Formation of atoll garnets in the UHP eclogites of the TSO Morari Complex, Ladakh, Himalaya

Mallika K. Jonnalagadda, Nitin R. Karmalkar, Raymond A. Duraiswami, Shivani Harshe, Sarah Gain, William L. Griffin

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The eclogites of the Tso Morari Complex, Ladakh, NW Himalayas preserve both garnets with spectacular atoll textures, as well as whole porphyroblastic garnets. Whole garnets are euhedral, idiomorphic and enclose inclusions of amphibole, phengite and zoisite within the cores, and omphacite and quartz/coesite towards the rims. Detailed electron microprobe analyses and back-scattered electron images show well-preserved prograde zoning in the whole garnets with an increase in Mg and decrease in Ca and Mn contents from the core to the rim. The atoll garnets commonly consist of euhedral ring over island/peninsular core containing inclusions of phengite, omphacite and rarely amphibole between the core and ring. Compositional profiles across the studied atoll grains show elemental variations with higher concentrations of Ca and Mn with low Mg at the peninsula/island cores; contrary to this low Ca, Mn and high Mg is observed at the outer rings. Temperature estimates yield higher values at the Mg-rich atoll garnet outer rings compared to the atoll cores. Atoll garnet formation was favoured by infiltration of fluid formed due to breakdown of hydrous phases, and/or the release of structurally bounded OH from nominally anhydrous minerals at the onset of exhumation. Infiltration of fluids along pre-existing fracture pathways and along mineral inclusion boundaries triggered breakdown of the original garnet cores and released elements which were subsequently incorporated into the newly-grown garnet rings. This breakdown of garnet cores and inward re-growth at the outer ring produced the atoll structure. Calibrated geo-thermobarometers and mineral equilibria reflect that the Tso Morari eclogites attain peak pressures prior to peak temperatures representing a clockwise path of evolution.

LanguageEnglish
Article number107
Pages1-23
Number of pages23
JournalJournal of Earth System Science
Volume126
Issue number8
DOIs
Publication statusPublished - Dec 2017

Fingerprint

atoll
garnet
omphacite
phengite
amphibole
infiltration
mineral
zoisite
coesite
fluid
regrowth
exhumation
electron probe analysis
zoning
texture
temperature
quartz
electron

Keywords

  • Atoll garnet
  • eclogite
  • fluid infiltration
  • retrograde metamorphism
  • Ladakh Himalayas
  • Tso Morari Complex

Cite this

Jonnalagadda, Mallika K. ; Karmalkar, Nitin R. ; Duraiswami, Raymond A. ; Harshe, Shivani ; Gain, Sarah ; Griffin, William L. / Formation of atoll garnets in the UHP eclogites of the TSO Morari Complex, Ladakh, Himalaya. In: Journal of Earth System Science. 2017 ; Vol. 126, No. 8. pp. 1-23.
@article{335a78db16e8471698ed9c31856725fb,
title = "Formation of atoll garnets in the UHP eclogites of the TSO Morari Complex, Ladakh, Himalaya",
abstract = "The eclogites of the Tso Morari Complex, Ladakh, NW Himalayas preserve both garnets with spectacular atoll textures, as well as whole porphyroblastic garnets. Whole garnets are euhedral, idiomorphic and enclose inclusions of amphibole, phengite and zoisite within the cores, and omphacite and quartz/coesite towards the rims. Detailed electron microprobe analyses and back-scattered electron images show well-preserved prograde zoning in the whole garnets with an increase in Mg and decrease in Ca and Mn contents from the core to the rim. The atoll garnets commonly consist of euhedral ring over island/peninsular core containing inclusions of phengite, omphacite and rarely amphibole between the core and ring. Compositional profiles across the studied atoll grains show elemental variations with higher concentrations of Ca and Mn with low Mg at the peninsula/island cores; contrary to this low Ca, Mn and high Mg is observed at the outer rings. Temperature estimates yield higher values at the Mg-rich atoll garnet outer rings compared to the atoll cores. Atoll garnet formation was favoured by infiltration of fluid formed due to breakdown of hydrous phases, and/or the release of structurally bounded OH from nominally anhydrous minerals at the onset of exhumation. Infiltration of fluids along pre-existing fracture pathways and along mineral inclusion boundaries triggered breakdown of the original garnet cores and released elements which were subsequently incorporated into the newly-grown garnet rings. This breakdown of garnet cores and inward re-growth at the outer ring produced the atoll structure. Calibrated geo-thermobarometers and mineral equilibria reflect that the Tso Morari eclogites attain peak pressures prior to peak temperatures representing a clockwise path of evolution.",
keywords = "Atoll garnet, eclogite, fluid infiltration, retrograde metamorphism, Ladakh Himalayas, Tso Morari Complex",
author = "Jonnalagadda, {Mallika K.} and Karmalkar, {Nitin R.} and Duraiswami, {Raymond A.} and Shivani Harshe and Sarah Gain and Griffin, {William L.}",
year = "2017",
month = "12",
doi = "10.1007/s12040-017-0887-y",
language = "English",
volume = "126",
pages = "1--23",
journal = "Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences",
issn = "0253-4126",
publisher = "Indian Academy of Sciences",
number = "8",

}

Formation of atoll garnets in the UHP eclogites of the TSO Morari Complex, Ladakh, Himalaya. / Jonnalagadda, Mallika K.; Karmalkar, Nitin R.; Duraiswami, Raymond A.; Harshe, Shivani; Gain, Sarah; Griffin, William L.

