Magmatic processes in developing oceanic crust revealed in a cumulate xenolith collected at the East Pacific Rise, 9°50′N
Magmatic processes in developing oceanic crust revealed in a cumulate xenolith collected at the East Pacific Rise, 9°50′N
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DOI：
10.1029/2006gc001316
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发表时间：
2006-12
期刊：
影响因子：
3.7
通讯作者：
W. Ridley;M. Perfit;Matthew C. Smith;D. Fornari
中科院分区：
文献类型：
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作者：
W. Ridley;M. Perfit;Matthew C. Smith;D. Fornari
新近爆发的海中脊（MOR）熔岩流中的捕虏岩（含熔体堆积的碎片）的岩石学和地球化学为东太平洋北部隆起（NEPR）下新形成的海洋地壳中发生的岩石形成过程提供了信息。捕虏体揭示了MOR岩浆系统的重要岩石学信息，包括：(1)熔体在以晶体为主的糊状体中的分布；(2)糊状物内的熔融结晶反应；(3)熔体的化学性质对堆积岩性有贡献；(4)进入轴向岩浆体系的轴向熔体的化学性质。捕虏体被包裹在1991年在NEPR的新火山带上喷发的中等原始的、正常的海中脊玄武岩（NMORB）中，大约在北纬9°50°。该样品为基质为主的累积橄榄石斜长岩，由钙长石（An94‐90）和橄榄石（An89‐70）、晶间橄榄石（Fo86±0.3）、少量硫化物和尖晶石以及晶间玻璃组成。斜长石的边缘腐蚀（可能还有橄榄石）和斜长石的内部重熔表明是合质。推测孔隙体积在中等原始玄武岩熔体的作用下被多次剥蚀，并在橄榄石的晶间结晶作用下减小。钙长石作为捕虏体中的堆积相存在，以及在NMORB熔岩中观察到的钙长石杂晶，以及在蛇绿岩辉长岩中观察到的钙长石堆积相，表明不属于NMORB系的富钙熔体在海洋地壳的构造中发挥了重要作用。
The petrology and geochemistry of a xenolith, a fragment of a melt‐bearing cumulate, within a recently erupted mid‐ocean ridge (MOR) lava flow provide information on petrogenetic processes occurring within the newly forming oceanic crust beneath the northern East Pacific Rise (NEPR). The xenolith reveals important petrologic information about MOR magmatic systems concerning (1) melt distribution in a crystal‐dominated mush; (2) melt‐crystal reactions within the mush; (3) the chemistry of melts that have contributed to the cumulate lithology; and (4) the chemistry of axial melts that enter the axial magma system. The xenolith was enclosed within a moderately primitive, normal mid‐ocean ridge basalt (NMORB) erupted in 1991 within the neovolcanic zone of the NEPR, at approximately 9°50′N. The sample is a matrix‐dominated, cumulate olivine anorthosite, composed of anorthite (An94‐90) and bytownite (An89‐70), intergranular olivine (Fo86±0.3), minor sulfide and spinel, and intergranular glass. Marginal corrosion of plagioclase, and possibly olivine, and internal remelting of plagioclase indicate syntexis. It is surmised that the pore volume was eviscerated several times with moderately primitive basaltic melts and reduced by intergranular crystallization of forsteritic olivine. The presence of anorthite as a cumulate phase in the xenolith and the observation of anorthite xenocrysts in NMORB lavas, and as a cumulate phase in ophiolite gabbros, indicate that Ca‐rich melts that are not a part of the NMORB lineage play an important role in the construction of the oceanic crust.