Crustal structure across the post-spreading magmatic ridge of the East Subbasin in the South China Sea; tectonic significance

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doi: 10.1016/j.jseaes.2016.03.003
Author(s): He Enyuan; Zhao Minghui; Qiu Xuelin; Sibuet, Jean-Claude; Wang Jian; Zhang Jiazheng
Author Affiliation(s): Primary:
South China Sea Institute of Oceanology, Guangzhou, China
Institut Français de Recherche pour l'Exploitation de la Mer, France
Volume Title: Journal of Asian Earth Sciences
Source: Journal of Asian Earth Sciences, Vol.121, p.139-152. Publisher: Elsevier, Oxford, United Kingdom. ISSN: 1367-9120
Note: In English. Includes appendices. 56 refs.; illus., incl. 2 tables, sketch maps
Summary: The 140-km wide last phase of opening of the South China Sea (SCS) corresponds to a N145° direction of spreading with rift features identified on swath bathymetric data trending N055° (Sibuet et al., 2016). These N055° seafloor spreading features of the East Sub-basin are cut across by a post-spreading volcanic ridge oriented approximately E-W in its western part (Zhenbei-Huangyan seamounts chain). The knowledge of the deep crustal structure beneath this volcanic ridge is essential to elucidate not only the formation and tectonic evolution of the SCS, but also the mechanism of emplacement of the post-spreading magmatism. We use air-gun shots recorded by ocean bottom seismometers to image the deep crustal structure along the N-S oriented G8G0 seismic profile, which is perpendicular to the Zhenbei-Huangyan seamounts chain but located in between the Zhenbei and Huangyan seamounts, where topographic changes are minimum. The velocity structure presents obvious lateral variations. The crust north and south of the Zhenbei-Huangyan seamounts chain is ca. 4-6 km in thickness and velocities are largely comparable with those of normal oceanic crust of Atlantic type. To the south, the Jixiang seamount with a 7.2-km thick crust, seems to be a tiny post-spreading volcanic seamount intruded along the former extinct spreading ridge axis. In the central part, a 1.5-km thick low velocity zone (3.3-3.7 km/s) in the uppermost crust is explained by the presence of extrusive rocks intercalated with thin sedimentary layers as those drilled at IODP Site U1431. Both the Jixiang seamount and the Zhenbei-Huangyan seamounts chain started to form by the intrusion of decompressive melt resulting from the N-S post-spreading phase of extension and intruded through the already formed oceanic crust. The Jixiang seamount probably formed before the emplacement of the E-W post-spreading seamounts chain. Abstract Copyright (2016) Elsevier, B.V.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 16 Structural Geology; 20 Geophysics, Applied; Basement tectonics; Basin analysis; Basins; Bathymetry; Crust; Data processing; East Subbasin; Expedition 349; Geophysical methods; Geophysical surveys; Huangyan Seamount; IODP Site U1432; Igneous rocks; International Ocean Discovery Program; Jixiang Seamount; Magmatism; North Pacific; Northwest Pacific; Ocean bottom seismographs; Ocean floors; Oceanic crust; Pacific Ocean; Plate tectonics; Rifting; Sea-floor spreading; Seamounts; Sedimentary rocks; Seismic methods; Seismic stratigraphy; Seismographs; South China Sea; Spreading centers; Surveys; Tectonics; Velocity structure; Volcanic rocks; Volcanism; West Pacific; Zhenbei Seamount
Coordinates: N182105 N182106 E1162327 E1162327
N143000 N153000 E1173000 E1162000
Record ID: 2017038858
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands