Journal of Tropical Oceanography >
Cenozoic tectonic stress inversion in the northern South China Sea and its dynamic background
Received date: 2017-04-18
Request revised date: 2017-06-30
Online published: 2018-04-11
Supported by
National Natural Science Foundation of China (41206037)
Doctoral foundation of Henan University of Engineering (D2015010)
Copyright
The northern part of the South China Sea (SCS) is one of the important oil and gas bearing areas in China. However, the evolution history of the basins located in the northern SCS and their relationship with the surrounding tectonic events are still unclear. Based on the drilling and seismic data, the tectonic stress evolution characteristics and the initial crustal thickness of the Qiongdongnan Basin and Pearl River Mouth Basin are calculated by using mathematical simulation. The results show that the basins of the northern SCS have thinner initial crust thickness and lithospheric thickness. There exist two stress relaxation periods in the Pearl River Mouth Basin, and two stress relaxation periods in the Qiongdongnan Basin, one in shallow water and the other in deep water. The first period of stress relaxation in the northern SCS was continuous in space, which is mainly distributed in the deep water area, and was earlier in the east and later in the west. The second period was different in the east and west. The analysis shows that the stress relaxation periods in the deep water of the northern SCS were related with shear rifting from east to west of the northwest sub-basin of the SCS. The second period of stress relaxation in the Pearl River Mouth Basin was related to local magmatic intrusion, and the stress relaxation period in the shallow water of the Qiongdongnan Basin corresponded to the quiet period of the Red River fault.
LIU Jianbao , SUN Zhen , WANG Zhenfeng , HUANG Anmin , ZENG Xiaoyu . Cenozoic tectonic stress inversion in the northern South China Sea and its dynamic background[J]. Journal of Tropical Oceanography, 2018 , 37(2) : 63 -71 . DOI: 10.11978/2017047
Tab. 1 Stratigraphic division of the marginal basins in the northern South China Sea表1 南海北部陆缘盆地地层单元划分 |
地层单元 | 琼东南盆地 | 珠江口盆地 | ||||||
---|---|---|---|---|---|---|---|---|
系 | 统 | 组 | 界面 | 时间/Ma | 组 | 界面 | 时间/Ma | |
第四系 | 乐东组 | T20 | 1.64 | T20 | 1.8 | |||
新近系 | 上新统 | 莺歌海组 | T30 | 5.5 | 万山组 | T30 | 5.3 | |
中新统 | 黄流组 | T40 | 10.5 | 粤海组 | T32 | 10.5 | ||
梅山组 | T41 | 13.8 | 韩江组 | T40 | 16 | |||
T50 | 15.5 | |||||||
三亚组 | T51 | 16.5 | 珠江组 | T50 | 18.5 | |||
T52 | 17.5 | |||||||
T60 | 21 | T60 | 23.8 | |||||
古近系 | 渐新统 | 陵水组 | T61 | 23 | 珠海组 | T70 | 30 | |
T62 | 25.5 | |||||||
T70 | 30 | |||||||
崖城组 | T71 | 32 | 恩平组 | T80 | 39 | |||
T80 | 36 | |||||||
始新统 | T100 | 54 | 文昌组 | T90 | 49 | |||
古新统 | 神狐组 | Tg | 65 | |||||
前新生界 |
Tab. 2 Values of parameters表2 相关参数取值 |
参数符号 | 参数名称 | 取值 |
---|---|---|
k | 温度扩散系数 | 10-6m2·s-1 |
