Geology topics

J. Toro

Publications and source records attributed to J. Toro.

3 recordsLinked to original sources

USGS2006

New insights into Arctic paleogeography and tectonics from U-Pb detrital zircon geochronology

To test existing models for the formation of the Amerasian Basin, detrital zircon suites from 12 samples of Triassic sandstone from the circum-Arctic region were dated by laser ablation-inductively coupled plasma-mass spectrometry (ICP-MS). The northern Verkhoyansk (NE Russia) has Permo-Carboniferous (265-320 Ma) and Cambro-Silurian (410-505 Ma) zircon populations derived via river systems from the active Baikal Mountain region along the southern Siberian craton. Chukotka, Wrangel Island (Russia), and the Lisburne Hills (western Alaska) also have Permo-Carboniferous (280-330 Ma) and late Precambrian-Silurian (420-580 Ma) zircons in addition to Permo-Triassic (235-265 Ma), Devonian (340-390 Ma), and late Precambrian (1000-1300 Ma) zircons. These ages suggest at least partial derivation from the Taimyr, Siberian Trap, and/ or east Urals regions of Arctic Russia. The northerly derived Ivishak Formation (Sadlerochit Mountains, Alaska) and Pat Bay Formation (Sverdrup Basin, Canada) are dominated by Cambrian-latest Precambrian (500-600 Ma) and 445-490 Ma zircons. Permo-Carboniferous and Permo-Triassic zircons are absent. The Bjorne Formation (Sverdrup Basin), derived from the south, differs from other samples studied with mostly 1130-1240 Ma and older Precambrian zircons in addition to 430-470 Ma zircons. The most popular tectonic model for the origin of the Amerasian Basin involves counterclockwise rotation of the Arctic Alaska-Chukotka microplate away from the Canadian Arctic margin. The detrital zircon data suggest that the Chukotka part of the microplate originated closer to the Taimyr and Verkhoyansk, east of the Polar Urals of Russia, and not from the Canadian Arctic. Copyright 2006 by the American Geophysical Union.

Tectonics↗

USGS2004

Origin of the Bering Sea salient

Our investigations in Alaska and Russia show that the curved orogen of the Bering Strait region is a composite feature that formed as a result of multiple superimposed events and cannot be related to latest Cretaceous–early Tertiary east-west shortening. Relations interpreted to record east-west shortening include the Chukchi syntaxis, deformation on Seward and Chukotka Peninsulas, the map pattern of Triassic-Jurassic mafic rocks, and plate reconstructions. These relations are reviewed in light of new data and show that the curved orogen cannot have been formed by east-west shortening. For example, the Chukchi syntaxis, the northeastern limb of the orogen, is a primary structural loop that originated during the Brookian orogeny in the Early Cretaceous and therefore predates postulated oroclinal bending. East-west shortening on Seward Peninsula and Chukotka is manifest by low-amplitude, long-wavelength folds that require only small strains. The Seward Peninsula/Yukon-Koyukuk province boundary was previously interpreted as a thrust fault, but it instead may be a left-lateral strike-slip fault. Triassic-Jurassic mafic rocks similar to the Angayucham terrane are found on the northern Chukotka Peninsula, but a better correlation is with rocks farther south in the South Anyui suture zone, resulting in a less-arcuate pattern. Mid-Cretaceous north-south extension in the Bering Strait region has enhanced the curvature of the margin. Recent plate reconstructions indicate that shortening between Eurasia and North America was previously overestimated and that significant east-west convergence probably did not occur in the region during the Tertiary. We conclude that the curved orogen in the Bering Strait region is not a true orocline and instead is a composite structural feature that is best described as a salient.

GSA Special Papers↗

USGS1997

An integrated model for the tectonic development of the frontal Brooks Range and Colville Basin 250 km west of the Trans-Alaska Crustal Transect

We present a kinematic model for the sequence of deformation and sedimentation in the frontal Brooks Range and adjacent Colville Basin in the Etivluk River region, 250 km west of the Trans-Alaska Crustal Transect (TACT). The model is based on a tectonic subsidence analysis of the foreland basin, combined with structural, stratigraphic, and thermal studies of the northern edge of the Brooks Range thrust belt. We interpret six discrete tectonic events that led to the present-day configuration of the thrust belt in this area: (1) emplacement of ophiolitic allochthons over the distal continental margin rocks in Valanginian time, hundreds of kilometers south of this study, (2) Hauterivian uplift of the Barrow Arch rift margin, affecting the northern part of the Colville Basin, (3) Barremian contraction involving emplacement of distal continental margin and ophiolitic allochthons onto the Endicott Mountains allochthon and creation of a southward dipping flexural basin on the North Slope autochthon, (4) mid-Cretaceous exhumation of imbricated rocks in the Brooks Range during northward propagation of the thrust front into the foreland, (5) minor thrusting in Late Cretaceous-Paleocene in the northern foreland to the northern limit of contractional structures, and (6) regional exhumation of the orogen and the foreland in Paleocene-Eocene time. This sequence of deformation agrees well with a simple model of a forward propagating thrust system.

Journal of Geophysical Research B: Solid Earth↗