Geochemistry and detrital zircon geochronology of metasedimentary rocks in the Sierra Madre Terrane, Mexico: Implications of deposition along the western margin of Pangea,Geological Journal

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Geochemistry and detrital zircon geochronology of metasedimentary rocks in the Sierra Madre Terrane, Mexico: Implications of deposition along the western margin of Pangea
Geological Journal ( IF 1.4 ) Pub Date : 2021-02-22 , DOI: 10.1002/gj.4108
Sonia Alejandra Torres Sánchez ₁ , Carita Augustsson ₂ , Uwe Jenchen ₃ , José Rafael Barboza Gudiño ₄ , Andreas Gärtner ₅ , Mandy Hofmann ₅ , Ulf Linnemann ₅

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The basement complex of the Sierra Madre region in north-eastern Mexico is classified into four domains: (a) granulite facies rocks of Grenville age (ca. 1 Ga) known as the Novillo Gneiss, (b) the Palaeozoic Granjeno Schist, (c) an unmetamorphosed succession of Palaeozoic marine siliciclastic and volcanic rocks, and (d) an Ordovician plagiogranite body. We present a geochemical and provenance study of the metasedimentary rocks of the Granjeno Schist, which are associated with metavolcanic and meta-ultramafic rocks. In the Granjeno Schist, trace element ratios (Th/Sc, La/Sch, La/Sc, and Zr/Sc) and REE compositions of the metasedimentary rocks are similar to values for the mean continental crust values and are consistent with derivation of detritus from felsic rocks. Chemical index of alteration values of 30–80 indicates low to moderate weathering of the source. The clastic metasedimentary rocks have moderately radiogenic Nd-isotopic compositions with initial εNd(t) values of −9 to −6, and model ages between 1.5 and 1.7 Ga. Ages of detrital zircon grains from the metasedimentary rocks are mostly 1.6–1.1 Ga, but some ages are 530–410 Ma. Such a Novillo Gneiss-like age spectrum argues for short transport for the majority of zircon grains, with potential additional transport from the Maya Block. Na-amphibole and mica geobarometer results of up to 6 kbar indicate high-pressure subduction-related metamorphism of the Granjeno Schist that was followed by a Pennsylvanian–Permian sub-greenschist to greenschist metamorphic overprint in an accretionary prism. Thus, the Granjeno Schist is a representative of ocean-plate stratigraphy that originated proximally close to a continent.

中文翻译：

墨西哥马德雷山脉变沉积岩的地球化学和碎屑锆石年代学：盘古大陆西缘沉积的意义

墨西哥东北部 Sierra Madre 地区的基底复合体分为四个领域：(a) 格伦维尔时代 (ca. 1 Ga) 的麻粒岩相岩石，被称为 Novillo Gneiss，(b) 古生代 Granjeno 片岩，(c ) 古生代海相硅质碎屑岩和火山岩的未变质系列，和 (d) 奥陶纪斜花岗岩体。我们对与变质火山岩和变质超镁铁质岩有关的 Granjeno 片岩变沉积岩进行了地球化学和物源研究。在 Granjeno 片岩中，变沉积岩的微量元素比（Th/Sc、La/Sch、La/Sc 和 Zr/Sc）和 REE 组成与平均大陆地壳值的值相似，并且与碎屑的推导一致来自长英质岩石。化学蚀变指数值 30-80 表明源的低到中度风化。碎屑变质沉积岩具有中等放射成因的 Nd 同位素组成，初始ε Nd( t ) 值为-9 到-6，模型年龄在1.5 到1.7 Ga 之间。变沉积岩中碎屑锆石颗粒的年龄大多为1.6-1.1 Ga，但有些年龄为530-410 Ma。这种类似 Novillo Gneiss 的年龄谱表明大多数锆石颗粒的短程运输，以及来自 Maya Block 的潜在额外运输。高达 6 kbar 的钠闪石和云母地质气压计结果表明 Granjeno 片岩的高压俯冲相关变质作用，随后是宾夕法尼亚-二叠纪亚绿片岩到绿片岩在增生棱柱中的变质叠印。因此，格兰杰诺片岩是起源于大陆附近的海洋板块地层的代表。

更新日期：2021-02-22

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