Accreted Terranes of Northern Cordillera

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Geol 456-556 Field Trip May 21-23, 2010 Accreted Terranes of Northern Cordillera This Field Trip: Insular Terrane Insular Terrane Western Domain Northwest Cascades System (NWCS) Nappes of Pz Mz eugeosynclinal strata EK blueschist Mostly shallow metamorphic dips Darrington-Devils Mountain Fault Zone Western and Eastern melange belts (WEMB): Little metamorphosed Mesozoic marine rocks, lenses of Pz limestone, faut bounded Mz plutons (gabbro to tonalite) Bedding and cleavage steep Straight Creek Fault Zone Crystalline Core Lower greenschist ‐> Amphibolite facies schist, gneiss, migmatite, plutons Wenatchee block recrystallization stopped by 75 Ma Entiat Fault Eocene Chiwaukum Graben fluvial, lacustrine Chelan Block Deformati0n and recrystallization until eT Methow Domain Methow Block: Little-metamorphosed Mz strata. East verging thrusts and folds Ross Lake Fault Zone: Rx of Methow block and Chelan block Oceanic greenstone, chert, argillite of Pz->Jr Hozameen group Cross Section of North Cascades Western Domain of North Cascades P-T conditions of Skagit Gneiss Complex Ross Lake fault system Methow Terrane Okanogan Batholith of Intermontane Terrane Pipestone Canyon Formation Stratigraphy of Southern Can Cordillera SuperTerranes and faults Eocene Features of North Cascades In this region: accreted terranes are allochthonous tectonostratigraphic terranes juxtaposed along regional fault systems and intruded by Jurassic to Tertiary plutons Grouped into 2 superterranes separated by major zone of mK to T contractional deformation and plutonism: Intermont ane superterrane (Stikinia, Cache Creek, Quesnellia terranes) Insular superterrane- Wrangellia and Alexander terranes Focus on the Cretaceous-> Tertiary development of Cordillera Controversy: estimates of timing and magnitude of terrane displacement along margin: -Large Translation: paleomagnetic data. Paleomagnetic data from stratified and plutonic rocks from Insular and Intermontain suggest large northward translations between 90 and 55 Ma Intermontane: 1100 ±600 km between 70 and 55 Ma Insular : 3000±500 km between 80-55 Ma -Small Translation: geologic data. Total translation: < 1000 km since mK. Terrane amalgamation at or slightly south of current location by mK Insular : < 400 km dextral translation based on structural and stratigraphic field observations, stratigraphic correlations, and lab analyses .

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THE JOURNAL of GEOLOGY March 1990
VOLUME 98 NUMBER 2 THE JOURNAL OF GEOLOGY March 1990 QUANTITATIVE FILLING MODEL FOR CONTINENTAL EXTENSIONAL BASINS WITH APPLICATIONS TO EARLY MESOZOIC RIFTS OF EASTERN NORTH AMERICA' ROY W. SCHLISCHE AND PAUL E. OLSEN Department of Geological Sciences and Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964 ABSTRACT In many half-graben, strata progressively onlap the hanging wall block of the basins, indicating that both the basins and their depositional surface areas were growing in size through time. Based on these con- straints, we have constructed a quantitative model for the stratigraphic evolution of extensional basins with the simplifying assumptions of constant volume input of sediments and water per unit time, as well as a uniform subsidence rate and a fixed outlet level. The model predicts (1) a transition from fluvial to lacustrine deposition, (2) systematically decreasing accumulation rates in lacustrine strata, and (3) a rapid increase in lake depth after the onset of lacustrine deposition, followed by a systematic decrease. When parameterized for the early Mesozoic basins of eastern North America, the model's predictions match trends observed in late Triassic-age rocks. Significant deviations from the model's predictions occur in Early Jurassic-age strata, in which markedly higher accumulation rates and greater lake depths point to an increased extension rate that led to increased asymmetry in these half-graben. The model makes it possible to extract from the sedimentary record those events in the history of an extensional basin that are due solely to the filling of a basin growing in size through time and those that are due to changes in tectonics, climate, or sediment and water budgets.
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