Abstract

Demagnetization treatment of 220 paleomagnetic samples collected from widespread stations in the 90 Ma Mount Givens pluton defines an overall mean direction of declination (D) = 1.9°, inclination (I) = 63.7° (α95 = 3.0°). This result is incongruous with the expected mean direction derived from neighboring coeval plutons and the 90 Ma North American reference direction. The discrepancy is best resolved via a tectonic model of 10° up-to-the-east tilting of the Mount Givens pluton about a horizontal axis that parallels the dominant regional fabric. Timing and kinematics of surrounding structures suggest that both tilt and rapid uplift occurred along pluton-bounding shear zones. Such a mechanism of forced vertical expulsion may explain the eastward-younging age progression and the diminishing pressure gradient of the Cretaceous plutons in the batholith.

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