U-Pb zircon age, geochemistry and petrogenesis of Mesoarchean anorthositic rocks from the Holenarsipur Greenstone Belt, Western Dharwar Craton: Implications for accretionary tectonics in southern India

The Doddakadanur Anorthosite Complex is a well-preserved sequence of anorthosites, gabbroic anorthosites, and anorthositic gabbros intrusive into amphibolites of the Mesoarchean Holenarsipur Greenstone Belt in the Western Dharwar Craton of southern India. Although the whole sequence is metamorphosed at upper amphibolite to lower granulite facies conditions, igneous cumulus texture is preserved in many of these rocks. The peak P-T conditions corresponding to metamorphic resetting, synchronous with 2.5 Ga regional metamorphism, is estimated to be similar to 650-700 degrees C and 7-11 kbar. The major and trace elemental systematics suggest a moderately fractionated parental magma (La/Yb)n = 3.3) with an overall tholeiitic affinity. The trace elemental systematics of these rocks indicates enrichment of the magma source regions by subduction-derived fluids. Uranium-Pb zircon ages yield an emplacement age of 3242 +/- 17 Ma and also help to constrain two metamorphic events at 3159 +/- 25 Ma and 2538 +/- 11 Ma. Considering the intrusive contact relationship between the anorthositic rocks of the Doddakadanur Anorthositic Complex and ultramafics of the Holenarsipur Greenstone Belt, the new U-Pb ages suggest that the mafic-ultramafic rocks of the Holenarsipur Greenstone Belt are at least 3.24 Ga old. Integrating the new age data with available ages for the different magmatic rocks of the region, a spatial and temporal link between anorthosite emplacement and crustal accretion processes in the Western Dharwar Craton can be established. On the basis of whole-rock geochemistry and mineral chemistry, we propose a convergent margin tectonic setting for the rocks of the Doddakadanur Anorthosite Complex.

Automated summary

The Doddakadanur Anorthosite Complex in the Western Dharwar Craton of southern India is a well-preserved sequence of anorthosites and related rocks intruded into amphibolites. The rocks have undergone metamorphism and preserve igneous cumulus textures, with peak P-T conditions estimated at 650-700 degrees C and 7-11 kbar. The geochemistry and ages of these rocks suggest enrichment by subduction-derived fluids and reveal a convergent margin tectonic setting for the complex.