Abstract The Late Silurian?–Devonian fluvial deposits of northern Spitsbergen were deposited on basement with Caledonian and earlier metamorphic ages in which two distinct terranes are recognized (Biskayerhalvøya and Krossfjorden). These form part of the central of three major terranes in Svalbard, assembled during the Caledonian Orogeny. The subsequent geological history of the Svalbard area has been strongly influenced by the north-trending structures which were active as transcurrent fault zones at this time. The unconformable base of the Siktefjellet Group, a Late Silurian?–earliest Devonian sequence of coarse conglomerates and breccias, overlain by fluvial sandstones, is preserved only on the Biskayerhalvøya terrane, and the final juxtaposition of the two terranes (during the Haakonian sinistral strike-slip phase) is interpreted to post-date the deposition of these sediments. The Lochkovian Red Bay Group, a sequence of conglomerates, fluvial sandstones and siltstones, was deposited on both terranes. This has been mapped and correlated throughout the basin exposure, allowing the reconstruction of the tectonic history. Sedimentation was influenced by active faulting during deposition of the oldest Wulffberget Formation, but subsequent deposits show little evidence of this. Deposition was interrupted in latest Lochkovian time by renewed sinistral strike-slip faulting, which broke up an area of the basin into rotating fault blocks, across which about 30 km of extension occurred. This was followed by east–west shortening, which uplifted the Red Bay basin and underlying basement, developing large folds, locally with related thrusting. The Monacobreen phase is defined to involve this deformation. The Andrée Land Group reflects a subsequent renewal of subsidence, and re-establishment of an extensive fluvial basin, occupying an area east of the inverted Red Bay basin. Conglomeratic units that overlie the Red Bay Group are interpreted as the products of the reworking of the uplifted Red Bay basin and its basement. The Latest Devonian–Earliest Carboniferous Svalbardian phase again involved east–west shortening, with limited strike-slip faulting, but it is difficult to discriminate these effects from the Monacobreen phase in the Siktefjellet and Red Bay groups. A review of North Atlantic and Arctic Devonian basins shows that during deposition of the Red Bay and Andrée Land groups, the tectonics of Svalbard was more similar to that of the developing Ellesmerian orogen, than to that of the collapsing Caledonian orogen. A model is proposed that links the repeated extension and shortening seen from Early Devonian time in north Spitsbergen to anticlockwise rotation of the Chukotka–Alaska plate, about an axis near the position of Svalbard during Ellesmerian collision, coupled with minor Caledonian-related strike-slip movement along reactivated fault zones.

Abstract Lithoteetonic terranes thot are now the northwestern eoms of North America record more than 500 m.y. of ore-forming processes. Almost all of Alaska’s mineral deposits older than 150 Ma knuicd in oceanic environments in blocks of oceanic crust island areas, or isolated continental fragments distant from North America or in platforms and basins adjacent to the Paleozoic North American continental margin, Most and dle Cretaceous and vounger ore systems, especially those couccntinted in the soothern part of the slate are associated with processes attendant to terrain accretion Hydrothernial activity and commonly related magmatism were principally prodnets of oceanic plate subdnetinn beneath the southern Alaska continental margin. Few significant lode deposits in Alaska arc poslacerelionary, anorogenic systems that are clearly unrelated to Mesozoic and Cetiozoic plate convergence. Late Proterozoie th rough Silurian poly metallic volcauogcnic massive sulfide deposits, some broadly contemporaneous with Fe-Cu-Au starts, are the oldest recognized major mineral deposits in Alaska. These deposits were formed during submarine-arc magmatism distant from the North American continent and are now located in rocks of the accreted Alexander terraue in the southernmost part of southeastern Alaska. Shale- and carbonate-hosted base metal deposits and polymetallic volcanogenie massive sulfide deposits developed along the North American continental shelf in the Devonian and Carbonilcrous Extension and probably rift-related voleanism along the continental margin were coeval with Antler-Ellesnicii an orogenesis landward on the eraton. Resulting submarine hydrothernial activity formed the mineral deposits now exposed in rocks of the Arctic Alaska terrain- in the western and central Brooks Range. They include stratilorm, shale-hosted bo the s such as Red Dog, massive syngenelic barite carbonate-hosted copper systems such as Rubv Creek, and the voleanogenie massive sulfide occurrences of the Ambler district. The late Paleozoic continental margin strata of the Yukon-Tanaua lerrane, where exposed in east-central and southeastern Alaska, contain additional volcauogcnic massive sulfide bo the s that may be of similar origin. Triassic lifting along the east side of the Alexander terraue, still distal to North America, was responsible for a third episode of polymetalle volcauogemc massive sulfide formation. Resulting deposits include Creens Creek, in the northern part of southeastern Alaska, and Windy Craggy, in adjacent British Columbia. By the Late Triassic, the Alexander terrane was amalgamated with the Wrangellia, Peninsular, and northern Taku terrenes inlo the Wrangclltn superterrane. A second, prohahlv unrelated Triassic lifting event along