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Collision of Gondwana and Laurentia in the late Palaeozoic created new topography, drainages, and foreland basin systems that controlled sediment dispersal patterns on southern Laurentia. We utilize sedimentological and detrital zircon data from early Permian (Cisuralian/Leonardian) submarine-fan deposits in the Midland Basin of west Texas to reconstruct sediment dispersal pathways and palaeogeography. New sedimentological data and wire-line log correlation suggest a portion of the early Permian deposits have a southern entry point. A total of 3259 detrital zircon U-Pb and 357 εHf data from 12 samples show prominent groups of zircon grains derived from the Appalachian (500–270 Ma) and Grenville (1250–950 Ma) provinces in eastern Laurentia and the peri-Gondwana terranes (800–500 Ma) incorporated in the Alleghanian-Ouachita-Marathon orogen. Other common zircon groups of Mesoproterozoic-Archaean age are also present in the samples. The detrital zircon data suggest throughout the early Permian, Appalachia and Gondwana detritus was delivered by a longitudinal river system that flowed along the Appalachian-Ouachita-Marathon foreland into the Midland Basin. Tributary channels draining the uplifted Ouachita-Marathon hinterland brought Gondwana detritus into the longitudinal river with headwaters in the Appalachians or farther northeast. This drainage extended downstream westward and delivered sediments into the Permian Basin near the west terminus of the Laurentia-Gondwana suture. Estimated rates of deposition and proportions of zircons from more local (Grenville) versus more distal (Pan-African) sources indicate that river strength decreased throughout early Permian time. Primary sediment delivery pathway was augmented by minor input from the Ancestral Rocky Mountains and wind deflation of fluvial sediments north and east of the basin. Slope failure associated with early Permian deposition in the southeastern margin of the Midland Basin triggered gravity flows leading to submarine fan deposition. [ABSTRACT FROM AUTHOR]

A 24-year-old man presented to a university health center in January with a persistent headache that began abruptly 6 days earlier. He noted nonpulsating discomfort in the right retro-orbital area that was not relieved by ibuprofen (400 mg four times daily). He reported no prodromal symptoms, sensitivity to light or sound, neurologic symptoms, nausea, or vomiting and had no history of headaches. A day before presentation, he noted subjective fevers. The patient was evaluated, and amoxicillin was prescribed for presumed acute rhinosinusitis. [ABSTRACT FROM AUTHOR]

Small-volume Late Cretaceous monogenetic alkaline volcanism along the southern margin of North America resulted in a broad igneous belt more than 1200 km long from the Trans Pecos region of west Texas to central Mississippi, collectively forming a northern Gulf of Mexico magmatic zone (NGMMZ). The locus of igneous activity is associated with the discontinuity separating Mesoproterozoic cratonic lithosphere and Jurassic transitional lithosphere, a zone approximating the southern margin of Laurentia, the subsurface trend of the Pennsylvanian Ouachita orogenic belt, and the trace of the Miocene Balcones fault zone in Texas. Although previous studies have attempted to determine the ages of igneous activity in the region, few well-constrained geochronologic data using modern high-resolution techniques are available. We determined the age of eruption for the Balcones igneous province (BIP), a 400-km-long subsegment of the NGMMZ, using modern 40Ar/39Ar and U-Pb geochronology methods. Our results suggest that previously reported 40K/40Ar and 40Ar/39Ar ages underestimate the age of igneous activity by as much as 17%. New ages from this study, along with reevaluation of previous results, suggest that BIP igneous activity occurred in two discrete phases, each lasting only 2.6 m.yr. and separated by 2.7 m.yr.: older mafic volcanism occurred between 81.5 and 84.1 Ma and younger felsic volcanism between 76.2 and 78.8 Ma. The total interval of 8 m.yr. for BIP igneous activity is much shorter than had previously been inferred. The best geochronologic results are obtained from U-Pb dating of zircon mineral (phonolites) separates and 40Ar/39Ar dating of phlogopite (nephelinites and basanites) and amphibole (phonolites) separates. [ABSTRACT FROM AUTHOR]

