摘要
近年团队在东昆仑大格勒地区发现了Nb、P矿化碱性杂岩体,并对杂岩体的岩石组合、岩石学特征及含矿性开展了研究,初步圈定了Nb、P矿化体,显示东昆仑具有寻找与碱性岩-碳酸岩型稀有稀土矿潜力。对碱性岩的形成时代、地球化学组成、矿物成分以及形成环境等方面的研究,不仅对重建东昆仑古构造环境具有重要的意义,还可推动东昆仑稀有金属成矿规律研究与找矿突破。本文在野外地质调查的基础上,选取杂岩体中重要的含矿辉石岩为研究对象,开展了单矿物电子探针原位分析、磷灰石和榍石U-Pb年代学、岩石地球化学及Sr-Nd同位素研究。结果显示,东昆仑大格勒地区辉石岩的形成时代为418 Ma。辉石岩主要矿物中存在似长石(霞石)、碱性暗色矿物(富铁黑云母),单斜辉石为透辉石,角闪石为钙质角闪石(铁韭闪石),黑云母为铁质黑云母和镁质黑云母。岩石地球化学特征显示辉石岩具有富K(K_(2)O>Na_(2)O)、CaO含量高、轻稀土元素强烈富集、富集Rb、Ba、Sr等大离子亲石元素,不亏损Nb、Ta元素,亏损Zr、U、Ti等高场强元素的特征。全岩的(87Sr/86Sr)i为0.704058~0.704278,ε_(Nd)(t)为-0.4~-0.2。矿物组成、元素和同位素地球化学特征均指示大格勒辉石岩为钾质碱性岩,具有与OIB相似的特征,岩浆源区为EMⅠ型地幔端元。岩石的形成过程为母岩浆在相对较深的地幔源区经历了1%~3%较低程度的部分熔融作用,在上侵过程中经历了较强的分离结晶作用和微弱的同化混染作用,其形成时代为该地区岩浆活动最强烈的时期,可能与碰撞后软流圈地幔的上涌和岩石圈的强烈伸展相关。
The discovery of an alkaline complex with Nb and P mineralization in the Dagele area of East Kunlun showed that the East Kunlun region has rare earth mineral resource potential of the alkaline rock-carbonattite-type.Research on the compositions of specific minerals,formation ages,geochemistry,and formation environment of the alkaline rocks will shed light on the reconstruction of the paleotectonic environment of East Kunlun,and promote research on the metallogeny and prospecting of rare metal ores in the East Kunlun region.On the basis of a field geological survey,in situ electron probe analyses,geochronological,whole-rock geochemical,and Sr-Nd isotopic investigations were conducted on the important ore-bearing pyroxenite in the complex.The results show that the Dagele pyroxene consists of feldspathoid(nepheline),alkaline dark minerals(iron-rich biotite),hornblende,calcareous amphibole.The pyroxene is characterized by K_(2)O>Na_(2)O,high CaO content,and strongly enriched light rare earth elements.LA-ICP-MS U-Pb dating of apatite and sphene showed that the pyroxene was formed at ca.418 Ma.The pyroxene has whole-rock(87Sr/86Sr)i values of 0.704058 to 0.704278 andε_(Nd)(t)values of−0.4 to−0.2.The above geochemical characteristics of minerals,major and trace elements,and isotopes indicate that the Daegle pyroxene is a potassic alkaline rock with a magmatic origin similar to that of OIB,showing trace element and isotope signatures of EM I-type mantle endmembers.In the relatively deep mantle source region,it experienced a low-degree partial melting of 1%to 3%,the mantle-derived parental magma and the high-level magma chamber in the crust experienced strong separation crystallization and weak assimilation and contamination in the upwelling process.Its formation time is equivalent to the period of the strongest magmatism in this region,which may be related to the upwelling of the asthenosphere mantle due to the strong extension of the lithosphere after the collision.
作者
王春涛
李五福
王秉璋
王强
张新远
王涛
郑英
金婷婷
刘建栋
袁博武
韩晓龙
曹锦山
王泰山
谭运鸿
李玉龙
WANG Chuntao;LI Wufu;WANG Bingzhang;WANG Qiang;ZHANG Xinyuan;WANG Tao;ZHENG Ying;JIN Tingting;LIU Jiandong;YUAN Bowu;HAN Xiaolong;CAO Jinshan;WANG Taishan;TAN Yunhong;LI Yulong(Qinghai Geological Survey Institute,Xining 810012,Qinghai,China;Key Laboratory of the Northern Qinghai-Tibet Plateau Geological Processes and Mineral Resources,Xining 810012,Qinghai,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China)
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2024年第1期125-143,I0008-I0011,共23页
Geotectonica et Metallogenia
基金
第二次青藏高原综合科学考察研究(STEP)项目(2019QZKK0702)
青海省地质矿产勘查开发局项目(青地矿科[2021]61号)
青海省系列地质图件数据处理与洋板块地质研究项目(DD20-029)联合资助。
