Crust Structure and Tectonostratigraphy of Liyue Block, Northeast of Nansha Area
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摘要: 礼乐地块位于南沙海域东北部, 主要由2部分组成: 礼乐滩和礼乐盆地.根据重力和地震数据研究礼乐地块的主要构造特征和地壳结构.基于多道地震数据, 主要研究了基底之上的地层和断裂构造, 并通过重力数据反演分析了地块深部地壳结构.礼乐滩区域主要为碳酸盐岩地层, 此区域地层较平, 断裂不发育.而礼乐盆地区域早期断裂较为发育, 并且主要发育2种构造: 翘倾断块和宽缓背斜; 中生代地层厚度自SW向NE减薄, 但张裂期地层自SW向NE增厚, 这表明在张裂阶段断层活动强度自SW向NE增强, 离张裂中心越近, 断裂活动强度越大.礼乐地块以正布格重力异常为主(60~140mGal), 莫霍面深度约16~27km, 拉张因子为1.3~2.0, 属于减薄型大陆地壳.Abstract: The Liyue block is composed of two parts, namely, Reed Bank and Liyue basin, which is separated by Zhongnan fault in west, Palawan trough in southeast and fault scarp in the north of Nansha area.Based on gravity and seismic data set, a systematic investigation on major tectonic and crust structure units in the Liyue block is made.Multichannel seismic data can better our understanding of the stratum and fault structure located in the sediment basement.In the Reed Bank, composed of reefs, the faults are undeveloped and the stratum is flat.In the basin area, the early faults are developed with two kinds of structures: tilted fault block and low relief anticline.The thickness of the Mesozoic strata in basin area decreases from SW to NE.But the thickness of rifting strata increases from SW to NE, which indicates the fault activity strength in the rift period increases from southwest to northeast.Gravity inversion is performed to understand the geometry of the MOHO surface and the crustal thicknesses beneath.The region is characterized by a large positive Bouguer gravity anomaly (60 to 140 mGal), and the MOHO depth generally varies from 16 to 27 km.In general, crustal structures can be distinguished from the thinned continental crust.The Liyue block is characterized by stretching factors ranging from 1.3 to 2.0, which indicates that the local region is lowly stretched.
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Key words:
- Liyue block /
- gravity inversion /
- tectonics /
- crust structure /
- marine geology
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图 1 礼乐地块区域位置及地貌
Fig. 1. Map of the survey area and the location (solid box) of Liyue block
图 9 研究区布格重力异常(a) 和莫霍面深度(b) (莫霍面深度是相对海底的深度)
Fig. 9. Computed Bouguer gravity anomaly (a) and MOHO depth (b)
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