Structure and Petrology of the La Perouse Gabbro Intrusion, Fairweather Range, Southeastern Alaska

Abstract
The middle Tertiary La Perouse gabbro intrusion occurs in a Mesozoic metamorphic terrane (Chugach terrane) in the Fairweather Range, southeastern Alaska. The intrusion is 12 km wide and 27 km long, and has an exposed cumulate layering thickness of about 6000 m. The contact consists of biotite and hornblende gneiss of the granulite facies, which forms a discontinuous belt as much as 200 m wide. The outer contact of the zone is a fault, along which it is in contact with regionally metamorphosed biotite schist and amphibolite of the amphibolite facies. This fault seems to be a peripheral fault along which the intrusion was uplifted to its present level. The layering in the intrusion forms an asymmetrical funnel that is elongate northwestward and is structurally deepest at the southeast end near Mount La Perouse where the layering has inward dips of as much as 85°.

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