摘要
对东马努斯盆地高镁安山岩做了全岩主微量和Sr-Nd-Pb同位素分析,并结合前人测试数据,探究了岩浆物质来源及演化过程。由主量元素[MgO、CaO、FeOT(全铁)、Al_2O_3、TiO_2和P_2O_5]含量随着硅含量的升高而降低和La/Sm随着La含量的升高而保持不变可知,岩浆在演化过程中只发生了矿物的分离结晶,分离的矿物可能为橄榄石、辉石、斜长石、钛铁矿和磷灰石。东马努斯盆地高镁安山岩的Pb和大离子亲石元素(K,Rb,Sr,Ba和U)的富集、高场强元素(Nb,Th,Ta和Ti)的亏损说明岩浆受到了俯冲板块脱水作用的影响。推测该区高镁安山岩是流体交代的地幔楔部分熔融形成的。由Sr-Nd同位素混合模拟结果可知东马努斯盆地高镁安山岩主要来源于马努斯MORB(洋中脊玄武岩),少量来自于太平洋蚀变洋壳和海底沉积物。根据Sr-Nd-Pb同位素特征推测岩浆混合作用发生在地幔源区,属于源区混染,岩浆在喷发的过程中没有发生同化混染作用,也没有加入其他体系的物质。
Bulk major and trace elements and Sr-Nd-Pb isotopic composition were analyzed for the high-Mg andesite from the Eastern Manus Basin,Papua New Guinea.We combined previous data with ours to explore the origination and evolution of the andesite.Results show that the contents of major elements（MgO,CaO,FeOT,MgO,Al2O3,TiO2,and P2O5） decrease as that of SiO2 increases,and La/Sm remains stable as the La content increases,reflecting the lavas was controlled by fractional crystallization（FC） but partial melting during magma evolution.The fractional minerals could be olivine,pyroxene,plagioclase,ilmenite,and apatite.The enrichments of Pb and LILEs（K,Rb,Sr,Ba,and U） and depletions of HFSEs（Nb,Th,Ta,and Ti） in the high-Mg andesite suggest that the magma has been influenced by fluids from a subducted slab.Therefore,we infer that the high-Mg andesite was formed by melting of a mantle wedge induced by water involvement.The magma sources were composed of mainly Manus MORB,some Pacific altered oceanic basalts,and abyssal sediments as indicated in the results of our simulation on mixing processes of Sr-Nd isotopic composition.In terms of Sr-Nd-Pb isotopic composition,we deduce that the subducted components have mixed homogeneously with the local mantle before the magma eruption and no subduction components added nor assimilation and fractional crystallization（AFC） occurred during magma upwelling.
出处
《海洋与湖沼》
CAS
CSCD
北大核心
2017年第1期8-21,共14页
Oceanologia Et Limnologia Sinica
基金
国家自然科学基金项目
41576055号
