PROVENANCE INTERPRETATIONS COMBINING PETROGRAPHY AND 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

Continental strata and volcanic rocks of the Huizachal Group in the Valle de Huizachal record arc magmatism and subsequent crustal extension prior to sea-floor spreading in the Gulf of Mexico. The La Boca Formation consists of two informal members, a lower siliciclastic and volcanic member discordantly overlain by a siliciclastic upper member. The La Joya Formation is an upward-fining, alluvial-braided fluvial succession with a basal conglomerate.

Sedimentary petrography (QFL) indicates two petrofacies (Pf). Pf₁, feldspathic-lithic arenite (Q₃₅F₃₀L₃₅), spans the lower member of La Boca and Pf₂, lithic arenite (Q₆₉F₇L₂₄), includes the upper member and La Joya. U-Pb detrital-zircon ages (n=576) from six sandstones (five from La Boca and one from La Joya) define four grain age groups: 1) Grenville (~1.3-1.0 Ga), derived from Gondwana (Novillo Gneiss); 2) Early-Middle Paleozoic (430–300 Ma), derived from peri-Gondwanan accreted rocks (Granjeno Schist); 3) Permo-Triassic (296-222 Ma), derived from volcanic and plutonic rocks (West Pangaean arc) and/or turbidites (Guacamaya Formation); and 4) Early-Middle Jurassic (199–164 Ma), locally derived from the Nazas arc. Groups 1-3 increase in abundance upsection resulting from unroofing of Jurassic volcanic and sedimentary carapace from uplifted basement. Pf data reinforce grain age observations by recognition of: (1) quartz content (Qp2-3₂₉Qmr₃₃Qmo₃₇; Qp>3₃₁Qmo₃₆Qmr₃₃) from low-mid-grade metamorphic and igneous rocks; and (2) metamorphic and volcanic lithic content (Pf₁: Lvf₄₁Lvmi₅₅Lvl₄; Pf₂: Lvf₂₃Lvmi₆₉Lvl₈) bias textural characterization.

The Huizachal Group records three stages in the pre-breakup history of Gondwana: 1) the lower member of La Boca Formation (max. depositional age 184-183 Ma; Pleinsbachian) was deposited in a transitional arc zone of dissected arc provenance (Qm₂₂F₃₆Lt₄₁), signifying Nazas arc activity; 2) the upper member (max. depositional age 168-163 Ma; Bathonian-Callovian) indicates continued arc magmatism as early crustal extension horsts supplied basement grains to an incipient rift basin; 3) La Joya Formation (single youngest grain age 164±3 Ma; Callovian) with a recycled orogen composition (Qm₅₉F₉Lt₃₂) represents late rift basin development and broad exposure of flanking basement rocks.