the superterrane led to extrusion of thick snbaerjal basalt flows within the Wrangellia Iciitine. These basalts served as the metal source for Kelinecott-type copper deposits during terrane accretion to the eraton later in the Mesozoic. Jurassic arc inaginalisin in the Pacific basin included formation of a series of mineral deposits in terranes that were obducted onto of accreted to western Alaska during a period of 100 m.y. Podifonn chroinite bo the s formed in ultramnlicplutonie rocks that were later nbdnded in the Brooks Range and Ruby geanticline as parts of the Augavucliam lerrane and formed part of the Talkeetna arc in the Peninsular lerrane that is now part of south-central Alaska Coeval volcanisni in the Talkeclna arc was characterized bv many small but widespread metalliferous events and the formation of at least one significant Jurassic volcaoogenic massive sulfide system at the Johnson River prospect. Are inagiuatisni that formed the Coodnews and Togiak terranes included crystallization of Fe-, Ti-. and Pt-rich zoned nllramafic bo the s. During the Quaternary, erosion of bo the s in the forniei lerrane led to major placer platinum aee-umulatktns that represent the largest resource of the metal in the United States. Middle to Late Cretaceous terraine accretion and magmatism were associated with vvidespread metalliferous events. Copper porphyries and Fe-Cu-Au-bearing skarns formed in rocks of ihe W’ rangcllia lerrane and in rocks of the inboard Gravina flysch basin soon afterttheir accrelinn along soutb-central Alaska and were coeval with continuing suhduction along the southern margin of these leiraues. The associated thermal event probably aLso drove fluid circulation that led to deposition of Keuneeott-type copper ores in littoral to supralitloral carbonate units above the Triassic rift basalts of the Wrangellia terrane. In the Gravina flysch basin in southeastern Alaska, and dle Cretaceous arc luaginalism included development of the Klukwan-Duke bell of Fe-rieh. Alaska-type zoned ultramafic bo the s. Late Cretaceous are magmatism in southwestern Alaska, also inboard of the accreted Wrangellia superterrane, is temporally associated with formation of einnabar-hearing epithermal lodes and Au-rieh voleano-piutonic completes. Farther north. Albian gold veins in the Seward and Arctic Alaska terrain’s could lie products of extensional events in compressional orogens or could be the result of simple, broad-scale erustal thinning. In contrast, early Late Cretaceous gold veins in the Yukon-Tanana terraue show a (lose genetic association with subdution-related plutons that were likelv derived from the underplaring of Gravina flysch. Late Gretaceous exlensiomil magmatism caused emplacement of tin granites on the Seward Peninsula. Collisional tectonics conlinued to direct Alaskan mineral deposit formation in the Cenozok, Plate eonvergepce and associated snbduetion led to the widespread development of Alaska’s productive mesothernial gold vein systems throughout the southeastern and south-central fere are, Metamorpliie fluid flow, in many cases aided by changing Eocene plate motions in the Pacific basin, resulted in lode gold formation in the Chichagof district, the Juneau gold belt, and the Willow Creek district and across the Kenai-Chugach mountain range, Beginning in the late Eocene, growth of the Meshik and Aleutian arcs in southwestern Alaska was associated with the formation ol Cu-Mo porphyry bo the s and related epithermal gold vein occurrences. In contrast to collision-driven ore genesis, localized late Oligocene and early Miocene extension in southeastern Alaska included crystallization of the Quartz Hill molybdenum porphyry and formation of Zn-Pb and tin skams in the Groundhog basin area.

Abstract Mesozoic continental basins of northern China, including the Junggar Basin, provide some of the most spectacular and important fossil assemblages in the world, but their climatic and environmental contexts have been shrouded in uncertainty. Here we examine the main factors that determine those contexts: palaeolatitude; the effects of changing atmospheric gases on the radiative balance; and orbitally paced variations in insolation. Empirical evidence of these factors is accumulating rapidly and promises to upend many long-standing paradigms. We focus primarily on the Junggar Basin in Xinjiang, NW China, with the renowned Shishugou Biota, and the basins in Liaoning, Hebei and Inner Mongolia with their famous Jehol and Yanliao biotas. Accurate geochronology is necessary to disentangle these various factors, and we review the Late Triassic to Early Cretaceous U–Pb ages for these areas and supply a new laser ablation inductively coupled plasma mass spectrometry age for the otherwise un-dated Sangonghe Formation of Early Jurassic age. We review climate-sensitive facies patterns in North China and show that the climatic context changed synchronously in northwestern and northeastern China consistent with a previously proposed huge Late Jurassic–earliest Cretaceous true polar wander event, with all the major plates of East Asia docked with Siberia and moving together since at least the Triassic when the North China basins were at Arctic latitudes. We conclude that this true polar wander shift was responsible for the coal beds and ice-rafted debris being produced at high latitudes and the red beds and aeolian strata being deposited at low latitudes within the same basin. The climatic and taphonomic context in which the famous Shishugou, Yanliao and Jehol biotas were preserved was thus a function of true polar wander, as opposed to local tectonics or climate change.