Successive episodes of reactive liquid flow through a layered intrusion (Unit 9, Rum Eastern Layered Intrusion, Scotland)

  • J. Leuthold
  • J. D. Blundy
  • M. B. Holness
  • R. Sides
Original Paper

DOI: 10.1007/s00410-014-1021-7

Cite this article as:
Leuthold, J., Blundy, J.D., Holness, M.B. et al. Contrib Mineral Petrol (2014) 168: 1021. doi:10.1007/s00410-014-1021-7

Abstract

We present a detailed microstructural and geochemical study of reactive liquid flow in Unit 9 of the Rum Eastern Layered Intrusion, Scotland. Unit 9 comprises an underlying lens-like body of peridotite overlain by a sequence of troctolite and gabbro (termed allivalite), with some local and minor anorthosite. The troctolite is separated from the overlying gabbro by a distinct, sub-horizontal, undulose horizon (the ‘major wavy horizon’). Higher in the stratigraphy is another, similar, horizon (the ‘minor wavy horizon’) that separates relatively clinopyroxene-poor gabbro from an overlying gabbro. To the north of the peridotite lens, both troctolite and gabbro grade into poikilitic gabbro. Clinopyroxene habit in the allivalite varies from thin rims around olivine in troctolite to equigranular crystals in gabbro and to oikocrysts in poikilitic gabbro. The poikilitic gabbros contain multiple generations of clinopyroxene, with Cr-rich (~1.1 wt% Cr2O3) anhedral cores with moderate REE concentrations (core1) overgrown by an anhedral REE-depleted second generation with moderate Cr (~0.7 wt% Cr2O3) (core2). These composite cores are rimmed by Cr-poor (~0.2 wt% Cr2O3) and REE-poor to -moderate clinopyroxene. We interpret these microstructures as a consequence of two separate episodes of partial melting triggered by the intrusion of hot olivine-phyric picrite to form the discontinuous lenses that comprise the Unit 9 peridotite. Loss of clinopyroxene-saturated partial melt from the lower part of the allivalite immediately following the early stages of sill intrusion resulted in the formation of clinopyroxene-poor gabbro. The spatial extent of clinopyroxene loss is marked by the minor wavy horizon. A second partial melting event stripped out almost all clinopyroxene from the lowest allivalite to form a troctolite, with the major wavy horizon marking the extent of melting during this episode. The poikilitic gabbro formed from clinopyroxene-saturated melt moving upwards and laterally through the remobilized cumulate pile and precipitating clinopyroxene en route. This process, called reactive liquid flow, is potentially important in open magma chambers.

Keywords

Reactive liquid flow Rum Eastern Layered Intrusion Picrite Partial melting Clinopyroxene 

Supplementary material

410_2014_1021_MOESM1_ESM.eps (728 kb)
Thermal evolution of the Rum Unit 9 cumulate (host gabbro temperature of 1,160 °C) when successively intruded by two picrite sills at 1,240 °C (at 0 and 200 years), using the equations of Furlong et al. (2001) (with time increments of 10 days and distance increments of 1.5 m). Dunite, troctolite and clinopyroxene-poor gabbro restite are respectively produced at 4.5, 15 and 84 m from the contact (EPS 727 kb)
410_2014_1021_MOESM2_ESM.xls (27 kb)
Supplementary material 2 (XLS 27 kb)
410_2014_1021_MOESM3_ESM.xls (32 kb)
Supplementary material 3 (XLS 32 kb)
410_2014_1021_MOESM4_ESM.xls (289 kb)
Supplementary material 4 (XLS 289 kb)
410_2014_1021_MOESM5_ESM.pdf (7 kb)
Supplementary material 5 (PDF 6 kb)

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • J. Leuthold
    • 1
    • 2
  • J. D. Blundy
    • 1
  • M. B. Holness
    • 2
  • R. Sides
    • 2
  1. 1.School of Earth SciencesUniversity of BristolBristolUK
  2. 2.Department of Earth SciencesUniversity of Cambridge, Downing SiteCambridgeUK