Heat flow and crustal thermal structure in the Late Archaean Closepet Granite batholith, south India

Abstract

The Late Archaean Closepet Granite batholith in south India is exposed at different crustal levels grading from greenschist facies in the north through amphibolite and granulite facies in the south along a *400 km long segment in the Dharwar craton. Two areas, Pavagada and Magadi, located in the Main Mass of the batholith, best represent the granitoid of the greenschist and amphibolite facies crustal levels respectively. Heat flow estimates of 38 mW m -2 from Pavagada and 25 mW m -2 from Magadi have been obtained through measurements in deep (430 and 445 m) and carefully sited boreholes. Measurements made in four boreholes of opportunity in Pavagada area yield a mean heat flow of 39 ± 4 (s.d.) mW m -2 , which is in good agreement with the estimate from deep borehole. The study, therefore, demonstrates a clear-cut heat flow variation concomitant with the crustal levels exposed in the two areas. The mean heat production estimates for the greenschist facies and amphibolite facies layers constituting the Main Mass of the batholith are 2.9 and 1.8 lW m -3 , respectively. The enhanced heat flow in the Pavagada area is consistent with the occurrence of a radioelement-enriched 2-km-thick greenschist facies layer granitoid overlying the granitoid of the amphibolite facies layer which is twice as thick as represented in the Magadi area. The crustal heat production models indicate similar mantle heat flow estimates in the range 12-14 mW m -2 , consistent with the other parts of the greenstone-granite-gneiss terrain of the Dharwar craton.

Crustal architecture beneath Madurai Block, southern India deduced from magnetotelluric studies: Implications for subduction–accretion tectonics associated with Gondwana assembly

“…The arc crust is thickest towards the northern domain and becomes thinner and disrupted towards the south in the MT model, probably indicating a combined process of tectonic erosion as well as thermal and material erosion through mantle upwelling. The mantle heat flow of Madurai Block (Ray et al, 2003;Sukanta Roy et al, 2008) is much higher (23-32 mW/m 2 ) than that of other granulite provinces such as the Kapuskasing uplift region (9-13 mW/m 2 ), Voisey Bay (10-14 mW/m 2 ) of Canadian shield region; Egersund anorthosite (8-13 mW/m 2 ) of Baltic shield, among other examples, except for a similarity with that of the Kola Peninsula (25-31 mW/m 2 ) of Baltic shield (Ray et al, 2003). The markedly higher mantle heat flow values in Madurai Block when compared to adjacent Dharwar craton (11-16 mW/m 2 ) and other granulite provinces mentioned above suggests an upwelled mantle beneath the Madurai Block.…”

“…Seismic reflection survey from Kalugumalai to Vattalkundu in the central Madurai Block (Rajendra Prasad et al, 2007) detected generally southern dipping of reflectors with a domal pattern at the center which was thought to represent block uplift (more discussion later). Recent heat flow studies (Ray et al, 2003;Sukanta Roy et al, 2008) indicated the Southern Granulite Terrain possess large heat flow values (28-56 mW/m 2 ) when compared to Dharwar craton (25-40 mW/m 2 ) and mantle heat flow values in SGT (23-32 mW/m 2 ) are significantly higher than Dharwar craton (11-16 mW/m 2 ).…”

“…2) in an attempt to understand the Santosh and Sajeev, 2006). Seismic reflection profile (Rajendra Prasad et al, 2007), heat flow data (Ray et al, 2003;Sukanta Roy et al, 2008) and MT stations are also shown. Geoelectric structure along the Palani-Kolattur (white line) profile presented in Naganjaneyulu and Santosh (2010) is shown in Fig.…”

The nature and thickness of lithosphere beneath the Archean Dharwar Craton, southern India: A magnetotelluric model

“…Several heat flow data were added to the existing information from the Dharwar Craton and the Deccan Traps region (Fig. 2) (Roy and Rao, 2000;Roy et al, 2008). However, as can be seen from The heat flow values shown in Fig.…”

Entropy-information perspective to radiogenic heat distribution in continental crust

“…Seismic images of the compression terrains show that the rocks at depth are exposed at the surface. Thus, from surface exposures of the rocks, depth distribution of rock compositions have been worked out for several continents (Nicolaysen et al, 1981;Roy et al, 2008). Concentration of radioactive elements in exposed rocks formed under different pressure-temperature conditions provided models for depth distribution of radioactive elements under the assumption that no further differentiation of radioactive elements took place since the major crust forming events.…”