Gabbroic xenoliths from the northern Gorda Ridge: Implications for magma chamber processes under slow spreading centers

Journal Article · Tue Jul 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB07p10885· OSTI ID:5316235

Davis, A S; Clague, D A ^[1]

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1. Geological Survey, Menlo Park, CA (USA)

On the basis of textures and mineral compositions, the xenoliths are divided into five types: Type A xenoliths consist of large clinopyroxene oikocrysts, enclosing euhedral to subhedral plagioclase. Olivine and glass are present only in trace amounts. Type B xenoliths consist of olivine and plagioclase ({plus minus}spinel) with abundant intersertal glass. Partially resorbed olivine with deeply embayed margins in places subophitically encloses small plagioclase crystals. Olivine and large plagioclase crystals often contain glass inclusions and/or spinel. Type C xenoliths are a composite of types A and B, with areas of large clinopyroxene oikocrysts adjoining areas of loosely joined clusters of olivine and plagioclase in glass. Type D is represented by a single large xenolith that, except for containing a larger proportion of crystals, appears identical to the host lava. Type E is represented by a single small xenolith that is mineralogically similar to type B but with a distinct, fine-grained, tightly interlocking texture, formed by small olivine oikocrysts enclosing euhedral plagioclase, in a small amount of intersertal glass. Chemistry of mineral phases in conjunction with textural features suggests that the xenoliths formed in different parts of a convecting magma chamber that underwent a period of closed system fractionation. The chamber was filled with a large proportion of crystalline mush when new, more primitive, and less dense magma was injected and mixed incompletely with the contents in the chamber, forming the hybrid host lava. Plagioclase-rich leucogabbro layers in ophiolites attest to similar processes in magma chambers of past spreading centers.

• OSTI ID: 5316235
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B7; ISSN 0148-0227
• Country of Publication: United States
• Language: English

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