Paleomagnetic reconstruction of Coahuila, Mexico: the Late Triassic Acatita intrusives

摘要: The Acatita plutons intrude the upper Paleozoic of Las Delicias, southern Coahuila. We collected 96 samples from 15 sites in two Valle El Sobaco and Sierra Los Remedios for paleomagnetic 40 Ar -39 analyses. Separates hornblende (215.9 ±1.9 Ma, 2σ confidence level), biotite (217.3 ±1.2 Ma), K-feldspar (205.6 ±1.4 Ma) yield nearly flat age spectra although none data satisfy strict plateau criteria, possibly reflecting slight alteration. preferred ages are interpreted as fairly precise records Late Triassic cooling plutonic suite, which has yielded concordant U-Pb Zircon ca. 220 Ma. Most north-directed steep positive magnetizations similar to late Cenozoic expected field direction. Some samples, mostly mafic enclaves, show northwest magnetization shallow inclination (southeast at one site) with alternating fields above ~30 mT thermal demagnetization ~400°C. overall mean direction, corrected 15° northeast dip overlying lower Cretaceous strata (dec=342.7°, inc=+4.2°; k=35.4, α95=9.4°, n=8 sites) indicates moderate counterclockwise (14°±8°) rotation respect cratonic reference (reference pole: 57.5°N / 84°E), southward displacement (7°±5°). pole falls within a cluster poles Africa, South America, North America restored American coordinates. A major difficulty is distinguishing local, small-scale rotations, such gentle tilt pluton after magnetization, regional events involving large-scale displacements. Rotations observed suggested by synfolding (Eocene age) transverse sector Madre Oriental rimary Eocene volcanic rocks near Chihuahua. Therefore rotations Coahuila Island may be attribute related Laramide deformation. Reconstructions western equatorial Pangea should place Coahuiltecano terrane or its present position America.