福建省新生代玄武岩^(40)Ar/^(39)Ar年代学及地质意义

^(40)Ar/^(39)Ar age characteristics of Cenozoic basalts in Fujian Province

对福建省沿海至内陆出露的4件新生代玄武岩进行^(40)Ar/^(39)Ar年龄测试,对玄武岩中橄榄石斑晶进行电子探针测试;其中洋底和柳城玄武岩首次获得精确的^(40)Ar/^(39)Ar年龄数据.结果显示,闽西明溪^(40)Ar/^(39)Ar年龄数据为(1.44±0.11)Ma,柳城为(17.35±0.93)Ma;闽中洋底玄武岩年龄为(11.71±0.44)Ma;闽东厦门玄武岩年龄为(17.0±0.36)Ma.结合前人年龄数据,福建省新生代玄武岩整体表现出从闽东至闽西年龄逐渐减小的趋势.橄榄石斑晶电子探针数据显示闽东至闽西玄武岩碱性程度逐渐增加,可能指示岩浆熔融程度由沿海至内陆逐渐减少,岩石圈厚度由东向西逐渐增厚.最新获得的闽西柳城玄武岩40Ar-39Ar年龄为(17.35±0.93)Ma,与东部沿海玄武岩相似,推测可能是太平洋板块北西向俯冲时引起的岩浆扰动作用形成的.

^(40)Ar/^(39)Ar age tests were carried out on 4 Cenozoic basalts exposed from the coast to inland in Fujian Province.The electron probe test was carried out for the olivine phenocrysts in the basalts.Among them,the ocean floor and Liucheng basalts obtained accurate^(40)Ar/^(39)Ar ages for the first time.The results show that the age of^(40)Ar/^(39)Ar in Mingxi in Western Fujian is(1.44±0.11)Ma,and that in Liucheng is(17.35±0.93)Ma.The age of oceanic bottom basalt in Central Fujian is(11.71±0.44)Ma,and the age of Xiamen basalt in Eastern Fujian is(17.0±0.36)Ma.Combined with the age data of predecessors,the Cenozoic basalts in Fujian Province as a whole show a decreasing trend from Eastern Fujian to Western Fujian.The olivine phenocryst electron probe data show that the alkalinity of basalts in Eastern Fujian to Western Fujian gradually increases,which may indicate that the degree of magma melting gradually decreases from the coast to the inland,and the thickness of the lithosphere gradually increases from east to west.At that time,the newly obtained40Ar-39Ar age(17.35±0.93)Ma of the Liucheng basalt in Western Fujian is similar to that of the eastern coastal basalt.It is speculated that it may be formed by the magmatic disturbance caused by the NW-trending subduction of the Pacific plate.