Clinopyroxene - a mineral telescoped through the processes of blueschist facies metamorphism.

S. Maruyama, J. G. Liou

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

The textural evolution and compositional variation of clinopyroxenes in Ward Creek metabasites, Cazadero, California, are described (42 probe analyses). The pyroxenes change, with increasing grade, from fine-grained aggregates, through fan-shaped medium-grained prisms to blocky coarse crystals. The first formed clinopyroxene (Jd20Aug65Ac15) in the lower lawsonite zone mimics the composition of relict igneous augite. It changes continuously, with increasing grade, at nearly constant low Jd content, towards acmite. At approx Jd20Aug30Ac50 the trend turns towards jadeite and intersects a solvus to form two coexisting clinopyroxenes in the middle lawsonite grade. At higher grade, the compositional gap becomes restricted towards the jadeite-omphacite join and the jadeite component increases. A reverse trend occurs at higher grade with a decrease in jadeite component at nearly constant Aug/Ac ratio of 1:1 and omphacite finally appears in the uppermost pumpellyite and epidote zones. The Na-Ca pyroxenes, close to the binary join Jd-Ac, occur in the lawsonite and pumpellyite zones. The estimated field-gradient indicates an inflection point at 7 kbar, 200oC. Below this, blueschist metamorphism proceeded under dominant P-increase from 4 to 7 kbar at nearly constant T (approx 150-200oC), whereas at higher grade recrystallization, above the inflection point, the metamorphic T increased from 200o to 350oC at a nearly constant P of approx 7- 8 kbar. Such an inflection point suggests the depth of underplating of either seamounts or accretionary packages in a subduction zone.-R.A.H.

Original languageEnglish
Pages (from-to)529-552
Number of pages24
JournalJournal of Metamorphic Geology
Volume5
Issue number4
Publication statusPublished - 1987
Externally publishedYes

Fingerprint

blueschist facies
jadeite
Theophylline
Prisms
lawsonite
clinopyroxene
Fans
Minerals
metamorphism
pumpellyite
Crystals
omphacite
mineral
Chemical analysis
metabasite
blueschist
underplating
augite
epidote
seamount

ASJC Scopus subject areas

  • Geology

Cite this

Clinopyroxene - a mineral telescoped through the processes of blueschist facies metamorphism. / Maruyama, S.; Liou, J. G.

In: Journal of Metamorphic Geology, Vol. 5, No. 4, 1987, p. 529-552.

Research output: Contribution to journalArticle

@article{2b4ea169243c436f8a3d5ab2ccdbf4ed,
title = "Clinopyroxene - a mineral telescoped through the processes of blueschist facies metamorphism.",
abstract = "The textural evolution and compositional variation of clinopyroxenes in Ward Creek metabasites, Cazadero, California, are described (42 probe analyses). The pyroxenes change, with increasing grade, from fine-grained aggregates, through fan-shaped medium-grained prisms to blocky coarse crystals. The first formed clinopyroxene (Jd20Aug65Ac15) in the lower lawsonite zone mimics the composition of relict igneous augite. It changes continuously, with increasing grade, at nearly constant low Jd content, towards acmite. At approx Jd20Aug30Ac50 the trend turns towards jadeite and intersects a solvus to form two coexisting clinopyroxenes in the middle lawsonite grade. At higher grade, the compositional gap becomes restricted towards the jadeite-omphacite join and the jadeite component increases. A reverse trend occurs at higher grade with a decrease in jadeite component at nearly constant Aug/Ac ratio of 1:1 and omphacite finally appears in the uppermost pumpellyite and epidote zones. The Na-Ca pyroxenes, close to the binary join Jd-Ac, occur in the lawsonite and pumpellyite zones. The estimated field-gradient indicates an inflection point at 7 kbar, 200oC. Below this, blueschist metamorphism proceeded under dominant P-increase from 4 to 7 kbar at nearly constant T (approx 150-200oC), whereas at higher grade recrystallization, above the inflection point, the metamorphic T increased from 200o to 350oC at a nearly constant P of approx 7- 8 kbar. Such an inflection point suggests the depth of underplating of either seamounts or accretionary packages in a subduction zone.-R.A.H.",
author = "S. Maruyama and Liou, {J. G.}",
year = "1987",
language = "English",
volume = "5",
pages = "529--552",
journal = "Journal of Metamorphic Geology",
issn = "0263-4929",
publisher = "Wiley-Blackwell",
number = "4",

}

TY - JOUR

T1 - Clinopyroxene - a mineral telescoped through the processes of blueschist facies metamorphism.

