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

Journal Article · Tue Jul 10 04:00:00 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]

---

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

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH METAL COMPOUNDS
ANORTHOSITES
BASALT
CALIFORNIA
CHEMISTRY
COMPOSITE MATERIALS
CRYSTAL STRUCTURE
DEVELOPED COUNTRIES
FEDERAL REGION IX
FEDERAL REGION X
GABBROS
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOTHERMAL SYSTEMS
GLASS
IGNEOUS ROCKS
INCLUSIONS
IRON COMPOUNDS
IRON SILICATES
LAVA
MAGMA SYSTEMS
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MATERIALS
MINERALOGY
MINERALS
NORTH AMERICA
OFFSHORE SITES
OLIVINE
OREGON
OXYGEN COMPOUNDS
PACIFIC OCEAN
PLUTONIC ROCKS
ROCKS
SEA-FLOOR SPREADING
SEAS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SURFACE WATERS
TEXTURE
TRACE AMOUNTS
TRANSITION ELEMENT COMPOUNDS
USA
VOLCANIC ROCKS
VOLCANISM