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U-Pb age spectra of detrital zircons in samples from the Paleogene Colton Formation in the Uinta Basin of northeastern Utah and the Late Cretaceous McCoy Mountains Formation of southwestern Arizona (United States) are statistically indistinguishable. This finding refutes previous inferences that arkosic detritus of the Colton was derived from cratonic basement exposed by Laramide tectonism, and instead establishes the Cordilleran magmatic arc (which also provided sediment to the McCoy Mountains Formation) as the primary source. Given the existence of a north-south-trending drainage divide in eastern Nevada and the north-northeast direction of Laramide paleoflow throughout Arizona and southern Utah, we infer that a large river system headed in the arc of the Mojave region flowed northeast ~700 km to the Uinta Basin. Named after its source area, this Paleogene California River would have been equal in scale but opposite in direction to the modern Green River-Colorado River system, and the timing and causes of the subsequent drainage reversal are important constraints on the tectonic evolution of the Cordillera and the Colorado Plateau. © 2010 Geological Society of America.

Abstract: The Taku terrane consists of metamorphosed Carboniferous through Triassic marine clastic strata, volcanic rocks, and limestone that occur along the western margin of the Coast Mountains in southeastern Alaska. [...]

Cape Kiber on the Arctic coast of Chukotka, northeast Russia, consists of a granite intruding Devonian (and older?) strata in the core of a large southeast trending anticline. These strata are structurally overlain by Carboniferous and younger strata. AU-Pb age of 351.4 ±5.6 (2σ)Ma shows that the granite is Early Carboniferous in age. A large granite cobble extracted from a Carboniferous conglomerate produced a Late Devonian or Early Carboniferous U-Pb age of ~355-361 Ma. Also, a deformed and altered granitic dyke yielded an age of 363.7 ± 5.7 (2cr) Ma. Major and trace elements suggest a syn-collisional (orogenic) setting. The granite's (biotite) Ar release spectrum is reset. The granitic dyke also shows a disturbed Ar-Ar whole-rock spectrum implying an Early Cretaceous age (~122-130 Ma) for closure of the Ar system. We interpret this as due to widespread greenschist metamorphism accompanying regional deformation of the Anyuy-Chukotka Fold Belt that accompanied closure of the South Anyuy Ocean. Regionally, this event predates deposition of Aptian and Albian strata and the eruption of Okhotsk--Chukotsk magmatic rocks. An Ar-Ar (biotite) plateau age of 96.4 [+ or -]1.0 (2σ) Ma from a mildly deformed, lamprophyre dyke reflects intrusion in a setting of regional extension. Its deformation reflects a younger tectonic event. The record of Devonian--Carboniferous magmatism and early Carboniferous unroofing is younger and less complex than that of Arctic Alaska. However, evidence for Early Devonian (Caledonian) or Late Devonian (Ellesmerian) deformation could have been masked by intense Mesozoic deformation. Outcrop data and geochronology support and refine regional interpretations of Early Cretaceous deformation and mineral growth accompanying accretion of Chukotka to north Asia, followed by regional extension and subsequent convergent deformation. Resume : Le cap Kiber sur la cote arctique de Chukotka, dans le nord-est de la Russie, est forme d'un granite qui penetre des strates datant du Devonien (et plus anciennes?) dans le creur d'un grand anticlinal a pendage vers le sud-est. Ces strates sont recouvertes de maniere structurale par des strates datant du Carbonifere et plus recentes. Un age, determine par U-Pb, de 351,4 ± 5,6 (2σ) Ma montre que le granite date du Carbonifere precoce. Un gros caillou de granite, extrait d'un conglomerat datant du Carbonifere, a donne un age U-Pb de Devonien tardif ou de Carbonifere precoce de ~355-361 Ma. De plus, un dyke de granite deforme et altere a donne un age de 363.7 ± 5.7 (2σ) Ma. Les elements majeurs et en trace suggerent un environnement de collision synchrone (orogenique). Le spectre du relachement d'Ar du granite (biotite) est reinitialise. Le dyke de granite montre aussi un spectre Ar-Ar perturbe de la roche entiere, ce qui signifierait un age Cretace precoce (environ 122-130 Ma) pour la fermeture du systeme Ar. Nous interpretons cela comme etant du a un metamorphisme au facies des schistes verts etendu qui accompagne la deformation regionale de la zone de plissements Anyuy-Chukotka, laquelle accompagne la fermeture de l'ocean Anyuy sud. A l'echelle regionale, cet evenement a eu lieu avant la deposition des strates aptiennes et albiennes et l'eruption des roches magmatiques d'Okhotsk-Chukotsk. Un age plateau de 96,4 ± 1,0 (2σ) Ma, determine par Ar-Ar (sur une biotite) d'un dyke de lamprophyre legerement deforme, correspond a une intrusion dans un environnement d'extension regionale. Sa deformation est le reflet d'un evenement tectonique plus jeune. L'enregistrement de magmatisme au Devonien-Carbonifere et le retrait du toit au Carbonifere precoce est plus recent et moins complexe que celui de l'Alaska arctique. Toutefois, les evidences pour une deformation au Devonien precoce (Caledonien) ou au Devonien tardif (Ellesmerien) pourraient avoir ete masquees par une deformation intense au Mesozoique. Les donnees provenant des affleurements et de la geochronologie supportent et peaufinent les interpretations regionales d'une deformation et d'une croissance mineralogique au Cretace precoce qui accompagnaient l'accretion de Chukotka a l'Asie septentrionale; cette accretion a ete suivie d'une extension regionale et d'une deformation subsequente de convergence. [Traduit par le Redaction], Introduction As part of the Canada-Russia Science and Technology Exchange Agreement, co-operative field projects were undertaken to clarify the distribution and correlation of circum-Arctic Phanerozoic strata. One project, in 1989, [...]

