Contact Relations Between The New Ross Leucomonzogranite and the Falls Lake Mafic Porphyry: Evidence for Magma Interactions in the South Mountain Batholith
DeWolfe, Vincent C.
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The South Mountain Batholith is a peraluminous composite batholith that intruded over a short interval of time. The batholith consists of 260 intrusive bodies, thus the possibility of magma-magma interactions is high. The types of contacts that form when one granite intrudes another granite depends on the temperatures, viscosities, densities, and the degree of crystallization of the two granites at the time of instrusion. In the New Ross Pluton, a wide range of unusual contact relations occur between the New Ross Leucomonzogranite and Falls Lake Mafic Porphyry. Contacts between the leucomonzogranite and mafic porphyry are diffuse and irregular, and large grains from the leucomonzogranite cut across contacts, and locally occur as xenocrysts in the mafic porphyry. Contact relations between the New Ross Leucomonzogranite and Falls Lake Mafic Porphyry suggest that the leucomonzogranite postdates the mafic porphyry, and that the degree of crystallization of the mafic porphyry was variable when the leucomonzogranite intruded. Field relations and petrography provide evidence that mingling of the leucomonzogranite and mafic porphyry occurred. Mineral compositions provide evidence that a limited degree of mixing accompanied mingling processes. Variances in the degree of crystallization (C) of the mafic prophyry result in sharp contacts where C is high, and irregular, crenulate contacts where C is lower. Kwywords: composite intrusion, leucomonzogranite, mafic porphyry, crenulate, fractal, contact relations, mingling, mixing. Pages: 106 Supervisors: D. Barrie Clarke and Rick Horne