James V. Jones

Age, provenance, and tectonic setting of Paleoproterozoic quartzite successions in the southwestern United States

New field studies combined with U-Pb zircon geochronology constrain the ages of deposition and sedimentary provenance of Paleoproterozoic quartzite successions exposed in the southwestern United States. Orthoquartzites were deposited in short-lived basins at two times (ca. 1.70 and 1.65 Ga) during crustal assembly of southern Laurentia. The more voluminous ca. 1.70 Ga successions occur in southern Colorado, northern New Mexico, and central Arizona and are interpreted here to be time correlative, though not necessarily deposited in the same basins. Detrital zircon from quartzites and metaconglomerates exposed in southern Colorado and northern New Mexico is characterized by a single population with a relatively narrow range of ages (1.80–1.70 Ga) and minimal Archean input (<5% of grains analyzed). Peak detrital zircon ages (1.76–1.70 Ga) vary slightly from location to location and mimic the age of underlying basement. Unimodal detrital populations suggest local sources and a first-cycle origin of the orthoquartzites within a short time interval (1.70–1.68 Ga) during unroofing of local underlying basement. The maximum age of quartzite exposed at Blue Ridge, Colorado, is constrained by the 1705–1698 Ma coarse-grained granitoid basement on which quartzite was deposited unconformably. The minimum age of Ortega Formation quartzite (New Mexico) is constrained by ca. 1680–1670 Ma metamorphic monazite overgrowths. These dates agree with direct ages on the lower Mazatzal Group, Arizona, and suggest that orthoquartzite deposition occurred over a wide region during and soon after the ca. 1.70 Ga Yavapai orogeny. Regional structural arguments and the thrust style of quartzite deformation suggest that the metasedimentary successions were deformed during the ca. 1.66–1.60 Ga Mazatzal orogeny, thus making them important time markers separating the Yavapai and Mazatzal orogenic events. Our model for syntectonic deposition involves extensional basin development followed by thrust closure, possibly due to opening and closing of slab rollback basins related to outboard subduction. The first-cycle origin of orthoquartzites near the end of the arc collisions of the Yavapai orogeny seems to contrast sharply with their extreme compositional maturity. This can be explained in terms of protracted, extreme diagenesis and/or special environmental influences that enhanced chemical weathering but were unique to the transitional atmosphere and ocean chemistry of the Proterozoic. Similarities among quartzites exposed throughout the southwestern United States and along the Laurentian margin suggest that they represent a widespread regional, and perhaps global, episode of sedimentation involving a distinctive syntectonic setting and unique climatic conditions, a combination that might make these units a signature lithology for Paleoproterozoic time.

Detrital zircon evidence for non-Laurentian provenance, Mesoproterozoic (ca. 1490–1450 Ma) deposition and orogenesis in a reconstructed orogenic belt, northern New Mexico, USA: Defining the Picuris orogeny

Detrital zircon and igneous zircon U-Pb ages are reported from Proterozoic metamorphic rocks in northern New Mexico. These data give new insight into the provenance and depositional age of a >3-km-thick metasedimentary succession and help resolve the timing of orogenesis within an area of overlapping accretionary orogens and thermal events related to the Proterozoic tectonic evolution of southwest Laurentia. Three samples from the Paleoproterozoic Vadito Group yield narrow, unimodal detrital zircon age spectra with peak ages near 1710 Ma. Igneous rocks that intrude the Vadito Group include the Cerro Alto metadacite, the Picuris Pueblo granite, and the Penasco quartz monzonite and yield crystallization ages of 1710 ± 10 Ma, 1699 ± 3 Ma, and 1450 ± 10 Ma, respectively. Within the overlying Hondo Group, a metamorphosed tuff layer from the Pilar Formation yields an age of 1488 ± 6 Ma and represents the first direct depositional age constraint on any part of the Proterozoic metasedimentary succession in northern New Mexico. Detrital zircon from the overlying Piedra Lumbre Formation yield a minimum age peak of 1475 Ma, and ~60 grains (~25%) yield ages between 1500 Ma and 1600 Ma, possibly representing non-Laurentian detritus originating from Australia and/or Antarctica. Detrital zircons from the basal metaconglomerate and the middle quartzite member of the Marquenas Formation yield minimum age peaks of 1472 Ma and 1471 Ma, consistent with earlier results. We interpret the onset of ca. 1490–1450 Ma deposition followed by tectonic burial, regional Al 2 SiO 5 triple-point metamorphism, and ductile deformation at depths of 12–18 km to reflect a Mesoproterozoic contractional orogenic event, possibly related to the final suturing of the Mazatzal crustal province to the southern margin of Laurentia. We propose to call this event the Picuris orogeny.

