冲绳海槽火山岩地球化学特征及岩浆源区地幔性质探讨  

Petrochemistry of volcanic rocks and characteristics of magma-derrived mantle in the Okinawa Trough

作　　者：张宇蛟 翟世奎[1,2] Zhang Yujiao;Zhai Shikui(Key Lab of Submarine Geosciences and Prospecting Techniques,Ministry of Education,Qingdao 266100,China;College of Marine Geosciences,Ocean University of China,Qingdao 266100,China)

机构地区：[1]海底科学与探测技术教育部重点实验室,山东青岛266100 [2]中国海洋大学海洋地球科学学院,山东青岛266100

出　　处：《海洋学报》2021年第1期44-54,共11页

基　　金：国家重点基础研究发展计划项目(2013CB429702)。

摘　　要：冲绳海槽是因菲律宾海板块俯冲于欧亚板块之下,在陆壳上发育起来的一个初始的弧后盆地,是研究弧后扩张作用早期盆地演化、岩浆作用和壳幔过程的天然实验室。尽管迄今对冲绳海槽已经做了大量的调查研究工作,但仍存在一些颇有争议或亟待解决的科学问题,如:冲绳海槽酸性浮岩与基性玄武岩之间的成因联系,冲绳海槽不同区段构造背景对岩浆作用的控制,冲绳海槽岩浆源区地幔的特征,俯冲板块组分(流体+熔体)对地幔楔部分熔融的贡献等。本文在系统收集和整理(剔除了一些存疑数据)了迄今已有冲绳海槽火山岩主量元素、微量元素(包括稀土元素)与Sr-Nd-Pb同位素数据的基础上,通过对资料的系统分析,进一步确认了酸性浮岩与基性玄武岩的岩浆同源性;认为在冲绳海槽北段与中段主要分布有酸性浮岩和中性安山岩,应该是两段区域目前正处于裂谷阶段的反映,而南段广泛分布的基性玄武岩说明在构造性质上已接近成熟性弧后盆地;冲绳海槽的火山岩岩浆源区具有Ⅱ型富集地幔(EMⅡ型)Dupal异常特征,岩浆源于流行地幔(PREMA)和EMⅡ型地幔端元混合的源区地幔,其中EMⅡ约占比15%,PREMA贡献率在85%左右;源于俯冲的菲律宾海板块(俯冲洋壳或沉积物)的流/熔体的加入是导致冲绳海槽下伏地幔具有EMⅡ型特征的原因,这一点不同于Dupal异常源于壳幔相互作用的观点。The Okinawa Trough is an initial back arc basin developed on the continental crust due to the subduction of Philippine Sea plate under Eurasian plate. It is a natural laboratory to study the basin evolution, magmatism and crust-mantle interactions in the early stage of back arc expansion. Although a lot of investigations and research works have been done so far, there are still some controversial or urgent scientific problems, such as the genetic relationship between acid pumice and basic basalts in the trough, the control of tectonic background on magmatism in different sections of the trough, the characteristics of magma-derrived mantle, and the influence of subduction plate components(fluid + melt) on the mantle wedge, etc. On the basis of systematically collecting and sorting out(excluding some doubtful data) the major element, trace element(including rare earth elements) and Sr-Nd-Pb isotopic data of volcanic rocks in the Okinawa Trough, the author further confirmed the magma homology of acid pumice and basic basalt through systematic analysis of the data, and believed that the distributions of acid pumice and neutral andesite in the north and middle sections of the trough should be the reflection of regional rift at present, while the basic basalts widely distributed in the south section indicate that they are close to mature back arc basin in structural property. The volcanic magma source area of Okinawa Trough has the characteristics of enriched mantle Ⅱ(EMⅡ)-type Dupal anomaly, and the magma comes from the source mixed by end-member of prevalent mantle(PREMA) and EMⅡ type mantle end-member, of which the ratio of EMⅡ is about 15% and PREMA about 85%.The addition of fluid/melt from subducted Philippine Sea plate(subducted ocean crust or sediment) is the reason for the EMⅡ type characteristics of magma-derrived mantle beneath the Okinawa Trough, which is different from the viewpoint that the Dupal anomaly originates from the interaction between crust and mantle.

关 键 词：火山岩 岩石地球化学特征 岩浆源区地幔 EMⅡ型Dupal异常 冲绳海槽 

分 类 号：P736[天文地球—海洋地质]