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首页> 外文期刊>South African Journal of Geology: Being the Transaction of the Geological Society of South African: Syndie die Verhandelinge van die Geologiese Vereniging van Suid-Afrika >GEOCHEMISTRY AND HEAVY MINERALS ANALYSES ON 'BLACK SANDS' OF THE LOWER CAMBRIAN FISH RIVER SUBGROUP (NAMA GROUP, NAMIBIA)
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GEOCHEMISTRY AND HEAVY MINERALS ANALYSES ON 'BLACK SANDS' OF THE LOWER CAMBRIAN FISH RIVER SUBGROUP (NAMA GROUP, NAMIBIA)

机译：下寒武纪鱼河子群（纳米比亚，纳米比亚）的“黑沙”的地球化学和重矿物分析

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摘要

Heavy mineral rich-sandstones ("black sands") of the Lower Cambrian upper Fish River Subgroup in Namibia were used to reveal the provenance of the detrital material. The host rocks of the black sands from the Haribes and Rosenhof Members are mainly composed of partially rounded quartz, feldspar (K-feldspar > plagioclase), polycrystalline quartz, few siltstone fragments and labile altered or metamorphosed volcanic lithoclasts. Geochemical proxies are similar to those from typical foreland deposits and point to slightly recycled upper continental crustal composition, e.g.: Th/Sc ratios between 1.23 and 1.95, Zr/Sc ranging from 24 to 38 and La/Sc from 4.8 to 10.8. Heavy mineral addition of up to 30% does not significantly change Th/Sc, La/Sc and La/Th values, but slightly changed the Zr/Sc ratios, which range from 38 to 53. The heavy mineral-enriched beds (50 to 75% of the whole rock), display nearly similar La/Sc ratios compared with other lithotypes. They are 9x enriched in rare earth elements and show a significantly stronger negative Eu-anomaly, and an enrichment of heavy over light rare earth elements, as well as higher Zr/Sc ratios (82 to 299), typical for reworked passive margin or foreland deposits.
机译：纳米比亚下寒武统上游鱼河子群的重矿物富砂岩（“黑沙”）被用来揭示该碎屑物的来源。哈里贝斯和罗森霍夫成员的黑沙宿主岩主要由部分圆形的石英，长石（钾长石>斜长石），多晶石英，少量粉砂岩碎片和不稳定的蚀变或变质火山碎石碎屑组成。地球化学代表与典型的前陆沉积物相似，并指出上大陆地壳成分略有回收，例如：Th / Sc比在1.23至1.95之间，Zr / Sc在24至38之间，La / Sc在4.8至10.8之间。最多添加30％的重矿物并不会显着改变Th / Sc，La / Sc和La / Th值，但会略微改变Zr / Sc的比值，范围从38到53。重矿物富集床（50到50岩石总数的75％）显示出与其他岩石类型相比几乎相似的La / Sc比。它们富集了9倍的稀土元素，并且表现出明显更强的负Eu异常，并且富集了重于轻稀土元素，以及更高的Zr / Sc比（82至299），通常用于返工的被动边缘或前陆存款。

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