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Preliminary U-Pb zircon ages of high-grade rocks in southern Kerala, India

Journal Article:

Abstract

South Kerala in southwestern India offers interesting khondalite-charnockite assemblages suitable for detailed multidisciplinary case studies on granulite petrogenesis. Arrested charnockite formation is also characteristic of the terrain. Absolute ages of the khondalites are poorly constrained; limited U-Pb zircon data for various rock types of south Kerala khondalite belt have been obtained. Zircons from khondalite sensu-stricto and garnet-biotite gneiss of possible sedimentary origin give a concordia upper-intercept apparent age of ca. 2200 Ma, suggesting that the khondalites contain detrital material that is at least early Proterozoic in age; the data yield a lower intercept apparent age of ca. 400-600 Ma, but it is not clear if this represents new zircon growth and episodic Pb loss at that time (preferred) or is an artifact of normal diffusive loss of radiogenenic Pb. Zircons from retrograded granulitic gneisses have zircon upper-intercept apparent ages of ca. 1550 Ma, indicating either a younger protolith age or, more probably, greater radiogenic Pb loss during subsequent migmatite-grade metamorphism that caused retrogression of the granulite. Since all the zircon populations are complex, more detailed analyses will need to be pursued to resolve age relationships of these rocks with greater certainty. Monazite from a retrograded granulitic gneiss, yields a concordant  More>>
Authors:
Soman, K; Narayanaswamy,; [1]  Van Schmus, W R [2] 
  1. Centre for Earth Science Studies, Trivandrum (India)
  2. University of Kansas, Lawrence (United States).Dept. of Geology
Publication Date:
Feb 01, 1995
Product Type:
Journal Article
Reference Number:
SCA: 400101; 580000; PA: AIX-26:062368; EDB-95:124806; SN: 95001457549
Resource Relation:
Journal Name: Journal of the Geological Society of India; Journal Volume: 45; Journal Issue: 2; Other Information: PBD: Feb 1995
Subject:
40 CHEMISTRY; 58 GEOSCIENCES; ZIRCON; ISOTOPE DATING; GNEISSES; GRANITES; INDIA; ISOTOPE RATIO; LEAD 206; LEAD 207; LEAD 208; METAMORPHISM; URANIUM 235; URANIUM 238
OSTI ID:
100064
Country of Origin:
India
Language:
English
Other Identifying Numbers:
Journal ID: JGSIAJ; ISSN 0016-7622; TRN: IN9501052062368
Submitting Site:
INIS
Size:
pp. 127-136
Announcement Date:
Oct 02, 1995

Journal Article:

Citation Formats

Soman, K, Narayanaswamy,, and Van Schmus, W R. Preliminary U-Pb zircon ages of high-grade rocks in southern Kerala, India. India: N. p., 1995. Web.
Soman, K, Narayanaswamy,, & Van Schmus, W R. Preliminary U-Pb zircon ages of high-grade rocks in southern Kerala, India. India.
Soman, K, Narayanaswamy,, and Van Schmus, W R. 1995. "Preliminary U-Pb zircon ages of high-grade rocks in southern Kerala, India." India.
@misc{etde_100064,
title = {Preliminary U-Pb zircon ages of high-grade rocks in southern Kerala, India}
author = {Soman, K, Narayanaswamy,, and Van Schmus, W R}
abstractNote = {South Kerala in southwestern India offers interesting khondalite-charnockite assemblages suitable for detailed multidisciplinary case studies on granulite petrogenesis. Arrested charnockite formation is also characteristic of the terrain. Absolute ages of the khondalites are poorly constrained; limited U-Pb zircon data for various rock types of south Kerala khondalite belt have been obtained. Zircons from khondalite sensu-stricto and garnet-biotite gneiss of possible sedimentary origin give a concordia upper-intercept apparent age of ca. 2200 Ma, suggesting that the khondalites contain detrital material that is at least early Proterozoic in age; the data yield a lower intercept apparent age of ca. 400-600 Ma, but it is not clear if this represents new zircon growth and episodic Pb loss at that time (preferred) or is an artifact of normal diffusive loss of radiogenenic Pb. Zircons from retrograded granulitic gneisses have zircon upper-intercept apparent ages of ca. 1550 Ma, indicating either a younger protolith age or, more probably, greater radiogenic Pb loss during subsequent migmatite-grade metamorphism that caused retrogression of the granulite. Since all the zircon populations are complex, more detailed analyses will need to be pursued to resolve age relationships of these rocks with greater certainty. Monazite from a retrograded granulitic gneiss, yields a concordant age of ca. 520 Ma; this age is probably related to late Proterozoic-early Cambrian regional thermal event is south Kerala and is correlative with a similar event in Sri Lanka. (author). 25 refs., 4 figs., 1 tab.}
journal = {Journal of the Geological Society of India}
issue = {2}
volume = {45}
journal type = {AC}
place = {India}
year = {1995}
month = {Feb}
}