U-Pb ages of igneous xenoliths in a salt diapir, La Popa basin: Implications for salt age in onshore Mexico salt basins

Lawton, Timothy F.; Amato, Jeffrey M.

doi:10.1130/l658.1

“…If the stratigraphic assignment of this sample to La Joya Formation is correct, it means that La Joya Formation is much younger than previously thought or, that in the locality La Ballena, the clastic sedimentation continues until the Oxfordian, as it happens in north-central Mexico with La Gloria Formation or as it has been previously described in some localities north of Charcas (Escalante-Martinez, 2006) or in the Galeana area in Nuevo León (Pérez-Aguilar, 2018). The above is consistent with the significantly younger age suggested by Lawton and Amato (2017)…”

Section: Detrital Zircon U-pb Agessupporting

confidence: 91%

Sediment provenance of Triassic and Jurassic sandstones in central Mexico during activity of the Nazas volcanic arc

Wengler

¹

,

Barboza-Gudiño

²

,

Thomsen

³

et al. 2019

Journal of South American Earth Sciences

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We have investigated the provenance of Late Triassic and Jurassic siliciclastic sediments (Zacatecas, Nazas and La Joya formations) in the Mesa Central region (areas of La Ballena, Charcas and Real de Catorce) in central Mexico. The sediments were deposited during activity of the Nazas volcanic arc at the western margin of Pangaea. Provenance characteristics are essential for reconstructing the palaeotectonic setting of the region. Overall, 26 sediment samples and 3 volcanic rock samples from the Nazas volcanic arc were analyzed. The latter are potential source lithologies. Petrographic analysis reveals that the 2 analyzed sediments are mainly composed of monocrystalline quartz, polycrystalline quartz (chert and composite quartz), feldspar, and rock fragments of mainly volcanic origin. Th/Sc vs. Zr/Sc values illustrate low sediment recycling in the source area(s). For the majority of the analyzed samples low Cr and Ni values exclude input from a mafic/ultramafic (ophiolitic) source. The majority of the translucent heavy minerals (Pxn, Amp, Ep, Spn, Grt, Chl, Tur, Ant, Rt) are scarce in almost all samples. The most abundant translucent heavy minerals occurring in the samples are apatite and zircon. Apatite grains decrease from the southeast (La Ballena) towards the northeast (Real de Catorce) either indicating stronger weathering conditions in the area of Real de Catorce or a source area that delivered detritus exclusively for the zone of Real de Catorce. Sediments of the Zacatecas Formation illustrate maximum depositional ages ranging from Norian (Late Triassic) to the Hettangian/Sinemurian boundary (Early Jurassic). Detrital zircon U-Pb ages suggest that they received detritus from the Amazonian craton (~1780-1300 Ma), the Oaxaquia microcontinent (~1290-900 Ma), the Maya (Yucatan-Chiapas), Oaxaquia, Coahuila and possible Chortis, and Florida blocks (~720-450 Ma) and the Permian-Triassic magmatic arc (~300-240 Ma). The Acatlán Complex and the Maya (Yucatan-Chiapas) block are likely source areas for ~445-310 Maold zircon grains. The source of the ~240-200 Ma-old detrital zircons are likely magmatic rocks related to the early disassambly of western Pangaea. Detrital zircons from sediments of La Joya Formation provide maximum depositional ages from the Pliensbachian (Early Jurassic) to Oxfordian (Late Jurassic). The most probably source areas are the Oaxaquia microcontinent (~1290-900 Ma), and the Maya (Yucatan-Chiapas), and Coahuila blocks (~720-450 Ma). Zircon ages ranging from ~200-150 Ma are indicative of detritus from the Nazas volcanic arc, which explains the presence of the volcanic fragments in La Joya Formation deposits.

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“…up to several kilometres in diameter) clasts of rock clearly denser than the encasing salt (e.g. igneous rock, anhydrite; Dalgano and Johnson, 1968;Kent, 1979;Richter-Bernberg, 1980;Gansser, 1992;Lawton and Amato, 2017). These clasts were carried up several kilometres from autochthonous levels within the rising salt and have not yet sunk, with numerical and physical models indicating this occurs because salt rise rate exceeds the descent rate of the denser clast (e.g.…”

