title: Bimodal magmatism produced by progressively inhibited crustal assimilation.
abstract: The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism.
authors.affiliation: Department of Earth Sciences, CEMPEG, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden.
authors.forename: F C
authors.initials: FC
authors.lastname: Meade
authors.affiliation: 1] Department of Earth Sciences, CEMPEG, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden [2] Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, 00143 Rome, Italy.
authors.forename: V R
authors.initials: VR
authors.lastname: Troll
authors.affiliation: Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride, G75 0QF Scotland, UK.
authors.forename: R M
authors.initials: RM
authors.lastname: Ellam
authors.affiliation: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, 00143 Rome, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Freda
authors.affiliation: Department of Petrology, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands.
authors.forename: L
authors.initials: L
authors.lastname: Font
authors.affiliation: School of Geography and Geosciences, University of St Andrews, North Street, St Andrews, KY16 9AL Scotland, UK.
authors.forename: C H
authors.initials: CH
authors.lastname: Donaldson
authors.affiliation: Department of Earth Sciences, CEMPEG, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden.
authors.forename: I
authors.initials: I
authors.lastname: Klonowska