Petrology and Nd–Sr isotopic composition of alkaline lamprophyres from the Early to Late Cretaceous Mundwara Alkaline Complex, NW India: evidence of crystal fractionation, accumulation and corrosion in a complex magma chamber plumbing system

Abstract

The Early to Late Cretaceous Mundwara alkaline complex (comprising the Musala, Mer and Toa plugs) displays a broad spectrum of alkaline rocks closely associated in space and time with the Deccan Large Igneous Province (DLIP) in NW India. Petrology and Nd-Sr isotopic data on two youngest and altogether compositionally different lamprophyre dykes of the Mundwara alkaline complex are presented in this paper to understand their petrogenesis and also to constrain the magmatic processes responsible for generation of the rock spectrum in the complex (pyroxenite, picrite ankaramite, carbonatite, shonkinite, olivine gabbro, feldspathoidal and foid-free syenite). The two lamprophyre dykes occurring in the Mer and the Musala hills are referred to as basaltic camptonite I and camptonite II, respectively. The basaltic camptonite-I is highly porphyritic and contains olivine, clinopyroxene and magnetite macrocrysts embedded within the groundmass of microphenocyrsts composed of clinopyroxene, phlogopite, magnetite and feldspar. Whereas camptonite-II, with more or less similar texture, contains amphibole, biotite, magnetite and clinopyroxene within the microphenocrystic groundmass of amphibole, biotite, apatite and feldspar. Pyroxenes are chemically zoned and display corrosion of the cores revealing that they are antecrysts developed during early stages of magma evolution and later on inherited by more evolved magmas. Mineral chemistry and trace element composition of the lamprophyres reveal that fractional crystallisation was a dominant process. Early segregation of olivine + Cr-rich clinopyroxene + Cr-spinel from a primary hydrous alkali basalt within a magmatic plumbing system is inferred which led to the generation of basaltic camptonitic magma (M1) forming the Mer hill lamprophyre. Subsequently, progressive fractionation of pyroxene and Fe-Ti oxides from the basaltic camptonitic (M1) magma generated camptonitic (M2) magma forming the Musala hill lamprophyre. Both lamprophyre dykes on the Sr-Nd isotopic array reflect plume type asthenospheric derivation which largely corresponds to the Réunion plume and other alkaline rocks of the Deccan LIP. Our study brings out a complex sequence of processes such as crystal fractionation, accumulation and corrosion in the magmatic plumbing system involved in the generation of the Mundwara alkaline complex.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5277073

Origin of Lower Cretaceous quartzose arenites in northern India and the Indus Basins of Pakistan—The result of provenance composition, weathering or diagenesis?

“…700 m in Ramgarh‐1 in the Jaisalmer Basin, NDR database, 2021; maximum 1800 m of Cretaceous recorded in the Jaisalmer Basin, Zadan & Arbab, 2015; <200 m on the Saraswati Terrace, Barmer Basin, Dolson et al, 2015). Strata were then subaerially exposed at the end‐Cretaceous Period when the main Palaeocene rifting in the Barmer Basin took place (Dolson et al, 2015; Millett et al, 2021; Naidu et al, 2017; Sharma et al, 2021; Vijayan et al, 2016). Although it is not possible to be definitive regarding the extent of diagenesis at this unconformity surface, the uplift was of long duration and resulted in the removal of all Upper Cretaceous sediments (Sheth, 2007).…”

Syn‐rift volcanism in the Barmer Basin: An intra‐basin extrusive complex at the northern limit of the Deccan volcanic province in India

“…Sheth (2016) and Krishnamurthy (2019) discussed the possibility of the presence of more than one sub‐crustal magma chambers in the evolution of the Deccan lavas. Non‐basaltic rocks (including rhyolites, andesitic tuffs, lamprophyres and andesites) are all common components of the DVP (Agrawal & Upadhyaya, 1991; Cucciniello et al, 2019; Cucciniello et al, 2020; Cucciniello et al, 2022; Krishnamacharlu, 1974; Sharma et al, 2021; Srivastava, 1989). The silicic rocks are considered to have been generated by partial melting of older granitic crust due to the proximity of large volumes of basic magma, but also by fractionation of basic melts (Chatterjee & Bhattacharji, 2008; Cucciniello et al, 2019).…”

The Hidden Magmatic Chamber from the Ponte Nova Mafic–Ultramafic Alkaline Massif, SE Brazil: Clues from Clinopyroxene and Olivine Antecrysts

“…These primitive diopside cores and their restricted evolution trend (Figure 4) imply the existence of a deeper magmatic chamber that could be connected to the shallow magmatic reservoir represented by the PN massif, in a complex plumbing system [3,30,64]. These relict cores can be classified as antecrysts, crystals that did not crystallize directly from the host magma in which they are contained, although they maintain a genetic relationship with the same system [3,10,29].…”

“…Although a quantitative determination of P estimates is not possible for the Ti-augite mantling and rim composition, their evolution trend suggests very low-P crystallization conditions (cf., [64,[72][73][74][75]). Ti-augite from all intrusions of PN presents a very positive correlation of Ti and the IV Al (Figure 5) [74] showed that there are compositional differences between high and low pressure clinopyroxenes based on trends of increasing Ti and IV Al at the expense of silica, the increase in the IV Al/ VI Al ratio and the increase in TiO 2 coupled with decreasing Mg# cpx .…”