The Post-rifting Subsidence History of the Nam Con Son Basin, Southwest South China Sea Margin

Abstract

The Nam Con Son Basin (NCSB) is situated at the southwestern tip of the South China Sea (SCS), contains one of the highest hydrocarbon potential of the region due to unusual thick sequences. In order to decipher the cause of this unique feature, and its relationship to the regional tectonic evolution, plate reconstruction of SCS region is conducted via Gplates software (www.gplates.org). The reconstruction results indicated major tectonic events affecting the Nam Con Son Basin and SCS region are: (1) the opening of SCS (30-16 Ma), which coincides with the timing of rifting of the NCSB. (2) The collision of India to Eurasia induced rotation and escape of Indochina block along the Ailao Shan-Red River Fault (ASRR) since 28 Ma. The unusual thick sequence within NCSB was deposited during 16-10 Ma, which is post of the major tectonic events. To further evaluate the triggering mechanism, the tectonic subsidence curves are calculated from three wells (NCS-A, NCS-B, NCS-C) by backstripping analysis. By comparing the theoretical subsidence curve, the stretching factor (β) changed from > 2 during 16-10 Ma to ~ 1.5 during 10-5 Ma. Such large stretching factors are unusual for non rifting basin, which suggested another process such as supporting heat of magmatism might have contributed to the subsidence of the NCSB rather than strike-slip fault activity. Due to the record of magmatism this region and the difference of stretching factors within three wells, between the NCSB and the Cuulong Basin, we can assumed that the uniqueness of the NCSB are related to the post-rift magmatism in the SCS region.

The Nam Con Son Basin (NCSB) is situated at the southwestern tip of the South China Sea (SCS), contains one of the highest hydrocarbon potential of the region due to unusual thick sequences. In order to decipher the cause of this unique feature, and its relationship to the regional tectonic evolution, plate reconstruction of SCS region is conducted via Gplates software (www.gplates.org). The reconstruction results indicated major tectonic events affecting the Nam Con Son Basin and SCS region are: (1) the opening of SCS (30-16 Ma), which coincides with the timing of rifting of the NCSB. (2) The collision of India to Eurasia induced rotation and escape of Indochina block along the Ailao Shan-Red River Fault (ASRR) since 28 Ma. The unusual thick sequence within NCSB was deposited during 16-10 Ma, which is post of the major tectonic events. To further evaluate the triggering mechanism, the tectonic subsidence curves are calculated from three wells (NCS-A, NCS-B, NCS-C) by backstripping analysis. By comparing the theoretical subsidence curve, the stretching factor (β) changed from > 2 during 16-10 Ma to ~ 1.5 during 10-5 Ma. Such large stretching factors are unusual for non rifting basin, which suggested another process such as supporting heat of magmatism might have contributed to the subsidence of the NCSB rather than strike-slip fault activity. Due to the record of magmatism this region and the difference of stretching factors within three wells, between the NCSB and the Cuulong Basin, we can assumed that the uniqueness of the NCSB are related to the post-rift magmatism in the SCS region.