Detrital zircon geochronology of the Roberts Mountains allochthon, Nevada

Abstract

U-Pb geochronologic analyses have been conducted on 205 individual detrital zircon grains from Cambrian through Devonian sandstones of the RobertsMountains allochthon in central Nevada. These strata were tectonically emplaced onto the Cordilleran margin during the mid-Paleozoic Antler orogeny, but their original depositional settings and provenance have been controversial. Our data, combined with previous detrital zircon studies, define four different age signatures for the eugeoclinal strata: (1) 690-7 15 and 1065-1350 Ma grains in a minor group of sandstones in the Upper Cambrian(?) Harmony Formation, (2) 1745-Comparison of these data with the detrital zircon reference for the Cordilleran miogeocline and with ages of basement provinces in cratonal North America indicates that sandstones in the lower Vinini and parts of the Harmony Formations were derived from 1.0-1.3,~1.43, and 1.6-1.8 Ga provinces of southwestern North America. In contrast, most older and younger units contain few grains of the appropriate ages to have come from the southwestern part of North America, and instead have strong similarities with the Peace River arch region of western Canada.We propose that detritus in most of the Harmony Formation was shed from off-shelf basement rocks exposed along the Canadian continental margin, perhaps as a western continuation of the Peace River arch or as extensional fault blocks. In contrast, detritus

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“…Samples from off-shelf assemblages include the Lower or Middle Ordovician Vinini Formation (Gehrels et al, 2000a) and the Ordovician Valmy Formation (Smith and Gehrels, 1994). We have also analyzed samples from Mississippian strata of the Tonka Formation and Pennsylvanian strata of the Battle Formation, which are widely interpreted to have been shed from off-shelf strata (e.g., Valmy and Vinini Formations) exposed in the Antler highlands to the west (Burchfi el et al, 1992;Dickinson, 1995, 2000).…”

Detrital zircon U–Pb reconnaissance of the Franciscan subduction complex in northwestern California

“…Before extensive burial by the ignimbrite flare-up and other Cenozoic volcanic rocks, sedimentary rocks exposed in Nevada included those making up the Roberts Mountain allochthon, the Golconda allochthon, the Cordilleran miogeocline, and the western Nevada Triassic back arc basin (Van Buer et al 2009;Long 2012). Considered together, the first three of these units are dominated by 1.7-2.0 Ga detrital zircons, with lesser amounts of older and younger zircons (Gehrels et al 1995Riley et al 2000;Harding et al 2000;Spurlin et al 2000; see also Cecil et al 2010, Figure 5). The back arc basin (Wyld 2000) contains zircon ages similar to the Jurassic erg deposits and apparently was similarly sourced (Dickinson and Gehrels 2008).…”

Tectonostratigraphy of the Lesser Himalaya of Bhutan: Implications for the along-strike stratigraphic continuity of the northern Indian margin

“…The lack of young detritus in some samples could represent a heterogeneous source region with an aerially limited source for Paleozoic zircons, or could refl ect limited sediment mixing during deposition (e.g., Gehrels et al, 2000;DeGraaff-Surpless et al, 2003;Mapes, 2009); or (2) although the lithology of the Jaishidanda Formation is remarkably uniform along strike, the unit could contain strata as old as Neoproterozoic and as young as Ordovician. Note that in the northern Kuru Chu valley, sample NBH-7 is low in the section and displays a Neoproterozoic (ca.…”