Progressive or continual exsolution in pyroxenes

an indicator of polybaric igneous crystallization for the Perinthatta anorthositic gabbro, northern Kerala, southwestern India

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Clinopyroxene and orthopyroxene from the Perinthatta anorthositic gabbro in southwestern India exhibit exsolution intergrowths of pyroxenes (occurring in five stages involving pigeonite, orthopyroxene and/or augite) and Fe-Ti oxides. The thicker irregular pyroxene lamellae appear to be the result of heterogeneous nucleation, indicating that this was the first unmixing process to begin. This was followed by homogeneous nucleation of regularly spaced, quite uniform pyroxene lamellae and defect-free fine pyroxene platelets between early-formed exsolution lamellae, suggesting progressive or continual nature of exsolution during slow cooling. Pyroxene thermometric calculations indicate that subcalcic augite and pigeonite equilibrated at ∼935 °C, with the different lamellar generations formed between ∼914 and ∼748 °C. Pre-metamorphic anorthositic gabbro crystallization is considered to have taken place at deep crustal levels (∼30 km; ∼9-10 kbar) and later emplacement at shallower crustal levels (∼15 km; ∼5-6 kbar) suggesting polybaric conditions. The apparent difference between the pressure of crystallization and the emplacement of the Perinthatta anorthositic gabbro supports the common Proterozoic anorthosite petrogenetic model, involving initial crystallization at depth, followed by intrusion as a crystal-rich mush. Following emplacement, the igneous assemblage was affected by granulite facies metamorphism on cooling, as indicated by smaller granulite minerals along grain boundaries and the partial re-equilibration of exsolved phases.

Original languageEnglish
Pages (from-to)541-553
Number of pages13
JournalJournal of Asian Earth Sciences
Volume26
Issue number5
DOIs
Publication statusPublished - Apr 1 2006

Fingerprint

exsolution
gabbro
pyroxene
crystallization
pigeonite
emplacement
augite
orthopyroxene
nucleation
cooling
anorthosite
granulite
grain boundary
granulite facies
clinopyroxene
defect
Proterozoic
metamorphism
oxide
crystal

All Science Journal Classification (ASJC) codes

  • Earth-Surface Processes
  • Geology

Cite this

@article{614e0274c6854591bbf3eaf307160b57,
title = "Progressive or continual exsolution in pyroxenes: an indicator of polybaric igneous crystallization for the Perinthatta anorthositic gabbro, northern Kerala, southwestern India",
abstract = "Clinopyroxene and orthopyroxene from the Perinthatta anorthositic gabbro in southwestern India exhibit exsolution intergrowths of pyroxenes (occurring in five stages involving pigeonite, orthopyroxene and/or augite) and Fe-Ti oxides. The thicker irregular pyroxene lamellae appear to be the result of heterogeneous nucleation, indicating that this was the first unmixing process to begin. This was followed by homogeneous nucleation of regularly spaced, quite uniform pyroxene lamellae and defect-free fine pyroxene platelets between early-formed exsolution lamellae, suggesting progressive or continual nature of exsolution during slow cooling. Pyroxene thermometric calculations indicate that subcalcic augite and pigeonite equilibrated at ∼935 °C, with the different lamellar generations formed between ∼914 and ∼748 °C. Pre-metamorphic anorthositic gabbro crystallization is considered to have taken place at deep crustal levels (∼30 km; ∼9-10 kbar) and later emplacement at shallower crustal levels (∼15 km; ∼5-6 kbar) suggesting polybaric conditions. The apparent difference between the pressure of crystallization and the emplacement of the Perinthatta anorthositic gabbro supports the common Proterozoic anorthosite petrogenetic model, involving initial crystallization at depth, followed by intrusion as a crystal-rich mush. Following emplacement, the igneous assemblage was affected by granulite facies metamorphism on cooling, as indicated by smaller granulite minerals along grain boundaries and the partial re-equilibration of exsolved phases.",
author = "Rajesh, {H. M.}",
year = "2006",
month = "4",
day = "1",
doi = "10.1016/j.jseaes.2004.11.004",
language = "English",
volume = "26",
pages = "541--553",
journal = "Journal of Asian Earth Sciences",
issn = "1367-9120",
publisher = "Elsevier Limited",
number = "5",

}

TY - JOUR

T1 - Progressive or continual exsolution in pyroxenes

T2 - an indicator of polybaric igneous crystallization for the Perinthatta anorthositic gabbro, northern Kerala, southwestern India

AU - Rajesh, H. M.

