GEOCHEMICAL AND PETROLOGICAL STUDIES OF A CARBONATISED METALAMPROPHYRE AT KALAGALLA -
EVIDENCE FOR SHOSHONITIC CALC-ALKALINE MAGMATISM WITHIN AURIFEROUS RAMAGIRI-PENAKACHERLA SCHIST BELT (2.5 Ga), EASTERN DHARWAR CRATON, SOUTHERN INDIA
DOI:
https://doi.org/10.21715/GB2358-2812.2020341001Abstract
Geochemical and petrological characteristics of a lamprophyre dyke at Kalagalla intruded into the auriferous schistose rocks of the Ramagiri-Penakacherla Schist Belt, Anantapur district, Andhra Pradesh, India are presented here. The Kalagalla lamprophyre (KGL) is a melanocratic rock exhibiting typical knobbly or pustular texture on the rock surface. The micro-textures and mineralogy typical of lamprophyres are obscured by metamorphism; however, it exhibits porphyritic, nemato-granoblastic texture representating greenschist facies metamorphism. The rock is sheared and carbonatised possessing several globules formed by polycrystalline aggregates of calcite rimmed by coronitic subhedral plagioclase and biotite-phlogopite, evidencing its magmatic origin. The mineral assemblages noticed in thin-sections include amphibole, plagioclase, biotite-phlogopite with calcite ocelli as essential while apatite, zircon, magnetite, ilmenite and several opaque minerals as accessory phases. The SEM-EDS investigation on the opaque minerals revealed accessory sulphide and silicate phases like As-free pyrite, haematitised Ni-bearing chalcopyrite and Ni-As-Co- minerals indicative of sulphidation associated with greenstonevauriferous lodes; along with oxide phases like LREE-bearing titanite partially transformed into leucoxene and goethite. Presence of amphibole and dominance of plagioclase, it is presumably a spessartite variety. Based on its geochemistry, the rock is classified as a shoshonitic calc-alkaline lamprophyre. The LREE-bearing titanite appears to be the contributor of LREE enrichment. The high Mg# (77-79), Ni (153-162 ppm) and Cr (380-470 ppm) support a mantle source. The trace and REE patterns (ƩREE:326-343 ppm, LREE>HREE) indicate ivolvement of residual garnet at the source enriched in phlogopite in a ‘subduction-related’ environment. The absence of Eu anomaly reflects lack of plagioclase fractionation. The high Zr/Hf ratio (163-202) indicates carbonatite metasomatism and lack of crustal contamination. Further investigations are in progress.
Downloads
Downloads
Published
How to Cite
Issue
Section
License
Copyright Transfer Statement
The copyright to this article is transferred to Sociedade Brasileira de Geoquímica effective if and when the article is accepted for publication. The author(s) warrant(s) that his/her/their contribution is original and that he/she/they has/have full power to make this grant. The author(s) sign(s) for and accept(s) responsibility for releasing this material The copyright transfer covers the exclusive right and license to reproduce, publish, distribute and archive the article in all forms and media of expression now known or developed in the future, including reprints, translations, photographic reproductions, electronic form (offline, online) or any other reproductions of similar nature.
Author(s) may self-archive an author-created version of his/her/their submitted version, accepted version and final published article on his/her/their own website and or in his/her/their institutional repository. He/she/they may also deposit this version on his/her/their funder’s or funder’s designated repository at the funder’s request or as a result of a legal obligation.
The author(s) retain(s) the right to use his/her/their submitted version, accepted version and final published article for his/her/their further scientific career by including the final article published by Geochimica Brasiliensis in other publications such as dissertations, theses and postdoctoral qualifications provided acknowledgement is given to the original source of publication.
After submission of the agreement signed by the corresponding author(s), changes of authorship or in the order of the authors listed will not be accepted by Sociedade Brasileira de Geoquímica.
Title of article:
Author(s):
Author’s signature:
Place and Date:
