STRUCTURAL AND METAMORPHIC SIMILARITIES BETWEEN PROTEROZOIC ROCKS IN THE CERBAT AND HUALAPAI MOUNTAINS, NORTHWESTERN ARIZONA

The Cerbat Mountains, northwestern Arizona, contain evidence for two major deformational events coincident with two discrete metamorphic pulses. D₁ (ca. 1740 Ma) is characterized by a gently dipping foliation and associated WSW-vergent recumbent folds, and metamorphism at T=675-725°C, P=5-6 kbar. We interpret this event as recording the amalgamation of the Mojave and Yavapai crustal provinces. D₂ (ca. 1700 Ma) records regional NW-SE crustal shortening associated with accretion of the composite Mojave-Yavapai province to Proterozoic terranes in Colorado. M₂ occurred at T=650-700°C, P=3.5-4.5 kbar suggesting that tectonic burial to 20 km during D₁ was followed by decompression to 10-14 km before or during D₂.

The northern Hualapai Mountains, southeast of the projected trace of the Gneiss Canyon shear zone (GCSZ), contain both fabrics and preserve a 250-270° trending, L₁ mineral lineation, consistent with the tectonic transport direction inferred for the Cerbat Mountains. Pelitic rocks in the Walnut Canyon area (Hualapai Mountains), contain the (D₁?) assemblage sill+Kspar+gar+bi +cord, a higher grade than previously reported for the Hualapai Mountains. Rocks as far south as Creamery Canyon (>25 km southeast of the projected trace of the GCSZ) contain the assemblage sill+Kspar+gar+bi+hercynite±cord, identical to the granulite assemblage in the Cerbat Mountains that yielded T > 700°C.

Pelites in Boriana Canyon, located between the Walnut and Creamery Canyons, contain the assemblage gar+sta+musc+and. The reason for lower-grade rocks in this area is uncertain, but may reflect either variable thermal conditions due to heterogeneous distribution of plutons, or speculatively, the Boriana Canyon rocks may represent a younger sequence that lies unconformably over an older higher-grade basement. The distribution of granulite-facies rocks in northwestern Arizona appears to be more complex than previously reported, and the GCSZ does not appear to mark either the eastern limit of granulites southwest of the Lower Granite Gorge (Grand Canyon) or a marked change in structural style between the Cerbat and Hualapai Mountains.