Alteration of primary Cr-spinel mineral composition from the Suru Valley ophiolitic peridotites, Ladakh Himalaya: Their low-temperature metamorphic implications
Alteration of primary Cr-spinel mineral composition from the Suru Valley ophiolitic peridotites, Ladakh Himalaya: Their low-temperature metamorphic implications
复制标题
喜马拉雅拉达克苏鲁河谷蛇绿橄榄岩原生铬尖晶石矿物成分的变化：其低温变质影响
DOI：
--
复制
发表时间：
2019
期刊：
影响因子：
--
通讯作者：
D. S. Rao
中科院分区：
文献类型：
--
作者：
I. Bhat;T. Ahmad;D. S. Rao
本文研究了出露于喜马拉雅拉达克卡吉尔地区特雷斯彭村附近的苏鲁谷蛇绿橄榄岩中的一种铬尖晶石的化学变质作用。苏鲁谷橄榄岩部分蛇纹化，保留了尖晶石和橄榄石和辉石的遗迹。这些橄榄岩含有特征的红棕色尖晶石颗粒，其晶界受到侵蚀。在对这些颗粒进行矿物化学分析时，观察到富铬岩芯的成分变化，其边缘为贫铬成分。沿原生铬尖晶石颗粒的边缘和裂隙观察到次生尖晶石成分，即铁铬矿和磁铁矿。原生铬尖晶石岩心为富铬岩心，具有较高的Cr3+#值(0.5-0.6)和较低的Al3+#值(0.42-0.54)。从原生尖晶石核到蚀变边，蚀变过程中，由于与寄主橄榄岩周围的硅酸盐发生交换，Cr3+#和Fe3+#增加，而Mg2+#减少。根据目前的尖晶石矿物化学，变质蚀变条件在绿片岩和下角闪岩之间处于过渡状态，与大多数新特提斯蛇绿岩橄榄岩相似。
The present study focuses on the chemical modification of a Cr-spinel from the Suru Valley ophiolitic peridotites exposed near Trespone Village of Kargil district, Ladakh Himalaya. The Suru Valley peridotite is partially serpentinised with the preservation of the spinel and relics of olivine and pyroxene. These peridotites contain characteristic red-brown spinel grains of corroded grain boundaries. While analysing these grains for mineral chemistry, compositional variation was observed with Cr-rich cores rimmed by Cr-poor compositions. Secondary spinel compositions, i.e., ferritchromite and magnetite were observed along the margins and cracks of primary Cr-spinel grains. The primary Cr-spinel cores are identified as Cr-rich and are characterised by higher values of Cr3+# (0.5–0.6) and lower values of Al3+# (0.42–0.54). From primary spinel cores to altered rims it was observed that Cr3+# and Fe3+# increase while Mg2+# decreases due to Mg2+–Fe2+ and Al3+–Fe3+ exchange with surrounding silicates of host peridotite during alteration. On the basis of present spinel mineral chemistry, metamorphic alteration conditions were transitional between greenschist and lower amphibolite similar to most of the Neo-Tethyan ophiolite peridotites.