Antler orogeny
The Antler orogeny was a tectonic event that began in the early
Two facies of lower Paleozoic rocks
There are two principal
Plate tectonics
From an early date,
Present knowledge
This much is known concerning the Antler orogeny:
- Great volumes of clastic rocks were deposited in Nevada and surrounding areas on both the western and eastern facies assemblages;[4][8]
- Almost all of the orogenic deposits range in age from Late Devonian to mid-Pennsylvanian; some may be of Middle Devonian age;[8]
- The orogenic deposits are in a generally disconformable relation to the underlying strata;[8]
- Some areas within the western facies domain were first elevated and eroded, then were depressed and received a blanket of conglomeratic sediments;[8]
- Some clasts in these deposits were derived from areas outside the western facies domain but the bulk were derived from the western facies assemblage;[4][5][8]
- Blocky exposures of eastern facies carbonate rocks, of Cambrian to Devonian age are scattered across the western facies domain;[2]
- No metamorphic rocks, volcanic arcs, or granitic intrusives associated with the Antler orogeny have been directly correlated with the Antler Orogeny; however, there is some evidence of arc magmatism in northern California that may be attributed. Intrusive bodies include Bowman Lake batholith, Wolf Creek granite stock, and smaller hypabyssal felsic bodies. These igneous bodies intrude the Shoo Fly Complex and date to the age of the Antler Orogeny.[9]
- The age of the earliest-known orogenic deposits coincides approximately with the age of the Alamo impact event of early Late Devonian age[5]—a possibly significant coincidence.
Origin of terminology
Based on stratigraphic relations near Antler Peak, of the Battle Mountains, Roberts introduced the term Antler orogeny in an abstract as follows: The earliest orogeny, here named the Antler orogeny ... took place during Mississippian (?) and early Pennsylvanian time.[10] That abstract was followed in 1951 by his geologic map of the Antler Peak quadrangle in the text of which he described the Antler orogeny in detail and somewhat refined its age span: During the Antler orogeny, formations in Battle Mountain ranging in age from Ordovician to Mississippian (?) were complexly folded and faulted. As these rocks are unconformably overlain by the Battle Formation of Early Pennsylvanian (Des Moines) age, the orogeny probably took place during the Late Mississippian. The orogeny may have continued into Early Pennsylvanian, however, for the coarse conglomerates of the Battle Formation indicate derivation from a rugged highland area.[11] In a subsequent influential paper, Roberts and others adjusted the age of the Antler orogeny as follows: This belt is now known to have been the locus of intense folding and faulting during the Antler orogeny in latest Devonian or Early Mississippian time ...[1] In the same paper the authors established a connection between the Antler orogeny and a major thrust fault as follows: A belt along the 116°-118° meridians—the Antler orogenic belt—was the locus of intense folding and faulting that culminated in the Roberts Mountains thrust fault... That age range and connection with the Roberts Mountains thrust were confirmed in a widely quoted paper by Silberling and Roberts: During the Late Devonian or Early Mississippian ... the Antler orogenic belt was intensely folded and faulted, and during Mississippian time the Roberts Mountains thrust sheet was emplaced.[12] The effect of this revision in the age of the orogeny was to exclude the evidence in the Antler Peak quadrangle cited above for a Late Mississippian to mid-Pennsylvanian age, on which the concept of the Antler orogeny originally had been based, and to establish the conventional age of that orogeny as Late Devonian to Early Mississippian.
The original date of the Roberts Mountains thrust fault was post-Paleozoic.[13] However, with publication of the 1958 and 1962 papers cited above, the authors revised the age of the Roberts Mountains thrust to coincide with the Late Devonian to Mississippian Antler orogeny and to extend the name far beyond the Roberts Mountains.
Theories
Over a period of 22 years numerous reports relating the Antler orogeny and Roberts Mountains thrust to plate convergence were published in various journals, and because their basic tenets have been widely accepted, they are here termed the conventional theories. The earliest effort to relate plate tectonics specifically to the Antler orogeny was briefly outlined by E.M. Moores: A collision of this continental margin with a subduction zone dipping away from it in late Devonian-early Mississippian time ... resulted in deformation of the pre-existing continental marginal rocks in the Antler Orogeny.[14]
Two principal contrasting tectonic theories were published in greater detail between 1972 and 1992 as related below. One theory involved closure of a back-arc basin between the western continental margin and a volcanic arc over an east-dipping subduction zone. A second theory involved collision of the continent with an island arc above a west-dipping subduction zone. Both were based on the basic understanding that the western facies assemblage is composed of oceanic deposits and that it is underlain by an extensive thrust fault.
