Magnetic fabric evidence for conduit-fed emplacement of a tabular intrusion: Dinkey Creek Pluton, central Sierra Nevada batholith, California

Alexander R. Cruden, Othmar T. Tobisch, Patrick Launeau

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Abstract

Anisotropy of magnetic susceptibility measurements in the Cretaceous Dinkey Creek Pluton (DCP), central Sierra Nevada batholith, reveal a well-defined structural pattern and zonation in bulk susceptibility (K). Outward decrease in K within the pluton is due to a decrease in ferrimagnetic contribution, corresponding to a compositional zoning from tonalite to granite. Magnetic fabrics in the pluton formed during supersolidus flow of a crystal-rich magma, except in the eastern domain where subvertical magnetic lineations and NW striking magnetic foliations are attributed to deformation associated with a regional shear zone. Magnetic foliations in the central domain of the DCP define a NNW trending synformal structure, passing structurally upward into a dome beneath a small roof pendant, interpreted to represent different structural levels in a zone of magma upwelling. Arcuate foliation trajectories in the pluton's SW lobe resemble deformed passive markers in two-dimensional, NW to SW, horizontal, channel flow of non-Newtonian magma. Analysis of the fabric pattern in cross-section estimates the preerosion thickness of the lobe to between 915 and 3660 m. The DCP was emplaced as a tabular body with vertical sides and a gently inclined roof. Magma with increasingly more mafic compositions entered the chamber continuously or episodically via a NNW trending conduit. Space for the pluton was created by vertical inflation, probably accommodated by depression of its floor. These results suggest that the mid crust to upper crust of magmatic arcs may be constructed by vertical stacking of tabular granitic plutons with high width/thickness ratios like the DCP.

Original languageEnglish
Article number1998JB900093
Pages (from-to)10511-10530
Number of pages20
JournalJournal of Geophysical Research: Solid Earth
Volume104
Issue numberB5
Publication statusPublished - 10 May 1999
Externally publishedYes

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