Geochemistry of Devonian–Carboniferous clastic sediments of the Tsetserleg terrane, Hangay Basin, Central Mongolia: Provenance, source weathering, and tectonic setting
Geochemistry of Devonian–Carboniferous clastic sediments of the Tsetserleg terrane, Hangay Basin, Central Mongolia: Provenance, source weathering, and tectonic setting
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DOI：
10.1111/j.1440-1738.2012.00821.x
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发表时间：
2012-12
期刊：
影响因子：
1.5
通讯作者：
N. Purevjav;B. Roser
中科院分区：
文献类型：
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作者：
N. Purevjav;B. Roser
蒙古的泥盆纪-石炭纪Tsetserleg盆地是复杂的中亚造山带（CAOB）的一部分。Tsetserleg盆地主要由碎屑沉积物组成，位于Hangay-Hentey盆地南部。内部划分为Erdenetsogt（中泥盆世），Tsetserleg（中-上泥盆世）和Jargalant（下石炭世）。Hangay-Hentey盆地的物源和构造背景仍然存在争议，建议从被动边缘到岛弧。收集了一套94块Tsetserleg砂岩和泥岩，目的是使用已建立的岩相学和全岩地球化学参数来约束物源、源风化和沉积环境。从岩石学上看，砂岩为未成熟砂岩，Erdenetsogt组、Tsetserleg组和Jargalant组的平均成分分别为Q22 F14 L 64、Q14 F17 L 69和Q18 F12 L70。Lv/L比值范围为0.81 - 1.00（平均0.95），P/F范围为0.68 - 0.93（平均0.83）。骨架组成表明沉积在未切割的或过渡的弧中。在地球化学上，砂岩被归类为灰岩。每个地层中砂岩和泥岩平均值之间的地球化学对比很小，SiO2的岩型平均值仅为65.54至68.62重量%。这些特征和变化图上的弱趋势反映了沉积物的不成熟。元素丰度与平均上陆壳，主要元素判别分数，和不动元素比值的比较表明英安岩和流纹岩之间的平均源组成。经K-交代校正后，Erdenetsogt组的蚀变化学指数最大值约为78，表明源岩风化程度中等。Tsetserleg组和Jargalant组的最大值较低（分别为61和63），表明它们来自几乎未风化的构造活动源。构造环境判别参数表明，大陆岛弧环境，类似于其他几个CAOB套房的类似年龄。这一弧源可能是在中泥盆世-下石炭世时期建立在蒙古-鄂霍次克洋内的大陆碎片上。
The Devonian–Carboniferous Tsetserleg terrane of Mongolia forms part of the complex Central Asian Orogenic Belt (CAOB). The Tsetserleg terrane consists mainly of clastic sediments, and is situated in the southern Hangay–Hentey Basin. Internally the terrane is divided into the Erdenetsogt (Middle Devonian), Tsetserleg (Middle‐Upper Devonian) and Jargalant (Lower Carboniferous) Formations. Provenance and tectonic setting of the Hangay–Hentey Basin remains controversial, with proposals ranging from passive margin through to island‐arc. A suite of 94 Tsetserleg sandstones and mudrocks was collected with the aim of constraining provenance, source weathering, and depositional setting, using established petrographic and whole‐rock geochemical parameters. Petrographically the sandstones are immature, with average compositions of Q22F14L64, Q14F17L69, and Q18F12L70 in the Erdenetsogt, Tsetserleg, and Jargalant Formations, respectively. Lv/L ratios range from 0.81 to 1.00 (average 0.95), and P/F from 0.68 to 0.93 (average 0.83). Framework compositions indicate deposition in an undissected or transitional arc. Geochemically, the sandstones are classified as greywackes. Geochemical contrasts between sandstone and mudrock averages in each formation are small, with lithotype means for SiO2 ranging only from 65.54 to 68.62 wt.%. These features and weak trends on variation diagrams reflect the immaturity of the sediments. Comparison of elemental abundances with average upper continental crust, major element discriminant scores, and immobile element ratios indicate a uniform average source composition between dacite and rhyolite. The maximum value for the Chemical Index of Alteration in the Erdenetsogt Formation is about 78 after correction for K‐metasomatism, indicating moderate source weathering. Lower maximum values (61 and 63, respectively) in the Tsetserleg and Jargalant Formations indicate they were derived from a virtually unweathered and tectonically active source. Tectonic setting discrimination parameters indicate a continental island‐arc environment, similar to several other CAOB suites of similar age. This arc source may have been built on a continental fragment situated within the Mongol–Okhotsk Ocean during Middle Devonian‐Lower Carboniferous time.