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首页> 外文期刊>Journal of Asian earth sciences >Geological and ~(40)Ar/~(39)Ar age constraints on late-stage Deccan rhyolitic volcanism, inter-volcanic sedimentation, and the Panvel flexure from the Dongri area, Mumbai
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Geological and ~(40)Ar/~(39)Ar age constraints on late-stage Deccan rhyolitic volcanism, inter-volcanic sedimentation, and the Panvel flexure from the Dongri area, Mumbai

机译：孟买东日地区晚期Deccan流纹火山作用，火山间沉积和Panvel弯曲对地质和〜（40）Ar /〜（39）Ar年龄的限制

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摘要

Post-K-Pg Boundary Deccan magmatism is well known from the Mumbai area in the Panvel flexure zone. Represented by the Salsette Subgroup, it shows characters atypical of much of the Deccan Traps, including rhyolite lavas and tuffs, mafic tuffs and breccias, spilitic pillow basalts, and "intertrappean" sedimentary or volcanosedimentary deposits, with mafic intrusions as well as trachyte intrusions containing basaltic enclaves. The intertrappean deposits have been interpreted as formed in shallow marine or lagoonal environments in small fault-bounded basins due to syn-volcanic subsidence. We report a previously unknown sedimentary deposit underlying the Dongri rhyolite flow from the upper part of the Salsette Subgroup, with a westerly tectonic dip due to the Panvel flexure. We have obtained concordant ~(40)Ar/~(39)Ar ages of 62.6 ± 0.6 Ma (2σ) and 62.9 ± 0.2 Ma (2σ) for samples taken from two separate outcrops of this rhyolite. The results are significant in showing that (ⅰ) Danian inter-volcanic sedimentary deposits formed throughout Mumbai, (ⅱ) the rock units are consistent with the stratigraphy postulated earlier for Mumbai, (ⅲ) shale fragments known in some Dongri tuffs were likely derived from the sedimentary deposit under the Dongri rhyolite, (ⅳ) the total duration of extrusive and intrusive Deccan magmatism was at least 8-9 million years, and (ⅴ) Panvel flexure formed, or continued to form, after 63 Ma, possibly even 62 Ma, and could not have formed by 65-64 Ma as concluded in a recent study.
机译：后K-Pg边界Deccan岩浆作用在Panvel弯曲带的孟买地区是众所周知的。由Salsette小组代表，它显示了许多Deccan陷阱的非典型特征，包括流纹岩熔岩和凝灰岩，镁铁凝灰岩和角砾岩，硅质枕形玄武岩，以及“圈套式”沉积或火山成岩沉积物，镁铁质侵入体以及含线状侵入体玄武岩飞地。圈间沉积物被解释为由于同火山作用而在小型断层带界盆地的浅海或泻湖环境中形成。我们报告了以前未知的沉积物沉积物，该沉积物来自Salsette子群上部的Dongri流纹岩流，由于Panvel弯曲而具有西风构造倾角。从流纹岩的两个独立露头中获取的样品，我们获得了一致的〜（40）Ar /〜（39）Ar年龄，分别为62.6±0.6 Ma（2σ）和62.9±0.2 Ma（2σ）。结果表明，（ⅰ）在整个孟买形成的达尼安火山间沉积沉积物，（ⅱ）岩石单元与之前为孟买假定的地层相一致，（ⅲ）在某些东日凝灰岩中已知的页岩碎片可能源自东里流纹岩下的沉积物沉积，（ⅳ）挤压和侵入性Deccan岩浆作用的总持续时间至少为8-9百万年，（ⅴ）Panvel弯曲在63 Ma（甚至62 Ma）之后形成或继续形成，并且不可能由最近研究得出的65-64 Ma形成。

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