Proterozoic mafic volcanism in the Aravalli-Delhi orogen, North-western India: geochemistry and tectonic framework

Abstract

The Aravalli-Delhi orogen in Rajasthan and northern Gujarat, NW India, hosts extensive bodies of mafic metavolcanic rocks within the Archaean Banded Gneissic Complex (BGC) basement and in the Proterozoic supracrustal belts of Bhilwara, Aravalli, Jharol and Delhi. There is no significant occurrence of mafic dykes in these terrains. All metavolcanic rocks within the supracrustal belts show typical tholeiitic compositions except for the samples from the Basantgarh area of the Delhi belt, which show calc-alkaline nature. The Bhilwara belt and Aravalli belt samples show light rare earth elements (LREE) enrichment, the Jharol belt samples are predominantly LREE depleted, whereas the Delhi belt samples show wide variations from slightly depleted through flat to highly fractionated REE patterns. Multi-element patterns are consistent with the REE patterns in terms of enrichment or depletion for the large ion lithophile elements (LILE) and with respect to high field strength elements (HFSE). The incompatible trace elements ratios (e.g. Nb/Zr, Y/Zr, Ce/Nd, etc.) are similar for the metavolcanic rocks of the Bhilwara and Aravalli belts. Samples from the Jharol and Delhi belts differ amongst themselves as well as with those from the Bhilwara and Aravalli belts. The Delhi belt samples show large variations in incompatible trace element ratios. Comparison of multi-element patterns for the volcanic rocks from the Aravalli-Delhi orogen with those from various modern tectonic settings, potentially allows constraining their tectonic setting of eruption. The tholeiitic metavolcanic rocks of the Bhilwara belt erupted along the incipient divergent eastern margin of the Archaean BGC continent and the basal Aravalli and Jharol metavolcanic rocks along its rifted western margin. The Delhi belt metavolcanic rocks indicate the evolution of the Delhi island arc through eastward subduction and emplacement of the Basantgarh-Ajari and Ranakpur-Desuri metavolcanic rocks close to the Phulad-Jetgarh suture zone on the western fringe of the arc and those of the Ambaji-Deri region along back arc spreading zones to the east, where protracted rifting led to the emplacement of gabbro-syenite plutons.