Origin of chromite nodules in podiform chromitite from the Kızıldağ ophiolite, southern Turkey
Origin of chromite nodules in podiform chromitite from the Kızıldağ ophiolite, southern Turkey
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土耳其南部 Kä±ldaä 蛇绿岩中豆状铬铁矿中铬铁矿结核的成因
DOI：
10.1016/j.oregeorev.2021.104443
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发表时间：
2021-12
影响因子：
3.3
通讯作者：
Zhuo-Sen Yao
中科院分区：
文献类型：
--
作者：
Chen Chen;Christina Yan Wang;Wei Tan;Zhuo-Sen Yao
铬铁矿结核是蛇绿岩系豆荚状铬铁矿中所特有的，其成因尚无定论。土耳其南部KızıLdağ蛇绿岩中的结核铬铁矿含有典型的铬铁矿结核，分析了它们的地球化学组成和晶体取向，研究了结核矿体的形成及相关的地球动力学过程。EBSD数据表明，铬铁矿结核是由具有随机晶向的铬铁矿颗粒拼接而成，且所有颗粒都具有低的取向角(<；6°)，没有广泛的亚晶旋转。这些特征与铬铁矿结核来源于骨架铬矿核的观点不一致。此外，结核中的铬铁矿晶体具有相对均一的成分，这意味着两个不同岩浆之间的混沌混合在铬铁矿结核形成中的重要性有限。根据铬铁矿中橄榄石和单斜辉石的H2O含量，我们计算出铬铁矿的母岩浆是含水的(~3.48%)，但其水含量远远低于流体和汽相出溶所需的H2O溶解度。此外，由于母岩浆的雷诺数较低，其动力学流动应该是准层流的，这与长期以来被认为是形成铬铁矿结核的关键因素的湍流不同。当向上的岩浆流穿过狭窄管道的透镜状段时，部分将与剩余的前向流分离，形成扩大区域的对流循环。这种对流促进了辉石沿橄榄岩围岩的熔融，形成了广泛的富硅和富铬的熔滴，这些熔滴又与原始岩浆混合，使铬铁矿颗粒结晶。这些不同大小的铬铁矿晶体的轨迹高度聚集在对流和向上上升的岩浆流边界内的准稳定区域，在那里铬铁矿颗粒之间发生多次碰撞和碰撞，导致铬铁矿颗粒簇聚合，最终形成铬铁矿结核。这种情况是由KızıLdağ蛇绿岩中豆荚状铬铁矿中的层流流动模式支持的，通常也可以转移到其他蛇绿质铬铁矿中。
Chromite nodule is unique in podiform chromitite of ophiolitic suites and there is no agreement on its petrogenesis. The nodular chromitites of the Kızıldağ ophiolite in southern Turkey contain typical chromite nodules, and here their geochemical compositions and crystallographic orientations have been analyzed to study the formation of nodular orebody and related geodynamic processes. The EBSD data reveal that chromite nodule is composed of a patchwork of chromite grains that have random crystallographic orientations, and all grains have low misorientation angles (<6°) without extensive subgrain rotation. These characteristics are inconsistent with the viewpoint that chromite nodule is emanating from a skeletal chromite core. In addition, chromite crystals in nodules have relatively homogeneous compositions, implying the limited importance of chaotic mixing between two distinct magmas in the formation of chromite nodules. Based on the H2O contents of olivine and clinopyroxene in chromitite, we calculated that the parental magma of chromitite is hydrous (<~3.48%), but its water content is far less than the required H2O solubility for exsolution of fluid and vapour phase. Moreover, the dynamic flow of the parental magma should be quasi-laminar due to its low Reynolds number, distinct from the turbulent flow that has long been recognized as a critical factor in forming chromite nodules. When an upward magma flow passes through the lenticular segment of a narrow conduit, some parts will be separated from the remaining forward flow to form a convective circulation in the enlarged area. This convective flow facilitates the melting of pyroxenes along the peridotite wall rock, forming extensive Si- and Cr-rich melt droplets which, in turn, mix with the primitive magma to crystallize chromite grains. Trajectories of these chromite crystals with different sizes highly gather in a quasi-steady area inside the boundary between the convective current and upward ascending magma flow, where allows numerous impacts and collisions between chromite grains, leading to the coalescence of clusters of chromite grains and eventually the formation of chromite nodules. This scenario is underpinned by the laminar flow pattern in the podiform chromitite from the Kızıldağ ophiolite, and may be also transferrable to other ophiolitic chromitite in general.
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影响因子：
3.9
作者：
Z. Yao;J. Mungall;K. Qin
通讯作者：
Z. Yao;J. Mungall;K. Qin
影响因子：
5.3
作者：
Chung, Hye-Yoon;Mungall, James E.
通讯作者：
Mungall, James E.
影响因子：
5
作者：
Iacono-Marziano, Giada;Morizet, Yann;Gaillard, Fabrice
通讯作者：
Gaillard, Fabrice
影响因子：
5.2
作者：
Aubaud, C;Hauri, EH;Hirschmann, MM
通讯作者：
Hirschmann, MM
克孜勒达蛇绿岩（土耳其东南部）中的中铬铁矿是在新特提斯洋俯冲起始过程中形成的
影响因子：
3.3
作者：
Chen Chen;Su Ben-Xun;Xiao Yan;Pang Kwan-Nang;Robinson Paul T;Uysal Ibrahim;Lin Wei;Qin Ke-Zhang;Avcı Erdi;Kapsiotis Argyris
通讯作者：
Kapsiotis Argyris