Geoscience Frontiers

Geoscience Frontiers

Volume 12, Issue 1, January 2021, Pages 53-80
Geoscience Frontiers

Focus Paper
Rhyolites in continental mafic Large Igneous Provinces: Petrology, geochemistry and petrogenesis

https://doi.org/10.1016/j.gsf.2020.06.011Get rights and content
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Highlights

  • Composition of rhyolites of 12 Phanerozoic continental mafic LIPs are presented.

  • Rhyolites formed in plagioclase stability field with significant crustal contribution.

  • High-T rhyolites (>900 ​°C) formed by fractional crystallization of mafic magma.

  • Low-T rhyolites (<900 ​°C) formed via pure crustal melting or AFC of mafic magma.

Abstract

We present a detailed review of the petrological and geochemical aspects of rhyolite and associated silicic volcanic rocks (up to 20 ​vol% of all rocks) reported to date from twelve well known Phanerozoic continental mafic Large Igneous Provinces (LIPs). These typically spread over ≤104 ​km2 (rarely 105 ​km2 for Paraná-Etendeka) area and comprise ≤104 ​km3 of extrusive silicic rocks, erupted either during or after the main basaltic eruption within <5 Myr, with some eruption(s) continuing for ≤30 Myr. These rhyolites and associated silicic volcanic rocks (60−81 ​wt.% of SiO2) are mostly metaluminous to peraluminous and are formed via (i) fractional crystallization of parental mafic magma with negligible crustal contamination, and (ii) melting of continental crust or assimilation and fractional crystallization (AFC) of mafic magma with significant crustal contribution. Rhyolites formed by extensive fractional crystallization are characterized by the presence of clinopyroxene phenocrysts, exhibit steep negative slopes in bivariate major oxides plots and weak to no Nb-Ta anomaly; these typically have temperature >900 ​°C. Rhyolites formed by significant crustal contribution are characterized by strong negative Nb-Ta anomalies, absence of clinopyroxene phenocrysts, and are likely to have a magma temperature <900 ​°C. Geochemical signatures suggest rhyolite melt generation in the plagioclase stability field with a minor fraction originating from lower crustal depths. A large part of the compositional variability in rhyolites, particularly the Sr-Nd-Pb-O isotope ratios, suggests a significant role of continental crust (upper crustal melting or AFC) in the evolution of these silicic rocks in the continental mafic LIPs.

Keywords

Large Igneous Province
Silicic rock
Rhyolite
Geochemistry
Petrogenesis
AFC

Cited by (0)

Mahesh Halder is a Senior Research Fellow (SRF) and a Ph.D. student in the Department of Earth Sciences, IIT Kanpur, India. He was awarded a JRF/SRF fellowship by the Council of Scientific & Industrial Research (CSIR), MHRD, Govt. of India. His areas of interests are petrology and geochemistry of igneous rocks and origin of Large Igneous Provinces.

Debajyoti Paul is a Professor in the Department of Earth Sciences, Indian Institute of Technology Kanpur. He uses the geochemical signatures preserved in the mantle-derived rocks to understand the evolution of the crust-mantle system. Currently, he and his Ph.D. students are working to understand the geochemical evolution of the Indian subcontinent. He has published around 60 papers and articles in peer-reviewed journals.

Prof. S. Sensarma combines field, petrography/microstructure, mineralogy and geochemistry to understand igneous processes and tectonics-lithology-climate control for sediment characteristics. He has edited LIP volume for the Geological Society, London, and the IGC 2020 Legacy volume (section Editor). He presented invited talk on rhyolite at the GSA Penrose Conference.

Peer-review under responsibility of China University of Geosciences (Beijing).