Abstract

In the La Madre Mountain area, Paleozoic miogeosynclinal carbonate rocks have been transported eastward on two major thrust faults, the Keystone and Red Spring thrusts, with an estimated minimum cumulative transport of 30.5 km. The Red Spring thrust cuts upsection eastward in its upper plate. The Keystone thrust is exposed along a ramp of complex geometry and cuts upsection in its upper plate at its eastern end. The character of upper- and lower-plate rocks suggests that high pore-fluid pressure probably was not developed on either thrust. Terrigenous clastic sediments of Middle Triassic to Jurassic or (?)Early Cretaceous age crop out in the autochthon. The youngest of these, the synorogenic conglomerate of Brownstone Basin, was deposited before and during the first major structural event, the emplacement of the Red Spring plate above or near an erosional surface. Precambrian or Early Cambrian clasts in the conglomerate record the uplift of the structurally higher Wheeler Pass thrust plate before uplift of the Red Spring plate. North- to northwest-trending high-angle normal(?) faults broke the Red Spring plate and parautochthon into northeast-tilted blocks; deep erosion followed. The Keystone plate was emplaced over these blocks. Renewed movement on the high-angle faults displaced the Keystone thrust. Deposition of a large (7 km2 minimum) landslide breccia postdated these high-angle fault movements.

First Page Preview

First page PDF preview
You do not currently have access to this article.