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Byline: Hetu C. Sheth (1), Jyotiranjan S. Ray (2), Ranjini Ray (1), LoA?c Vanderkluysen (3), John J. Mahoney (3), Alok Kumar (2), Anil D. Shukla (2), Partha Das (1), Subhrashis Adhikari (1), Bikashkali Jana (1) Keywords: Volcanism; Continental flood basalt; Dyke swarm; Deccan Traps; Gondwana Abstract: Many tholeiitic dyke-sill intrusions of the Late Cretaceous Deccan Traps continental flood basalt province are exposed in the Satpura Gondwana Basin around Pachmarhi, central India. We present field, petrographic, major and trace element, and Sr--Nd--Pb isotope data on these intrusions and identify individual dykes and sills that chemically closely match several stratigraphically defined formations in the southwestern Deccan (Western Ghats). Some of these formations have also been identified more recently in the northern and northeastern Deccan. However, the Pachmarhi intrusions are significantly more evolved (lower Mg numbers and higher TiO.sub.2 contents) than many Deccan basalts, with isotopic signatures generally different from those of the chemically similar lava formations, indicating that most are not feeders to previously characterized flows. They appear to be products of mixing between Deccan basalt magmas and partial melts of Precambrian Indian amphibolites, as proposed previously for several Deccan basalt lavas of the lower Western Ghats stratigraphy. Broad chemical and isotopic similarities of several Pachmarhi intrusions to the northern and northeastern Deccan lavas indicate petrogenetic relationships. Distances these lava flows would have had to cover, if they originated in the Pachmarhi area, range from 150 to 350 km. The Pachmarhi data enlarge the hitherto known chemical and isotopic range of the Deccan flood basalt magmas. This study highlights the problems and ambiguities in dyke-sill-flow correlations even with extensive geochemical fingerprinting. Author Affiliation: (1) Department of Earth Sciences, Indian Institute of Technology Bombay (IITB), Powai, Mumbai, 400076, India (2) Planetary and Geosciences Division, Physical Research Laboratory (PRL), Navrangpura, Ahmedabad, 380009, India (3) Department of Geology and Geophysics, School of Ocean and Earth Science and Technology (SOEST), University of Hawaii, Honolulu, HI, 96822, USA Article History: Registration Date: 22/01/2009 Received Date: 08/09/2008 Accepted Date: 22/01/2009 Online Date: 14/02/2009 Article note: Communicated by T. L. Grove.

The St Mary's Islands (southwestern India) expose silicic volcanic and sub-volcanic rocks (rhyolites and granophyric dacites) emplaced contemporaneously with the Cretaceous igneous province of Madagascar. roughly 88-90 Ma ago. The St Mary's Islands rocks have phenocrysts of plagioclase, clinopyroxene, orthopyroxene and opaque oxide, moderate enrichment in the incompatible elements (e.g. Zr = 580-720 ppm, Nb = 43-53 ppm, La/[Yb.sub.n] = 6.9-7.2), relatively low initial [sup.87]Sr/[sup.86]Sr (0.7052-0.7055) and near-chondritic initial [sup.143]Nd/[sup.144]Nd (0.51248-0.51249). They have mineral chemical, whole-rock chemical and isotopic compositions very close to those of rhyolites exposed between Vatomandry-Ilaka and Mananjary in eastern Madagascar, and are distinctly different from rhyolites from other sectors of the Madagascan province. We therefore postulate that the St Mary's and the Vatomandry-Ilaka-Mananjary silicic rock outcrops were adjacent before the Late Cretaceous rifting that split Madagascar from India. If so, they provide a valuable tool to check and aid traditional Cretaceous India Madagascar reconstructions based on palaeomagnetism, matching Precambrian geological features, and geometric fitting of continental shelves. Supplementary material: Mineral analyses, mass-balance calculations and locality information are available at http://www.geolsoc.org.uk/SUP18332.

This article is an appeal for the adoption of a correct and appropriate terminology with respect to the so-called Large Igneous Provinces (LIPs). The term LIP has been widely applied to large basaltic provinces such as the Deccan Traps, and the term Silicic Large Igneous Province (SLIP) to volcanic provinces of dominantly felsic composition, such as the Whitsunday Province. However, neither term (LIP, SLIP) has been applied to the large granitic batholiths of the world (e.g., Andes) to which both terms are perfectly applicable. LIP has also not been applied to broad areas of contemporaneous basalt magmatism (e.g., Indochina, Mongolia) and sizeable layered mafic intrusions (e.g., Bushveld) which in many significant respects may also be considered to represent 'Large Igneous Provinces'. Here, I suggest that the term LIP is used in its broadest sense and that it should designate igneous provinces with outcrop areas [greater than or equal to] 50,000 [km.sup.2]. I propose a simple hierarchical classification of LIPs that is independent of composition, tectonic setting, or emplacement mechanism. I suggest that provinces such as the Deccan and Whitsunday provinces should be called Large Volcanic Provinces (LVPs), whereas large intrusive provinces (mafic--ultramafic intrusions, dyke/sill swarms, granitic batholiths) should be called Large Plutonic Provinces (LPPs). LVPs and LPPs thus together cover all LIPs, which can be felsic, mafic, or ultramafic, of sub-alkalic or alkalic affinity, and emplaced in continental or oceanic settings. LVPs are subdivided here into four groups: (i) the dominantly/wholly marie Large Basaltic Provinces (LBPs) (e.g., Deccan, Ontong Java); (ii) the dominantly felsic Large Rhyolitic Provinces (LRPs) (e.g., Whitsunday, Sierra Madre Occidental); (iii) the dominantly andesitic Large Andesitic Provinces (LAPs) (e.g., Andes, Indonesia, Cascades), and (iv) the bimodal Large Basaltic--Rhyolitic Provinces (LBRPs) (e.g., Snake River--High Lava Plains). The intrusive equivalents of LRPs are the Large Granitic Provinces (LGPs) (e.g., the Andean batholiths), although an equivalent term for intrusive equivalents of LBPs is not necessary or warranted. The accuracy and usefulness of the terms flood basalt, plateau basalt, and trap are also examined. The largest LBP, LVP, and LIP is, of course, the bulk of the ocean floor. It is contended that the proposed LIP nomenclature and classification will lead to more accurate and precise terminology and hence better understanding of the wide variety of Large Igneous Provinces. Keywords: Large igneous province; magmatism; volcanism; classification; nomenclature