Abstract This book is the final product of the Circum-Arctic Lithosphere Evolution (CALE) project. The project's ultimate goal is to link the onshore and offshore geology in order to develop a self-consistent set of constraints for the opening of the Amerasia Basin. The circum-Arctic is divided into seven regions, each with its own research team; the teams included geophysicists and geologists working together to integrate geological and geophysical data, from onshore to offshore. This work is summarized in the 18 papers contained in this volume.
Abstract Thermochronologic and thermobarometric data reveal the timing, distribution and intensity of thermal events associated with detachment faulting in the Sacramento Mountains metamorphic core complex. In the northwest Sacramento Mountains, cooling rates of c. 100°C Ma −1 are associated with Late Cretaceous plutonism followed by cooling of the crust by thermal conduction. Post-Late Cretaceous cooling slowed to c. 1–6°C Ma −1 . Finally, the region records average cooling rates of 38–53°C Ma −1 between c. 20 and 15 Ma. In contrast, the thermal profile of the northeast Sacramento Mountains is dominated by syntectonic Tertiary plutonism followed by very rapid cooling. A granodioritic suite intruded at c. 680°C and c. 3 kbar at c. 20 Ma, records cooling to <100°C by c. 15 Ma. Such rapid cooling and exhumation suggests that unroofing by tectonic denudation was the driving mechanism for the final cooling. The similarity of the miocene cooling profiles between these two areas clearly suggests that the Sacramento Mountains experienced a regional cooling event associated with tectonic unroofing driven by regional Miocene crustal extension. Estimates of the initial angle of the Sacramento Mountains detachment fault using palaeothermal gradients suggest that it was active at a dip of 25°.
The Arabian Shield was a major site of early Neoproterozoic to late Ediacaran juvenile magmatic addition at the northern end of the East African Orogen (EAO) and provides important insights into th ...
Abstract Detrital U–Pb zircon age data from five stratigraphically controlled Mesozoic sandstones collected from a relatively continuous section in northwestern Axel Heiberg Island are used to evaluate the sediment dispersal patterns and source areas of the northern Sverdrup Basin. Three distinctive provenance types are identified. Early Triassic, Late Triassic and Middle Jurassic samples are dominated by Permo-Triassic zircons and are inferred to be derived from the Taimyr Peninsula/Polar Urals, the New Siberian Islands or some unexposed source submerged beneath the Arctic Ocean. The presence of chrome spinel in these samples suggests a component of mafic–ultramafic material in the source. An Early Jurassic sample is dominated by late Neoproterozoic–early Silurian zircons, which correlate with the Caledonian and Timanian orogens of the Barents Shelf region. A Late Jurassic sample is dominated by Meso-, Palaeoproterozoic and Archaean zircons interpreted to be sourced from the Canada–Greenland shield. Supplementary material: Heavy mineral data (Table S1) and U–Th–Pb ion microprobe analytical data (Table S2) are available at http://www.geolsoc.org.uk/SUP18475 .
We present a heavy minerals study of several sedimentary units deposited within the Yukon-Koyukuk basin (YKB) in Alaska. The YKB started to form in middle to late Jurassic after the collision between an intraoceanic volcanic arc and the Arctic Alaska margin. The collision led to thrusting of the seafloor (mafic and ultramafic rocks of the Angayucham Terrane), over the future Brooks Range and Ruby Terrane. The basin is flanked on three sides by metamorphic rocks of the Seaward Peninsula to the west, the Ruby terrane to the east and the Brooks Range to the north. The remnants of the volcanic arc (Koyukuk Arc Terrane, KAT) divide the basin into a northern Kobuk-Koyukuk basin (KKB) and a southern Lower-Yukon basin (LYB). We present results from the Kv, Kvg, Ks, Kms, Kmc, and Kqc units (after Patton et al.2009), collected along the Koyukuk and the Yukon rivers. The units are as follows: Kv: formed by basaltic and andesitic lava flows interbedded with volcanogenic conglomerate to mudstone rocks. K-Ar ages vary from 134 Ma and 118 Ma with a U-Pb age obtained through a tuff of about 138 Ma. Kvg: mainly consists of volcaniclastic greywacke and mudstone interbedded with tuffaceous layers which gave U-Pb ages comprised between 112 and 110 Ma (Albian). Molluscs of the same time have been reported throughout the entire unit. Kms: mainly fine to coarse sandstone interbedded with shaly layers. Interpreted to be the marine tongue of the Ks deposits. Ks: late Cretaceous in age, this unit consists of alternations of sandstone and shale layers deposited in fluvial to shallow marine environments. Kmc: mafic igneous clasts conglomerate with mafic and calcareous greywacke and mudstone. Marine molluscs of Cretaceous age have been found. Kqc: overall a quartz rich unit composed of conglomerate, sandstone and mudstone. Plant fossils date the unit to the Cretaceous. We use Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN®) for heavy mineral (HM) analysis to establish a clear relationship between sediments and source regions and build a model for the basin formation and evolution. Kv and Kmc samples reflect a volcanic source, while Kvg, Kms, Ks, and Kqc display the progressive unroofing of deeper and higher grade metamorphic rocks. Combining these data with DZ and U-Pb absolute ages, we interpret the YKB to be formed prior to 138 Ma as the forearc basin of the intraoceanic arc. It evolved into a hinterland setting at about 110 Ma when the first deposition of metamorphic detritus is recorded by the Kvg unit, mainly derived from erosion of the Brooks Range.  Limited paleocurrent data along with the novel HM data attribute the Ks, Kms, Kmc and the Kqc to the erosion of the Ruby terrane as it uplifted during middle to late Cretaceous time.