PY - 2006/4/1

Y1 - 2006/4/1

N2 - Clinopyroxene and orthopyroxene from the Perinthatta anorthositic gabbro in southwestern India exhibit exsolution intergrowths of pyroxenes (occurring in five stages involving pigeonite, orthopyroxene and/or augite) and Fe-Ti oxides. The thicker irregular pyroxene lamellae appear to be the result of heterogeneous nucleation, indicating that this was the first unmixing process to begin. This was followed by homogeneous nucleation of regularly spaced, quite uniform pyroxene lamellae and defect-free fine pyroxene platelets between early-formed exsolution lamellae, suggesting progressive or continual nature of exsolution during slow cooling. Pyroxene thermometric calculations indicate that subcalcic augite and pigeonite equilibrated at ∼935 °C, with the different lamellar generations formed between ∼914 and ∼748 °C. Pre-metamorphic anorthositic gabbro crystallization is considered to have taken place at deep crustal levels (∼30 km; ∼9-10 kbar) and later emplacement at shallower crustal levels (∼15 km; ∼5-6 kbar) suggesting polybaric conditions. The apparent difference between the pressure of crystallization and the emplacement of the Perinthatta anorthositic gabbro supports the common Proterozoic anorthosite petrogenetic model, involving initial crystallization at depth, followed by intrusion as a crystal-rich mush. Following emplacement, the igneous assemblage was affected by granulite facies metamorphism on cooling, as indicated by smaller granulite minerals along grain boundaries and the partial re-equilibration of exsolved phases.

AB - Clinopyroxene and orthopyroxene from the Perinthatta anorthositic gabbro in southwestern India exhibit exsolution intergrowths of pyroxenes (occurring in five stages involving pigeonite, orthopyroxene and/or augite) and Fe-Ti oxides. The thicker irregular pyroxene lamellae appear to be the result of heterogeneous nucleation, indicating that this was the first unmixing process to begin. This was followed by homogeneous nucleation of regularly spaced, quite uniform pyroxene lamellae and defect-free fine pyroxene platelets between early-formed exsolution lamellae, suggesting progressive or continual nature of exsolution during slow cooling. Pyroxene thermometric calculations indicate that subcalcic augite and pigeonite equilibrated at ∼935 °C, with the different lamellar generations formed between ∼914 and ∼748 °C. Pre-metamorphic anorthositic gabbro crystallization is considered to have taken place at deep crustal levels (∼30 km; ∼9-10 kbar) and later emplacement at shallower crustal levels (∼15 km; ∼5-6 kbar) suggesting polybaric conditions. The apparent difference between the pressure of crystallization and the emplacement of the Perinthatta anorthositic gabbro supports the common Proterozoic anorthosite petrogenetic model, involving initial crystallization at depth, followed by intrusion as a crystal-rich mush. Following emplacement, the igneous assemblage was affected by granulite facies metamorphism on cooling, as indicated by smaller granulite minerals along grain boundaries and the partial re-equilibration of exsolved phases.

UR - http://www.scopus.com/inward/record.url?scp=33646516614&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=33646516614&partnerID=8YFLogxK

U2 - 10.1016/j.jseaes.2004.11.004

DO - 10.1016/j.jseaes.2004.11.004

M3 - Article

VL - 26

SP - 541

EP - 553

JO - Journal of Asian Earth Sciences

JF - Journal of Asian Earth Sciences

SN - 1367-9120

IS - 5

ER -