Tectonics of the Neoproterozoic basin and age of the Macaoyuan Group on the northern margin of the Yangtze Block

doi:10.13745/j.esf.sf.2022.8.9

Abstract

Abstract:

There are two key tectonic units—the Shennongjia uplift in the west and the Huangling uplift in the east—exposed in the Proterozoic in western Hubei and eastern Chongqing on the northern margin of the Yangtze Block, where prolonged sedimentation and extended deformation form the current Dabashan and East Sichuan thrust systems. In this paper, the regional Proterozoic deep basin framework is studied using comprehensive sedimentological and geophysical methods. Through the identification of rift fault boundary and internal basin tectonics, the topography of the Zhushan mountain of Nanchong in the west and the Yichang rift zone of Zhongxian in the east is revealed—they are considered to be the rift systems developed during the breakup of the Neoproterozoic Rodinia supercontinent, and separated by a rift block consisting of the Fenghuangshan anticline, Shennongjia uplift and Huangling uplift. Meanwhile, the chronology and sedimentology of the long-disputed Macaoyuan conglomerate on the south side of Shennongjia are studied by in-situ U-Pb isotope dating method. Dating of carbonate rocks yields ages of 759.2±17.6 Ma and 566.8±13.8 Ma, which confirms the Macaoyuan Group was filled in the Nanhua rift and formed on a depositional slope on the west side of the Zhongxian-Yichang rift. Subsequently, the sedimentary sequence of the Macaoyuan Group is established, and then the sedimentary filling framework of the Neoproterozoic rift basin in the northern Yangtze Plate is reconstructed by combining several sedimentary profiles across the rift belt and uplift.

Key words: northern margin of the Yangtze Block, Macaoyuan Group, Neoproterozoic, rift tectonics

CLC Number:

LI Lushun, WANG Zecheng, XIAO Ancheng, HU Anping, CHEN Youzhi, Wang Qianqian. Tectonics of the Neoproterozoic basin and age of the Macaoyuan Group on the northern margin of the Yangtze Block[J]. Earth Science Frontiers, 2022, 29(6): 291-304.

Figures/Tables 17

Fig.1 Simplified geological maps showing the tectonic domains in the study area. Modified from [20-21].

Fig.2 Residual gravity anomaly map of the Xianshuihe section, northern edge of Yangtze, showing the locations of the survey lines AA' and BB' (thickness data adapted from [12-13,39⇓⇓⇓⇓-44])

Fig.3 U-Pb dating results for samples from the Macaoyuan Group and Doushantuo Formation

Table 1 Geochemical characteristics of trace and rare earth elements and selected U-Pb ages of the Machaoyuan Group, Xianshuihe section, Xingshan

样品	w_B/10^-6			²³⁸U/²⁰⁶U	2σ	²⁰⁷U/²⁰⁶U	2σ
样品	U	Th	Pb	²³⁸U/²⁰⁶U	2σ	²⁰⁷U/²⁰⁶U	2σ
样品1 (110°39'E, 39°26'N)	0.094 1	0.010 1	0.295	0.932 117	0.070 83	0.713	0.017
	0.088 7	0.009 01	0.166 2	1.572 65	0.043 013	0.697	0.018
	0.099 2	0.012 22	0.157 3	1.749 05	0.036 577	0.683	0.019
	0.086 7	0.010 19	0.200 7	1.234 899	0.061 331	0.687	0.015
	0.088 4	0.011 91	0.212	1.212 121	0.059 089	0.696	0.016
	0.063 3	0.007 71	0.214 8	0.859 813	0.026 518	0.71	0.016
	0.066 5	0.010 77	0.165 2	1.148 564	0.037 282	0.675	0.016
	0.192	0.037 9	0.282	1.732 58	0.150 092	0.646	0.017
	0.094 8	0.008 19	0.160 4	1.657 658	0.038 828	0.704	0.018
	0.084 7	0.009 09	0.229	1.076 024	0.059 15	0.707	0.014

Fig.4 Lithology histogram of the Macaoyuan Group-Doushantuo Formation, Xianshuihe section, Xingshan

Fig.5 Typical rock sedimentary characteristics of the Macaoyuan Group and Doushantuo Formation, Xianshuihe section, Xingshan

Fig.6 (a) Location of survey line AA' in the Nanbu-Wanyuan area of northern Sichuan, and (b) seismic profile and (c) interpreted geological profile along line AA' (profiles from [10])

Fig.7 (a) Location of survey line BB' in the Guangyuan-Lichuan area, and (b) seismic profile and (c) interpreted geological profile along line BB'

Fig.8 (a) Location of survey line CC' in the Nanchong-Baolongzhen area, and (b) seismic profile and (c) interpreted geological profile along line CC' (profiles from [8])

Fig.9 (a) Regional gravity anomaly structure profiles (after [58]) and (b) P-wave velocity profile (after [59]). Profile locations see Fig.10.

Table 2 Drilling data for wells around the Huangling uplift

钻井	钻遇地层	井深/km	位置
阳页1井	南华系南沱组	3.60	黄陵隆起南部
秭地5井	震旦系灯影组	2.90
宜页1井	震旦系陡山沱组	3.90
阳页2HF井	南华系南沱组	3.45
秭地2井	南华系南沱组	1.45
宜参1井	南华系南沱组	2.50
宜地3井	震旦系陡山沱组	1.80
宜探2井	震旦系陡山沱组	5.70	黄陵隆起东部
X1井	南华系南沱组	0.65	黄陵隆起北部

Fig.10 Buried depth of basement top boundary in the northern edge of Yangtze. Modified from [57].

Table 3 Statistics for the thickness of the Sinian-Jurassic strata, Zigui region (data from [24,27,56])

地层	岩性	厚度/m
侏罗系	含砾砂岩、泥岩、砂岩组合	2 050~5 220
三叠系	灰岩、白云岩组合	994~3 273
二叠系	灰岩、白云岩组合	300~580
石炭系	灰岩、泥岩组合	0~92
泥盆系	灰岩、砂岩组合	0~131
志留系	砂岩、泥岩组合	910~1 500
奥陶系	灰岩、白云岩组合	150~250
寒武系	灰岩、白云岩组合	683~1 293
震旦系	灰岩、白云岩组合	100~784

Fig.11 Stratigraphic division of the northern edge of the Yangtze Block and adjacent areas

Fig.12 Distribution of rift zones in the northern margin of the Yangtze Block

Fig.13 Model map of the Neoproterozoic rift basin, northern margin of the Yangtze Block

Fig.14 Sedimentary framework of the Neoproterozoic rift basin (profiles from [12,28-29,32,57-58])

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