A multidisciplinary approach for the quantitative provenance analysis of siltstone: Mesozoic Mandawa Basin, southeastern Tanzania
A multidisciplinary approach for the quantitative provenance analysis of siltstone: Mesozoic Mandawa Basin, southeastern Tanzania
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DOI：
10.1144/sp484-2018-136
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发表时间：
2019-01
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通讯作者：
L. Caracciolo;S. Andó;P. Vermeesch;E. Garzanti;Ross.;McCabe;M. Barbarano;Chiara I. Paleari;M. Rittner;T. Pearce
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作者：
L. Caracciolo;S. Andó;P. Vermeesch;E. Garzanti;Ross.;McCabe;M. Barbarano;Chiara I. Paleari;M. Rittner;T. Pearce
摘要本文介绍了如何在粉土（代表c。50%的世界沉积物）沉积物，以获得定量数据一样有效的沙子大小的沉积物。分析工作流程包括使用宽粒度窗口（15-355 μ）进行重矿物分离，通过集成光学分析、拉曼光谱、QEMSCAN显微镜和碎屑锆石U-Pb测年进行分析。本研究选择了坦桑尼亚中南部Mandawa盆地的上侏罗纪-白垩纪粉砂级沉积物。拉曼光谱辅助重矿物分析表明，石榴石和磷灰石是最常见的矿物，以及耐用的锆石，电气石和次要的金红石。副相但诊断相是钛铁矿、十字石、绿帘石和独居石。石榴子石上的蚀坑和十字石上的鸡冠状特征记录了成岩作用对原始重矿物组合的重要影响。多变量统计分析突出了耐用矿物（锆石，电气石和金红石，ZTR）之间的密切联系，而石榴石和磷灰石图单独反映三组变量之间的独立性与石榴石增加侏罗纪样品。石榴石端元分析的拉曼数据记录了侏罗纪（富含A、Bi和Bii型）和白垩纪（占优势的A、Ci和Cii型）样品之间的不同组合。碎屑锆石的U-Pb定年及其与上述数据集的统计整合提供了对物源和/或水系变化的进一步了解。早、晚期泛非造山带的莫桑比克带和伊鲁米德带的变质岩是侏罗纪沉积的主要物源。白垩纪沉积物记录了一个扩大的排水系统，远至Usagran-Ubendian带和坦桑尼亚太古代盆地。
Abstract This paper shows how heavy minerals and single-grain varietal studies can be conducted on silt (representing c. 50% of world's sediments) sediments to obtain quantitative data as efficiently as for sand-sized sediments. The analytical workflows include heavy mineral separation using a wide grain-size window (15–355 μ) analysed through integrated optical analysis, Raman spectroscopy, QEMSCAN microscopy and U–Pb dating of detrital zircon. Upper Jurassic–Cretaceous silt-sized sediments from the Mandawa Basin of central-southern Tanzania have been selected for the scope of this research. Raman-aided heavy mineral analysis reveals garnet and apatite to be the most common minerals together with durable zircon, tourmaline and subordinate rutile. Accessory but diagnostic phases are titanite, staurolite, epidote and monazite. Etch pits on garnet and cockscomb features on staurolite document the significant effect of diagenesis on the pristine heavy mineral assemblage. Multivariate statistical analysis highlights a close association among durable minerals (zircon, tourmaline and rutile, ZTR) while garnet and apatite plot alone reflecting independence between the three groups of variables with garnet increasing in Jurassic samples. Raman data for garnet end-member analysis document different associations between Jurassic (richer in A, Bi and Bii types) and Cretaceous (dominant A, Ci and Cii types) samples. U–Pb dating of detrital zircon and their statistical integration with the above-mentioned datasets provide further insights into changes in provenance and/or drainage systems. Metamorphic rocks of the early and late Pan-African orogeny terranes of the Mozambique Belt and those of the Irumide Belt acted as main source of sediment during the Jurassic. Cretaceous sediments record a broadening of the drainage system reaching as far as the Usagran–Ubendian Belt and the Tanzanian Archean Craton.