Crustal structure beneath Yinggehai basin and adjacent Hainan Island, and its tectonic implications

Abstract

Two NE-SW trending wide-angle seismic profiles were surveyed across the Chinese side of the Yinggehai (莺歌海) basin (YGHB) with ocean bottom hydrophones (OBHs) and piggyback recorded by onshore stations located on the Hainan (海南) Island. Detailed velocity-depth models were obtained through traveltime modeling and partially constrained by amplitude calculations. More than 15 km Tertiary sedimentary infill within the YGHB can be divided in to three layers with distinct velocity-depth distribution. Overall, the upper layer has a high velocity gradient with 3.8–4.1 km/s at its bottom, consistent with progressive compaction and diagenesis. Its thickness increases gradually towards the basin center, reaching 4.5 km along the southern profile. The middle layer is characterized in its most part as a pronounced low velocity zone (LVZ) with average velocity as low as 3.0 km/s. Its thickness increases from 3.0 to over 4.5 km from NW towards SE. The primary causes of the velocity inversion are high accumulation rate and subsequent under-compaction of sediments. The velocity at the top of the lower layer is estimated at about 4.5 km/s. Despite strong energy source used (4 × 12L airgun array), no reflections can be observed from deeper levels within the basin. Towards NE the basin is bounded sharply by a clear and deep basement fault (Fault No. 1), which seems to cut through the entire crust. A typical continental crust with low-velocity middle crust is found beneath the coast of the western Hainan Island. Its thickness is determined to be 28 km and shows no sign of crustal thinning towards the basin. The sharp change in crustal structure across Fault No. 1 indicates that the fault is a strike-slip fault. The crustal structure obtained in this study clearly favors the hypothesis that the YGHB is a narrow pull-apart basin formed by strike-slip faulting of the Red River fault zone.

Keywords

crustal structure / strike-slip fault / pull-apart basin / Yinggehai / South China Sea

References

[1] Basile C., Brun J. P.. Transtensional Faulting Patterns Ranging from Pull-Apart Basins to Transform Continental Margins: An Experimental Investigation. Journal of Structural Geology, 1999, 21(1): 23-37.

[2] Chung S. L., Lee T. Y., Lo C. H., . Intraplate Extension Prior to Continental Extrusion along the Ailao Shan-Red River Shear Zone. Geology, 1997, 25: 311-314.

[3] Clift P. D., Lin J.. Variations in Extensional Deformation with Depth during Continental Break-up in the South China Sea. Mar. Petrol. Geol., 2001, 18: 929-945.

[4] Flueh E. R., Bialas J.. A Digital, High Data Capacity Ocean Bottom Recorder for Seismic Investigations. Int. Underwater Systems Design, 1996, 18: 18-20.

[5] Fuchs K., Muller G.. Computation of Synthetic Seismograms with the Reflectivity Method and Comparison with Observations. Geophys. J. R. Astr. Soc., 1971, 23: 417-433.

[6] Gajewski D., Holbrook W. S., Prodehl C.. A Three-Dimensional Crustal Model of Southwest Germany Derived from Seismic Refraction Data. Tectonophysics, 1987, 142(1): 49-70.

[7] Gong Z., Li S.. Continental Margin Basin Analysis and Hydrocarbon Accumulation of the Northern South China Sea, 1997, Beijing: Science Press 510

[8] Harrison T. M., Chen W., Leloup P. H., . An Early Miocene Transition in Deformation Regime within the Red River Fault Zone, Yunnan, and Its Significance for Indo-Asian Tectonics. Journal of Geophysical Research, 1992, 97(B5): 7159-7182.

[9] Holbrook W. S., Mooney W. D.. The Crustal Structure of the Axis of the Great Valley, California, from Seismic Refraction Measurements. Tectonophysics, 1987, 140(1): 49-63.

[10] Leloup P. H., Harrison T. M., Ryerson F., . Structural, Petrological and Thermal Evolution of a Tertiary Ductile Strike-Slip Shear Zone, Diancang Shan, Yunnan. Journal of Geophysical Research, 1993, 98(B4): 6715-6743.

[11] Leloup P. H., Lacassin R., Tapponnier P., . The Ailao Shan-Red River Shear Zone (Yunnan, China), Tertiary Transform Boundary of Indochina. Tectonophysics, 1995, 251(1–4): 3-84.

[12] Li S. T., Lin C. S., Zhang Q. M., . Dynamic Process of the Periodic Rifting and Tectonic Events since 10 Ma in the Marginal Basins North of the South China Sea. Chinese Science Bulletin, 1998, 43(8): 797-810.

[13] Li S. T., Mooney W. D.. Crustal Structure of China from Deep Seismic Sounding Profiles. Tectonophysics, 1998, 288(1–4): 105-113.

[14] Liao Q., Wang Z., Zhu Z., . China Earthquake Administration Crust and Upper Mantle Structure in the Quanzhou-Shantou Region of China. Developments in the Research of Deep Structures of China Continent, 1988, Beijing: Geological Publishing House 227-235.

[15] Luetgert L. J.. MacRay: Interactive Two-Dimensional Seismic Raytracing for the Macintosh, 1992, Menlo Park, California: USGS 44

[16] Mueller S., Heacock J. G.. The Earth’s Crust. Am. Geophys. Union Geophys. Monogr., 1977, 20: 28-317.

