西藏松多榴辉岩的矿物原位微量元素地球化学研究  

In situ trace element geochemistry of minerals in eclogite from Somdo,Tibet

作　　者：李天福[1,2] 杨经绥[1,2] 李兆丽[1,2] 徐向珍[1,2] 任玉峰[2] 陈松永[1,2] 

机构地区：[1]大陆动力学与构造国家重点实验室,北京100037 [2]中国地质科学院地质研究所,北京100037

出　　处：《岩石矿物学杂志》2012年第6期858-874,共17页Acta Petrologica et Mineralogica

基　　金：地质调查项目(1212010610107)

摘　　要：对松多榴辉岩中单矿物进行的LA-ICP-MS原位微区微量元素分析研究结果表明,石榴石主要富集中、重稀土元素和Y,同时具有高丰度的Sc、V、Cr和Co等元素;绿辉石中的微量元素以中稀土元素、Sr、Sc、V、Cr、Co、Ni和Ti为主,含有一定量的Zr、Hf等。石榴石、绿辉石、角闪石和绿帘石中均显示轻稀土元素亏损的特点,表明在退变质过程中没有发生明显的富轻稀土元素的外来流体交代作用,因而其微量元素矿物地球化学的某些特点不同于苏鲁地区的榴辉岩。石榴石变斑晶中某些元素(如Ti、Zr)的分带性暗示了榴辉岩在紧随峰期变质之后的折返过程中发生了降压增温过程。榴辉岩主要变质矿物中微量元素的分配显然受到矿物主量元素的分配所控制,如MgO在石榴石和绿辉石之间的分配对Ni、Co、Ti分配的控制以及CaO的分配对Sr、Y、REE分配的控制等。退变质过程中矿物的形成或分解以及物理化学条件的改变都可以引起矿物间微量元素的重新分配。由绿辉石退变质而形成的角闪石,较之原先的绿辉石,其微量元素配分曲线总体特征会发生变化,但元素总体丰度相近,某些元素特点相似,又反映了绿辉石和角闪石之间的成生联系。金红石是Ti、Nb、Ta、Zr、Hf的主要赋存矿物,而与之共生的绿帘石所表现出来的高场强元素的亏损特征表明了金红石的存在所带来的影响。LA-ICP-MS in situ trace element analysis was performed for minerals in eclogite from Somdo. According to the results, garnet mainly contains MREE, HREE and Y, with high concentrations of Sc, V, Cr and Co; omphacite contains high concentrations of MREE, Sr, Sc, V, Cr, Co, Ni and Ti, with certain amounts of Zr and Hf; garnet, omphacite, amphibole and epidote all exhibit LREE depletion, indicating the nonexistence of metasomatism by exotic LREE-rich fluid during the retrogressive metamorphism of the eelogite, and this accounts for somewhat different trace element characteristics between eclogite here and Su-Lu UHP eclogites that are characterized by LREE enrichment. Zoning of some trace elements（e, g., Ti and Zr）demon- strates the pressure decreasing and temperature increasing closely after peak metamorphism during the turning back to the shallow position. Trace element partitioning between rock-forming minerals is controlled by the par- titioning of major elements between minerals, e.g., MgO partitioning between garnet and omphacite controls the partitioning of Ni, Co, Ti, whereas CaO partitioning controls the partitioning of St, Y and REE. The formation and decomposition of minerals and the change of physical-chemical conditions might result in new par- titioning of trace elements between minerals during retrogressive metamorphism. Amphibole formed by om- phacite retrogression would not wholly inherit the trace element distribution pattern of omphacite without any diversification, as indicated by differences in their trace element distribution patterns; nevertheless, the some- what similar specific characteristics of trace element distribution patterns between omphacite and amphibole demonstrate their certain genetic linkage. Rutile is the main bearer of HFS elements such as Ti, Nb, Ta, Zr and Hf, which strongly effects the depletion of HFS elements in coexisting epidote.

关 键 词：榴辉岩 原位 微量元素 松多 西藏 

分 类 号：P575[天文地球—矿物学] P588.3[天文地球—地质学]