Understanding the Neoproterozoic geodynamics of NW India: clues from tectonomagmatic studies of the Cryogenian Sindreth Basin at the eastern Malani Igneous Province
Final Report Abstract
Small-scale Neoproterozoic basins within the Marwar block of NW India have been repeatedly target of petrological, geochemical and geochronological work and results from these regionally restricted areas have been transferred tothe whole MIS, one of the most voluminous felsic large igneous provinces on Earth. Geochemical composition of the MIS rocks was so far poorly defined and most projects concentrated on regional age-dating and major element analysis. It was common sense that the MIS rocks comprise peraluminous as well as metalumious felsic rocks classified as A-type magmatites. Mafic dykes are spread all over the MIS. Our study here concentrated on the geochemical classification of the Erinpura and Malani granites using major and trace elements as well as Sr and Nd isotopes. We here present new results on the source rocks for Erinpura granites and MIS , their host rock and the basement of MIS magmatites. The geochemical and isotope data suggest that the Erinpura granites represent a first step melting product of the Archean BGC, with possibly some mixing with a mafic component. In contrast, the Malani granites are further developed and have a much more mafic source compared to the Erinpura granites and a heterogenous source, probably including more juvenile components. We could substantiate the spatial discrimination of the MIS terrain into regions with positive and negative εNd values and relate the inferred lineament separating these two areas to represent a lithospheric-scale boundary. The deformed basement west of our study area shows a positive εNd value (+4.7), while all the Erinpura magmatites east of the inferred boundary are characterized by negative values (-2 to -8). This leads to our hypotheses that the crustal structure has been formed during a pre-Malani event and that the MIS rocks just mimic a preexisting crustal configuration which has been developed in the early Neoproterozoic. A reactivation of N-S trending segments of this system during later rifting (Deccan) is suspected. We could reject the model of ocean floor stratigraphy and an active continental margin setting delineated by small scale Neoproterozic basins as has been proposed by earlier studies. Basaltic MIS rocks indicate that the mantle source was not metasomatized by hydrous fluids or melts and thus, we do not find evidence for the formation of the MIS in a subduction zone as suspected by previous workers. Rather, we suggest that MIS rocks were formed in a continental rift system, potentially with the influence of a deep mantle plume. A more detailed analyses and comparison with similar settings is underway. Our findings call for the need of a revision of pre-existing models for the Neoproterozoic evolution of NW India. In addition our results leave some open questions, which we would like to address in a new project proposal. It is necessary to better define the boundaries and the characteristics of the two lithospheric mantle parts E and W of the Jaswandtpura fold belt. Thus we would like to study basement samples from the Barmer and Nagarparkar areas and we plan for a new proposal in continuation of the here reported project.
Publications
- Uranium enrichment along fault planes in the Sindreth basin, NW India, inferred from in-situ GR measurements – possible sources and pathways. Conference: Sedimentary Basins, Jena 23 - 25 September 2015
Anetzberger, L., Donhauser, I., Scharfenberg, L., Bestmann, M., de Wall, H.
- 2016. Treasure rock fabric: Integrating multiple fabric analysis techniques in refining the Neoproterozoic tectonic evolution of NW India. Geological Society of India Seminar: Developments in Geosciences in the Past Decade – Emerging trends for the future, Indian Institute of Technology Kharagpur, 21-23. October
de Wall, H.
- (2017). Continental rift-setting and evolution of Neoproterozoic Sindreth Basin in NW-India, J. Earth System Sciences 126, 90
Schöbel, S., Sharma K. K., Hörbrand, T., Böhm, T., Donhauser, I., de Wall, H.
(See online at https://doi.org/10.1007/s12040-017-0855-6) - (2018). Evolution and tectonic setting of the Malani – Nagarparkar Igneous Suite: a Neoproterozoic Silicic LIP in NW India-SE Pakistan, J. Asian Earth Sciences 160, 136-158
de Wall, H., Pandit, M.K., Donhauser, I., Schöbel, S., Wang, W. Sharma, K.K.
(See online at https://doi.org/10.1016/j.jseaes.2018.04.016)