East-dipping subduction
Burchfiel and Davis presented the first detailed paper that explained the Antler orogeny and the Roberts Mountains thrust in terms of the subduction aspect of plate tectonics, stating: ... the paleogeography of this part of the Cordilleran geosyncline probably consisted of an offshore island complex separated from the continental slope and shelf by a small ocean basin of behind-the-arc type. Initial regional deformation within the Cordilleran geosyncline—the Mid-Paleozoic Antler orogeny—was characterized by the eastward displacement (Roberts Mountains thrust) of eugeosynclinal units from within the small ocean basin over miogeosynclinal strata deposited on the continental shelf.[15] Their now-outdated terms eugeosynclinal and miogeosynclinal refer respectively to the western facies and eastern facies domains. In that paper, Burchfiel and Davis set the parameters for future discussions of the nature and origins of the Antler orogeny and associated thrusts. Their basic concept of east-dipping subduction was reflected in modified form by others, including Miller and others.[16][17]
West-dipping subduction
Dickinson and others argued for an opposing theory, that west-dipping subduction and volcanic
Strike-slip faulting
As an alternative to the two conventional theories described above, Ketner proposed that (1) left-lateral strike-slip faulting along the western margin of the North American continent, rather than plate convergence, was the engine of Paleozoic tectonics in the region; (2) the Roberts Mountains allochthon, as such, does not exist, and the Ordovician to Devonian western facies assemblage was deposited essentially in situ; and (3) blocks of shelf carbonate rocks earlier thought to be exposures of the shelf in windows of the Roberts Mountains allochthon are slide blocks from the carbonate shelf. The slide blocks probably were dislodged by the Alamo impact event of Late Devonian age.[5] In this scheme, the deep-water aspects of the western facies assemblage are due to sea-level rise in the Cambrian[25][26] rather than displacement from an ocean basin.[8]
The sedimentary effects of the Antler orogeny are well known and well described in many published reports,[2][3][4][27] but the exact nature of that event and the driving force remain unsettled. Among the unanswered questions are these: what aspect of plate tectonics was involved; what effect did the Alamo impact event have; why did marine basins appear in the area of general uplift; why did the western facies assemblage, and not the eastern assemblage, include bedded chert, basaltic bodies, barite deposits, and sulfide deposits.
References
- ^ .
- ^ a b c d e f g Stewart, J.H. (1980). Geology of Nevada. Reno, Nev.: Nevada Bureau of Mines and Geology. Special Publication no. 4.
- ^ .
- ^ a b c d Poole, F.G. (1974). "Flysch Deposits of Antler Foreland Basin, Western United States" (PDF). In Dickinson, W.R. (ed.). Tectonics and Sedimentation. Society of Economic Paleontologists and Mineralogists. pp. 58–82. Special Publication 22.
- ^ a b c d e Ketner, K.B. (2012). An alternative hypothesis for the mid-Paleozoic Antler orogeny in Nevada (PDF). U.S. Geological Survey. Professional Paper 1790.
- ISBN 9780922152766.
- .
- ^ a b c d e f Ketner, K.B. (2013). Stratigraphy of lower to middle Paleozoic rocks of northern Nevada and the Antler orogeny. U.S. Geological Survey. Professional Paper 1799.
- S2CID 214466880.
- .
- ^ Geology of the Antler Peak quadrangle (Map). Roberts, R.J. 1951.
- ISBN 9780813720722. Geological Society of America Special Paper 72.
- .
- S2CID 4243830. Archived from the original on 2014-03-08.)
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- ^ a b Miller, E.L.; Miller, M.M.; Stevens, C.H.; Wright, J.E.; Madrid, Raul (1992). "Late Paleozoic paleogeographic and tectonic evolution of the western U.S. Cordillera". In Burchfiel, B.C.; Lipman, P.W.; Zoback, M.L. (eds.). The Cordilaeran orogen: Conterminous U.S. The Geology of North America. Vol. G-3pages=57-106. Boulder, Colorado: Geological Society of America.
- ^ Dickinson, W.R. (April 22, 1977). Stewart, J.H; Stevens, C.H. (eds.). Paleozoic plate tectonics and the evolution of the Cordilleran continental margin. Pacific Coast Paleogeography Symposium. Vol. 1. Pacific Section of the Society of Economic Paleontologists and Mineralogists. pp. 137–155.
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ignored (help) - ^ .
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- ^ Speed, R.C.; Elison, M.W.; Heck, F.R. (1988). "Phanerozoic tectonic evolution of the Great Basin". In Ernst, W.G. (ed.). Metamorphism and crustal evolution of the western United States. Rubey. Vol. VII. Englewood Cliffs, N.J.: Prentice-Hall. pp. 572–605.
- ^ Poole, F.G.; Stewart, J.H.; Palmer, A.R.; Sandberg, C.A.; Madrid, Raul; Ross, R.J. Jr.; Hintze, L.F.; Miller, M.M.; Wrucke, C.T. (1992). "Latest Precambrian to latest Devonian time—Development of a continental margin". In Burchfiel, B.C.; Lipman, P.W.; Zoback, M.L. (eds.). The Cordilleran Orogen—Conterminous U.S. The Geology of North America, Decade of North American Geology. Vol. G-3. Boulder, Colo.: Geological Society of America. pp. 9–56.
- ISBN 978-0813752174.
- .
- OCLC 123201439.
- ^ Harbaugh, D.W.; Dickinson, W.R. (1981). "Depositional facies of Mississippian clastics, Antler foreland basin, central Diamond Mountains, Nevada". Journal of Sedimentary Petrology. 51 (4): 1223–1234.