NEW INSIGHTS INTO THE GEOLOGY OF THE LANE MOUNTAIN AND NORTH CALICO MOUNTAINS AREA, CENTRAL MOJAVE DESERT, CALIFORNIA

Detailed mapping and geochronologic data provide new insights into the geologic history of the Lane Mountain - North Calico Mountains area north of Barstow, California. Geochronologic data include zircon ages of plutonic rocks and detrital zircon ages from metasedimentary rocks.

About 8 km of tectonically assembled offshore metasedimentary and metavolcanic rocks are present, including meta-andesite, quartzite, argillite, conglomerate, hornfels, and carbonate rocks. Detrital zircon dates from an orthoquartzite suggest an Ordovician age. Several impure quartzites yielded Late Permian to Triassic detrital zircons. These metamorphic rocks do not appear to correlate with the “Northwest Mojave Terrane” Paleozoic strata of the El Paso Mountains. Allochthonous carbonate rocks resemble Paleozoic miogeoclinal units. Detrital zircon age spectra confirm a distinctive fault-bounded assemblage of hornfels, metasandstone, and metaconglomerate correlates with the Early Jurassic Fairview Valley Formation (FVF).

Intrusive rocks include Permo-Triassic ( 252-245 Ma) diorite/tonalite with Sri ~.704 suggesting oceanic affinity, Late Jurassic (150-146 Ma) diorite with Sri ~.705, and 150 Ma leucocratic dikes and plugs. Late Cretaceous (84-81 Ma) quartz monzonite with Sri ~.708, a felsite dike (84.5 Ma), and granite porphyry dikes and plutons (80-73 Ma) with Sri ~.710 suggest continental basement. Several bodies of undated Jurassic(?) gabbro are also present. All metamorphic rocks predate Jurassic intrusives and some appear to be intruded by the Permo-Triassic suite.

Major pre-Miocene structural events include tectonic assembly of offshore sequences, low-angle emplacement of miogeoclinal carbonates, repeated folding and bedding plane faulting, and low-angle emplacement of Jurassic diorite and folded FVF roof pendants.

The oldest of the unconformably overlying volcanic dominated Miocene sequences is the Jackhammer Formation that includes a distinctive basal conglomerate. The Jackhammer is locally overlain by the rhyolite of Lane Mountain (22.3 Ma). Younger Miocene rocks include the Pickhandle Formation and dacite plugs, sills and flows (19.3-18 Ma). Deformation of Miocene rocks includes many syn- and post-depositional faults, and localized folding including recumbent folds adjacent to dacite sills.