Division and Age of the Upper Jurassic Mandetou Orbo Formation in Central and Eastern Inner Mongolia

被引：0
|
作者：
Zhang Y. [1 ,2 ]
机构：
[1] Inner Mongolia Key Laboratory of Magmatic Mineralization and Ore-Prospecting, Huhhot
[2] Inner Mongolia of Geological Surver, Huhhot
来源：
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | 2021年 / 46卷 / 01期
关键词：
Geochemistry; Late Jurassic-Early Cretaceous; Manketou Ebo Formation; Middle east area of Inner Mongolia autonomous region; Zircon LA-MC-IC-MS isotope;
D O I：
10.3799/dqkx.2020.248
中图分类号：
学科分类号：
摘要：
The volcanic rocks in Manketou'ebo Formation, located in the middle east area of Inner Mongolia, are mainly composed of rhyolitic pyroclastic rocks, mixed with intermountain lacustrine facies continental clastic rocks and a small amount of rhyolite or dacite. Sedimentary rocks contain fossils of Estherians (Magumbonia paramecia, Nestoria reticulate, N. xishunjingensis, N. cf. pissoui, Lioestheria sp. ), Bivalves (Ferganoconcha curta, F. subcentralis, F. elongate) and vegetation (Ginkgoites sp., Cladophlebis sp., Lycopodites sp., Baiera gracilis, Phoenicopsis sp.). Geochemical study shows that the chemical constitutes of these fossils are SiO2 71.47%-75.96%, Ai2O3 12.50%-14.18%, K2O 3.84%-4.98%, Na2O 3.22%-4.14% and ALK 7.84%-9.12%, indicating richness in silicon and alkali. In terms of trace elements, all specimens are characterized by high ratio of Rb, K, Th, U, La and LREE, and lack of Ba, Nb, Sr, P and Ti. Rare earth element ΣREE ranges from 118.71×10-6 to 189.99×10-6; significant fractionation of HREE and LREE ((La/Yb)N = 4.79-25.56) and moderate negative Eu anomalies (δEu=0.05-0.61) are detected. All 4 specimens, on the basis of the logδ-logτ diagram, are classified into orogenic belt mountain granite area. Meanwhile according to the Rb-Y+Nb diagram, these specimens belong to volcanic arc granite area, and the Nb-Y diagram suggests 4 specimens pertain to the same volcanic arc granite with collision granite area. The ages of 4 zircon LA-MC-IC-MS isotope samples collected from Abagaqi-Zarutqi-Bahrainyouqi are respectively 138.89±0.93 Ma, 137.70±1.40 Ma, 147.70±1.20 Ma and 137.27±0.96 Ma, which therefore suggests that the era of Manketou'ebo Formation lies between Late Jurassic and Early Cretaceous. © 2021, Editorial Department of Earth Science. All right reserved.
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页码：162 / 171
页数：9
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