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 plate 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.

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Cretaceous thrust structures are found along the front of the Verkhoyansk miogeoclinal fold belt along the eastern boundary of the Siberian platform in northeast Asia. The Verkhoyansk thrust front is subdivided into a number of segments, each of which has its own thrust system geometry. Balanced cross sections have been constructed for each segment on the basis of the structural study of surface geology and available seismic and drilling data. Distinctions between the segments are also expressed in gravity anomalies and modern topography. Analysis of vitrinite reflectance shows that folding of the Ver-khoyansk thrust front was initiated during sedimentation as early as in the Late Jurassic. This period marks the beginning of the collision between the Siberian continent and the Kolyma-Omolon superterrane, now located 500 km to the east of the Verkhoyansk thrust front. Deformation of the thrust front ended by the late Late Cretaceous; erosion of the frontal anticlines began in the early Late Cretaceous. The t¾ontal fixrust structures formed in the Late Cretaceous were rejuvenated during a middle to late Pleistocene reactivation, which produced the modern mountain topography. The least an•ount of erosion of the Verkhoyansk thrust front, 840 m, is observed in its central part, in the Kuranakh segment. To the north and south the erosion increases to 1500 m and 2100 m, respectively. The general configuration of the Verkhoyansk fold belt and its frontal structures are defined by the geometry of Devonian riff-related structures on the eastem Siberian platform and the principal direction, approximately east-west, of Late Cretaceous compressional stresses. Introduction The Ver •khoyansk fold belt is located along the eastern margin of the Siberian platform. It forms part of the margin of a vast Mesozoic to Cenozoic orogenic belt which extends far to the east, to the coast of the Pacific [Patfenov, 1991; Parfenov et al., 1993]. The fold belt, 2000 km long and 500 km wide, stretches from the Lena River delta in the north to Uda Bay of the Sea of Okhotsk in the south (Figure 1). The fold belt has a typical miogeoclinal structure. An offset and sharp bend in the regional structure located north of the lower Aldan River divide the fold belt into the west Ver•oyansk and south Verkhoyansk sectors. Close to the Siberian platform, the west Ver •khoyansk sector is composed primarily Copyright 1995 by the American Geophysical Union. Paper number 94TC03088. 0278-7407/95/94TC-03088 $10.00 of Carboniferous and Permian deposits, while Triassic and Jurassic rocks are exposed to the east. The formations are composed of a thick (up to 20 kin) wedge of marine littoral, deltaic, and shelf clastics prograding to the east (Figure 2). To the west, these deposits change into synclxronous marine littoral and alluvial accun•ulations of the Siberian platform, which are most widespread within the Vilyui basin. To the east, the shelf clastics of the west Verkhoyansk sector grade into turbidires and deepwater black shales. Along the bom•dary with the S...