Abstract

New insights into the nature and construction of granitic intrusions provide an opportunity to correlate the rock record of an intrusion to the rock record of volcanism related to the intrusion. We attempt such a correlation between the Silurian Vinalhaven (Maine, USA) intrusive complex and associated volcanic rocks. The largely granitic Vinalhaven intrusion includes a stratigraphic sequence of interlayered gabbro, diorite, and minor granite that preserves field evidence for mingling of coexisting mafic and silicic magmas in a series of ephemeral silicic magma chambers. Within this stratigraphy, blocks of country rocks occur at a number of stratabound horizons in association with mafic sheets. The along-strike lithologic variation of the blocks mirrors the lithologic variation of country rocks along the northern margin of the intrusion, which appears to be the only preserved portion of the intrusion's roof. The limited stratigraphic distribution and correlation of lithologies to the roof suggest that the country-rock blocks were stoped during short-lived roof collapse events rather than continuously over the lifetime of the chamber. We suggest that these stratabound roof blocks record collapse of the roof during eruptions from the system, perhaps triggered by the influx of mafic magma, and represent one large caldera-forming eruption followed by a series of smaller eruptions. This interpreted eruptive history of the pluton is consistent with the overall stratigraphy of spatially, temporally, and compositionally related volcanic rocks.

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