【摘要】 南海西北部雷琼区域出露大量晚新生代碱性玄武岩,且地震层析成像结果显示其地幔存在类似地幔热柱特征的低速异常体.为了揭示该异常体的活动信息及其对表层地质过程的影响,本文选择位于雷琼区域的北部湾盆地和珠三坳陷为研究对象,系统分析了它们早中新世以来的构造沉降、与基底隆升有关的剥蚀面和岩浆活动特征.结果显示,研究区晚中新世构造沉降速率表现为低速异常;晚中新世以来,研究区发育了2个因基底隆升形成的局部剥蚀面,剥蚀范围大致以雷琼火山区为中心呈环状分布,中心区域剥蚀量较大,累积厚度100～200m;中中新世后研究区部分区域因岩浆活动导致上覆地层隆起和沉积环境变化.分析表明雷琼地区深部低速异常体对表层升降影响有限,推测该深部异常体规模较小,可能是深部更大规模异常体的一个分支.更多还原

【Abstract】 A large amount of alkaline basalts developed in the Leiqiong area,northwestern South China Sea during the Late Cenozoic.Seismic tomography shows that just below the Leiqiong region,there is a mantle plume-like low-velocity thermal anomalous structure(LVA).In orderto reveal the LVA′s activity and effect on surface processes,we have systematically analyzed the Late Cenozoic subsidence history,erosion surfaces and magma activity of the Zhu III depression and the Beibuwan Basin.The results show that tectonic subsidence in these basins slow down abnormally in the Late Miocene.Furthermore,since the Late Miocene two erosion surfaces(T1 and T0)have been developed due to local basement uplift events.The T1 and T0 erosion surfaces distributed annularly around the Leiqiong volcanic region,and the accumulated erosion thickness in interior is larger,ranging from 100 to 200 m.In addition,since the end of Middle Miocene,local magmatism leaded to arching of overlying strata and sedimentary environment changing.Our analysis show that the observed LVA has limited effect on superficial vertical motion.We speculate that the LVA is small in scale,and might be just a branch of deep much larger lowvelocity abnormal structure.更多还原