The Assembly of East Gondwana: A Proterozoic Perspective from India

Bhander Sandstones-Rajastan

Supported by the National Science Foundation EAR04-09101

Project Summary
The Assembly of East Gondwana : A Proterozoic Perspective from India

Summary

                The Proterozoic unity of East Gondwana is the topic of considerable debate.  Although there are myriad options regarding the exact timing of East Gondwana amalgamation, they can be simplified as follows.  Rogers (1996) suggested that the cratonic core of East Gondwana was the ‘original’ continent formed during the Archean time ( Ur ).  Yoshida and others (2003) argued that East Gondwana assembly occurred during the Mesoproterozoic culminating with ‘Grenville’ age events assembling various parts of East Antarctica to the “ Ur ” protocontinent.  Meert (2003), Fitzsimons (2000) and Powell and Pisarevsky (2002) argue that East Gondwana assembly took place in parallel with the assembly of greater Gondwana in the Late Neoproterozoic to Early Cambrian time. This project is aimed at improving the paleomagnetic database for East Gondwana via the acquisition of radiometric ages for well-resolved paleomagnetic poles, field tests and additional paleomagnetic and geochronologic data from mafic dikes, kimberlites and sedimentary sequences in India .  These data will then be used to test myriad models of supercontinent assembly and dispersal by comparing the results to the published literature and in conjunction with ongoing projects.  The proposal targets rocks ranging in age from 800 Ma to 2.1 Ga that have promising preliminary paleomagnetic data and/or good age control.  Well constrained ages and paleomagnetic poles may also help test models of true polar wander and rapid plate motion proposed for Proterozoic times.        

 Intellectual Merit

                The research outlined in this proposal is meant to both complement and expand our current knowledge of Proterozoic paleogeography.  Results from the Indian subcontinent can be used in developing global paleogeographic models through detailed analysis of existing paleomagnetic and geochronologic data from other continents.  Paleomagnetic data can provide evidence for the orientation of geologic features such as orogenic belts and dikes used in developing supercontinental hypotheses. In addition to published studies, potential correlations are possible due to ongoing and currently supported paleomagnetic research in Amazonia (R. Trindade, D’Agrella-Filho and NSF post-doctoral fellow E. Tohver, Brazil), Australia, South China and Siberia (Z.X. Li, S. Pisarevsky, M. Wingate Tectonics Special Research Centre, Australia; David Evans-NSF supported research, USA), Baltica (L. Pesonen, S. Mertanen, T. Torsvik, Finland and Norway), Laurentia (J. Geissman, New Mexico, S. Harlan, Virginia, D. Evans-NSF supported research, USA).  New paleomagnetic and geochronologic data from India will add to the database and allow us to more easily test the proposed continental configurations.  The paleomagnetic data will also allow us to document drift and apparent polar wander rates for India that can be compared to other continents.  Global geodynamic proposals such as true polar wander and inertial interchange true polar wander require coverage from all continents in order to be critically evaluated. 

Broader Impacts and Personnel

                The University of Florida is committed to enhancing geologic education in the USA through the active recruitment of under-represented groups.  We will involve undergraduate students in this research in order to train future generations of geologists and have requested funds to support undergraduate research projects within the current proposal.  Our work also involves the assistance of Indian colleagues from the University of Rajasthan (see attached letter of support from Manoj Pandit) and M. Santosh (southern India ). The work will also be supported by a consortium of Indian geologists who are members of the Gondwana Research Group (see letter of support from M. Santosh).  These types of collaborative efforts allow investigators in 2^nd and 3^rd world countries to gain exposure to modern scientific methods and publish in the geologic literature.  Meert has actively involved foreign colleagues in his work elsewhere in East Africa and Madagascar . Results from this project will be shared via the published literature (i.e. with other scientists); with undergraduate and graduate students (via formal and informal departmental seminars) and with the general public.  PI Meert has been active in giving talks at all levels of K-12 in Indiana and is making efforts to continue this at Florida .  PI Meert is participating in a program called First-year Florida aimed at easing the transition from high school to the University.  One of the features of this course is helping the students become acquainted with cutting-edge research projects at Florida .  In addition, our K-12 outreach involves summer research initiatives that bring underrepresented groups to UF for summer research opportunities.    One of these programs ( University of Florida Summer Science Training Program ), involves the training of a high school junior in some aspect of geological research (7 weeks long).  The PI’s most recent participant has submitted an article that is currently in review (Flanigan and Meert).