Abstract In northern Alaska, the Early Cretaceous sedimentary Yukon-Koyukuk basin documents the progressive unroofing of the adjacent Brooks Range orogen. Igneous clasts in the lower conglomerate are believed to originate from ophiolitic rocks of the two uppermost allochthons in the Brooks Range, the Brooks Range ophiolite and the Angayucham terrane. The emplacement of these oceanic terranes onto the continental margin of the Arctic Alaska terrane documents the initiation of Brookian orogenesis. While most agree that the Angayucham terrane represents a widespread distribution of Late Devonian oceanic crust and Triassic-Early Jurassic oceanic plateau(s)/island(s), the age and origin of the Brooks Range ophiolite remains controversial. We present new age, whole-rock chemistry, and isotopic data from igneous clasts as well as a few Angayucham terrane outcrop samples from the NE Yukon-Koyukuk basin. Our results show that the igneous clasts are mostly subduction-related and more likely to represent eroded material from the Brooks Range ophiolite rather than the Angayucham terrane. Our Late Triassic, and Early and Middle Jurassic zircon crystallization ages for the igneous clasts, combined with their immobile trace element compositions documenting various stages of oceanic subduction (mature arc and later rifting), suggest a long-lived subduction system that was active in the Late Triassic and throughout the Middle Jurassic. Radiogenic lead and neodymium isotopic results yield juvenile signatures for both the igneous clasts and the Angayucham terrane, pointing to their formation in an intraoceanic setting distal from the continental rocks and sediments of the Arctic Alaska terrane. These new data, combined with the published data of others, allow us to propose a revised tectonic model that integrates Late Triassic island arc formation with the tectonic development and emplacement of the Brooks Range ophiolite.
The Arabian-Nubian Shield (ANS) includes Middle Cryogenian-Ediacaran (790–560 Ma) sedimentary and volcanic terrestrial and shallow-marine successions unconformable on juvenile Cryogenian crust. The oldest were deposited after 780–760 Ma shearing and suturing in the central ANS. Middle Cryogenian basins are associated with ~700 Ma suturing in the northern ANS. Late Cryogenian basins overlapped with and followed 680–640 Ma Nabitah orogenesis in the eastern ANS. Ediacaran successions are found in pull-apart and other types of basins formed in a transpressive setting associated with E-W shortening, NW-trending shearing, and northerly extension during final amalgamation of the ANS. Erosion surfaces truncating metamorphosed arc rocks at the base of these successions are evidence of periodic exhumation and erosion of the evolving ANS crust. The basins are evidence of subsequent subsidence to the base level of alluvial systems or below sea level. Mountains were dissected by valley systems, yet relief was locally low enough to allow for seaways connected to the surrounding Mozambique Ocean. The volcanosedimentary basins of the ANS are excellently exposed and preserved, and form a world-class natural laboratory for testing concepts about crustal growth during the Neoproterozoic and for the acquisition of data to calibrate chemical and isotopic changes, at a time in geologic history that included some of the most important, rapid, and enigmatic changes to Earth’s environment and biota.
Abstract The juxtaposition of the composite Pearya terrane and the northern Laurentian margin at Ellesmere Island, Nunavut, Canada, has significant ramifications for the Paleozoic tectonic history of the circum-Arctic region. Published tectonic models rely upon interpretation of the subduction-related Kulutingwak Formation as an indicator of Ordovician and/or Silurian accretion (Trettin, 1998). New igneous and detrital zircon U-Pb and Lu-Hf isotopic data from 16 samples collected in the Yelverton Inlet–Kulutingwak Fiord region of northern Ellesmere Island suggest that the Kulutingwak Formation of Trettin (1998) contains structural blocks derived from both the Pearya terrane and Silurian strata associated with the ancestral Laurentian margin. Data from this study demonstrate a complex provenance history for rocks within the Petersen Bay, Kulutingwak Fiord, and Emma Fiord fault zones, with age probability peaks of ca. 470 Ma, 650 Ma, and 960–980 Ma that suggest affinity with the Pearya terrane, and age probability peaks of ca. 1800 Ma and 2700 Ma that indicate connections to the Laurentian margin. The combination of these signatures in Kulutingwak Formation rocks suggests that the Pearya terrane was proximal to the northern Laurentian margin by Late Ordovician time. Silurian and younger strike-slip displacement on the major fault zones resulted in the incorporation of blocks derived from the Pearya terrane basement and Silurian clastic rocks into the Kulutingwak Formation. Silurian displacement along these strike-slip faults, which are integral components of the Canadian Arctic transform system, is recorded by syndepositional deformation structures in the Danish River Formation and prevented the transition from soft to hard collision of the Pearya terrane. The two-stage model for the Pearya terrane—accretion followed by significant translation—provides a process for developing complex steep terrane boundaries with contentious displacement histories that are common in accretionary orogens.
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