229 Crustal Petrology (Posters)
This session explores various igneous and metamorphic processes that have shaped Earth’s crust. We welcome contributions from the micro- to macroscale, from the deep to shallow crust, and from field- to laboratory- to modeling-based.
Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1
Integrated Spectroscopic and Petrographic Analysis of Metamorphic Rocks from the Attappadi Valley, Kerala, Southern India
Paper number: 229-20
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
Abstract
The Attappadi Valley in Kerala, part of the Southern Indian Granulite Terrain, comprises diverse lithologies, including hornblende-biotite gneiss, hornblende gneiss, amphibolites, charnockite, and metapyroxenites within the Bhavani Suture Zone. This study combines spectroscopic and petrographic methods to investigate the mineral assemblages and metamorphic history of the region, emphasizing both the host rocks and alteration zones. Field studies and petrographic analysis reveal the dominance of medium- to coarse-grained hornblende gneiss with enclaves of amphibolites and metapyroxenites. The hornblende gneiss consists of plagioclase, quartz, green hornblende, potash feldspar, and biotite, with sphene and iron minerals as accessories. Patches of charnockite with gradational contacts within the gneiss, along with hornblende-quartz intergrowths and the development of hydrous minerals, suggest retrogressive metamorphism. Spectral characteristics of hand specimens and powdered samples were analyzed in the UV-Visible-NIR range using ASD-FieldSpec3. Reflectance spectra from ten samples collected across the valley were processed to identify spectral endmembers, cross-referenced with USGS spectral libraries, and used to estimate mineral abundances. This integrated approach highlights the utility of spectroscopy as a rapid, complementary tool to conventional field and laboratory techniques for mineral identification and quantification in high-grade metamorphic terrains. The study provides insights into the complex mineralogical and metamorphic evolution of the Attappadi Valley, offering a framework for future investigations in granulite and suture zone terrains.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-412183
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