75 D1. Recent Advances in Economic Geology

Monday, 23 September 2024
8:00 AM - 12:00 PM
204A

CRUSTAL ANATEXIS DROVE PORPHYRY COPPER ORE FORMATION DURING LARAMIDE FLAT-SLAB SUBDUCTION

Paper number: 75-6
Program: Technical Sessions
Time: 9:00 AM – 9:15 AM

Authors

  • Thomas Lamont Presenting Author
    University of Nevada Las Vegas, Las Vegas, Nevada, NV

Abstract

The prevailing paradigm for the formation of porphyry copper deposits along convergent plate boundaries involves deep crustal differentiation of metal-bearing juvenile magmas derived from the mantle-wedge above a subduction zone. However, many major porphyry districts formed during periods of flat-slab subduction when the mantle-wedge would have been reduced or absent, leaving the source of the ore-forming magmas unclear. To resolve this paradox, we investigate deep-crustal processes during the genesis of the Late Cretaceous–Paleocene Laramide Porphyry Province in Arizona, which formed during flat-slab subduction of the Farallon Plate beneath North America. We show that: (1) Isotopic signatures of Laramide granitic rocks are consistent with a Proterozoic crustal source; and (2) Proterozoic crustal rocks were pre-enriched in copper and underwent water-fluxed anatexis between 73–60 Ma, coincident with the zenith of granitic magmatism (78–50 Ma), porphyry genesis (73–56 Ma) and flat-slab subduction (70–40 Ma). To explain the formation of the Laramide Porphyry Province, we propose that volatiles derived from the leading-edge of the Farallon flat-slab promoted anatexis of both mafic and felsic pre-enriched lower-crust, without requiring significant magmatic input from the mantle-wedge.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-405797

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