Basin formation near the end of the 1.60–1.45 Ga tectonic gap in southern Laurentia: Mesoproterozoic Hess Canyon Group of Arizona and implications for ca. 1.5 Ga supercontinent configurations

Detrital zircon data from the upper parts of the Proterozoic Hess Canyon Group of southern Arizona reveal abundant 1600–1488 Ma detrital zircons, which represent ages essentially unknown from southern Laurentia. This basinal succession concordantly overlies a >2-km-thick-section of 1657 ± 3 Ma rhyolite of the Redmond Formation. The rhyolite is intercalated with and hence contemporaneous with the lower parts of the overlying White Ledges Formation, a 300-m-thick orthoquartzite unit at the base of the Hess Canyon Group. These quartzites contain a unimodal detrital zircon age probability distribution with peak ages of 1778, 1767, and 1726 Ma, supporting regional correlation with other ca. 1.65 Ga quartzite exposures in southwestern Laurentia. However, the ∼900-m-thick argillaceous Yankee Joe and minimum 600-m-thick quartzite-rich Blackjack Formations contain younger detrital zircons, with peak ages ranging from 1666 to 1494 Ma and a maximum depositional age of 1488 ± 9 Ma. Prominent age peaks at 1582–1515 Ma and 1499–1488 Ma represent detritus that is exotic and not derived from known southern Laurentian sources. The Blackjack Formation is cut by the 1436 ± 2 Ma Ruin Granite, indicating that deposition, deformation, and intrusion occurred between 1488 and 1436 Ma. This basin likely developed before or in the early stages of the 1.45–1.35 Ga intracontinental tectonism in southwestern Laurentia. Our findings necessitate the presence of an ∼170 m.y. disconformity within the Hess Canyon Group and document a previously unrecognized episode of Mesoproterozoic basin sedimentation (>1.5 km of section) between 1488 and 1436 Ma in southern Laurentia. This new record helps to fill the 1.60–1.45 Ga magmatic gap in southern Laurentia and supports hypotheses for a long-lived Proterozoic tectonic margin along southern Laurentia from 1.8 to 1.0 Ga. The 1.6–1.5 Ga detrital zircon ages offer important new constraints for ca. 1.5 Ga Nuna reconstructions and for the paleogeography of contemporaneous basins such as the Belt Basin in western Laurentia.

Three proterozoic orogenic episodes and an intervening exhumation event in the Black Canyon of the Gunnison Region, Colorado

U/Pb zircon/titanite geochronology, in situ monazite geochronology, and 40Ar/39Ar thermochronology provide an unusually complete data set for reconstructing the tectonic history of Proterozoic rocks exposed in the Black Canyon, Gunnison, Colorado. These new geochronologic data record three protracted orogenic episodes and an exhumation event between orogenic pulses: (1) Yavapai orogeny (1741–1689 Ma), (2) exhumation marked by an angular unconformity beneath post‐Yavapai, pre‐Mazatzal quartzites, (3) Mazatzal orogeny (postquartzite deposition), and (4) 1434–1403 Ma intracratonic tectonism. Supracrustal rocks of the Black Canyon succession were deposited or crystallized at or prior to \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Revised regional correlations and tectonic implications of Paleoproterozoic and Mesoproterozoic metasedimentary rocks in northern New Mexico, USA: New findings from detrital zircon studies of the Hondo Group, Vadito Group, and Marqueñas Formation

1741\pm 4

Late Oligocene to present contractional structure in and around the Susitna basin, Alaska—Geophysical evidence and geological implications

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The Mystic subterrane (partly) demystified: New data from the Farewell terrane and adjacent rocks, interior Alaska

1713\pm 2