Journal of Petrology | Volume 39 | Number 3 | Pages 519-550 | 1998
© Oxford University Press 1998
The Loch Scridain Xenolithic Sill Complex, Isle of Mull, Scotland: Fractional Crystallization, Assimilation, Magma-Mixing and Crustal Anatexis in Subvolcanic Conduits
1 Department of Geology and Applied Geology, University of Glasgow Glasgow G12 8QQ, UK
2 Isotope Geosciences Unit, Scottish Universities Research and Reactor Centre East Kilbride, Glasgow G75 0QF, UK
Received October 7, 1996; Revised typescript accepted October 21, 1997
 |
Abstract |
|---|
The petrogenesis of a suite of high-level minor intrusions which intruded the Palaeogene lava field and older rocks in the vicinity of Loch Scridain, Isle of Mull, NW Scotland, has been investigated using mineral chemistry data together with whole-rock major and trace element and radiogenic Sr–Nd–Pb isotope data. Three distinct magma groups are present. Group I consists of aphyric tholeiitic basalts and basaltic andesites, the most primitive of which have MORB-like chemical affinities. Group I rocks are markedly xenolithic, containing both crustal and cognate gabbroic xenoliths. Group II comprises plagioclase- and pyroxene-phyric andesites and dacites. Group III consists solely of fine-grained rhyolites. Compositional trends displayed by the Group I basic magmas can be explained in terms of relatively low-pressure fractionation of the assemblage olivine + clinopyroxene + plagioclase, followed by plagioclase + clinopyroxene + low-Ca pyroxene. The extreme incompatible-element enrichment, the high initial Sr isotope ratios, and radiogenic Pb isotope ratios of the more evolved members of Group I can, however, only be explained through a process of combined fractional crystallization and crustal assimilation of the underlying Moine pelitic schists. The isotope and trace element data imply that the contaminant was a high-Nd partial melt of Moine metasediments rather than a bulk addition of Moine pelite. The major, trace element and Sr–Nd isotope geochemistry of the Group III rhyolites is consistent with their derivation mainly from the partial melting of a pelitic crustal source. The geochemical characteristics of the Group II intermediate rocks suggest that they represent simple mixtures between basic magma and Group III silicic melts.
KEY WORDS: fractional crystallization; assimilation; subvolcanic; sill complex
* Present address: Department of Geology and Petroleum Geology, Meston Building, Kings College, University of Aberdeen, Old Aberdeen AB24 3UE, UK. Telephone:+44 (0)1224 273467 e-mail: j.preston{at}abdn.ac.uk
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  A. C. Kerr, R. W. Kent, B. A. Thomson, J. K. Seedhouse, and C. H. Donaldson Geochemical Evolution of the Tertiary Mull Volcano, Western Scotland J. Petrology, June 1, 1999; 40(6): 873 - 908. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. J. Preston, T. J. Dempster, B. R. Bell, and G. Rogers The Petrology of Mullite-bearing Peraluminous Xenoliths: Implications for Contamination Processes in Basaltic Magmas J. Petrology, April 1, 1999; 40(4): 549 - 573. [Abstract] [Full Text] [PDF]
|
|