Interpreting detrital modes and geochemistry of sandstones from the late Paleozoic Tepuel-Genoa Basin: Paleogeographic implications (Patagonia, Argentina)
Interpreting detrital modes and geochemistry of sandstones from the late Paleozoic Tepuel-Genoa Basin: Paleogeographic implications (Patagonia, Argentina)
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解释晚古生代特普埃尔-热那亚盆地砂岩的碎屑模式和地球化学：古地理意义（阿根廷巴塔哥尼亚）
DOI：
10.1016/j.jsames.2020.102858
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发表时间：
2020
影响因子：
1.8
通讯作者：
Gulbranson, E.L.
中科院分区：
文献类型：
--
作者：
Ciccioli, P. L.;Limarino, C. O.;Isbell, J.L.;Taboada, A. C.;Pagani, M. A.;Gulbranson, E.L.
本文分析了晚古生代特普埃尔-热那亚盆地沉积砂岩的物源。在Esquel、Sierra de Tepuel、Sierra de Tecka、El Molle和Río Genoa地区采集了五个剖面样本，用于岩相学和地球化学研究。Tepuel-Genoa盆地砂岩主要为粗面岩屑砂岩和岩屑砂岩，其中瓦莱Chico组为火山岩和沉积岩岩屑，其余为中-高级变质岩碎屑。7个模态分量（Qm、Qi、Lv、Lmm-h、Lm-Lp、Lm、Qpm）对物源区的判别有一定的价值。这些模态分量允许识别三种岩相：1。石英岩-岩屑质（Qm 69 Lv 2Lm 29），2.石英（Qm 89 Lv 4Lm 7）和3.火山-沉积（Qm 60 Lv 38 Lm 1）。石英岩屑岩相主要由单晶石英、中、高级变质碎屑和碎裂结构的多晶石英组成，这一组合被解释为来自形成Deseado地块的结晶岩。石英岩相由单晶石英组成，变质碎屑和火山碎屑的痕迹很少;物源区归因于沉积地形，很可能覆盖了Deseado地块的一部分。火山-沉积岩相由火山碎屑（酸性和中间岩）和沉积碎屑（砂岩和泥岩）组成，具有离散量的具有自形形状和海湾的石英颗粒。这一组合可能对应于智利发育的泥盆纪-早石炭世增生杂岩或巴塔哥尼亚中部西部火山弧的去顶物质供给。三个定义的岩相的有效性进行了评估，使用主成分分析和三角形组成图，这两种方法显示出良好的分离和缺乏重叠的三个岩相之间。主量元素（Si、Al、Fe、Na、K）和微量元素（Zr、Th、Sc、Hf）用于改善岩相学信息。SiO2与K2 O/Na 2 O的关系表明，Pampa de Tepuel组和Mojón de Hierro组对应于被动大陆边缘，而瓦莱奇科组和Río Genoa组则代表不同类型的活动大陆边缘。Th/Sc、Zr/Sc比值和Th、Hf、Co分布表明，Tepuel群砂岩的岩石成分与上陆壳的平均成分一致。
The provenance of sandstones deposited in the late Paleozoic Tepuel-Genoa Basin is analyzed in this paper. Five sections were sampled in Esquel, Sierra de Tepuel, Sierra de Tecka, El Molle, and Río Genoa areas for petrographic and geochemical studies. The sandstones in the Tepuel-Genoa Basin are dominated by feldspathic litharenites and litharenites, showing lithic fragments of volcanic and sedimentary rocks in the Valle Chico Formation and medium-to high-grade metamorphic rock clasts in the rest of the units.Detrital modes of seventy-five sandstones samples from the Valle Chico, Pampa de Tepuel, Mojón de Hierro, and Río Genoa formations were counted and analyzed. Seven modal components have discriminant value for identifying provenance areas (Qm, Qi, Lv, Lmm-h, Lm-Lp, Lm, Qpm). These modal components allow identification of three petrofacies: 1. Quartzose-lithic (Qm69Lv2Lm29), 2. Quartzose (Qm89Lv4Lm7) and 3. Volcanic-sedimentary (Qm60Lv38Lm1). The quartzose-lithic petrofacies is mainly composed of monocrystalline quartz, medium- and high-grade metamorphic clasts and polycrystalline quartz with cataclastic texture, this assemblage is interpreted as being derived from the crystalline rocks that form the Deseado Massif. The quartzose petrofacies is composed of monocrystalline quartz with scarce contributions of metamorphic clasts and traces of volcanic fragments; the provenance area is ascribed to sedimentary terrains, which most likely covered part of the Deseado Massif. The volcanic-sedimentary petrofacies is comprised of volcanic (acidic and intermediate rocks) and sedimentary (sandstone and mudstone) clasts, with discrete amounts of quartz grains with idiomorph shapes and embayments. This assemblage may correspond to material supply from the Devonian-Early Carboniferous accretionary complex developed in Chile or the unroofing of the western volcanic arc located in the central part of Patagonia. The validity of the three defined petrofacies was evaluated using Principal Component Analysis and triangular compositional diagrams; both methods show good separation and lack of overlap between the three petrofacies. Major (Si, Al, Fe, Na, K) and trace-REE elements (Zr, Th, Sc, Hf) were used to improve the petrographic information. The relation SiO2against K2O/Na2O indicates that the Pampa de Tepuel and the Mojón de Hierro formations correspond to a passive margin, while the Valle Chico and Río Genoa formations represent different types of active continental margins. The Th/Sc and Zr/Sc ratios and the Th-Hf-Co distributions indicate that the sandstones of the Tepuel Group were formed from rocks compatibles with the average composition of the upper continental crust.
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