Element and Sr isotope zoning in plagioclase in the dacites from the southwestern Okinawa Trough: Insights into magma mixing processes and time scales

doi:10.1016/j.lithos.2020.105776

IOCAS-IR > 海洋地质与环境重点实验室

	Element and Sr isotope zoning in plagioclase in the dacites from the southwestern Okinawa Trough: Insights into magma mixing processes and time scales
	Chen, Zuxing 1,2,3; Zeng, Zhigang 1,2,3,4; Wang, Xiaoyuan 1,2,3; Peng, Xing 5; Zhang, Yuxiang 1,2,3; Yin, Xuebo 1,2,3; Chen, Shuai 1,2,3; Zhang, Le 6; Qi, Haiyan 1,2,3
	2020-12-01
发表期刊	LITHOS
ISSN	0024-4937
卷号	376 页码:14
通讯作者	Chen, Zuxing(chenzuxing@qdio.ac.cn) ; Zeng, Zhigang(zgzeng@ms.qdio.ac.cn)
摘要	The processes and time scales of magma mixing in shallow silicic magma chambers prior to eruptions in the Okinawa Trough (OT) are still poorly understood. Here, we employed in situ major-trace elements and Sr isotopic analyses, coupled with textural investigations, on plagioclase phenocrysts in the mafic magmatic enclaves (MMEs) and their host dacites from the southwestern OT to address this issue. The plagioclase phenocrysts in the MMEs have high An% contents (82-88) and Sr/Ba ratios (7.2-17.2) and relatively unradiogenic Sr-87/Sr-86 ratios (0.70536-0.70595), suggesting that they crystallized in the chilled basaltic andesitic magma. In contrast, plagioclase phenocrysts in the host dacites show a wide composition range, with An% contents of An(47) to An(93), Sr/Ba ratios of 3.4-18.0, and Sr-87/Sr-86 ratios of 0.70535-0.70791. The plagioclase phenocrysts are zoned, with high-An% cores characterized by resorption textures and mantled by euhedral low-An% rims. The transition between cores and rims is very abrupt, with a decrease of 30 to 40 mol% An. This shift coincides with large and abrupt changes in Sr/Ba ratios. The plagioclase phenocryst rims have low Sr/Ba values (3.4-5.1) and Sr-87/Sr-86 ratios (0.70632-0.70675) that are similar to those of the whole-rock dacites, suggesting that the plagioclase rims grew from the host dacitic magma. In contrast, Sr isotopes in the plagioclase cores are either radiogenic (0.70724-0.70791) or unradiogenic (0.70535-0.70595) compared with rims, combined with glomerocryst textures, consistent with their derivation from distinct deep mafic crystal mush zones, and were then entrained by ascending melts and transported rapidly to the shallow silicic magma chamber and underwent decompression during ascent, leading to plagioclase core resorption. Mg diffusion calculations indicate that incorporation of the calcic cores into the shallow silicic magma chamber experienced a long pre-eruptive storage (similar to 600 years). The distinct Sr isotopes of the plagioclase, particularly the different compositions of titanomagnetite in the MMEs and host dacites, reflect the mafic magma injection into the silicic magma chamber and formation of the MMEs must have occurred over very short time scales before eruption to inhibit complete re-equilibration, which likely triggered the dacitic magma to finally erupt. Hence, the silicic magma in the southwestern OT contains a crystal cargo with a complex, open-system crystallization history and that magma mixing/mingling is an important process for controlling the chemical and textural diversity of these silicic magmas as well as a likely eruption trigger. (C) 2020 Elsevier B.V. All rights reserved.
关键词	Sr isotope Magma mixing Time scales Plagioclase Dacite Okinawa Trough
DOI	10.1016/j.lithos.2020.105776
收录类别	SCI
语种	英语
资助项目	National Natural Science Foundation of China[91958213] ; Open Fund of the Key Laboratory of Marine Geology and Environment, Chinese Academy of Sciences[MGE2020KG11] ; Strategic Priority Research Program (B) of Chinese Academy of Sciences[XDB42020402] ; National Programme on Global Change and Air-Sea Interaction[GASI-GEOGE-02] ; International Partnership Program of Chinese Academy of Sciences[133137KYSB20170003] ; National Special Fund for the 13th Five Year Plan of COMRA[DY135-G2-1-02] ; Special Fund for the Taishan Scholar Program of Shandong Province[ts201511061] ; Qingdao Postdoctoral Applied Research Project, the National Key Basic Research Program of China[2013CB429700] ; Shandong Provincial Natural Science Foundation, China[ZR2019BD010]
WOS研究方向	Geochemistry & Geophysics ; Mineralogy
WOS类目	Geochemistry & Geophysics ; Mineralogy
WOS记录号	WOS:000580897000040
出版者	ELSEVIER
引用统计	被引频次：30[WOS] [WOS记录] [WOS相关记录]
文献类型	期刊论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/169154
专题	海洋地质与环境重点实验室
通讯作者	Chen, Zuxing; Zeng, Zhigang
作者单位	1.Chinese Acad Sci, Inst Oceanol, CAS Key Lab Marine Geol & Environm, Seafloor Hydrothermal Act Lab, Qingdao 266071, Peoples R China 2.Qingdao Natl Lab Marine Sci & Technol, Lab Marine Mineral Resources, Qingdao 266071, Peoples R China 3.Chinese Acad Sci, Ctr Ocean Megasci, 7 Nanhai Rd, Qingdao 266071, Peoples R China 4.Univ Chinese Acad Sci, Beijing 100049, Peoples R China 5.Chaohu Univ, Dept Comp Sci & Technol, 1 Bantang Rd, Chaohu 238000, Peoples R China 6.Chinese Acad Sci, Guangzhou Inst Geochem, State Key Lab Isotope Geochem, Guangzhou 510640, Peoples R China
第一作者单位	中国科学院海洋研究所; 中国科学院海洋大科学研究中心
通讯作者单位	中国科学院海洋研究所; 中国科学院海洋大科学研究中心
推荐引用方式 GB/T 7714	Chen, Zuxing,Zeng, Zhigang,Wang, Xiaoyuan,et al. Element and Sr isotope zoning in plagioclase in the dacites from the southwestern Okinawa Trough: Insights into magma mixing processes and time scales[J]. LITHOS,2020,376:14.
APA	Chen, Zuxing.,Zeng, Zhigang.,Wang, Xiaoyuan.,Peng, Xing.,Zhang, Yuxiang.,...&Qi, Haiyan.(2020).Element and Sr isotope zoning in plagioclase in the dacites from the southwestern Okinawa Trough: Insights into magma mixing processes and time scales.LITHOS,376,14.
MLA	Chen, Zuxing,et al."Element and Sr isotope zoning in plagioclase in the dacites from the southwestern Okinawa Trough: Insights into magma mixing processes and time scales".LITHOS 376(2020):14.

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