Progressive hybridisation between Late Devonian mafic-intermediate and felsic magmas in the Meguma Zone of Nova Scotia, Canada |
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| Authors: | Marcus C Tate D Barrie Clarke Larry M Heaman |
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| Institution: | (1) School of Earth Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia, AU;(2) Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 3J5, CA;(3) Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3, CA |
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| Abstract: | Two felsic plutons of Late Devonian (385–370 Ma) age in the Meguma Zone of southwestern Nova Scotia contain three circa 376
Ma synplutonic mafic-intermediate intrusions that collectively record progressive stages of in situ hybridisation. A 5 m wide
spessartite dyke in the Port Mouton Pluton probably underwent rapid cooling and crystallisation immediately after intrusion,
which heated and coarsened the adjacent tonalite. An 85 m long sheet of pillowed kersantite (also in tonalite of the Port
Mouton Pluton) presumably contained residual magma after quenching and obtained K, P, Ba, Rb, more radiogenic Sr, Zr, Nb,
and light REE from the tonalite during magma mingling. The third synplutonic body, a >100 m wide diorite sheet, intrudes granodiorite
of the adjacent Shelburne Pluton and has a circa 45 m wide gradational contact of metaluminous hornblende-tonalite. This tonalite
dominantly records magma mixing by the transfer of Ti, Mg, Fe, Ca, and V in hornblende, biotite, plagioclase, and (at least
in part) apatite xenocrysts derived from dioritic pillows that were originally disaggregated in the granodiorite, probably
in response to convection. Scattered data points, unusual “concave-down” variation trends for Al2O3, P2O5, and Sr, and non-hyperbolic Sr-Nd isotopic characteristics in the tonalite, apparently reflect syn- or post-mixing fractionation
and accumulation of xenocrysts from residual magma. Phosphorus may have assisted diffusion of Sr, Zr, Nb, and light REE, and
caused premature quenching of the hybrids at Mcleods Cove and Birchtown, during magma mingling and mixing.
Received: 1 January 1996 / Accepted: 3 August 1996 |
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