Mantle xenoliths in 83 Ma basanites from south-central Texas provide a rare opportunity to examine the lithospheric mantle beneath southern Laurentia. These peridotites represent lithosphere at the boundary between Mesoproterozoic continental lithosphere and transitional Gulf of Mexico passive margin. Here we report petrographic, mineral, and major element data for 29 spinelperidotite xenoliths from Knippa and use these to characterize the lithospheric mantle beneath south central Texas. The xenoliths comprise spinel-bearing lherzolites and harzburgites with coarse, equigranular textures. Some peridotites contain veins of lizardite. There are no pyroxenites or eclogites. The peridotites contain olivine( Fo89-92), orthopyroxene (En89-92), clinopyroxene (Wo40-45En45-49Fs3-5), and spinel. SpinelCr# (Cr/(Cr+Al)) distinguishes lherzolites (Cr# = 0.14–0.21) and harzburgites (Cr# = 0.25–0.36). Mineral and major element compositionsindicate that the lherzolites are residues after <10% melt extraction from primitive upper mantle and the harzburgitesformed by <15% melt extraction. Calculated oxygen fugacities indicate equilibration of the harzburgites at –1 to +0.61 and lherzolites at 0 to –2.6 log units with respect to fayalite-magnetite-quartz (FMQ) buffer, similar to lightly metasomatized spinel peridotites elsewhere. The degree of melt depletion and oxidation of the Knippa peridotites are consistent with present data sets for slightly metasomatized lithospheric mantle and/or backarc samples rather than forearc settings. Equilibration temperatures range from 824 to 1058 °C (mean= 916 °C), calculated at reference pressure of 2.0 GPa. Calculated mean seismic velocities Vs =4.44 km/sec and Vp =7.87 km/sec show no systematic difference between lherzolites and harzburgites, and agree with present geophysical measurements of upper mantle velocity beneath Texas. The seismic velocities calculated for these samples will provide important constraints for interpretation of EarthScope and other geophysical data sets. [ABSTRACT FROM AUTHOR]

We use U-Pb ages for 2655 individual detrital zircon grains in 30 samples of Upper Triassic (Carnian-Norian) sandstones of the southwestern USA (our data) and northern Mexico (other data) to infer regional Late Triassic provenance relations and tectonic features, which included a prerift uplift in Texas precursory to Jurassic opening of the Gulf of Mexico. Detrital zircons in sandstones from central paleorivers of the Chinle-Dockum fluvial system on the High Plains (USA) and Colorado Plateau, and from the marine terminus of the fl uvial system along the eastern flank of the Auld Lang Syne backarc basin in the Great Basin, reflect regional dispersal of sediment from the Ouachita orogen and adjacent Mesoproterozoic basement exposed on the northern flank of the rift uplift. The composite grain population of Ouachita-derived sands displays dominant U-Pb age peaks at 1100-1050 Ma (Grenvillian) and subordinate Neoproterozoic (630-550 Ma) and Paleozoic (475-400 Ma) age peaks inferred to document recycling of sand grains from the Ouachita system. The Ouachita detritus was supplemented by contributions from Mesoproterozoic basement rocks of southwest Laurentia (compound 1805-1655 Ma and unitary 1440 Ma age peaks) and from Permian-Triassic arc assemblages of northeastern Mexico (composite 285-215 Ma age peak). Master Chinle-Dockum paleodrainages extended east-southeast-west-northwest for 2000 km from Texas to Nevada, fl owing along the axis of a backarc trough formed by dynamic subsidence behind the Cordilleran magmatic arc, from headwaters in the Texas prerift uplift to the sediment trap of the backarc marine basin where the Auld Lang Syne Group accumulated. Sandstones from peripheries of the linked fluvial and marine depositional systems contain contrasting populations of detrital zircons derived either from the relict Amarillo-Wichita uplift, which fed abundant Cambrian zircons derived from an uplifted aulacogen-floor igneous assemblage, to selected basal units of the fluvial system, or from the Cordilleran arc assemblage to the south and west. The youngest Dockum sample from the Ouachita foreland on the High Plains contains abundant Devonian zircons probably derived from the Ouachita metamorphic core zone now present only in the Texas subsurface. Sandstones along the southern flank of the Chinle backarc basin on the southern Colorado Plateau contain populations of detrital zircons similar to those in sandstones of the Antimonio- Barranca forearc basin (Sonora) that was farther south beyond the arc axis. Sediment transported longitudinally from the Texas uplift to the El Alamar paleoriver and Potosí subsea fan of northeastern Mexico contains populations of detrital zircons similar but not identical to those in Chinle-Dockum fluvial strata of the High Plains shed transversely from the rift uplift. [ABSTRACT FROM AUTHOR]