金红石-榍石转变过程中元素地球化学行为——以雅鲁藏布江缝合带角闪岩为例

发布时间：2018-03-16 18:21

  本文选题：榍石　切入点：金红石　出处：《岩石学报》2017年08期 　论文类型：期刊论文

【摘要】：金红石边缘形成榍石冠状边结构在变质中-基性岩中普遍存在,是金红石与退变质流体携带的SiO_2与CaO作用的结果,反应形成的榍石微量元素特征受到金红石和流体的共同影响。雅鲁藏布江缝合带中角闪岩LZ06-04在抬升过程经历近等温降压退变质作用,石榴子石分解导致同一样品中含石榴子石部分与不含石榴子石部分的退变质流体成分的差异。两种流体分别与金红石反应,对应形成的榍石具有相似的Nb、Ta含量和Nb/Ta比值特征,但截然不同的REE特征。榍石的Nb、Ta来源于金红石,残余金红石与含水流体再平衡Nb、Ta的分配系数增大,且D_(Nb)~(Rt/Fluid)≥D_(Ta)~(Rt/Fluid);虽然Nb和Ta在含水流体中都表现为不活动元素,但相对于Nb,Ta在含水流体中活动性较高。榍石的Zr-Hf体系特征受到锆石、石榴子石等矿物的综合影响,并且Zr-Hf在含水流体中表现出比Nb-Ta更高的活动性。榍石的REE特征受流体中REE特征、榍石与流体配分系数以及共生矿物的影响。在岩浆或变质体系,榍石形成过程中,REE富集矿物(如石榴子石、锆石、褐帘石、独居石、磷灰石等)形成或分解将影响榍石的REE分布特征或形成REE环带结构。含水流体中金红石退变质形成榍石反应的进行受流体中TiO_2、CaO和SiO_2活度的影响。因此榍石常见于钙碱性岩浆岩、富Ca基性变质岩和矽卡岩中。流体中CaO活度的变化影响榍石的形成,进而影响Ti、Nb、Ta在流体中的运移能力。俯冲板片产生流体在交代上覆富Ca地幔楔物质过程中形成榍石残留同样可以造成部分熔融体具有亏损HFSE特征。
[Abstract]:The formation of sphene coronal edge structure at the rutile edge is common in metamorphic basic rocks, which is the result of the interaction between rutile and retrograde fluid carrying SiO_2 and CaO. The trace element characteristics of sphene formed by the reaction are influenced by both rutile and fluid. The amphibolite LZ06-04 in the Yalu Zangbo suture zone experienced near isothermal depressurization retrograde metamorphism during the uplift process. The decomposing of pomegranate leads to the difference of retrograde fluid composition between the part containing pomegranate and the part without pomegranate. The two fluids react with rutile respectively. The corresponding sphene has similar characteristics of NB Ta content and Nb/Ta ratio. However, the REE characteristics of sphene are quite different. The NB / Ta of sphene is derived from rutile, and the partition coefficient of residual rutile and water bearing fluid reequilibrium NB / Ta increases, and the D T / T / Fluid) 鈮，

本文编号：1621134