Appalachian Mountain Building: Collisional Tectonics Begin

• Western belt of shale, limestone, sandstone (plateau & valley and ridge province)
• Eastern belt of graywacke, volcanics, siliceous shale (mostly metamorphosed & intruded by granite batholiths occurring in Blue Ridge and Piedmont Provinces)
• Early Paleozoic Margin
• Passive with deeper water deposits (flysch -rapidly deposited poorly sorted marine sediments usually cyclical sandstone/ shale) seaward along continental rise.
• Indicating ocean spreading.
• Mid-Ordovician Margin
• Carbonate deposition stopped.
• Carbonate platform downwarped.
• Graptolitic black shales and immature sands deposited
• Coarse clastics, volcanics and interbedded lavas indicative of subduction zone and ocean closure.
• Volcanic chain formed to the west of the subduction zone (on cratonic edge).
• Early Paleozoic Tectonic Activity
• Early Cambrian plate convergence closing ancestral Atlantic
• Seafloor subducted under N. Am.
• Island Arc developed adjacent to subduction zone
• Taconic Orogeny - Appalachians
• Orogenic pulses begin in Mid-Cambrian
• Intense deformation in Middle & Late Ord
• Apparent in the northern Appalachian belt.
• Late Ordovician to Early Silurian when continental fragment collides with N. Am.
• Fragment thrust as sheets of xline rock over Ordovician sediments
• Now recognized as Blue Ridge & Piedmont
• Evidence in Northern U.S.
• Suture zone U.S.-Canada is Logan's Line (Taconic Mountains)
• Queenston clastic wedge (600,000 km²) in terrestrial and transitional environments (NY, PA, OH & W. VA)
• Silurian-aged coarse clastics (conglomerates) overlain by sandstones.
• "Blount delta" - the southern margin of the clastic wedge prograded into Virginia
• Volcanism and lava flows in Newfoundland covered the area and volcanic flows as far south as present Cape Hatteras.
• Late Paleozoic Orogenic Episodes: North America Becomes the Central Car in a Multi-Car Pileup
• Mid-Devonian Acadian Orogeny
• Newfoundland to W. Va. affected by collisional tectonism
• Thick, folded turbidites with volcanics and granitic intrusions
• Eastern marine basin gone
• Suturing of N.Am., Britain, and Baltica resulted in Caledonian mountains.
• Mechanism of Acadian Orogeny
• Oblique convergence of a displaced continental fragment (Avalon Terrane)
• Erosion provided the westward transported sediments of the Catskill Clastic Wedge
• Deposits span 50MY(middle-late Dev-Pa)
• Late Devonian Antler Orogeny
• Subduction on western margin resulted in volcanic island arc (Klamath Arc) that converged on the craton
• Intervening sediments and oceanic crust (including ophiolites) deformed and thrust faulted onto the margin
• Roberts Mountain Thrust Fault -Nevada
• Consequences of Antler Orogeny
• Sequence 10 km thickness thrust approx. 160 miles westward
• Ocean basins accumulated shelf sediments (>9000 m) into the Permian
• Coarse clastics and volcanic deposits characterize erosion and tectonics during the Carboniferous
• Ellesmere Orogeny
• Northern Canada affected in Late Devonian-Early Carboniferous
• Associated Mississippian Sverdrup basin continued to accumulate sediment into Cenozoic
• Subsidence resulted in Late Paleozoic deep marine deposits.
• Exposures in Arctic Islands.
• Allegheny Orogeny
• Building of >1600 km Appalachians
• Begins in the Pennsylvanian
• Closure of the ocean tract (Proto-Atlantic) and convergence of continents (NW Africa contacting Southeast N. Am.)
• Thin-Skinned Tectonics
• Basement rocks little affected by closure
• Overlying "weaker" rocks break into multiple thrust faults
• Consequences of Closure
• Folded Valley and Ridge province
• Thrusted strata (faults inclined SE; folds overturned to NW) along southern Appalachians
• Piedmont and Blue-Ridge provinces thrust westward
• Plateau province slightly folded (Sequatchie Anticline).
• Ouachita & Associated Orogenies
• Collision of northern margin of Gondwana (northern S. America and NW Africa)
• Southeastern margin resulting in linear Ouachita Mountains over 2000 km
• Late Mississippian evidence for aulocogens in Mississippi and Oklahoma
• Began in Mississippian with minor disturbances in shelf areas accumulating novaculites (microcrystalline quartz).
• Areas filled with thick graywacke and shale deposits (>8000 m) indicating basin formed in response to collision
• Intense tectonism in Pennsylvanian and development of many small foredeep basins from Alabama through west Texas.
• Associated Crustal Activity
• Ancestral Rockies (Colorado Mountains > 1000 m height) and Oklahoma Mountains
• Movement crustal blocks along large, nearly vertical faults
• Colorado Front Range and Perdernal Uplift
• Zuni-Fort Defiance Uplift - Arizona
• Linear uplift in SE CO to OK - Oklahoma mountains (Amarillo-Wichita-Arbuckle)
• Sonoma & Cassiar Orogenies
• Latest Paleozoic disturbances of the western margin identified by extensive angular unconformities between Permian and Triassic deposits
• Sonoma Orogeny similar to former Antler Orogeny with collision of eastward-moving volcanic island arc in west-central Nevada
• Island arc and ocean deposits thrust onto the craton margin.

GE 142