Planar deformation features and impact glass in inclusions from the Vredefort Granophyre, South Africa
Planar deformation features and impact glass in inclusions from the Vredefort Granophyre, South Africa
复制标题
南非弗里德堡花斑岩内含物的平面变形特征和冲击玻璃
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
W. Reimold
中科院分区：
文献类型：
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作者：
P. Buchanan;W. Reimold
摘要：Vredefort Granophyre 代表了向下注入南非 Vredefort 冲击构造底部裂缝的冲击熔体。该单元包含来自撞击构造内不同位置的围岩内含物，主要由石英岩、长石石英岩、长石岩和花岗岩材料组成，还有少量的页岩和绿帘岩。两种再结晶程度最低的夹杂物含有具有单组或多组平面变形特征的石英。其他包裹体中的石英颗粒呈现蠕虫状纹理，让人想起棋盘长石。长石的范围从一些包裹体中的大型孪生晶体到细粒聚集体，这些聚集体显然是较大原生晶体分解的产物。在罕见的包裹体中，镁铁质矿物（可能是黑云母或角闪石）已转化为非常细粒的次生相聚集体，其中包括富铁尖晶石的小型自形晶体。这些数据表明，Vredefort 花斑岩内的包裹体暴露于 <5 至 8-30 GPa 的冲击压力下。
Abstract— The Vredefort Granophyre represents impact melt that was injected downward into fractures in the floor of the Vredefort impact structure, South Africa. This unit contains inclusions of country rock that were derived from different locations within the impact structure and are predominantly composed of quartzite, feldspathic quartzite, arkose, and granitic material with minor proportions of shale and epidiorite. Two of the least recrystallized inclusions contain quartz with single or multiple sets of planar deformation features. Quartz grains in other inclusions display a vermicular texture, which is reminiscent of checkerboard feldspar. Feldspars range from large, twinned crystals in some inclusions to fine‐grained aggregates that apparently are the product of decomposition of larger primary crystals. In rare inclusions, a mafic mineral, probably biotite or amphibole, has been transformed to very fine‐grained aggregates of secondary phases that include small euhedral crystals of Fe‐rich spinel. These data indicate that inclusions within the Vredefort Granophyre were exposed to shock pressures ranging from <5 to 8–30 GPa.