Petrogenetic evolution of Cretaceous Samchampi-Samteran Alkaline Complex, Mikir Hills, Northeastern India

Author(s)

Abhishek Saha, Sohini Ganguly, Jyotisankar Ray, Christian Koeberl, Martin Thoeni, C. Sarbajna, S. S. Sawant

Abstract

The Samchampi (26° 13′N: 93° 18′E)-Samteran (26° 11′N: 93° 25′E) alkaline complex (SSAC) occurs as an intrusion within Precambrian basement gneisses in the Karbi-Anglong district of Assam, Northeastern India. This intrusive complex comprises a wide spectrum of lithologies including syenite, ijolite-melteigite, alkali pyroxenite, alkali gabbro, nepheline syenite and carbonatite (nepheline syenites and carbonatites are later intrusives). In this paper, we present new major, trace, REE and Sr-Nd isotope data for different lithologies of SSAC and discuss integrated petrological and whole rock geochemical observations with Sr-Nd isotope systematics to understand the petrogenetic evolution of the complex. Pronounced LILE and LREE enrichment of the alkaline-carbonatite rocks together with steep LREE/HREE profile and flat HREE-chondrite normalized patterns provide evidence for parent magma generation from low degree partial melting of a metasomatized garnet peridotite mantle source. LILE, HFSE and LREE enrichments of the alkaline-silicate rocks and carbonatites are in agreement with the involvement of a mantle plume in their genesis. Nb-Th-La systematics with incompatible trace element abundance patterns marked by positive Nb-Ta anomalies and negative K, Th and Sr anomalies suggest contribution from plume-derived OIB-type mantle with recycled subduction component and a rift-controlled, intraplate tectonic setting for alkaline-carbonatite magmatism giving rise to the SSAC. This observation is corroborated by enriched

⁸⁷Sr/

⁸⁶Sr

_initial (0.705562 to 0.709416) and

¹⁴³Nd/

¹⁴⁴Nd

_initial (0.512187 to 0.512449) ratios for the alkaline-carbonatite rocks that attest to a plume-related enriched mantle (~ EM II) source in relation to the origin of Samchampi-Samteran alkaline complex. Trace element chemistry and variations in isotopic data invoke periodic melting of an isotopically heterogeneous, metasomatized mantle and generation of isotopically distinct melt batches that were parental to the different rocks of SSAC. Various extents of plume-lithosphere interaction also accounts for the trace element and isotopic variations of SSAC. The Sr

_initial and Nd

_initial (105 Ma) isotopic compositions (corresponding to ε

_Nd values of − 6.37 to − 1.27) of SSAC are consistent with those of Sung Valley, Jasra, Rajmahal tholeiites (Group II), Sylhet Traps and Kerguelen plateau basalts.

Organisation(s)

Department of Lithospheric Research

External organisation(s)

Council of Scientific and Industrial Research (CSIR) and JSS MVP, Goa University, University of Calcutta, Naturhistorisches Museum Wien (NHM), Atomic Minerals Directorate for Exploration and Research, National Geophysical Research Institute India

Journal

Gondwana Research

Volume

48

Pages

237-256

No. of pages

20

ISSN

1342-937X

DOI

https://doi.org/10.1016/j.gr.2017.04.022

Publication date

08-2017

Peer reviewed

Yes

Austrian Fields of Science 2012

105105 Geochemistry, 105120 Petrology

Keywords

ASJC Scopus subject areas

Geology

Portal url

https://ucrisportal.univie.ac.at/en/publications/3a806920-425a-43a2-9165-57af5bf2b56d