Project Participants
Dr. Joseph G. Meert (Project Director and all around nice guy)
Dr. Manoj K. Pandit (Project Leader in India and an even nicer guy)
Vimal Pradhan (Ph.D. student and Inspirational Leader)
Shawn Malone (M.Sc. student and Laboratory Rat)
Laura Gregory (M.Sc. student and all around nice gal)
Luke Gommerman (B.Sc. student)

Major Findings & Publications Associated with this proposal:

Gregory, L.C., Meert, J.G., Pandit, M.K. and Pradhan, V., Paleomagnetic and geochronologic study of Malani late phase mafic dikes: implications for the Neoproterozoic drift history of India , Precambrian Research,  under review. pdf of submission

Pradhan, V.R., Pandit, M.K. and Meert, J.G., A cautionary note on the age of the paleomagnetic pole obtained from the Harohalli dyke swarms, Dharwar craton, southern India, in: R.K. Srivastava et al. (eds) Geochemistry  and Geophysics of Indian Dykes,   Indian Association  of Geochemists Special publication. pdf of submission.z

Malone, S.J., Meert, J.G., Pandit, M.K., Kamenov, G.D., Pradhan, V.R. and Tamrat, E., Paleomagnetism and Detrital zircon geochronology of the Upper Vindhyan Sequence, Son Valley and Rajasthan, India: A possible downward revision in the age of the Purana Basins, Precambrian Research, submitted. 

Meert, J.G and Lieberman, B.S., The Neoproterozoic Assembly of Gondwana and its relationship to the Ediacaran-Cambrian Radiation, Gondwana Research, in press, doi;10.1016/j.gr.2007.06.007.  pdf of submission

Gregory, L.C., Meert, J.G., Tamrat, E., Malone, S., Pandit, M.K. and Pradhan, V., A paleomagnetic and geochronologic study of the Majhgawan kimberlite, India : Implications for the age of the Upper Vindhyan Supergroup, Precambrian Research , v. 149, 65-75. pdf of proofs. (Currently Dec 2006- The 11th most downloaded article)

Gommerman, L., Pradhan, V., Meert, J.G., Pandit, M.K. and Gregory, L.C., 2006. Paleomagnetic study of Proterozoic dikes in India, GSA Abstracts w/programs, paper 143-5. pdf of abstract.

Malone, S.J., Meert, J.G., Pandit, M.K., Endale, T. and Pradhan, V., 2006. Magnetostratigraphy and geochronology of the Vindhaynchal basin, India, GSA Abstracts w/program, paper 164-8, pdf of abstract

Gregory, L.**, Meert, J.G., Pandit, M.K., Pradhan, V.*, 2005. Paleomagnetic study of mafic dikes in India : implications for supercontinent assembly and dispersal, GSA Abstracts w/Programs, v37,  303.

Malone, S.J.*, Meert. J.G., Pandit, M.K., Tamrat, E.#, Pradhan, V.*, 2005. A paleomagnetic view of the Vindhyanchal basin, India , GSA Abstracts w/Programs, v37,  p. 207.

Meert, J.G., Pandit, M.K., Tamrat, E.#, Sohl, L., Banerjee, D., Pradhan, V.*, Malone, S.* and Gregory, L.**, 2005.  Preliminary paleomagnetic results from the Vindhyan Supergroup, India , Australia Supercontinent Meeting.

Gommerman, L., Meert, J.G., Pradhan, V. and Pandit, M.K., Paleomagnetic study of Proterozoic dikes in India, GSA Abstracts with programs, 2006 submitted.

