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《地学前缘(英文版)》2020,11(6):2103-2125
The investigated mantle bodies from the External Ligurians (Groppo di Gorro and Mt. Rocchetta) show evidences of a complex evolution determined by an early high temperature metasomatism, due to percolating melts of asthenospheric origin, and a later metasomatism at relatively high temperature by hydrothermal fluids, with formation of rodingites. At Groppo di Gorro, the serpentinization and chloritization processes obliterated totally the pyroxenite protolith, whereas at Mt. Rocchetta relics of peridotite and pyroxenite protoliths were preserved from serpentinization. The rodingite parageneses consist of diopside + vesuvianite + garnet + calcite + chlorite at Groppo di Gorro and garnet + diopside + serpentine ± vesuvianite ± prehnite ± chlorite ± pumpellyite at Mt. Rocchetta. Fluid inclusion measurements show that rodingitization occurred at relatively high temperatures (264–334 °C at 500 bar and 300–380 °C at 1 kbar). Garnet, the first phase of rodingite to form, consists of abundant hydrogarnet component at Groppo di Gorro, whereas it is mainly composed of grossular and andradite at Mt. Rocchetta. The last stage of rodingitization is characterized by the vesuvianite formation. Hydrogarnet nucleation requires high Ca and low silica fluids, whereas the formation of vesuvianite does not need CO2-poor fluids. The formation of calcite at Groppo di Gorro points to mildly oxidizing conditions compatible with hydrothermal fluids; the presence of andradite associated with serpentine and magnetite at Mt. Rocchetta suggests Fe3+-bearing fluids with fO2 slightly higher than iron-magnetite buffer. We propose that the formation of the studied rodingite could be related to different pulses of hydrothermal fluids mainly occurring in an ocean-continent transitional setting and, locally, in an accretionary prism associated with intra-oceanic subduction. 相似文献
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西天山异剥钙榴岩的地球化学研究 总被引：5，自引：4，他引：1
西天山长阿吾子的蛇绿混杂岩带的超基性岩及其伴生岩石异剥钙榴岩位于伊犁中天山板块和塔里木板块碰撞造山带。微量元素特征表明退变榴辉岩原岩成因与俯冲带环境有关。异剥钙榴岩中稀土元素和微量元素全面、大幅度降低,反映出来自于蛇纹岩化,作用于异剥钙榴岩化流体的强大的淋滤作用。因而异剥钙榴岩的稀土和微量元素特征都不能反映原始岩浆的特点,无法据此推断原始岩浆产生的大地构造环境。对退变榴辉岩的主元素和微量元素稀土元素的研究表明,长阿吾子异剥钙榴岩的原岩钙碱性玄武岩可能形成于俯冲上板片(SSZ)的岛弧环境。 相似文献
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蛇纹岩体中的硬玉岩与异剥钙榴岩 总被引：1，自引：4，他引：1
硬玉岩是一种稀少的岩类，常以构造岩包体和脉体的型式产出在蛇纹岩中。本文着重介绍与蛇纹岩化过程密切相关的硬玉岩。这类硬玉岩总是出现在洋壳俯冲碰撞带中，常常与蓝片岩、偶尔也与榴辉岩伴生。通过研究硬玉岩的矿物组合、化学成分和结构构造，综合世界各地硬玉岩产状，可将硬玉岩从广义的变质成因上分为三类，即：在蛇纹岩体中、或其它岩类包体中由交代作用形成的硬玉岩脉体；蛇纹岩中的构造岩成因岩石包体经固相变质作用后形成的块状硬玉岩：以及介于上述两者之间，由变质和交代的共同作用形成的硬玉岩。此外，还对交代成因的硬玉岩在蛇纹岩化过程中与异剥钙榴岩化作用的关系从流体及其化学成分演化的角度进行了分析和研究。提出了在海底和俯冲带上板片的构造背景下硬玉岩形成的模式。 相似文献
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新疆西天山长阿吾子异剥钙榴岩是目前首例发现的在俯冲带形成的原岩为榴辉岩的异剥钙榴岩,与其作用的流体为俯冲带流体。该异剥钙榴岩与大洋底变质作用形成的异剥钙榴岩相比,岩石学特征非常相似,但是元素迁移方面存在一定的差别。为了推断流体成分,我们使用了三种方法。一、测试了异剥钙榴岩化前后主要矿物相石榴石和辉石化学成分。二、在ACF图上,可以看出全岩成分从F端元向C端元演化,代表Fe减少,Ca增加的趋势,而且完全异剥钙榴岩成分落在了前人所做的异剥钙榴岩成分区间内。三、假设Al为不迁移元素,根据Grant的计算方法,做出主量元素、微量元素和REE的等浓度图。综合以上分析结果推断,俯冲带中流体的成分是复杂和变化的:部分异剥钙榴岩化阶段流体富集Ca、Si、Ti、Mn、Nb、Ta、Zr、Hf,贫乏Fe、Mg、Na、K、REE、Tb、Y,氧逸度升高,流体属于不饱和状态,因此导致不平衡结构发育;完全异剥钙榴岩阶段,流体富集Ca、Mg、LREE、Ni、Cr,贫乏Fe、Ti、Rb、Ba、MREE、HREE等元素,此时流体作用强烈,富水流体相的强烈淋滤作用,使得大部分元素发生了迁移。 相似文献
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