Detrital zircon U-Pb ages of sandstones in continental red beds at Valle de Huizachal, Tamaulipas, NE Mexico: Record of Early-Middle Jurassic arc volcanism and transition to crustal extension

Abstract

Valle de Huizachal record arc magmatism and subsequent crustal extension prior to seafl oor spreading in the Gulf of Mexico. The older La Boca Formation consists of two informal members, a lower unit of siliciclastic and volcanic rocks discordantly overlain by a predominantly siliciclastic upper member. The younger La Joya Formation is an upwardfi ning, alluvial-braided fl uvial succession with a basal conglomerate. U-Pb detrital-zircon ages (n = 576) from six Huizachal Group sandstones (fi ve from La Boca and one from La Joya) consist of four groups indicating a mixed provenance: (1) Grenville grains (~1.3-1.0 Ga) derived from Gondwana (Novillo Gneiss); (2) earlymiddle Paleozoic grains (430-300 Ma) derived from peri-Gondwanan accreted rocks (Granjeno Schist); (3) Permo-Triassic grains (296-222 Ma) derived from volcanic and plutonic rocks (West Pangaean arc) and/or turbidites (Guacamaya Formation); and (4) Early-Middle Jurassic grains (199-164 Ma), locally derived from the Nazas arc. Groups 1-3 increase in abundance upsection as a result of unroofi ng of Jurassic volcanic and sedimentary carapace from uplifted basement. The Huizachal Group records three stages in the pre-breakup history of Gondwana: (1) The lower member of La Boca Formation (maximum depositional age 184-183 Ma; Pleinsbachian) indicates Nazas arc activity; (2) the upper member (maximum depositional age 167-163 Ma; Bathonian-Callovian) indicates continued arc magmatism as early crustal extension formed horsts that supplied basement grains to an incipient rift basin; and (3) the La Joya Formation represents late rift basin development and widespread exposure of fl anking basement rocks. Although our La Joya sample lacks a coherent age group of young grains, its single youngest grain age (164 3 Ma; Callovian) is consistent with its stratigraphic position beneath inferred Oxfordian strata. RESUMEN Depsitos continentales y rocas volcnicas del Grupo Huizachal en el Valle de Huizachal registran magmatismo de arco y subsecuente extensin cortical previa a la generacin de piso ocenico en el Golfo de Mxico. La formacin la Boca consiste en dos miembros informales, una unidad inferior de rocas siliciclsticas y volcnicas discordantemente sobreyacidas por un miembro superior siliciclstico. La formacin La Joya es una sucesin aluvial-fl uvial trenzada grano decreciente con un conglomerado basal. Edades U-Pb en circones detrticos (n = 576) de seis muestras de areniscas del Grupo Huizachal (cinco de la La Boca y una de La Joya) consisten en cuatro grupos que indican una procedencia de mezcla: (1) granos Grenvilianos (~1.3-1.0 Ga) derivados de Gondwana (Gneis Novillo); (2) granos del Paleozico temprano-medio (430-300 Ma) derivados de rocas peri-Gondwnicas acrecionadas (Esquisto Granjeno); (3) Permo-Trisicos (296-222 Ma) derivados de rocas volcnicas y plutnicas (arco oeste de Pangea) y/o turbiditas (formacin Guacamaya); y (4) granos del Jursico Temprano-Medio (199-164 Ma), localmente derivados del arco Nazas. Los grupos 1-3 incrementan en abundancia hacia la cima de la seccin como resultado de la exhumacin de la cubierta de rocas volcnicas y sedimentarias del Jursico de bloques levantados.