LATE PALEOZOIC TECTONIC EVENTS OF THE WESTERN U.S. CONTINENTAL MARGIN; A COMPARISON OF EAST-CENTRAL CALIFORNIA AND EASTERN AND CENTRAL NEVADA

A complex sequence of tectonic events took place on the U.S. continental margin in east-central California (EC-Ca) and eastern and central Nevada (EC-Nv) during late Paleozoic time. These events temporally overlap development of the Ancestral Rocky Mountains to the east. The tectonic connection between these two regions, however, is at present, uncertain.

Events in EC-Ca include: (1) emplacement of the Antler allochthon in the Early Mississippian with minor uplift of the belt in the Late Mississippian, (2) initiation of a continental truncational fault and stage 1 in development of the Darwin Basin in the Middle Pennsylvanian, (3) emplacement of the Last Chance Thrust and stage 2 in development of the Darwin Basin in the Sakmarian, (4) intrusion of plutons and development of the Sierra Nevada-Death Valley thrust system in the late Capitanian, and (5) displacement of the El Paso terrane along the truncational fault in latest Permian and Triassic time.

In EC-Nv, the #2 Middle Pennsylvanian event is reflected in the development of the lower Strathearn Formation and related units in distinct basins and sub-basins. The Last Chance thrust of EC-Ca (#3) coincides approximately with late Sakmarian to earliest Artinskian folding and thrust faulting that separates the lower and upper Strathearn and related units in EC-Nv and the subsequent development of the Dry Mountain trough. The late Capitanian magmatic activity and thrust system of EC-Ca (#4) does not have a direct expression in EC-Nv but does correspond to the disruption and end of deposition in most of the Phosphoria basin. Event #5 in EC-Ca was coeval with the internal deformation and perhaps initial emplacement of the Golconda allochthon (Sonoma Orogeny in a classic sense) and its overlap by the earliest Triassic Koipato volcanics farther north in EC-Nv.

Thus, Mississippian to Early Permian events in Nevada and California are comparable. Emplacement of the Antler allochthon and later uplift of the belt occurred at approximately the same time. Later, emplacement of the Last Chance Thrust and enlargement of the Darwin Basin in the Sakmarian coincides with development of the Dry Mountain trough in Nevada. Displacement of the El Paso terrane on the truncational fault in California may have been coeval with emplacement of the Golconda allochthon in Nevada.