In: Journal of Earth System Science, Vol. 126, No. 8, 107, 12.2017, p. 1-23.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Formation of atoll garnets in the UHP eclogites of the TSO Morari Complex, Ladakh, Himalaya

AU - Jonnalagadda, Mallika K.

AU - Karmalkar, Nitin R.

AU - Duraiswami, Raymond A.

AU - Harshe, Shivani

AU - Gain, Sarah

AU - Griffin, William L.

PY - 2017/12

Y1 - 2017/12

N2 - The eclogites of the Tso Morari Complex, Ladakh, NW Himalayas preserve both garnets with spectacular atoll textures, as well as whole porphyroblastic garnets. Whole garnets are euhedral, idiomorphic and enclose inclusions of amphibole, phengite and zoisite within the cores, and omphacite and quartz/coesite towards the rims. Detailed electron microprobe analyses and back-scattered electron images show well-preserved prograde zoning in the whole garnets with an increase in Mg and decrease in Ca and Mn contents from the core to the rim. The atoll garnets commonly consist of euhedral ring over island/peninsular core containing inclusions of phengite, omphacite and rarely amphibole between the core and ring. Compositional profiles across the studied atoll grains show elemental variations with higher concentrations of Ca and Mn with low Mg at the peninsula/island cores; contrary to this low Ca, Mn and high Mg is observed at the outer rings. Temperature estimates yield higher values at the Mg-rich atoll garnet outer rings compared to the atoll cores. Atoll garnet formation was favoured by infiltration of fluid formed due to breakdown of hydrous phases, and/or the release of structurally bounded OH from nominally anhydrous minerals at the onset of exhumation. Infiltration of fluids along pre-existing fracture pathways and along mineral inclusion boundaries triggered breakdown of the original garnet cores and released elements which were subsequently incorporated into the newly-grown garnet rings. This breakdown of garnet cores and inward re-growth at the outer ring produced the atoll structure. Calibrated geo-thermobarometers and mineral equilibria reflect that the Tso Morari eclogites attain peak pressures prior to peak temperatures representing a clockwise path of evolution.

AB - The eclogites of the Tso Morari Complex, Ladakh, NW Himalayas preserve both garnets with spectacular atoll textures, as well as whole porphyroblastic garnets. Whole garnets are euhedral, idiomorphic and enclose inclusions of amphibole, phengite and zoisite within the cores, and omphacite and quartz/coesite towards the rims. Detailed electron microprobe analyses and back-scattered electron images show well-preserved prograde zoning in the whole garnets with an increase in Mg and decrease in Ca and Mn contents from the core to the rim. The atoll garnets commonly consist of euhedral ring over island/peninsular core containing inclusions of phengite, omphacite and rarely amphibole between the core and ring. Compositional profiles across the studied atoll grains show elemental variations with higher concentrations of Ca and Mn with low Mg at the peninsula/island cores; contrary to this low Ca, Mn and high Mg is observed at the outer rings. Temperature estimates yield higher values at the Mg-rich atoll garnet outer rings compared to the atoll cores. Atoll garnet formation was favoured by infiltration of fluid formed due to breakdown of hydrous phases, and/or the release of structurally bounded OH from nominally anhydrous minerals at the onset of exhumation. Infiltration of fluids along pre-existing fracture pathways and along mineral inclusion boundaries triggered breakdown of the original garnet cores and released elements which were subsequently incorporated into the newly-grown garnet rings. This breakdown of garnet cores and inward re-growth at the outer ring produced the atoll structure. Calibrated geo-thermobarometers and mineral equilibria reflect that the Tso Morari eclogites attain peak pressures prior to peak temperatures representing a clockwise path of evolution.

KW - Atoll garnet

KW - eclogite

KW - fluid infiltration

KW - retrograde metamorphism

KW - Ladakh Himalayas

KW - Tso Morari Complex

UR - http://www.scopus.com/inward/record.url?scp=85038880780&partnerID=8YFLogxK

U2 - 10.1007/s12040-017-0887-y

DO - 10.1007/s12040-017-0887-y

M3 - Article

VL - 126

SP - 1

EP - 23

JO - Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences

T2 - Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences

JF - Proceedings of the Indian Academy of Sciences - Earth and Planetary Sciences

SN - 0253-4126

IS - 8

M1 - 107

ER -