78 JAGATBIKAS NANDA AND OTHERS Analysis of Deformation Fabric in an Alkaline Complex (Koraput): Implications for Time Relationship between Emplacement, Fabric Development and Regional Tectonics

• Main Authors: Jagatbikas Nanda, Saibal Gupta, Manish A. Mamtani
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2009
• Subjects: Anisotropy of magnetic susceptibility; Alkaline complex; Fabric; Eastern Ghats Belt; Indo-Antarctica; Indian; Nanda; Antarc*; Antarctica
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.670.3926; http://www.geosocindia.org/abstracts/2009/july/fullpapers/f10.pdf

Abstract: The Koraput Alkaline Complex (KAC) lies on the NE-SW trending Sileru Shear Zone (SSZ) separating the Proterozoic Eastern Ghats Province from the Archaean Indian craton. The core of the KAC is made of hornblende gabbro, which is rimmed by a band of nepheline syenite in the east and syenodiorite in the west. The timing of magmatism with respect to the SSZ is disputed. The KAC was deformed during emplacement, and a magmatic foliation related to the syn-emplacement deformation, D1, is present in the gabbroic core. The dominant D2-related field fabric strikes NE-SW and is penetrative in parts of the gabbro and marginal lithologies. E-W trending D3 shear zones cut across the complex. Distinct textural domains resulted from strain partitioning during deformation. Parts of the complex with magmatic textures constitute Domain-1, while D2 and D3 fabric zones comprise Domains-2 and 3 respectively. Temperatures in the KAC initially decreased following D1, but increased through D2 and D3. Anisotropy of magnetic susceptibility (AMS) studies show that the magnetic fabric generally follows S1 in Domain-1. While the magnetic fabric in Domain-2 is dominantly parallel to S2, some of it parallels S1. The latter is a relict D1 fabric that is recognized from AMS analysis but is obliterated in the field, which confirms that the KAC pre-dates the SSZ. The response of magnetic fabrics to temperature and implications of the study for Indo-Antarctica amalgamation are discussed.