Geochronology and Geochemistry of the Lakhna dykes swarm of the eastern Bastar Craton, Central India and its Implication on tectonics setting

Kamleshwar Ratre¹, Tapas Kumar Biswal¹, Bert De Walaev²

1Department of Earth Sciences, Indian Institute of Technology Bombay; 2Principal Consultant, srk Consulting (Australasia) Pty Ltd., Australia.

kratre@iitb.ac.in

Bastar Craton around Lakhna in the western part of the State Odisha, India is occupied by 2.5 Ga old granites that have been intruded by N-S and WNW-ESE trending Lakhna dyke swarm which varies in composition from rhyolite, dolerite, trachyte to alkali gabbro. SHRIMP geochronology of the dykes indicates a 1450 Ma age of emplacement, this has constrained the initiation of deposition of overlying Purana Groups of rocks in the Bastar Craton to < 1.4 Ga [1]. Major, trace and REE geochemistry of the dykes suggest rhyolites are peraluminous and potassic, enriched in Rb, Zr, Hf, Nb and Ta, poor in Ba, Ti and highly fractionated REE pattern with LREE enrichment and –ve Eu anomaly. Dolerites show tholeiitic to subalkaline, meta-aluminous character, richer in LILE and Ti, but poorer in Ba, Zr and Nb, poorly REE fractionated. Trachytes are ultrapotassic, unfractionated REE, enriched in LILE and Ti. The alkali gabbros show phonolite composition with dominance of alkali feldspar and hornblende in the rock; they are enriched in LILE but do not show good fractionation of REE. Through there are variations, in many plots, the rhyolite and alkali gabbro form single trend line while dolerite and trachyte follow another. Therefore, this preliminary study suggests that the rhyolite and alkali gabbro might have come from an enriched mantle while the dolerite and trachyte might have come from normal asthenospheric mantle. Tectonic setting derived from various discriminatory diagrams suggests that except for few dolerite most of the dykes show within plate continental setting.

References:

1. Kamleshwar Ratre, Bert De Waele, Tapas Kumar Biswal, Suspa Sinha (2010). Evidence of Eoarchaean crust in the Bastar Craton and new zircon U-Pb SHRIMP Geochronology for the 1.4 to 0.51 Ga Purana Basin (Khariar), Eastern Indian Peninsula. Journal of Asian Earth Sciences, Vol.39, pp.565-577.

Mesozoic-Cenosoic North Kazakhstan tectonic activation, evidence by apatite fission track analyses

Kokh D.A., Soloboeva E.V., Buslov M.M.

V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia

Last decade is marked by advanced research activity associated with thermal history modeling of Central Asia regions. Those models constrain a low temperature evolution of sampled rocks. At present days a apatite fission track analysis data is published for different regions (etc. Kirgiz Tien-Shan, Kazakhstan Altai, Mongolia, China). Thermal models manifest both mesozoic and Cenozoic intraplate reactivation in Asia. Incorporate with geological data it was proposed that Mesozoic orogeny related to distant effect of Gondvana-derived terranes to Eurasia margin convergence. Central Asian orogen grew in same way caused by distant effect of India-Eurasia collision. North Kazakhstan is within, as it considered, stable Kazakhstan plate far (1500-2000) from mesozoic-cenozoic reactivation zones. Kokchetav zone located north and north-west from Tien-Shan and Altai-Sayan reactivation zones respectively.

Pattern of thermochronological models reveals two stages. First one kept on from elder than 130 Ma to 3 Ma and characterized by midangle t-T path recorded cooling up to 60°C. Second stage took place from 3 Ma to present with fast cooling from 60°C to surface temperature. Whereas normal geothermal gradient (30° per 1 km) Kokchetav region denudate more than 2500 m in frist stage and 750-900 m in following period. Thus the denudation speed can be calculated, first stage has about 20-25 m/Ma, second – 250-300 m/Ma.

Comparison of data gained from Kazakhstan, Tien-Shan and Altai regions help in understanding of the collision consequences. Tien-Shan and Altai rocks exhibit three step thermal history models. The first stage resumed until 130 Ma and 80 Ma respectively with similar denudation speed about 2-3 km/Ma. Jurasic (200-130 Ma) tectonic activity in Tien-Shan related to Trarim-Eurasia collision and North China-Eurasia collision has affected the Altai territory in Cretaceous (140-80 Ma). During second stage the both regions rocks uplifted for about 10-20°C and it took 120 Ma in Tien-Shan and 75 Ma in Altai. This periods are considered as peneplation time when no significant tectonic activity recorded. Last bend in thermochronological path shows fast cooling of the rocks that can be interpreted as denudation with 150-180 m/Ma in Tien-Shan and 250-300 m/Ma in Altai velocities. That are correspond with North Kazakhstan denudation speed.

Thus it is concluded that orogeny and tectonic reactivation of shear zones attributed to convergence events. Resent 3Ma reactivation in Kazakhstan considered as far distant effect of India-Eurasia collision.

T he investigations carried out with support of “Interdisciplinary project of integration fundamental surveys SB RAS N 261” and grant School 7201.2012.5

References:

1. J. De Grave, M.M. Buslov, P. Van den haute. Distant effect of India-Eurasia convergence and Mesozoic intracontinental deformation in Central Asia: Constrains from apatite fission-track thermochronology.// Jornal of Asian Earth Sciencees, 2007, v. 29, pp. 188-204

2. J. De Grave, P. Van den haute. Denudation and cooling of the Lake Teletskoye Region in the Altai Mountains (South Siberia) as revealed by apatite fission-track thermochronology.// Tectonophysics. 2002. T. 349.pp. 145-159

3. J. De Grave, M.M. Buslov, P. Van den haute. Intercontinental deformation in Central Asia: distant effect of India-Eurasia convergence revealed by apatite fission-track thermochronology.// Himalayan Joranl of Sciences. 2004. V. 21.

4. М.М. Буслов. Д.А. Кох. Де Граве И. Мезозойско-Кайнозойская тектоники и геодинамика Алтая, Тянь-Шаня и Северного Казахстана по результатам трекового датирования апатитов.// Геология и Геофизика. 2008. Т. 49. N 9. сс. 862-870.