Formation of amphibole after clinopyroxene by dehydration reactions: Implications for pseudomorphic replacement and mass fluxes

Timothy Jay Fagan, Howard W. Day

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The replacement of anhydrous by hydrous minerals is commonly used to infer infiltration of a rock by H2O. However, our work indicates that the formation of pseudomorphic amphibole after clinopyroxene (uralitization) in low-grade metavolcanic rocks is a net dehydration process. In the ophiolitic Slate Creek complex, northern California, clinopyroxene exhibits four textural stages of alteration: (1) clinopyroxene, (2) clinopyroxene + chlorite ± amphibole, (3) amphibole + chlorite, and (4) amphibole. This transformation occurs in subgreenschist to greenschist facies rocks with a common matrix assemblage: quartz, albite, chlorite, epidote, titanite, ± amphibole, ± white mica, ± rare pumpellyite. A simple reaction space model based on these observations indicates that consumption of chlorite in the rock matrix releases more water than required to produce amphibole pseudomorphs of clinopyroxene. Thus, the net flux of H2O during uralitization of greenschist facies metavolcanic rocks is outward. These results imply that uralitization in metavolcanic rocks results from heating rather than whole-rock hydration, and that natural mass fluxes may be counter to fluxes inferred from textural evidence alone.

Original languageEnglish
Pages (from-to)395-398
Number of pages4
JournalGeology
Volume25
Issue number5
DOIs
Publication statusPublished - 1997
Externally publishedYes

Fingerprint

dehydration
amphibole
clinopyroxene
replacement
metavolcanic rock
chlorite
greenschist facies
rock
hydrous mineral
pumpellyite
matrix
slate
titanite
epidote
albite
hydration
mica
infiltration
quartz
heating

ASJC Scopus subject areas

  • Geology

Cite this

Formation of amphibole after clinopyroxene by dehydration reactions : Implications for pseudomorphic replacement and mass fluxes. / Fagan, Timothy Jay; Day, Howard W.

In: Geology, Vol. 25, No. 5, 1997, p. 395-398.

Research output: Contribution to journalArticle

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