Abstract

Magnetic fabric patterns of two mid-Cretaceous nested plutons (102 ± 1 and 96 ± 3 Ma) in the central Sierra Nevada batholith provide evidence that felsic magma emplacement (and ascent?) occurred via north-trending, steeply dipping, planar fracture conduits oriented obliquely to the arc. U-Pb geochronology data indicate that emplacement of the plutons was separated by 2 to 10 m.y. and that they were emplaced in part via the same conduit. Magnetic fabrics in the younger pluton are related to its final emplacement, which was strongly influenced by a system of host-rock joints. Formation of the north-trending conduits at ≈100 Ma can be related to a small, arc-parallel, dextral-shear component that produced tension fractures and that was associated with high-angle oblique convergence. By ≈90 Ma, convergence had become sufficiently oblique for the development of nearly arc-parallel structures, which were then favored as magma conduits.

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