Paper No. 10
Presentation Time: 4:05 PM
DYNAMIC EMPLACEMENT AND AUTOMETAMORPHISM OF SUBLAYER FACIES OF THE SUDBURY IGNEOUS COMPLEX, CANADA
ABSTRACT WITHDRAWN
, s.prevec@ru.ac.za
It has been demonstrated
1 that convective cooling of the SIC melt sheet from a superheated initial state (consistent with impact genesis models) would result in significant melting and partial melting of the adjacent country rock, and that cooling of such a melt could crystallise olivine
2 of the appropriate Fo content (~Fo
70) as the initial solid phase to justify the formation of dunitic to lherzolitic rocks. However, some issues relating to the timing of melting, mixing with crystalline mush from the cooling melt sheet, and subsequent crystallisation of ultramafic rocks remain unresolved. Specifically, there are complications relating to the thermal gradient wherein our crystallising basaltic liquid must be underlying a clast-rich noritic mush. A mechanism involving depression of the sublayer liquidus temperature facilitated by dehydration of assimilated footwall and target rock material is proposed to remedy this. An alternative model involving the development of secondary magmatic olivine using incongruent melting of norite is rejected on textural grounds.
This model is supported indirectly by new work3 on the milky spheroidal xenoliths from the mafic norite and contact sublayer. The identification of a combination of melt textures involving a variety of silicate phases and sanidine oikocrysts, comprising the milky spheroids, characterised by a chadocryst population dominated by partially resorbed plagioclase laths, is consistent with the development of insitu melt pods. Geochemical and petrological evidence demonstrates that these melt pods are hosted in xenoliths of unshocked, igneous-textured SIC material, or autoxenoliths from earlier crystallised material. This again requires a mechanism involving complex cooling, hydration-facilitated liquidus depression, and remelting and cooling.
References:
1. PREVEC, S.A. and CAWTHORN, R.G. (2002) JGR 107(0), 10.1029/2001JB000525.
2. PREVEC, S.A. (2000) Min. Pet. 68, p. 141-157.
3. PREVEC, S.A., KUHN, B.K. and BÜTTNER, S.H. (in prep.).
