东马努斯盆地普通火山岩、高镁安山岩及蚀变岩石地球化学特征研究

发布时间：2018-05-09 12:25

本文选题：东马努斯盆地 + 高镁安山岩　；参考：《中国科学院大学(中国科学院海洋研究所)》2017年硕士论文

【摘要】：本文使用水下机器人获取了东马努斯盆地的玄武质安山岩、英安岩和热液蚀变岩石样品,通过对样品进行全岩主微量、Sr-Nd-Pb同位素和斜长石电子探针分析,并结合前人数据,发现了该区一直被忽视的高镁安山岩,探究了岩浆物质来源及热液活动中元素的迁移规律。东马努斯盆地的2个玄武质安山岩样品具有高镁含量,其MgO含量分别为5.3%和5.54%,FeOT含量分别为8.35%和8.22%,FeOT/MgO比值分别为1.575和1.484,Al2O3含量分别为15.77%和15.82%,CaO含量分别为9.22%和9.28%,属于高镁安山岩。东马努斯盆地是一个活跃的弧后盆地,伴随着太平洋板块和所罗门板块双重俯冲的影响,俯冲物质来源存在争议。有学者认为俯冲物质来自于太平洋板块,也有学者认为来自于所罗门板块。本文首先通过岩浆中具有Pb和大离子亲石元素(K,Rb,Sr,Ba,和U)富集、高场强元素(Nb,Th,Ta和Ti)亏损的特征,证实了俯冲板块脱水作用产生了大量的含水物质注入到岩浆源区。再由87Sr/86Sr比值沿太平洋板块俯冲方向连续变化和238U过剩的现象证明岩浆受到了太平洋板块和所罗门板块双重俯冲的影响,并且,太平洋板块物质在东马努斯盆地滞留了很长一段时间,而所罗门板块物质是最近才加入的。高镁安山岩由地幔橄榄岩演化而来,地幔橄榄岩的同位素特征与马努斯MORB一致;俯冲板块物质包含了海底沉积物和蚀变洋壳,因此,东马努斯岩浆物质来源可能包括:马努斯MORB、太平洋和所罗门板块的海底沉积物和蚀变洋壳。如果这5个端元都对东马努斯岩浆有贡献,那么计算可得,太平洋蚀变洋壳与沉积物的比值为86.5:13.5,这二者的总含量与马努斯MORB的比值为8.2:91.8,所罗门蚀变洋壳与沉积物的比值为93.5:6.5,在马努斯MORB含量不变的情况下,每增加一份太平洋俯冲物质,需要增加9份所罗门俯冲物质来与之平衡。文章还对蚀变岩石与新鲜火山岩之间的全岩主微量及斜长石电子探针数据进行对比,深入探究了蚀变火山岩的元素迁移特征及影响因素。结果显示,蚀变火山岩的硫化物以黄铜矿、方铅矿和闪锌矿为主,为富Cu型热液硫化物。岩石蚀变区的SiO2含量极高,为硅化蚀变。蚀变岩石的化学成分约为同区玄武质安山岩和英安岩成分总含量的平均值,原岩可能为安山岩。在热液蚀变的过程中,蚀变岩石的质量增加了150%,其中元素Cu、Zn、Ga、Sr、Cd、Ba和Pb超强烈富集,Ti、V、Mn、Co、Ni、Mo和U强烈富集,Si和Fe中等富集;Sc、Cr、Nb、Ta、W和Bi轻微富集;Be和Ca超强烈亏损;Li、Na、Mg、K、Rb、REE和Y强烈亏损;Zr、Cs和Th轻微亏损;Al、P和Hf稳定不变。推测影响蚀变岩石元素迁移的因素有3种:成矿作用、交代作用(绿泥石化、硅化)和元素在流体中的活动性。
[Abstract]:In this paper, the samples of Black Tortoise andesite, dolomite and hydrothermal alteration rock from the East Manus Basin were obtained by using underwater vehicle. The samples were analyzed by the main trace Sr-Nd-Pb isotopes and plagioclase electron probe analysis of the whole rock, and combined with previous data. The high mafic andesite which has been neglected in this area has been discovered, and the source of magmatic material and the law of element migration in hydrothermal activity have been explored. The two samples of Black Tortoise andesite in East Manus Basin have high magnesium content, their MgO contents are 5.3% and 5.54%, respectively, and the content of FeOT / MgO are 8.35% and 8.22%, respectively. The ratios of Al _ 2O _ 3 _ 2O _ 3 and Al _ 2O _ 3 are 15.77% and 15.82%, respectively, and 9.28% and 9.28, respectively, which belong to the high mafic andesite. The East Manus Basin is an active back-arc basin. With the influence of the double subduction of the Pacific plate and the Solomon plate, the subduction material source is controversial. Some scholars believe that the subduction material comes from the Pacific plate, and others think it comes from the Solomon plate. In this paper, the characteristics of Pb and large ion lithophile element K ~ (+) Rb ~ (+) Sr ~ (+) Baand U) and the depletion of high field strength elements such as NB ~ (2 +) T _ (Th) Ta and Ti) in magma have proved that dehydration of subduction plate resulted in a large amount of water-bearing material being injected into the magma source region. The continuous variation of the 87Sr/86Sr ratio along the subduction direction of the Pacific plate and the phenomenon of 238U excess prove that the magma is affected by the double subduction of the Pacific plate and the Solomon plate. Pacific plate material remained in the East Manus Basin for a long time, and Solomon Plate material was only recently added. The high-mafic andesite evolved from the mantle peridotite, and the isotopic characteristics of the mantle peridotite are consistent with those of Manus MORB. Sources of East Manus magmatic material may include: Manus MORBB, seabed sediments and altered oceanic crust in the Pacific and Solomon plates. If all five end elements contribute to the East Manus magma, then the calculations are available. The ratio of altered oceanic crust to sediment in the Pacific Ocean is 86.5: 13.5.The ratio of total content of these two to Manus MORB is 8.2: 91.8, and the ratio of Solomon altered oceanic crust to sediment is 93.5: 6.5. Under the condition of constant MORB content in Manus, each Pacific subduction material is added. Nine more parts of Solomon's subduction material are needed to balance it. The electron probe data of major trace and plagioclase between altered rocks and fresh volcanic rocks are compared, and the characteristics of element migration and influencing factors of altered volcanic rocks are discussed. The results show that the sulfides of altered volcanic rocks are mainly chalcopyrite galena and sphalerite and are Cu-rich hydrothermal sulfides. The content of SiO2 in rock alteration zone is very high, which is silicified alteration. The chemical composition of altered rocks is about the average of the total contents of Black Tortoise andesite and dolomite in the same area, and the original rock may be andesite. In the process of hydrothermal alteration, The quality of altered rocks has increased by 150, in which the ultrastrong enrichment of Cu ~ (2 +) Zn ~ (Zn) Ga _ (Sr) CD ~ (2 +) Ba and Pb ~ (2 +) ~ (2 +) ~ (2 +) Ti ~ (2 +) V ~ (2 +) mn ~ (2 +) Co ~ (2 +) Mo ~ (2 +) and U ~ (2 +) enriched Si ~ (2 +) and Fe ~ (2 +) ~ (2 +) Cr ~ (2 +) C ~ (2 +) and Fe ~ (2 +) ~ (2 +) ~ (2 +) ~ (2 +) ~ (2 +) ~ (2)? It is inferred that there are three factors influencing the element migration of altered rocks: mineralization metasomatism (green mud fossilization silicification) and the activity of elements in fluid.
【学位授予单位】：中国科学院大学(中国科学院海洋研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P588.1

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