Kurzfassung des Vortrags: Stratigraphy and structural Geology of Long Canyon in the Dos Cabezas Mountains (Cochise County, Arizona, USA) Jürgen Eisele Steeply dipping rock sequences from Early Proterozoic to Upper Cretaceous age are exposed in Long Canyon in the Dos Cabezas Mountains (Cochise County, Arizona, USA). An area of about 11 km2 close to Apache Pass was mapped. Nine stratigraphic units are described. Field petrography of the rock units is supported by thin-section petrology. The Early Proterozoic rocks form a volcano-sedimentary assemblage, striking NE to N, which was metamorphosed to upper greenschist facies grade and intruded by a Late Proterozoic gneissic quartz monzonite in the northern part of the mapping area. At their southern margin the Precambrian rocks are separated from the Phanerozoic units by Apache Pass fault. The Cambrian transgression is documented by a basal conglomerate and sandstone deposits of the Coronado Sandstone, followed by Lower to Middle Paleozoic carbonate deposition in a relatively stable platform environment. Facies analysis in a thin-section of a sample from the fossiliferous Mississipian Escabrosa Limestone containing mainly crinoids and algae (dasycladaceae, rhodophyceae) points to a lagoonal environment, which could however be of local importance only. The Lower Cretaceous Bisbee Group, consisting of the basal Glance Conglomerate, sand-, siltstones and shales of the Mural Limestone and the Cintura Formation, lies discomformably on the Paleozoic sediments and is overlain by an Upper Cretaceous volcano-sedimentary sequence. The Phanerozoic sediments dip consistently SW, parallel to Apache Pass fault. Northeast striking Miocene rhyolite dikes intruded the rock sequences. Thin-section petrology of a sample from the Ordovician El Paso Limestone from the mine tailings of Silverstrike Mine within the mapping area shows that hydrothermal alteration and mineralization occurred at intermediate values of oxygen fugacity (log(fO2(= -37 to -42) and at low pH (3 to 5). Mineralization is probably related to Paleocene volcanism adjacent to the mapping area and migration of fluids along Apache Pass fault system. Rocks in southeastern Arizona have been deformed in various phases of tectonism. The following structural trends and features, reflecting the large-scale tectonic regime, can be recognized in the mapping area: (1) A primary foliation in the Early Proterozoic rocks, parallel to bedding, which may be a load related feature of this period strikes ENE; (2) A NW striking secondary foliation and crenulation cleavage, associated with a large-scale fold and secondary folds exist in the Early Proterozoic rocks that abut Apache Pass fault. Folding, formation of boudins and small scale faults can be observed in the Phanerozoic sediments. Steeply plunging principal directions of the primary and secondary foliations and steeply plunging fold axes support an interpretation of lateral movement. These deformational features probably developed in the Late Cretaceous and Paleocene during Laramide tectonism. (3) North trending faults that developed from Miocene to Holocene time in response to east-west oriented tension of the Basin and Range deformation.

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