Hydrothermal alteration of plagioclase microphenocrysts and glass in basalts from the East Pacific Rise near 13°N: An SEM-EDS study  

作　　者：ZENG ZhiGang QI HaiYan CHEN Shuai YIN XueBo LI ZhaoXue 

机构地区：[1]Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences

出　　处：《Science China Earth Sciences》2014年第7期1427-1437,共11页中国科学（地球科学英文版）

基　　金：supported by the National Special Fund for the Twelfth Five Plan of the China Ocean Mineral Resources Research and Develop-ment Association(Grant No.DY125-12-R-02);the National Basic Research Program of China(Grant No.2013CB429700);the National Natural Science Foundation of China(Grant Nos.41325021,40830849 and 40976027);Shandong Provincial Natural Science Foundation of China for Distinguished Young Scholars(Grant No.JQ200913)

摘　　要：The interactions of seafloor hydrothermal fluid with igneous rocks can result in leaching elements from the rocks,creating potential ore-forming fluids and influencing the chemical compositions of near-bottom seawater.The hydrothermal alteration of plagioclase microphenocrysts and basaltic glass in the pillow basalts from one dredge station(103°57.62′′W,12°50.55′N,water depth 2480 m)on the East Pacific Rise(EPR)near 13°N were analyzed using a scanning electron microscope(SEM)and energy dispersive X-ray spectrometry(EDS).The results show that the edges of the plagioclase microphenocrysts and the basaltic glass fragments are altered but the pyroxene and olivine microphenocrysts in the interior of the pillow basalts appear to be unaffected by the hydrothermal fluids.In addition,our results show that the chemical alteration at the rims of the plagioclase microphenocrysts and the edges of basaltic glass fragments can be divided into separate types of alteration.The chemical difference in hydrothermal alteration of the plagioclase microphenocrysts and the basaltic glass indicate that different degrees of hydrothermal fluid-solid phase interaction have taken place at the surface of the pillow basalts.If the degree of hydrothermal fluid-solid phase interaction is relatively minor,Si,Al,Ca and Na diffuse from the inside of the solid phase out and as a result these elements have a tendency to accumulate in the edge of the plagioclase microphenocrysts or basaltic glass.If the degree of hydrothermal fluid-solid phase interaction is relatively strong,Si,Al,Ca and Na also diffuse from the inside of solid phase out but these elements will have a relatively low concentration in the edge of the plagioclase microphenocrysts or basaltic glass.Based on the chemical variation observed in the edges of plagioclase microphenocrysts and basaltic glass,we estimate that the content of Si,Al and Fe in the edges of plagioclase microphenocrysts can have a variation of 10.69%,17.59%and 109%,respectively.Similarly,the Si,Al and Fe concThe interactions of seafloor hydrothermal fluid with igneous rocks can result in leaching elements from the rocks, creating potential ore-forming fluids and influencing the chemical compositions of near-bottom seawater. The hydrothermal alteration of plagioclase microphenocrysts and basaltic glass in the pillow basalts from one dredge station （103°57.62＂W, 12°50.55＇N, water depth 2480 m） on the East Pacific Rise （EPR） near 13°N were analyzed using a scanning electron microscope （SEM） and energy dispersive X-ray spectrometry （EDS）. The results show that the edges of the plagioclase microphenocrysts and the basaltic glass fragments are altered but the pyroxene and olivine microphenocrysts in the interior of the pillow basalts appear to be unaffected by the hydrothermal fluids. In addition, our results show that the chemical alteration at the rims of the plagioclase microphenocrysts and the edges of basaltic glass fragments can be divided into separate types of alteration. The chemical difference in hydrothermal alteration of the plagioclase microphenocrysts and the basaltic glass indicate that different degrees of hydrothermal fluid-solid phase interaction have taken place at the surface of the pillow basalts. If the degree of hydrothermal fluid-solid phase interaction is relatively minor, Si, Al, Ca and Na diffuse from the inside of the solid phase out and as a result these elements have a tendency to accumulate in the edge of the plagioclase microphenocrysts or basaltic glass. If the degree of hydrothermal fluid-solid phase interaction is relatively strong, Si, Al, Ca and Na also diffuse from the inside of solid phase out but these elements will have a relatively low concentration in the edge of the plagioclase microphenocrysts or basaltic glass. Based on the chemical variation observed in the edges of plagioclase microphenocrysts and basaltic glass, we estimate that the content of Si, Al and Fe in the edges of plagioclase microphenocrysts can have a variation of 10.69%, 17.59% and 109%, re

关 键 词：hydrothermal alteration plagioclase microphenocrysts basaltic glass pillow basalt East Pacific Rise near 13°N 

分 类 号：P736.3[天文地球—海洋地质]