Pre-impact tectonothermal evolution of the crystalline basement-derived rocks in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure
Pre-impact tectonothermal evolution of the crystalline basement-derived rocks in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure
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切萨皮克湾撞击构造 ICDP-USGS 艾尔维尔 B 核心中结晶基底衍生岩石的撞击前构造热演化
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发表时间：
2009
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影响因子：
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通讯作者：
W. Reimold
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作者：
R. Gibson;Gabrielle N. Townsend;J. Horton;W. Reimold
来自切萨皮克湾撞击构造的Eyreville B钻孔岩芯最低215 m处的撞击前结晶岩由一系列泥质云母片岩和次级变岩脉或长英质变火山岩、角闪岩和钙硅酸盐岩组成，后者被白云母（±黑云母、石榴石）花岗岩和花岗岩伟晶岩侵入。这些片岩通常为石墨质和黄铁矿质，局部含有斜长石变斑晶、纤维状硅线石和石榴石，表明中上部角闪岩相的峰值变质条件，估计约为0.4-0.5 GPa和600-670 °C。片岩显示出强烈的浅倾S1复合剪切面理，局部具有微米至分米级的平卧褶皱和高温下形成的S-C′剪切带结构。区域的混乱定向叶理，类似角砾岩，但没有退化的迹象，是当地开发和剪切破坏褶皱铰链解释。云母片岩中的矿物结构关系表明，变质峰期在D1。然而，组构分析表明，在逆冷却过程中，近水平剪切变形仍在继续，形成了高温剪切组构（S-C和S-C′）被逐渐降低的温度组构叠加的糜棱岩带。在更坚固的岩性中的碎裂岩和碳酸盐胶结角砾岩，如钙硅酸盐单元和长英质片麻岩中的碎裂岩和碳酸盐胶结角砾岩，在上覆的 *roger.吉布森@wits.ac.za吉布森，R.L.中发现，汤森，G.N.，霍顿，J.W.，小的，以及华盛顿大学的雷默德2009年，ICDP-USGS Eyreville B岩芯中结晶基底衍生岩石的撞击前构造演化，切萨皮克湾撞击构造，Gohn，G.S.，Koeberl，C.，米勒，K.G.，以及华盛顿大学的雷默德编辑，切萨皮克湾冲击构造中的ICDP-USGS深钻项目：来自Eyreville岩心孔的结果：美国地质学会专题论文458，第1-20页，doi：10.1130/2009.2458（12）。如需复制许可，请联系editing@geosociety.org。©2009美国地质学会。All rights reserved. 2吉布森等人spe 458 -12第1页第2页
Pre-impact crystalline rocks of the lowermost 215 m of the Eyreville B drill core from the Chesapeake Bay impact structure consist of a sequence of pelitic mica schists with subsidiary metagraywackes or felsic metavolcanic rocks, amphibolite, and calc-silicate rock that is intruded by muscovite (±biotite, garnet) granite and granite pegmatite. The schists are commonly graphitic and pyritic and locally contain plagioclase porphyroblasts, fi brolitic sillimanite, and garnet that indicate middleto upper-amphibolite-facies peak metamorphic conditions estimated at ~0.4–0.5 GPa and 600–670 °C. The schists display an intense, shallowly dipping, S1 composite shear foliation with local micrometerto decimeter-scale recumbent folds and S-C′ shear band structures that formed at high temperatures. Zones of chaotically oriented foliation, resembling breccias but showing no signs of retrogression, are developed locally and are interpreted as shear-disrupted fold hinges. Mineral textural relations in the mica schists indicate that the metamorphic peak was attained during D1. Fabric analysis indicates, however, that subhorizontal shear deformation continued during retrograde cooling, forming mylonite zones in which high-temperature shear fabrics (S-C and S-C′) are overprinted by progressively lowertemperature fabrics. Cataclasites and carbonate-cemented breccias in more competent lithologies such as the calc-silicate unit and in the felsic gneiss found as boulders in the overlying *roger.gibson@wits.ac.za Gibson, R.L., Townsend, G.N., Horton, J.W., Jr., and Reimold, W.U., 2009, Pre-impact tectonothermal evolution of the crystalline basement-derived rocks in the ICDP-USGS Eyreville B core, Chesapeake Bay impact structure, in Gohn, G.S., Koeberl, C., Miller, K.G., and Reimold, W.U., eds., The ICDP-USGS Deep Drilling Project in the Chesapeake Bay Impact Structure: Results from the Eyreville Core Holes: Geological Society of America Special Paper 458, p. 1–20, doi: 10.1130/2009.2458(12). For permission to copy, contact editing@geosociety.org. ©2009 The Geological Society of America. All rights reserved. 2 Gibson et al. spe458-12 1st pgs page 2