同位素分析和微量元素分析等方法，研究了不同时期侵入岩和MMEs的物质来源和幔-壳相互作用。我们的研究结果表明，Xiuwacu MMEs从第一阶段侵入结晶熔体。锆石Hf-O同位素组成（εHf（t）= +0.4 ~+5.3，δ 18 O = 4.80‰ ~ 7.79‰）表明它们是幔源玄武质熔体和长英质熔体混合形成的。第一期侵入体的锆石Hf-O同位素组成（εHf（t）= +1.3 ~+3.9，δ 18 O = 6.58‰ ~ 7.31‰）均在中尺度微细粒级几个继承的锆石和一个小的重结晶长英质微粒包体的发现，由一个MME主机显示，MMEs包含相对更多的长英质成分。尽管如此，MMEs的硅含量（62.1- 63.4wt%）仍然低于第一阶段侵入体（63.4- 70.5wt%），这表明安山质MMEs是由玄武质和长英质熔体直接混合而成，而闪长质第一阶段侵入体则需要晶体分馏过程。第2期和红山岩体形成于第1期之后的216 Ma左右，具有较高的氧逸度和结晶温度。鉴于前人关于板片断裂可能发生在216 Ma的结论，我们认为秀瓦库二期和红山岩体形成于板片断裂过程中，前者是MASH带新底侵的玄武质下地壳部分熔融的产物，后者是幔源玄武质熔体在相对高压下分异的产物。
The genesis of andesitic and dioritic rocks in continental arcs is hotly debated, and proposed models include slab melting, juvenile mafic lower-crustal melting, mafic and felsic magma mixing, and mantle-derived melts that underwent a MASH (melting, assimilation, storage, and homogenization) process. The controversy comes from the possibility of their polygenesis and the ambiguity of bulk-rock isotope tracers, not to mention the processes of magma evolution. Here, we report on our investigations in the southern Yidun Terrane (a Triassic continental arc in SW China) into the petrogenesis of two stages of the dioritic Xiuwacu intrusions (phases 1 and 2), the mafic microgranular enclaves (MMEs) hosted by the phase 1 intrusion, as well as the andesitic Hongshan intrusions. We used U-Pb zircon dating, in situ zircon Hf-O isotope analyses, bulk-rock Sr-Nd isotope analyses, and trace element analyses of the zircons from different stages of the intrusions and the MMEs to shed light on their sources and mantle–crust interactions involved in their petrogenesis. Our results suggest that the Xiuwacu MMEs from the phase 1 intrusion crystallized from a melt. Their variable zircon Hf-O isotopic compositions (εHf(t) = +0.4 to +5.3 and δ18O = 4.80‰ to 7.79‰) indicate they were formed by the mixing of mantle-derived basaltic melts and felsic melts. The phase 1 intrusion have an origin similar to that of the MMEs, as indicated by their homogeneous zircon Hf-O isotopic compositions (εHf(t) = +1.3 to +3.9 and δ18O = 6.58‰ to 7.31‰), which fall within the range of the isotopic compositions of the MMEs. The discovery of several inherited zircons and a small recrystallized felsic microgranular enclave hosted by an MME reveals that the MMEs contain relatively more felsic components. Even so, the MMEs still have lower silica contents (62.1–63.4 wt%) than those of the phase 1 intrusion (63.4–70.5 wt%), and this indicates that direct magma mixing of basaltic and felsic melts generated the andesitic MMEs, whereas a crystal fractionation process is required for the dioritic phase 1 intrusion. The porphyritic phase 2 and Hongshan intrusions formed at ~216 Ma, after the phase 1 intrusion, and they had higher oxygen fugacities and crystallization temperatures than the phase 1 intrusion. Given the conclusions of previous researchers that slab breakoff probably occurred at ~216 Ma, we propose that the Xiuwacu phase 2 and Hongshan intrusions formed during the slab breakoff process, the former by partial melting of the newly underplated basaltic lower crust in the MASH zone, and the latter by differentiation of mantle-derived basaltic melts at relatively high pressures.
登录
查看更多内容
影响因子：
3.5
作者：
Tao Wu;Long Xiao;S. Wilde;Changqian Ma;Jia-Xi Zhou
通讯作者：
Tao Wu;Long Xiao;S. Wilde;Changqian Ma;Jia-Xi Zhou
影响因子：
2.9
作者：
A. Weislogel
通讯作者：
A. Weislogel
影响因子：
3.9
作者：
Yin, Hongwei;Zhang, Kaijun;Yang, Jiedong;Xu, Shijin;Wu, Weihua;Lu, Huayu
通讯作者：
Lu, Huayu
影响因子：
5.8
作者：
L. Wenchang;Zeng Pu-sheng;Hou Zengqian;N. White
通讯作者：
L. Wenchang;Zeng Pu-sheng;Hou Zengqian;N. White
通过增生洋弧的大陆生长：秦岭造山带花岗岩类的锆石 Hf-O 同位素证据
影响因子：
5
作者：
Hao Wang;Yuan-Bao Wu;Shan Gao;Zheng-Wei Qin;Zhao-Chu Hu;Jian-Ping Zheng;Sai-Hong Yang
通讯作者：
Sai-Hong Yang