The plate- boundary conditions of the Mesozoic North American Cordillera remain poorly constrained, but most studies support large (>800 km) southward motion of the Insular and Intermontane superterranes during Jurassic– Cretaceous time. An implicit feature in these models of large coastwise displacements is the presence of one or more continental- scale sinistral strike- slip faults that could have dismembered and displaced terrane fragments southward along the western margin of North America prior to the onset of mid- Cretaceous shortening and dextral strike- slip faulting. In this study, we documented a system of sinistral intra- arc shear zones within the Insular superterrane that may have accommodated large southward motion. Employment of a new large-n igneous zircon U-Pb method more than doubled the precision of measurements obtained by laser ablation– inductively coupled plasma– mass spectrometry (from ~1% to 0.5%) and allowed us to demonstrate the close temporal- spatial relationship between magmatism and deformation by dating comagmatic crosscutting phases. Crystallization ages of pre-, syn-, and postkinematic intrusions show that the intra- arc shear zones record an Early Cretaceous phase of sinistral oblique convergence that terminated between 107 and 101 Ma. Shear zone cessation coincided with: (1) collapse of the Gravina basin, (2) development of a single voluminous arc that stitched the Insular and Intermontane superterranes together, and (3) initiation of east- west contractional deformation throughout the Coast Mountains. We interpret these concurrent tectono- magmatic events to mark a shift in plate kinematics from a sinistral- oblique system involving separate terranes and intervening ocean basins to a strongly convergent two- plate margin involving a single oceanic plate and the newly assembled western margin of North America. [ABSTRACT FROM AUTHOR]

The Santa Catalina Mountains, SE Arizona, was one of the first metamorphic core complexes to be described. Despite its status as a type example, relatively little is known about precise ages and origins of the intrusive rocks that make up most of the crystalline core. U-Pb and Hf isotopic data by laser ablation-inductively coupled plasma-mass spectrometry from zircons and Nd isotopic results from whole rocks were obtained for 12 granitoids ranging from 1,440 to 26 Ma. Results confirm that the 1.44-Ga Oracle Granite extends through the Catalina Range as variably mylonitic granite and banded gneiss. Laramide intrusions (67-73 Ma) display initial [ζ.sub.Nd] values -5to -8 and [ζ.sub.Hf] from -7.5 to -9. Magmatic ages for the prominent white granite sills of the Wilderness suite are 46-57 Ma, in agreement with Terrien (2012), and these granites have initial [ζ.sub.Nd] values -8 to -10 and [ζ.sub.Hf] from -7 to -14. Lastly, the undeformed Catalina Granite has an age of 26 Ma, with an initial [ζ.sub.Nd] and [ζ.sub.Hf] of -6 and -8, respectively. Our Nd results agree with limited results from Farmer and DePaolo (89:10141-10160, 1984). Although the Catalina Granite seems to have a significant juvenile component based on Nd and Hf, most of the Laramide and Wilderness intrusions contain Nd and Hf compositions lying close to the evolution of 1.44-Ga Oracle Granites, a fact that is confirmed by the U-Pb data, which show both 1.7- and 1.4-Ga zircon cores in these samples, with 1.4 Ga as the dominant core age. In order to become the dominant source of most of the 72-45-Ma magmas, the Oracle pluton must not only extend across the whole Catalina region, but also have abundant deep-seated equivalents to provide magma sources. Keywords Santa Catalina metamorphic core complex * Granite origins * U-Pb ages * Hafnium isotopes * Neodymium isotopes, Introduction The Santa Catalina metamorphic core complex (Fig. 1), part of a chain of NW-trending metamorphic core complexes stretching across Arizona (Banks 1980; Davis 1980), is among the first occurrence [...]