[17] Nissen S. S., Hayes D. E., Buhl P., . Deep Penetration Seismic Soundings across the Northern Margin of the South China Sea. Journal of Geophysical Research, 1995, 100(B11): 22407-22434.

[18] Qiu X. L., Ye S., Wu S. M., . Crustal Structure across the Xisha Trough, Northwestern South China Sea. Tectonophysics, 2001, 341(1–4): 179-193.

[19] Qiu X. L., Shi X., Wu S. M.. Recent Progress of Deep Seismic Experiments and Studies of Crustal Structure in Northern South China Sea. Progress in Natural Science, 2003, 13(7): 481-488.

[20] Rangin C., Klein M., Roques D., . The Red River Fault System in the Tonkin Gulf, Vietnam. Tectonophysics, 1995, 243(3–4): 209-222.

[21] Roques D., Matthews S. J., Rangin C.. Constraints on Strike-Slip Motion from Seismic and Gravity Data along the Vietnam Margin Offshore Da Nang: Implications for Hydrocarbon Prospectivity and Opening of the East Vietnam Sea. Geological Society Special Publications, 1997, 126: 341-353.

[22] Ru K.. The Development of Superimposed Basin on the Northern Margin of the South China Sea and Its Tectonic Significance. Oil and Gas Geology, 1988, 9(1): 22-31.

[23] Sage F., Basile C., Mascle J., . Crustal Structure of the Continent-Ocean Transition off the Cote d’Ivoire-Ghana Transform Margin: Implications for Thermal Exchanges across the Palaeotransform Boundary. Geophys. J. Int., 2000, 143(3): 662-678.

[24] Schaerer U., Zhang L., Tapponnier P.. Duration of Strike-Slip Movements in Large Shear Zones: The Red River Belt, China. Earth and Planetary Science Letters, 1994, 126(4): 379-397.

[25] Sun Z., Zhou D., Zhong Z. H., . Experimental Evidence for the Dynamics of the Formation of the Yinggehai Basin, NW South China Sea. Tectonophysics, 2003, 372(1–2): 41-58.

[26] Tapponnier, P., Peltzer, G., Armijo, R., 1986. On the Mechanics of the Collision between India and Asia. In: Coward, M. P., Ries, A. C., eds., Collision Tectonics. Geol. Soc. Spec. Publ., 19: 115–157

[27] Tapponnier P., Lacassin R., Leloup P. H., . The Ailao Shan/Red River Metamorphic Belt: Tertiary Left Lateral Shear between Indochina and South China. Nature, 1990, 343(6257): 431-437.

[28] Wang H., Zhu W. L., Wang Y.. Characteristics of Middle- Deep Reservoir and Sedimentray History in Yinggehai Basin. Oil and Gas Geology, 1999, 20(1): 55-61.

[29] Wu S. M., Zhou D., Qiu X. L., . Chacteristics and Genesis of Low Velocity Layer in Yinggehai Basin, NW South China Sea. Journal of Tropical Oceanography, 2001, 20(3): 8-14.

[30] Xia K., Zhou D., Su D., . The Velocity Structure of the Yinggehai Basin and Its Hydrocarbon Implication. Chinese Science Bulletin, 1998, 43(24): 2047-2059.

[31] Xie X. N., Li S. T., Dong W. L., . Evidence for Episodic Expulsion of Hot Fluids along Faults near Diapiric Structures of the Yinggehai Basin, South China Sea. Marine and Petroleum Geology, 2001, 18(6): 715-728.

[32] Yan P., Zhou D., Liu Z.. A Crustal Structure Profile across the Northern Continental Margin of the South China Sea. Tectonophysics, 2001, 338(1): 1-21.

[33] Ye S., Ansorge J., Kissling E., . Crustal Structure beneath the Eastern Swiss Alps Derived from Seismic Refraction Data. Tectonophysics, 1995, 242(3–4): 199-221.

[34] Ye, S., 1997. Cruise Report “Shiyan 2”: Wide-Angle Reflection Seismic Survey in the Northwestern South China Sea, Guangzhou-Shekou, Sept. 17–Oct. 8 1996. GEOMAR

[35] Ye S., Flueh E. R., Klaeschen D., . Crustal Structure along the EDGE Transect beneath the Kodiak Shelf off Alaska Derived from OBH Seismic Refraction Data. Geophys. J. Int., 1997, 130(2): 283-302.

[36] Ye S., Canales J. P., Rihm R., . A Crustal Transect through the Northern and Northeastern Part of the Volcanic Edifice of Gran Canaria, Canary Islands. J. Geodynamics, 1999, 28(1): 3-26.

[37] Zhang Q. M., Zhang Q. X.. Zhang Q. M.. A Distinctive Hydrocarbon Basin—Yinggehai Basin. A Collection on Petroleum Geology of Yinggehai Basin, South China, 1993, Beijing: Seismic Press 10-17.

[38] Zhang Q. M.. Evolution of Yinggehai-Qiongdongnan Basin and Its Tectonic-Thermal System. Natural Gas Industry, 1999, 19(1): 12-18.

[39] Zhou D., Ru K., Chen H.. Kinematics of Cenozoic Extension on the South China Sea Continental Margin and Its Implications for the Tectonic Evolution of the Region. Tectonophysics, 1995, 251(1–4): 161-177.