Premium
Petrology of amphibolite‐facies mafic and ultramafic rocks from the Catalina Schist, southern California: metasomatism and migmatization in a subduction zone metamorphic setting
Author(s) -
SORENSEN S.S.
Publication year - 1988
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1988.tb00431.x
Subject(s) - geology , ultramafic rock , geochemistry , metamorphic facies , metasomatism , partial melting , greenschist , petrology , schist , metamorphic rock , mafic , blueschist , migmatite , mantle wedge , subduction , mantle (geology) , gneiss , tectonics , geomorphology , facies , seismology , eclogite , structural basin
The Catalina Schist of southern California is a subduction zone metamorphic terrane. It consists of three tectonic units of amphibolite‐, high‐ P greenschist‐ and blueschist‐facies rocks that are structurally juxtaposed across faults, forming an apparent inverted metamorphic gradient. Migmatitic and non‐migmatitic metabasite blocks surrounded by a meta‐ultramafic matrix comprise the upper part of the Catalina amphibolite unit. Fluid‐rock interaction at high‐ P , high‐ T conditions caused partial melting of migmatitic blocks, metasomatic exchange between metabasite blocks and ultramafic rocks, infiltration of silica into ultramafic rocks, and loss of an albitic component from nonmigmatitic, clinopyroxene‐bearing metabasite blocks. Partial melting took place at an estimated P =˜8–11 kbar and T =˜640–750°C at high H 2 O activity. The melting reaction probably involved plagioclase + quartz. Trondhjemitic melts were produced and are preserved as leucocratic regions in migmatitic blocks and as pegmatitic dikes that cut ultramafic rocks. The metasomatic and melting processes reflected in these rocks could be analogous to those proposed for fluid and melt transfer of components from a subducting slab to the mantle wedge. Aqueous fluids rather than melts seem to have accomplished the bulk of mass transfer within the mafic and ultramafic complex.