高分异花岗岩的识别与研究

发布时间：2018-05-09 08:34

本文选题：结晶分异作用 + 堆晶作用　；参考：《中国科学:地球科学》2017年07期

【摘要】：作为大陆地壳的重要组成部分,花岗岩一直是地质学中经久不衰的研究课题.从小型岩枝、岩脉,到大型岩基,花岗岩在不同尺度上表现出结构、构造、矿物组成及化学成分的不均一性.对导致花岗岩成分变异的原因,目前学术界则存在不同的认识.争论的焦点在于,花岗岩浆是否能够发生有效的结晶分异作用,以及如果有的话,将发生何种类型的结晶分异作用.本文通过资料的归纳与整理认为,尽管花岗岩浆由于较高的SiO_2含量导致其较高的粘度,但花岗岩浆的结晶分异作用既有野外宏观地质资料证据,也有微观尺度矿物组成及其成分变化的证据,更有大量地球化学资料的支持.这些资料显示,单纯的重力分异并不是花岗岩浆结晶分离作用的主导机制.相反,流动导致的分异可能是花岗岩浆成分变异最主要的原因.根据结晶分异程度,花岗岩可划分为低分异花岗岩、高分异花岗岩以及与之伴生的堆晶花岗岩,它们都将是未来花岗岩岩石学研究的前沿.在大型岩浆房中,高分异花岗岩的出现主要与它的高温及富挥发分相关;而沿伸展构造的侵位也是花岗岩浆能够发生强结晶分异作用的重要控制因素.在高度结晶分异作用情形下,花岗岩浆较长的结晶时间使其极易受到围岩同化混染的影响.因而,花岗岩在很多情况下并不能反映源区的特征及岩浆形成的物理化学条件.从目前的研究来看,高分异花岗岩有可能是大陆地壳成分成熟度的重要标志,且与W、Sn、Nb、Ta、Li、Be、Rb、Cs和REE等稀有金属成矿作用关系密切.
[Abstract]:As an important part of continental crust, granite has been an enduring research subject in geology. From small branches, veins to large bedrock, granites show heterogeneity in structure, structure, mineral composition and chemical composition on different scales. At present, there is a different understanding of the causes of granite composition variation. The focus of the debate is whether granitic magma can produce effective crystallization differentiation and, if so, what kind of crystallization differentiation will occur. In this paper, we conclude that although the high SiO_2 content of the granite magma leads to its higher viscosity, the crystallization differentiation of the granite magma is based on the evidence of field macroscopic geological data. There is also evidence of changes in mineral composition and composition at the micro scale, supported by a great deal of geochemical data. These data indicate that pure gravity differentiation is not the dominant mechanism for the crystallization separation of granitic magma. On the contrary, the differentiation caused by flow may be the main reason for the variation of magma composition. According to the degree of crystallization differentiation, granites can be divided into low-differentiated granites, high-grade isomorphic granites and associated heap-grained granites, all of which will be the frontiers of future granite petrology. In large magma chambers, the appearance of high grade isomerite is mainly related to its high temperature and rich volatilization, and emplacement along extensional structure is also an important controlling factor for strong crystallization differentiation of granitic magma. Under the condition of high crystallization differentiation, the granitic magma is easily affected by the assimilation of surrounding rock due to its long crystallization time. Therefore, granite can not reflect the characteristics of the source area and the physical and chemical conditions of magma formation in many cases. According to the present studies, the high grade isomorphic granites may be an important indicator of continental crustal maturity, and are closely related to the mineralization of rare metals such as REE and NbSN.
【作者单位】：中国科学院地质与地球物理研究所岩石圈演化国家重点实验室;中国科学院青藏高原地球科学卓越创新中心;中国科学院大学地球科学院;
【基金】：国家自然科学基金项目(批准号:41130313) 中国科学院战略性先导科技B类专项项目(编号:XDB03010200)资助
【分类号】：P588.121

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