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首页> 外文会议>Hypervelocity Impact Symposium >Remnants of Early Archean Impact Deposits on Earth: Search for a Meteoritic Component in the BARB5 and CT3 Drill Cores (Barberton Greenstone Belt, South Africa)
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Remnants of Early Archean Impact Deposits on Earth: Search for a Meteoritic Component in the BARB5 and CT3 Drill Cores (Barberton Greenstone Belt, South Africa)

机译：地球上早期的Archean影响沉积物的残余：在Barb5和CT3钻孔核心中搜索陨石组件（南非贝伯尔顿Greenstone Belt）

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The first 2.5 billion years of the terrestrial impact history are not documented by any impact structures. Only a few spherule layers of impact origin are known, most of them of late Archean to early Proterozoic age. In the Barberton Greenstone Belt (South Africa), several spherule horizons (layers SI to S4, possibly up to S8, with ages between-3.5 and-3.2 Ga) are amongst the oldest deposits from large bolide impacts onto Earth. Impact evidence is limited to (highly) elevated siderophile element contents and Cr isotopic compositions. Other isotope tools, such as the ~(187)Re-~(188)Os radionuclide system in combination with high-precision concentration data for siderophile elements, might be useful to confirm the propositions regarding the presence of meteoritic components made so far. Two recently recovered drill cores from the central and northern Barberton area (CT3 and BARB5) with as many as 18 spherule layer intersections of Paleoarchean age (some of which may be due to tectonic duplication, some might correlate with the S2 to S4 layers) provide an outstanding opportunity to gain new insight into the early impact bombardment of Earth. We present new mineralogical, chemical, and ~(187)Re-~(188)Os isotope data on CT3 and BARB5 drill core samples. Spherules in most layers exhibit undeformed shapes and include vesicles. Sulfides frequently are present in both matrix and spherules. Osmium data reveal a trend between the spherule-free horizons (intercalating the spherule layers) and spherule-matrix aggregates. Whereas the former typically exhibit elevated ~(187)Os/~(188)Os ratios of up to-1.2 and low Os and Ir concentrations below several hundred ppt, spherule-matrix aggregates tend to be less radiogenic (down to subchondritic present day ~(187)Os/~(188)Os ratios) with Os and Ir concentrations as high as in chondrites. Ghromium-Ir correlations for CT3 and BARB5 samples mirror earlier results on SI to S4 layers and can be interpreted in favor of an impact origin of the here investigated spherule horizons.
机译：任何影响结构都没有记录第一个25亿年的地面影响历史。只有几个撞击源的球形层都是已知的，其中大多数都是初级前进年龄的前兆子代。在Barberton Greenstone皮带（南非），几个球形视野（层Si至S4，最多可在-3.5和-3.2 Ga之间的时间为-3.2 Ga）是从大型血管影响到地球上的最古老的存款中。影响证据仅限于（高度）升高的西参元素内容物和Cr同位素组合物。其他同位素工具，例如〜（187）Re-〜（188）OS放射性核素系统与具有高精度集中元素的高精度浓度数据，可能有助于确认到目前为止所制定的陨石成分的存在。最近从中央和北部的博尔顿地区（CT3和BARB5）的两个最近回收的钻孔核心，与古地基年龄的数量（CT3和BARB5）（其中一些可能是由于构造复制而言，有些可能与S2到S4层相关）提供一个杰出的机会，以获得新的洞察力轰炸地球的早期影响。我们呈现出新的矿物学，化学品，〜（187）Re-〜（188）〜（188）OS同位素数据上CT3和BARB5钻孔核心样品。大多数层的球形表现出未变形的形状并包括囊泡。硫化物经常存在于矩阵和球形中。锇数据揭示了自由球之间的趋势（嵌入了球形层）和球素 - 基质聚集体。而前者通常表现出升高〜（187）OS /〜（188）OS /〜（188）OS比率高达-1.2和低于OS和IR浓度低于几百个PPT的效果，球基质聚集体趋于较少的辐射（下降到亚基氏囊炎的当前〜 （187）OS /〜（188）OS比率，OS和红外浓度高达Chondrites。用于CT3和BARB5样品的GHROMIUM-IR相关性镜像SI至S4层上的结果，并且可以解释有利于HILS调查的球形视野的影响。

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