EVIDENCE OF SYNEXTENSIONAL DEPOSITION OF THE PICKHANDLE AND JACKHAMMER FORMATIONS IN THE NORTHERN CALICO MOUNTAINS, CENTRAL MOJAVE DESERT, CALIFORNIA
The Calico Mountains of the central Mojave Desert, CA are located on the hanging wall block of the Waterman Hills detachment fault in the CMMCC. New geologic mapping in the northern Calico Mountains has found direct evidence of synextensional deposition of the Pickhandle Formation and underlying Jackhammer Formation in an intra-hanging-wall half-graben basin bounded on the east by a high-angle NW-trending, SW-dipping normal fault. The Jackhammer Formation is deposited on nonmylonitic basement composed of Paleozoic metasedimentary and metavolcanic rocks and Mesozoic plutonic rocks. It is composed of fluvially-reworked tuff and lapilli tuff that transitions eastward into a welded ignimbrite, tuffaceous sandstone, and local conglomeratic sandstone, mafic lava, avalanche breccia, and lacustrine limestone. In the Calico Mountains, the Pickhandle Formation is deposited conformably over the Jackhammer Formation. It consists of a lower section of dacitic volcaniclastic breccia with a local dacitic block and ash flow deposits and an upper section of tuffaceous sandstone, conglomeratic sandstone, and fluvially-reworked tuff and lapilli tuff. Evidence of growth strata indicates synextensional deposition of both formations, including sedimentary and volcanic deposits that thicken and coarsen toward the basin-bounding normal fault to the east with some deposits thinning on the half-graben footwall, fanning bedding dips that decrease upsection, and internal angular unconformities.