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The results of more than 20 years of geochronological studies in the Yukon Crystalline Terrane in east-central Alaska and the western Yukon Territory suggest at least six igneous and thermal (metamorphic?) events. Plutonism during Mississippian, Early Jurassic, mid-Cretaceous, Late Cretaceous, and early Tertiary times is indicated. Evidence also indicates that Mississippian, Early Jurassic, late Early Cretaceous, and late Cretaceous thermal (metamorphic?) events have affected parts of the terrane. The western part of the terrane was affected by a significant regional metamorphic event in late Early Cretaceous time, followed by a terrane-wide mid-Cretaceous plutonic event. The pattern of K-Ar ages allows division of the terrane into domains, bounded by northeast-trending lineaments.L'examen des rksultats de plus de 20 annkes d'ktudes gkochronologiques de la plate-forme cristalline du Yukon rkvkle au moins la prCsence de six kvknements ignks et thermiques (mktamorphiques?). Le plutonisme fut actif durant le Mississippien, le Jurassique infkrieur, le Crktack moyen, le Crktack supkrieur et le Tertiaire infkrieur. On observe que des manifestations thermiques (mktamorphiques?) ont affectk des parties de la plate-forme cristalline du Yukon durant le Mississippien, le Jurassique infkrieur, le CrktacC tardi-infkrieur et le Crktace supkrieur. Durant le Crktack tardi-infkrieur est survenu un important kvknement de mktamorphisme regional qui a affectk la partie occidentale de la plate-forme cristalline, lequel fut suivi au CrktacC moyen par un kvknement plutonique englobant toute la largeur de la plate-forme cristalline. Le motif d'ktalement des Lges K-Ar permet de diviser la plate-forme cristalline en domaines, lesquels sont limitks par des lineaments de direction nord-est.[Traduit par le journal]Can.

Qal Alluvium along streams (Holocene)-Mainly in active flood plains of major and some minor streams. Locally, includes outwash related to older phases of the Alaska glaciations. Chiefly stratified boulders, cobbles, gravel, and sand; silt locally common. Qaf Alluvium in fans (Holocene)-Mainly large active fans and cones on steep to gentle slopes adjacent to the broad glaciated valley of the Copper River. Chiefly poorly stratified boulders, cobbles, gravel, and sand. COLLUVIAL DEPOSITS Qc Colluvium, undifferentiated (Holocene and Pleistocene)-Chiefly talus but also includes deposits of small landslides, rock glaciers, and other mass-wasting processes; in places includes large proportion of alluvium in small fans and cones and locally includes remnants of morainal deposits. Chiefly unsorted boulders, cobbles, gravel, and sand. GLACIAL DEPOSITS Qrg Rock glacier deposits (Holocene and Pleistocene)-Deposits in both active rock glaciers, which have well-defined lobate forms, and inactive rock glaciers, which have smooth forms. Chiefly angular blocks and diamicton. Qag Drift of Alaskan glaciation (Holocene)-End, lateral, and ground moraine of the Alaskan glaciations which were deposited during the recession of existing glaciers. In the extensive areas of glacial drift west of Copper Glacier three stages of Alaskan glaciation are recognized (H. Schmoll, written comm., 1994). The youngest stage includes ground, lateral, and end moraines that have been deposited near the margins of present-day glaciers. The two older stages, related to an older phase of Alaskan glaciation and marked by prominent and well-defined lateral moraines, occur further beyond the present-day glacier margins. Dashed line with hachures indicates extent of youngest stage of Alaskan glaciation and locally includes areas within which glaciers have been advancing and retreating during the late 20th century. Plain dashed line separates the two older stages of Alaskan glaciation. Drift is locally modified by colluvial processes, especially along steep eastside of the large nunatak west of Copper Glacier. Diamicton and rubble; local gravel and sand. Qwg Drift of Wisconsin glaciation (Pleistocene)-Chiefly lateral and ground moraine of both younger and older stages of Wisconsin glaciation. Diamicton and rubble; local gravel and sand. Qog Drift of older glaciations (Pleistocene)-Glacial and fluvioglacial deposits observed only in the north wall of the Jacksina Glacier valley where unit is overlain by an agglutinate flow (unit Qaa) that may be as old as 1.38 Ma (Richter and Smith, 1976). Chiefly diamicton; local sand, gravel and boulders. VOLCANIC ROCKS Wrangell volcano-Mount Wrangell (el. 14,163 ft [4317 m]) is a large shield volcano, whose summit area lies mostly to the southwest in tMe contiguous Gulkana A-l and Valdez D-l quadrangles. Only a part of the northeast flank of the shield is exposed in the quadrangle. A porphyritic high-silica andesite lava, similar to that found elsewhere on the Wrangell shield (Richter and others, 1994) is the predominant rock ...

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