P-T conditions of metamorphism of the supracrustal rocks in the southern part of the Holenarsipur schist belt and the genesis of the associated asbestos mineralization

Saved in:
Authors:Rao, Ashok V.; Rao, B. Krishna; Govindaiah, S.; Sethumadhav, M. S.
Author Affiliations:Primary:
University of Mysore, Department of Studies in Geology, Mysore, India
Volume Title:Indian Mineralogist
Source:Indian Mineralogist, 33(2), p.81-95. Publisher: Mineralogical Society of India, Mysore, India. ISSN: 0019-5928
Publication Date:1999
Note:In English. 34 refs.; illus., incl. 1 plate, 3 tables, sketch map
Summary:The southern part of the Holenarsipur schist belt consists of Sargur group of supracrustal rocks, which are composed mainly of hornblende schists/amphibolites, pelites, rhyodacite and ultrabasic-basic intrusive complex (dunite, harzburgite, pyroxenite and gabbro-anorthosite and hornblendite). These rocks are intruded by Gunjur betta granite. Based on the mineral chemistry (EPMA) data of the prograde mineral assemblages, it is inferred that the supracrustal rocks were subjected to upper amphibolite facies metamorphism at T ∼600°C and P ∼5-7 Kbars. Asbestos mineralization is confined to the ultrabasic rocks (dunite, harzburgite, lherzolite) and carbonates (dolomite/calcite). Three types of asbestos are identified: 1. Chrysotile asbestos (cross-fiber type) confined to the dunite, 2. Anthophyllite asbestos (mixed-fiber type) encountered mainly in the harzburgite and to a lesser extent in the lherzolite and 3. Tremolite asbestos (slip-fiber type) found in the carbonate pockets, confined to lherzolite and at its contacts with the pelite. The development of the different types of asbestos in different rocks is controlled mainly by the chemical composition of the host rocks, especially with respect to their SiO2:MgO:CaO ratio. Asbestos mineralization post-dates the amphibolite facies metamorphic event, the latter being prior to or syn-kinematic with the emplacement of the c. 3000 Ma old Gunjur betta granite. Genesis of the asbestiform anthophyllite and tremolite may be attributed to the intense shearing event and the associated CO2-rich fluid influx, which possibly took place at c. 2500 Ma ago. Subsequently, chrysotile asbestos developed under near surface conditions at low temperatures (<200°C) and in the presence of CO2-poor fluids.
Sections:Mineral data; Petrology
Subsections:Metamorphism: regional, dynamic
Mineral Groups:Double-chain silicates
Subjects:Amphibole group; Amphibolite facies; Amphibolites; Anthophyllite; Asbestos deposits; Carbon dioxide; Chain silicates; Chrysotile; Clastic rocks; Clinoamphibole; Dunite; Electron probe data; Facies; Fluid phase; Gabbros; Harzburgite; Hornblende schist; Igneous rocks; Metamorphic rocks; Metamorphism; Mineral deposits, genesis; Mineralization; Orthoamphibole; P-T conditions; Peridotites; Plutonic rocks; Pyroxenite; Rhyodacites; Schists; Sedimentary rocks; Serpentine group; Shale; Shear stress; Sheet silicates; Silicates; Sulfides; Supracrustals; Tremolite; Ultrabasite; Ultramafics; Volcanic rocks; Holenarsipur schist belt
Coordinates:N124000 N130000 E0763000 E0760000
Abstract Numbers:06M/554
Record ID:2000069451
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
Tags: Add Tag
No Tags, Be the first to tag this record!