Spatio-temporal distribution and mechanism of Cenozoic magmatism in the South China Sea and adjacent areas: Insight from seismic, geochemical and geochronological data

Cenozoic magmatism was highly active in the South China Sea (SCS), and mostly dominated by basalts. The magmatic rocks are mainly distributed in the lower slope and subbasins of the SCS, in addition to sporadic and small-scale Cenozoic volcanism on the SCS shelf. This paper presents a complete map of the Cenozoic magmatic rocks of the SCS with magmatic rock boundaries. This paper also presents an analysis of geological survey and published data in terms of seismic profiles, ages, geochemistry and isotopic systematics of the Cenozoic magmatic complexes of the SCS and adjacent areas. Many of wells or dredges are located in magmatic rocks identified by seismic profiles. Three periods of magmatic activity are distinguished: (1) a pre-spreading period (>33 Ma); (2) a syn-spreading period (33–15 Ma) and (3) a post-spreading period (<15 Ma). The thickest volcanic rocks encountered more than 1000 m (possibly Oligocene to Miocene) in the Boayan 1/1A well in the Palawan Trough of the southern SCS during Cenozoic. The oldest magmatic rocks are andesites (62.5 ± 2.2 Ma) in the northern SCS (offshore) and andesites (65 ± 3 Ma) in Penghu (on land). The latest modern magmatic activity was detected in 1923 offshore of a submarine volcanic eruption (10°09´29″N, 109°00′50″E, 20 m below sea level) and along the shore of a volcanic eruption in the Philippines. Cenozoic magmatic rocks of the SCS include at least 1008 rock bodies: the smallest is 0.00012 km², the largest is 1528 km² and the total area covers 46,309 km². The Yangjiang-Yitong fault and Zhongnan-Reedbank fault divide the magmatic rocks into two different sections in the eastern and western SCS. The ages of the magmatic rocks in the eastern SCS are mostly older than those in the western SCS. The magmatic rocks in the northern, southern, eastern, western SCS and adjacent areas, and SCS basin are related to extension, subduction+collision, subduction, extrusion, extension+cooling+subsidence, respectively.

南海（South China Sea, SCS）新生代岩浆活动极为活跃，且以玄武岩类为主导。这些岩浆岩主要分布于南海的陆坡下段与次级海盆，此外南海陆架上还存在零星的小规模新生代火山活动。本文绘制了完整的南海新生代岩浆岩分布图，并标注了岩浆岩边界；同时整合地质调查与公开数据，对南海及邻区新生代岩浆杂岩的地震剖面、年代学、地球化学及同位素系统特征开展了分析。诸多钻井与拖网采样点均位于经地震剖面识别出的岩浆岩分布区内。研究识别出三期岩浆活动：（1）张裂前阶段（>33 Ma）；（2）张裂同期阶段（33–15 Ma）；（3）张裂后阶段（<15 Ma）。南海南部巴拉望海槽的博岩1/1A井在新生代地层中钻遇了厚度超1000米的火山岩（时代可能为渐新世至中新世）。南海北部（海域）最古老的岩浆岩为安山岩（62.5 ± 2.2 Ma），而陆域澎湖地区的安山岩时代为65 ± 3 Ma。1923年观测到最新的近代岩浆活动：一处海底火山喷发（坐标10°09′29″N，109°00′50″E，水深20米），以及菲律宾沿岸的火山喷发事件。南海新生代岩浆岩共计至少1008个岩体：最小岩体面积为0.00012 km²，最大岩体面积达1528 km²，总面积约为46309 km²。阳江-一统断裂与中南-礼乐滩断裂将南海岩浆岩划分为东西两个分布区带；东部南海的岩浆岩时代整体老于西部南海。南海北部、南部、东部、西部及邻区、南海海盆的岩浆岩分别与伸展作用、俯冲+碰撞作用、俯冲作用、挤出作用、伸展+冷却+沉降作用相关。