Polychronous (Early Cretaceous to Palaeogene) emplacement of the Mundwara alkaline complex, Rajasthan, India: 40Ar/39Ar geochronology, petrochemistry and geodynamics

Abstract

The Mundwara alkaline plutonic complex (Rajasthan, north-western India) is considered a part of the Late Cretaceous–Palaeogene Deccan Traps flood basalt province, based on geochronological data (mainly 40Ar/39Ar, on whole rocks, biotite and hornblende). We have studied the petrology and mineral chemistry of some Mundwara mafic rocks containing mica and amphibole. Geothermobarometry indicates emplacement of the complex at middle to upper crustal levels. We have obtained new 40Ar/39Ar ages of 80–84 Ma on biotite separates from mafic rocks and 102–110 Ma on whole-rock nepheline syenites. There is no evidence for excess 40Ar. The combined results show that some of the constituent intrusions of the Mundwara complex are of Deccan age, but others are older and unrelated to the Deccan Traps. The Mundwara alkaline complex is thus polychronous and similar to many alkaline complexes around the world that show recurrent magmatism, sometimes over hundreds of millions of years. The primary biotite and amphibole in Mundwara mafic rocks indicate hydrous parental magmas, derived from hydrated mantle peridotite at relatively low temperatures, thus ruling out a mantle plume. This hydration and metasomatism of the Rajasthan lithospheric mantle may have occurred during Jurassic subduction under Gondwanaland, or Precambrian subduction events. Low-degree decompression melting of this old, enriched lithospheric mantle, due to periodic diffuse lithospheric extension, gradually built the Mundwara complex from the Early Cretaceous to Palaeogene time

Composition and U—Pb ages of apatite in the Amba Dongar carbonatite–alkaline complex, India

“…However, notable exceptions have been recognized recently. The new age constraints on the Mundwara and Sarnu‐Dandali complexes (Pande et al, ; Sheth et al, , see Section ) have revealed that some components of the alkaline magmatism are significantly older than regional Deccan volcanism. It is evident from these new age data and the data of Rathore, Venkatesan, and Srivastava () and Basu et al () that alkaline magmatism at Mundwara and Sarnu‐Dandali is polychronous and consists of distinct components which both predate and overlap with Deccan volcanism.…”

“…The Mundwara (68.53 ± 0.16 Ma) and Sarnu‐Dandali (68.57 ± 0.08 Ma) complexes have been dated using the 40 Ar– 39 Ar technique on biotite and alkali pyroxenite, respectively (Basu et al, ). Recently, Pande et al () have obtained 40 Ar/ 39 Ar plateau ages of 80.4 ± 0.4 to 84.6 ± 0.4 Ma on biotite separates from tephriphonolite and foid diorite, respectively, for the Mundwara complex. Nephelinite whole‐rock samples from the complex were also dated at 102.4 ± 0.6 and 110.4 ± 0.7 Ma.…”

“…Rock exposures in these areas are typically intrusive and silica‐undersaturated and include basanites, ijiolites, nepheline syenites, lamprophyres, gabbros, pyroxenites, and carbonatites. Pande et al (); Sheth, Pande, Vijayan, Sharma, and Cucciniello (); and Vijayan, Sheth, and Sharma () have collectively provided new geochemical data, emplacement ages, petrography, and field relations from these complexes. The Mundwara (68.53 ± 0.16 Ma) and Sarnu‐Dandali (68.57 ± 0.08 Ma) complexes have been dated using the 40 Ar– 39 Ar technique on biotite and alkali pyroxenite, respectively (Basu et al, ).…”

Buds of Santonian magmatism associated with Marion hotspot in southern India

“…A recent study by Sheth et al () reported syenites, nephelinite, phonolite, and rhyolite from the Sarnu‐Dandali alkaline complex in Rajasthan, north‐western India, which show 40 Ar/ 39 Ar ages of 88.9–86.8 Ma coinciding with the timeframe of flood basalt volcanism (~93–84 Ma) associated with the break‐up of India and Madagascar. The counterparts of all these rock suites in the Mundwara complex, corresponding to the post‐break‐up stage of the same flood basalt volcanism, show an age of 84–80 Ma as obtained from biotite‐bearing mafic plutonic rocks (Pande et al, ). The Sarnu‐Dandali rhyolites near Kamthai are geochronologically comparable to the St. Mary's Islands rhyolites on the southern Indian coast, their equivalents in the Vatomandry‐Ilaka‐Mananjary on the eastern Madagascar coast (Melluso et al, ) and the Ezhimala complex south of the St. Mary's Islands (Mohan et al, ).…”

REEs associated with carbonatite-alkaline complexes in western Rajasthan, India: exploration targeting at regional-scale

“…1; Table 1). The Mer-Mundwara carbonatite-alkaline complex intrudes the Neoproterozoic Erinpura Granite and displays a characteristic ring structure, wherein the alkaline-mafic rock suites form two ring structures and a dome (Pande et al, 2017). Carbonatites mainly occur in the form of linear dykes at Mer-Mundwara.…”