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Paper No. 3
Presentation Time: 2:00 PM
INTERPRETATION OF PALEOZOIC GRANJENO SCHIST IN THE CABALLEROS CANYON, HUIZACHAL-PEREGRINA ANTICLINORIUM, CIUDAD VICTORIA, NE MEXICO
At the Eastern front of the Sierra Madre Oriental (SMO) is located a major folded structure, Huizachal Peregrina Anticlinorium. This important structure has an eroded core showing four contrasting basement units: a) Precambrian Novillo Gneis (NG), correlated with the Grenvillian Orogeny, b) Paleozoic Granjeno Schist (GS) related to the Appallachian Orogeny, c) A Ordovician to Permian deformed sedimentary sequence, and d) A ±317 Ma tonalite linked with an ancient arch that divides NG from GS by faulting. All these units comprise the SMO basement that is covered by a thick Mesozoic column composed by red beds, evaporites, limestones and shales. Granjeno schist outcrops in Caballeros Canyon as a narrow (~1.6 km) NW-SE trending stripe of metasedimentary lithologies consisting of pelites and psammites interstratifications. They are massive, greenish and gray to black.The mineralogy is dominated by quartz, albite, graphite, muscovite, biotite, chlorite tourmaline and actinolite. No garnet has been recognized, in opposition to former reports. The GS unit where affect by at least three foliations and a mesoscopic folding. The predominant directions of these schistosities are 150/55, 320/60, 99/58 respectively and mesoscopic folding has the orientation 240/54.There are other structural patterns that define the compressive stress that deformed the area such as fractures, lenticular and neck boudinage structures dextral and sinistral shear structures, kink folds, conjugate kink bands and crenulation structures.According to field and laboratory analysis GS is the result of pelitic and psammitic sedimentary secuence metamorphism, accumulated during the Early Devonian – Mississippian in a deep basin and an acrecional prism environment, between the continental masses of Laurentia and Gondwana.The closure of this basin was responsible for the GS metamorphism and could represent vestiges of the closure of the Rheic Ocean during the latest stages of the formation of Pangea.