42-10 DNA of the East Pacific Rise: Mn-Ba-Cu-Zn-Pb-Ag at Detachment Faults in Arizona

Session: Cordilleran Mineral Systems: Interdisciplinary Perspectives on Critical Metal Ore Deposits

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Abstract:

Overriding of a part of the 13,000 km long, 2,000-4,000 km wide East Pacific Rise (EPR) mantle convection cell (~700 km thick) by the southwestern part of the North American plate provides an ideal regional mechanism that explains ‘black smoker’/VMS mineralization burned into the overriding crust.  This suite includes mainly Mn-Ba-Cu-Zn-Pb-Ag that are present in the upper-plate volcanic rocks of pathway detachment faults that include: 1) the Harcuvar Mountains detachment, AZ [5300 ppm Mn, 2300 ppm Ba, 14000 ppm Cu, 1000 ppm Zn, 180 ppm Pb, 3-6 ppm Ag] and, 2) the Picacho Peak detachment, AZ [2700 ppm Mn, 2469 ppm Ba, 120 ppm Cu, 1100 ppm Zn, 470 ppm Pb, 2-3 ppm Ag].  Elsewhere this EPR metal suite is present at EPR-overriding plate mineral occurrences such as Boleo/Lucifer [Mn-Cu-Zn], Baja California, MX and Artillery Peaks [230,000 ppm Mn, 44,000 ppm Ba, 1600 ppm Cu, 2300 ppm Zn, 5900 ppm Pb] AZ.  Other regional effects in southwestern Arizona that are consistent with, and fingerprint, overriding of the EPR mantle convection cell by the North American plate include: 1). shallow seismicity known since the 1960s; 2). thinned continental crust, extension, and regional detachment faulting in Arizona; 3). K2O metasomatism (~12 wt% K2O; ~1.0 wt% Na2O), typical of VMS alteration haloes, in upper-plate volcanic rocks at several detachments; 4). low temperature (~200°C) alteration resulting in reset fission-track ages of 17-18 Ma in upper-plate volcanic rocks at pathway detachments in Arizona and Nevada; and 5). heat flow of ~1.5-3.0 HFU in southwest Arizona comparable to EPR heat flow of 3 HFU.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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