摘要
目前国内外对冲绳海槽槽底火山岩的研究尚处在初级阶段。笔者对槽底八个样点的浮岩进行了系统的矿物岩石学研究。本文首次对酸性浮岩的中、基性火山岩包体进行了研究,揭示了酸性浮岩下部有相当面积的玄武岩及安山岩存在的事实。旨次提出海槽浮岩具有由基性→酸性较完整的火山活动旋回的认识。提出酸性浮岩是基性熔浆演化到后期的产物的观点,从而解释了存在多年的关于冲绳海槽构造问题争议中的焦点问题之一——“冲绳海槽既为弧后盆地,何以有大量酸性火山岩分布”的质疑。提出冲绳海槽浮岩属于岛弧火山岩的观点,对冲绳海槽构造的科学认识起了一定的积极作用。
Okinawa Trough is tectonically a back-arc basin of a trencharc-basin system. The unceasing extension of the basin has caused intensive and repeated volcanic activities in the bottom of the trough. During the volcapic activities of the latest stage large amounts of intermediate or acid pumice were formed, which constitute the main submarine rocks emerged from the bottom of the trough.The pumice in Okinawa Trough is distributed in a NE-SW direction and in an intermittent linear way, which is closely related with the submarine mountains. The pumice encountered on the bottom of the through represents the cognate and isogenetic volcanic eruptive material, i. e., the liparite-pumice that is intermediate and acid yet meta-acid in acidity and belongs under the calc-alkaline series. The submarine eruption is of effusivetype.The pumice is with typical pumiceous structure and porphyritic texture. The phenocryst is usually high-temperature andesine or hypersthene and occasionally quartz. It is character istic of the phenocryst containing relatively more vitric as well as monocyclic and binary enclosures of vitric and gas. The ground mass is acid volcanic glass (N=1.496-1.500). There is a lot of CO_2 in the bubbles. The temperature for crystallization of the phenocryst of high-temperature andesine is 1050-1100％.The pumice contains fine debris enclosures of basalt and andesite, indicating it represents the eruptive material following basal+ and andesite. Judged from the rocks, the pumice falls iu the following rock assemblages tholeiite, andesite-, liparite-andesite-pumice and liparite-pumice.The age of the pumice determined by the method of thermoluminescence is 35400-37100yers, which shows the pumice was formed in the late pleistocene. The pu-mice is arc-volcanic rock.
出处
《岩石矿物学杂志》
CAS
CSCD
1989年第3期193-202,共10页
Acta Petrologica et Mineralogica
关键词
冲绳海槽
浮岩
liparite-pumice
hypersthene
glass
andesine
arcvolcanic rock
Okinawa Trough
