Rb-Sr ages of Precambrian dolerite and alkaline dikes, southeast Mysore state, India

India's changing place in global Proterozoic reconstructions: A review of geochronologic constraints and paleomagnetic poles from the Dharwar, Bundelkhand and Marwar cratons

“…In this paper, we review our updated ∼1.2 Ga paleomagnetic pole from the Harohalli alkaline dyke swarm at 24.9 • S, 258 • E (␣95 = 15 • ; Pradhan et al, 2008) in an attempt to better constrain the position of India during this period. Pradhan et al (2008) reported concordant U-Pb age of 1192 ± 10 Ma that is far older than all previously published ages on the Harohalli and supposedly correlative dykes (Ikramuddin and Stuber, 1976;Anil Kumar et al, 1989;Devaraju et al, 1995). Discordant ages ranging from 580 to 1139 Ma was also calculated the zircon fragments of sample I5143 .…”

“…A high precision baddeleyite age of 1885.4 ± 3.1 Ma for the Pullivendla mafic sill from the Cuddapah basin has been interpreted to coincide with the widespread ∼1.9 Ga basaltic magmatism occurred in the widely separated Large Igneous Provinces (French et al, 2008). The whole rock Rb-Sr isochron age of 2370 ± 230 Ma (Ikramuddin and Stuber, 1976) and a Sm-Nd isochron age of 2454 ± 100 Ma (Zachariah et al, 1995) for other easterly trending dykes are further refined by a highly precise U-Pb baddeleyite age of 2367 ± 1 Ma (Halls et al, 2007). These age data suggest that most of the easterly dykes in the vicinity of Cuddapah are Paleoproterozoic in age and intruded during two major magmatic episodes centered at ∼2.1 and ∼2.4 Ga. …”

Precambrian crustal evolution of Peninsular India: A 3.0 billion year odyssey

“…The Bangalore dyke swarm provided two robust U-Pb ages of 2365.5 ± 1.1 Ma and 2370 ± 1 Ma (French et al, 2004;Halls et al, 2007). Initial Rb-Sr whole rock measurements of the Harohalli alkaline dykes constrained ages to 850-800 Ma (Ikramuddin and Stueber, 1976;Anil-Kumar et al, 1989). However, recent U-Pb ages of 1192 ± 10 Ma produced by Pradhan et al (2008) on the alkaline dykes challenge these earlier estimates.…”

Palaeomagnetic and rock magnetic study of charnockites from Tamil Nadu, India, and the ‘Ur’ protocontinent in Early Palaeoproterozoic times

“…Charnockite formation is bracketed by field relationships between these two ages, an interval that also correlates with large scale K metasomatism (Divchara Rao et al, 1982). The subsequent uplift and cooling history is not well constrained although the shield was probably elevated to high levels by the time of emplacement of mafic dyke swarms into brittle crust at $2100 Ma (Ikramuddin and Steuber, 1976;Radhakrishna et al, 1995) and levels similar to the present were reached by the time of deposition of the Cuddapah Supergroup ($1800 Ma); basement consolidation and cooling would have been complete by this time.…”