AU - Maruyama, S.

AU - Liou, J. G.

PY - 1987

Y1 - 1987

N2 - The textural evolution and compositional variation of clinopyroxenes in Ward Creek metabasites, Cazadero, California, are described (42 probe analyses). The pyroxenes change, with increasing grade, from fine-grained aggregates, through fan-shaped medium-grained prisms to blocky coarse crystals. The first formed clinopyroxene (Jd20Aug65Ac15) in the lower lawsonite zone mimics the composition of relict igneous augite. It changes continuously, with increasing grade, at nearly constant low Jd content, towards acmite. At approx Jd20Aug30Ac50 the trend turns towards jadeite and intersects a solvus to form two coexisting clinopyroxenes in the middle lawsonite grade. At higher grade, the compositional gap becomes restricted towards the jadeite-omphacite join and the jadeite component increases. A reverse trend occurs at higher grade with a decrease in jadeite component at nearly constant Aug/Ac ratio of 1:1 and omphacite finally appears in the uppermost pumpellyite and epidote zones. The Na-Ca pyroxenes, close to the binary join Jd-Ac, occur in the lawsonite and pumpellyite zones. The estimated field-gradient indicates an inflection point at 7 kbar, 200oC. Below this, blueschist metamorphism proceeded under dominant P-increase from 4 to 7 kbar at nearly constant T (approx 150-200oC), whereas at higher grade recrystallization, above the inflection point, the metamorphic T increased from 200o to 350oC at a nearly constant P of approx 7- 8 kbar. Such an inflection point suggests the depth of underplating of either seamounts or accretionary packages in a subduction zone.-R.A.H.

AB - The textural evolution and compositional variation of clinopyroxenes in Ward Creek metabasites, Cazadero, California, are described (42 probe analyses). The pyroxenes change, with increasing grade, from fine-grained aggregates, through fan-shaped medium-grained prisms to blocky coarse crystals. The first formed clinopyroxene (Jd20Aug65Ac15) in the lower lawsonite zone mimics the composition of relict igneous augite. It changes continuously, with increasing grade, at nearly constant low Jd content, towards acmite. At approx Jd20Aug30Ac50 the trend turns towards jadeite and intersects a solvus to form two coexisting clinopyroxenes in the middle lawsonite grade. At higher grade, the compositional gap becomes restricted towards the jadeite-omphacite join and the jadeite component increases. A reverse trend occurs at higher grade with a decrease in jadeite component at nearly constant Aug/Ac ratio of 1:1 and omphacite finally appears in the uppermost pumpellyite and epidote zones. The Na-Ca pyroxenes, close to the binary join Jd-Ac, occur in the lawsonite and pumpellyite zones. The estimated field-gradient indicates an inflection point at 7 kbar, 200oC. Below this, blueschist metamorphism proceeded under dominant P-increase from 4 to 7 kbar at nearly constant T (approx 150-200oC), whereas at higher grade recrystallization, above the inflection point, the metamorphic T increased from 200o to 350oC at a nearly constant P of approx 7- 8 kbar. Such an inflection point suggests the depth of underplating of either seamounts or accretionary packages in a subduction zone.-R.A.H.

UR - http://www.scopus.com/inward/record.url?scp=0023498681&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0023498681&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0023498681

VL - 5

SP - 529

EP - 552

JO - Journal of Metamorphic Geology

JF - Journal of Metamorphic Geology

SN - 0263-4929

IS - 4

ER -