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Title: Petrographic significance of zoned allanite in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California

Abstract

Zoned allanite is a minor mineral in highly altered blocks of garnet amphibolite that occur in a metaultramafic melange matrix in the amphibolite unit of the Catalina Schist, southern California. Blocks and matrix alike were affected by a high-T, relatively high-P hydrothermal event, which locally induced partial melting of blocks and apparently was accompanied by considerable trace element metasomatism. In blocks that show evidence for light rare earth element (LREE) enrichment, allanite contains almost all of the LREE in the rock. Allanite from four LREE-enriched samples that have different whole-rock REE abundances and fractionations was analyzed with the electron microprobe. Three samples are migmatites, and one shows no evidence for partial melting. The analyses were obtained for empirically defined zones of uniform brightness in backscattered electron images from the scanning electron microscope (SEM). The zoned allanite displays large ranges of anticorrelated Ca and LREE contents. Variations of these elements and of Al, Cr, Sr, Fe, Mg, and Mn within zoned grains indicate a fairly continuous nature for many substitutions of Mg{sup 2+} and M{sup 3+} cations in allanite. The apparent reverse zoning of allanite in migmatites suggests that LREE were added to the rock volume from an external source duringmore » allanite growth. Metamorphic textures and petrologic considerations indicate that at least some of the growth of allanite in migmatites predates the partial melting event. The variations of LREE within grains and between samples may in part reflect local, time-dependent charges of fluid compositions in the subduction-related, hydrothermal and metasomatic system the rocks represent.« less

Authors:
 [1]
  1. (Smithsonian Inst., Washington, DC (United States))
OSTI Identifier:
5738649
Alternate Identifier(s):
OSTI ID: 5738649
Resource Type:
Journal Article
Journal Name:
American Mineralogist; (United States)
Additional Journal Information:
Journal Volume: 76:3-4; Journal ID: ISSN 0003-004X
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ALLANITE; CHEMICAL COMPOSITION; CALIFORNIA; SUBDUCTION ZONES; GEOCHEMISTRY; ALUMINIUM; CALCIUM; CHROMIUM; ELECTRON MICROPROBE ANALYSIS; ENRICHMENT; GEOLOGIC HISTORY; IRON; MAGNESIUM; MANGANESE; METAMORPHISM; MINERALOGY; PETROGRAPHY; RARE EARTHS; SCANNING ELECTRON MICROSCOPY; STRONTIUM; TRACE AMOUNTS; ALKALINE EARTH METALS; CHEMICAL ANALYSIS; CHEMISTRY; DEVELOPED COUNTRIES; ELECTRON MICROSCOPY; ELEMENTS; MATERIALS; METALS; MICROANALYSIS; MICROSCOPY; MINERALS; NONDESTRUCTIVE ANALYSIS; NORTH AMERICA; RADIOACTIVE MATERIALS; RADIOACTIVE MINERALS; SILICATE MINERALS; THORIUM MINERALS; TRANSITION ELEMENTS; USA 580000* -- Geosciences

Citation Formats

Sorensen, S.S. Petrographic significance of zoned allanite in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California. United States: N. p., Web.
Sorensen, S.S. Petrographic significance of zoned allanite in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California. United States.
Sorensen, S.S. . "Petrographic significance of zoned allanite in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California". United States.
@article{osti_5738649,
title = {Petrographic significance of zoned allanite in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California},
author = {Sorensen, S.S.},
abstractNote = {Zoned allanite is a minor mineral in highly altered blocks of garnet amphibolite that occur in a metaultramafic melange matrix in the amphibolite unit of the Catalina Schist, southern California. Blocks and matrix alike were affected by a high-T, relatively high-P hydrothermal event, which locally induced partial melting of blocks and apparently was accompanied by considerable trace element metasomatism. In blocks that show evidence for light rare earth element (LREE) enrichment, allanite contains almost all of the LREE in the rock. Allanite from four LREE-enriched samples that have different whole-rock REE abundances and fractionations was analyzed with the electron microprobe. Three samples are migmatites, and one shows no evidence for partial melting. The analyses were obtained for empirically defined zones of uniform brightness in backscattered electron images from the scanning electron microscope (SEM). The zoned allanite displays large ranges of anticorrelated Ca and LREE contents. Variations of these elements and of Al, Cr, Sr, Fe, Mg, and Mn within zoned grains indicate a fairly continuous nature for many substitutions of Mg{sup 2+} and M{sup 3+} cations in allanite. The apparent reverse zoning of allanite in migmatites suggests that LREE were added to the rock volume from an external source during allanite growth. Metamorphic textures and petrologic considerations indicate that at least some of the growth of allanite in migmatites predates the partial melting event. The variations of LREE within grains and between samples may in part reflect local, time-dependent charges of fluid compositions in the subduction-related, hydrothermal and metasomatic system the rocks represent.},
doi = {},
journal = {American Mineralogist; (United States)},
issn = {0003-004X},
number = ,
volume = 76:3-4,
place = {United States},
year = {},
month = {}
}