Section: Composition Of Salt Weldsmentioning

confidence: 99%

Subsurface expression of a salt weld, Gulf of Mexico

Jackson

¹

,

Zhang

²

,

Herron

³

et al. 2018

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Salt welds form due to salt expulsion and thinning by mechanical (e.g. salt flow) and/or chemical (e.g. salt dissolution) processes. Despite being ubiquitous in salt-bearing sedimentary basins, where they may trap large volumes of hydrocarbons, little is published on weld thickness and composition. We here use 3D seismic reflection, borehole, and biostratigraphic data from the Atwater Valley protraction area of the northern Gulf of Mexico to constrain the thickness and composition of a tertiary salt weld. Seismic data image an 'apparent weld' (sensu Wagner and Jackson, 2011) at the base of a Plio-Pleistocene minibasin that subsided into allochthonous salt. Borehole data indicate the weld is actually 'incomplete', being c. 24 m thick, and containing an upper 5 m thick halite and a lower 15 m thick halite, separated by a 4 m thick mudstone. The age and origin of the intra-weld mudstone is unclear, although we speculate it is either: (i) Late Jurassic, representing material transported upwards from the autochthonous level within a feeder, and subsequently trapped as allochthonous salt thinned and welded, or, perhaps more likely; (ii) Pliocene, representing a piece of salt carapace reworked from the top of and eventually trapped in, the now locally welded sheet. We show that 3D seismic reflection data may not resolve salt weld thickness, with the presence of relatively thin remnant salt lending support to models of welding based on viscous flow. Furthermore, the halite-dominated character of the weld supports the hypothesis that tectonic purification may occur during salt flow. below or between minibasins (Jackson and Cramez, 1989). Based on their structural position and attitude, welds are described as 'primary' (i.e. subhorizontal, joining strata originally above and below autochthonous salt), 'secondary' (i.e. subvertical, joining minibasins originally situated either side of squeezed and now-evacuated salt diapirs, or 'tertiary' (i.e. subhorizontal, joining strata originally above and below allochthonous salt (Jackson and Cramez, 1989). Depending on how much salt they contain (or are inferred to contain), welds are also described as 'complete' (i.e. contains no remnant salt; cf. Jackson and Cramez, 1989), 'incomplete' (i.e. contains up to 50 m of remnant salt), 'discontinuous' (i.e. contains complete and incomplete parts), or 'apparent' (i.e. appears free of salt at a particular scale

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“…up to several kilometres in diameter) clasts of rock clearly denser than the encasing salt (e.g. igneous rock, anhydrite; Dalgano and Johnson, 1968;Kent, 1979;RichterBernberg, 1980;Gansser, 1992;Lawton and Amato, 2017). These clasts were carried up several kilometres from autochthonous levels within the rising salt and have not yet sunk, with numerical and physical models indicating this occurs because salt rise rate exceeds the descent rate of the denser clast (e.g.…”

Section: Composition Of Salt Weldsmentioning

confidence: 99%

Subsurface expression of a tertiary salt weld, Gulf of Mexico

Jackson¹,

Zhang²,

Herron³

et al. 2017

Preprint

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Salt welds form due to salt expulsion and thinning by mechanical (e.g. salt flow) and/or chemical (e.g. salt dissolution) processes. Despite being ubiquitous in salt-bearing sedimentary basins, where they may trap large volumes of hydrocarbons, little is published on weld thickness and composition. We here use 3D seismic reflection, borehole, and biostratigraphic data from the Atwater Valley protraction area of the northern Gulf of Mexico to constrain the thickness and composition of a tertiary salt weld.Seismic data image an 'apparent weld' (sensu Wagner and Jackson, 2011) at the base of a PlioPleistocene minibasin that subsided into allochthonous salt. Borehole data indicate the weld is actually 'incomplete', being c. 24 m thick, and containing an upper 5 m thick halite and a lower 15 m thick halite, separated by a 4 m thick mudstone. The age and origin of the intra-weld mudstone is unclear, although we speculate it is either: (i) Late Jurassic, representing material transported upwards from the autochthonous level within a feeder, and subsequently trapped as allochthonous salt thinned and welded, or, perhaps more likely; (ii) Pliocene, representing a piece of salt carapace reworked from the top of and eventually trapped in, the now locally welded sheet. We show that 3D seismic reflection data may not resolve salt weld thickness, with the presence of relatively thin remnant salt lending support to models of welding based on viscous flow. Furthermore, the halite-dominated character of the weld supports the hypothesis that tectonic purification may occur during salt flow.

show abstract

U-Pb ages of igneous xenoliths in a salt diapir, La Popa basin: Implications for salt age in onshore Mexico salt basins

Cited by 13 publications

References 36 publications

Sediment provenance of Triassic and Jurassic sandstones in central Mexico during activity of the Nazas volcanic arc

Sediment provenance of Triassic and Jurassic sandstones in central Mexico during activity of the Nazas volcanic arc

Subsurface expression of a salt weld, Gulf of Mexico

Subsurface expression of a tertiary salt weld, Gulf of Mexico

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