Malone, S.J., Meert, J.G., Pradhan, V. and Pandit, M.K., 2006. Magnetostratigraphy and geochronology of the Vindhyanchal Basin, India, GSA Abstracts w/programs, submitted.

Gregory, L.C., Meert, J.G., Pandit, M.K., Torsvik, T.H. and Bingen, B., 2006. A Paleomagnetic and Geochronologic Study of Malani Mafic Dikes in Northwest India: Implications for the Configuration of Rodinia, AGU abstracts, 2006.

Pradhan, V., Pandit, M.K. and Meert, J.G.,  Paleomagnetic and Geochronologic study of Proterozoic dikes in Central India, AGU Abstracts, 2006.

Age of the Harohalli Dikes

     Radiometric dating of mafic intrusive and extrusive rocks poses a problem due to the paucity of dateable minerals. A significant amount of paleomagnetic work has been done for the Precambrian mafic dyke swarms of Harohalli region of the Dharwar craton, southern India.  Two suites of dikes are present in the Harohalli region.  The first, a series of ~E-W trending doleritic dikes have an Rb-Sr whole rock isotopic age of 2370 ± 230 Ma and a U-Pb age of 2365.5 ± 1.1 Ma. Isotopic ages reported for the ~N-S trending younger suite of dikes range between 800-850 Ma.    We sampled three dykes in the Harohalli region with the goal of providing a robust age for the younger alkaline dykes and also to add additional sites to the paleomagnetic pole.  A new paleomagnetic pole is calculated at 24.9° S, 258° E (A95=15°).  A secondary component observed in this and previous studies yields a paleomagnetic pole at 76.5° S, 68.8° E (a₉₅=8.4°) that we interpret as a remagnetization of Ediacaran age.  Two of the dikes yielded zircon crystals and fragments for U-Pb dating using LA-MS-ICP-MS methods.  Six laser spots from three different zircons yielded a concordant U-Pb age of 1192 ± 10 Ma. In addition, a discordia fit using these grains and several fragments yielded a lower intercept age of 506 ⁺¹⁸/_-19 Ma and an upper intercept at 1212 ⁺²⁰/_-21 Ma.  The lower age may represent Pb-loss event associated with the final assembly of Gondwana and the upper intercept is interpreted as being close to the crystallization age of the dikes.  A second dike yielded a total of 15 concordant zircons with an age of 2941 ± 14.2 Ma (MSWD=1.3) reflecting inheritance from the Peninsular gneisses.

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We also now have a preliminary age for the Majhgawan Kimberlite of 1073.5 +/- 13.7 Ma (⁴⁰Ar/³⁹Ar on phlogopite samples)

Winter 2005/2006 Field Work was conducted from 150 dikes in the Proterozoic of India (including samples from the Harohalli dikes)

Some Field Shots

       
Closepet Granite-Andrha Pradesh                                            Dike in Closepet Granite

The Malani Rhyolites Paleomagnetic Pole

Photo of the Malani Dikes (courtesy of Google Earth)

New U-Pb age:

           
Concordia plot of Malani Rhyolite Sample                    Reverse directions in dikelets with an overprint by the
                                                                                    larger dikes.  Positive baked contact test.

The Upper Vindhyan Sequence

 We have completed demagnetizing samples from the Upper Vindhyanchal basin (Kaimur, Rewa and Bhander Groups).

Map of the Vindhyanchal basin in India.

Reverse and Normal Paleomagnetic directions in the Bhander and Rewa Sandstones and Limestones

Figure: Normal and reverse polarity VGP's from the Bhander (purple, red) sandstones, the
Lhakeri limestone (green) and the Rewa sandstones (orange)

As part of the study we have also removed detrital zircons from the Bhander-Rewa sandstones (Rajasthan) in order to help
constrain the age of these units.

Figure: (left): Detrital zircon ages obtained from the Upper Vindhyan rocks.  (right) Example of concordia plots for some of the detrital zircons used in
our study.  We note the lack of Malani-age (771 Ma) zircons in the rocks despite close proximity to this 50,000 km^2 felsic province.