α | 热膨胀系数 | 3.0×10-5K-1 |
φ | 随深度变化的脆性破坏 | 24.0MPa·km-1 |
υ* | 孔隙水与岩石基质的密度比 | 0.38 |
c | 比热 | 1050J·kg-1·K-1 |
ρ0uc | 0℃状态上地壳密度 | 2800kg·m-3 |
ρ0lc | 0℃状态下地壳密度 | 2900kg·m-3 |
ρ0m | 0℃状态地幔密度 | 3300kg·m-3 |
H | 放射热源 | 0.647μW·m-3 |
R | 气体常数 | 8.314J·mol-1·K-1 |
A*uc | 上地壳材料常数 | 1.10000×10-21Pa-n·s-1 |
nuc | 上地壳应力幂指数 | 2.61 |
Quc | 上地壳蠕变活化能 | 145kJ·mol-1 |
A*lc | 下地壳材料常数 | 5.60000×10-23Pa-n·s-1 |
nlc | 下地壳应力幂指数 | 3.20 |
Qlc | 下地壳蠕变活化能 | 238kJ·mol-1 |
A*m | 地幔材料常数 | 1.90000×10-15Pa-n·s-1 |
nm | 地幔应力幂指数 | 3.00 |
Qm | 地幔蠕变活化能 | 420kJ·mol-1 |
Fig. 1 Tectonic background of the South China Sea. The base map stands for depth of water, which is from http://www. ngdc.noaa.gov/mgg/global/global.html; SCS: South China Sea; QB: Qiongdongnan Basin; PRMB: Pearl River Mouth Basin图1 南海区域构造背景 |
Fig. 2 Schematic of the one-dimensional model of lithospheric extension. Pure shear thinning is assumed for the entire lithosphere. The applied extensional force Fa is as a function of time. The lithosphere is composed of three material layers: upper crust, lower crust and mantle. The initial crustal thickness is tc-. The mass density of the upper crust, lower crust and mantle is 2800, 2900 and 3300 kg·m-3, respectively. The thickness of thermal lithosphere is defined by the depth of the 1350℃ isotherm. The temperature at the upper and lower boundary of the model is 0 and 1350℃, respectively图2 岩石圈伸展一维模型示意图 |
Tab. 3 Estimate of initial crustal thickness表3 初始地壳厚度估算 |
钻井 | 现今水深/m | 位置 | tc+/km | tc- (a=60km) | tc- (a=90km) | tc- (a=125km) | tc- (a=150km) |
---|---|---|---|---|---|---|---|
ZHU001 | 120 | 浅水 | 17.0 | 27~30 | 28~31 | 30~33 | 32~34 |
ZHU003 | 100 | 浅水 | 17.0 | 32~35 | 34~36 | 37~39 | 39~41 |
QB001 | 195 | 浅水 | 17.0 | 25 | 25~26 | 27~29 | 30~31 |
QB002 | 195 | 浅水 | 14.7 | 29~32 | 31~34 | 35~37 | 37~39 |
QB003 | 180 | 浅水 | 13.5 | 26~28 | 28~30 | 32~33 | 35~36 |
QB004 | 100 | 浅水 | 9.5 | 20~21 | 23~24 | n/a | n/a |
QB005 | 110 | 浅水 | 8.5 | 23 | 26~28 | 31~32 | n/a |
QB006 | 150 | 浅水 | 14.9 | 25~28 | 28~30 | 32~33 | 36 |
ZHU002 | 950 | 深水 | 15.0 | 35~38 | 37~39 | 41~42 | 43~45 |
SIMUE0 | 1670 | 深水 | 6.5 | 30~32 | 34~35 | 38~40 | 41~42 |
SIMUW0 | 710 | 深水 | 3.5 | 29 | n/a | n/a | n/a |
QB007 | 1730 | 深水 | 7.9 | 25~27 | 29~30 | 34 | 37 |
QB008 | 1500 | 深水 | 13.9 | 31~34 | 34~36 | 38~40 | 41~42 |
QB009 | 1460 | 深水 | 17.0 | 32~34 | 34~36 | 38~39 | 40~42 |
注: tc+为现今地壳厚度; tc-为初始地壳厚度; a为岩石圈厚度; n/a 代表不适用, 即在假设的岩石圈厚度和现今地壳厚度的约束下, 没有适合的初始地壳厚度使得模拟的沉降曲线和回剥的沉降曲线相吻合 |
Fig. 3 Structural stress and strain rate inversion based on tectonic subsidence of borehole in shallow water图3 基于钻孔构造沉降的构造应力及应变速率反演(浅水区) |
Fig. 4 Structural stress and strain rate inversion based on tectonic subsidence of borehole in deep water图4 基于钻孔构造沉降的构造应力及应变速率反演(深水区) |
The authors have declared that no competing interests exist.
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