CONGLOMERATIC FAN DELTAS AND SUBMARINE FANS OF THE JURASSIC LABERGE GROUP, WHITEHORSE TROUGH, YUKON-TERRITORY, CANADA - FORE-ARC SEDIMENTATION AND UNROOFING OF A VOLCANIC ISLAND-ARC COMPLEX

The Lower and Middle Jurassic Laberge Group consists of conglomerates, sandstone turbidites and shales that were deposited within a deep-water fore-are trough. The conglomerate of the Laberge Group accounts for most of the preserved basin-fill within the Whitehorse Trough, and was derived from exhumed plutons, comprising multiple intrusives and extrusives of varying composition, that formed an island are terrane in the western margin of the Whitehorse Trough. The island are complex docked against North America in the Late Triassic and the Laberge conglomerates record the sedimentary and unroofing processes that predominated in the intervening trough during are-continent collision and accretion. Coarse-grained sediment shed from the are constructed fan deltas along the western margin of the basin. These deposits were resedimented into deep water (below wave base) through shelf-break chutes and submarine channels. Gravel was emplaced within submarine channel-and-fan complexes; sandy turbidites formed lobes along the margins of the gravelly submarine fans and muds were deposited in inter-fan settings. Stratigraphic changes within the Laberge Group reflect: (1) collision of the are, with plutonism and resultant uplift, and subsequent unroofing of the are highlands; and (2) overlap of coarse-grained deep-water fans across the shelf as a response of crustal flexure to collisional tectonism and/or a eustatic sea-level change. Later deposition of the overlying Tantalus Formation records a diachronous overlap of successor paralic-alluvial deposits over the Laberge sediments associated with final-stage accretion events in the Whitehorse Trough.