Alteration and metasomatism of the UG2 melanorite and its stratiform pegmatoids, Bushveld Complex, South Africa –characteristics, timing and origins.
Alteration and metasomatism of the UG2 melanorite and its stratiform pegmatoids, Bushveld Complex, South Africa –characteristics, timing and origins.
复制标题
南非布什维尔德杂岩体 UG2 黑云岩及其层状伟晶岩的蚀变和交代作用——特征、时间和起源。
DOI：
--
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
N. Beukes
中科院分区：
文献类型：
--
作者：
R. J. Voordouw;N. Beukes
两河铂矿（Bushveld杂岩东部分支）的UG2铬铁矿完全包裹在UG2黑锰矿中，该黑锰矿在这里分为五个亚单元，它们都是由同一母岩浆结晶而成的。这些亚单位从上到下依次为上远端、上层状伟晶状、上裂、下裂和下层状伟晶状。上部远端和下部分裂亚单元表现出最主要的特征，而热液流体和/或含水熔体渗透到其余三个亚单元以及UG2铬铁矿中。在层状伟晶状亚单位内，变形虫状橄榄石的网状脉、高丰度的次生硅酸盐、不相容元素的富集和晶粒尺寸的变粗表明流体和（或）熔体的渗透。上分裂亚单元富铬铁矿，局部蚀变为角闪岩。这种由流体和熔融引起的蚀变/交代作用发生在高温下，沿至少7公里的走向长度普遍存在，表明岩浆起源。这些岩浆流体可能与下伏堆积物的压实作用或铬铁矿晶体浆料的侵入有关。
The UG2 chromitite at Two Rivers Platinum Mine (eastern limb, Bushveld Complex) is fully enclosed within a UG2 melanorite that is here divided into five sub-units, all of which crystallised from the same parental magma. From top to bottom, these sub-units are the upper distal, upper stratiform pegmatoid, upper split, lower split and lower stratiform pegmatoid. The upper distal and lower split sub-units exhibit the most primary characteristics whereas hydrothermal fluids and/or hydrous melts infiltrated the remaining three sub-units, as well as the UG2 chromitite. Within the stratiform pegmatoid sub-units, network veins of amoeboidal troctolite, high abundances of secondary silicates, enrichment in incompatible elements and the coarsening of grain sizes indicate this infiltration of fluids and/or melts. The upper split sub-unit is chromite-rich and locally altered to amphibolite. This fluid- and melt-induced alteration/metasomatism occurred at high temperatures and is pervasive along at least 7 km of strike length, suggesting magmatic origins. These magmatic fluids are probably related to the compaction of underlying cumulates or the intrusion of chromite crystal slurries.