caa a22 4500 475826248 CHVBK 20180406123829.0 cr unu---uuuuu 170329e20001101xx s 000 0 eng 10.1007/s004450000099 doi (NATIONALLICENCE)springer-10.1007/s004450000099 Caldera formation in the Rum Central Igneous Complex, Scotland [Elektronische Daten] [Valentin R. Troll, C. Henry Emeleus, Colin H. Donaldson] Abstract.: The Northern Marginal Zone of the Rum Central Igneous Complex in NW Scotland represents part of the early, felsic phase of the volcano. The marginal zone is a relic of the early caldera floor and the infilling of sedimentary and igneous rocks. Its formation has been explored through field examination of the ring fracture system of the Complex and its pyroclastic and epiclastic intracaldera facies. A sequence of magmatic tumescence and chamber growth caused initial doming, followed by the formation of a collapse structure without accompanying volcanism. This collapse structure, circular in plan, is akin in origin to a salt basin formed by crustal stretching above a rising diapir. We call this the proto-caldera. Collapse breccias, which represent the slumping and sliding of megablocks, blocks and boulders of the Torridonian sandstones which form the walls of the basin, were the original infilling. Logs of these deposits reveal considerable variation in thickness of the breccias (from 80-170m) in the Complex, indicating an uneven floor to the proto-caldera, consistent with piecemeal collapse. Following accumulation of up to >70m thickness of breccia, thin interbedded rhyodacitic crystal tuffs (10-30cm) record the earliest eruptions of felsic magma in the caldera. Caldera formation was then interrupted by a period of quiescence, recorded by the presence of an epiclastic sandstone of locally several metres thickness, formed by washout of fines from the breccias. Subsequent resurgence created a fracture pattern characteristic of doming, along which rhyodacite magma rose in dykes and erupted up to perhaps 10km3 of rhyodacitic intracaldera ignimbrites. This major eruption caused further incremental subsidence of the caldera floor into a now partly emptied magma chamber. Mafic inclusions in the ignimbrites point to the eruption being triggered by multiple injections of basic magma into a chamber occupied by felsic magma. Springer-Verlag, 2000 Pre-eruptive caldera collapse Proto-caldera Rum igneous complex Intracaldera stratigraphy Ignimbrite feeder dykes Caldera resurgence nationallicence Troll Valentin R. School of Geosciences, University of St. Andrews, St. Andrews, KY16 9ST Scotland aut Emeleus C. Henry Department of Geological Sciences, University of Durham, Durham, DH1 3LE England aut Donaldson Colin H. School of Geosciences, University of St. Andrews, St. Andrews, KY16 9ST Scotland aut https://doi.org/10.1007/s004450000099 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s004450000099 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Troll Valentin R. School of Geosciences, University of St. Andrews, St. Andrews, KY16 9ST Scotland aut NATIONALLICENCE 700 1- Emeleus C. Henry Department of Geological Sciences, University of Durham, Durham, DH1 3LE England aut NATIONALLICENCE 700 1- Donaldson Colin H. School of Geosciences, University of St. Andrews, St. Andrews, KY16 9ST Scotland aut Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer