Showing papers on "Terrane published in 1986"
TL;DR: In this paper, the authors present stratigraphic and petrologic data from Chile and Argentina between 29° and 33°S latitude that demonstrate the "suspect" nature of several major terranes, which they infer to have been accreted during the Paleozoic.
Abstract: The recognition of accreted terranes and their importance in orogenesis has spurred the search for allochthonous fragments along the western and southern margins of South America. Here we present stratigraphic and petrologic data from Chile and Argentina between 29° and 33°S latitude that demonstrate the “suspect” nature of several major terranes, which we infer to have been accreted during the Paleozoic. Three lower-middle Paleozoic terranes are described (from east to west): (1) the Pampeanas terrane, a Cambrian-Devonian magmatic and metamorphic province built on late Precambrian basement at the margin of South America, (2) the Precordillera terrane, a Cambrian-Devonian shelf-slope-oceanic basin assemblage bounded by melanges on both sides and bearing many stratigraphic similarities to the lower-middle Paleozoic of the Northern Appalachians, and (3) the “Chilenia” terrane, which has largely been obliterated by late Paleozoic magmatism and metamorphism. The distribution of Carboniferous continental, deltaic, and marine strata demonstrates that these three terranes were sutured together and part of South America by the end of the Devonian. Subsequent Permo-Carboniferous plate interactions more closely resembled the modern Andean margin, with eastward subduction, accretionary prism formation, and minor terrane emplacement exposed along the present coast of Chile and eastward migrating arc magmatism from the present coast of Chile to western Argentina.
507 citations
TL;DR: In this paper, an analysis of earthquake slip vectors indicates that modern sliver terranes typically migrate at rates of 1-2 cm/yr. But this rate increases with greater convergence obliquity.
Abstract: Forearc slivers, bounded by a trench and an active strike-slip fault, occur in about 50% of modern subduction zones. Analysis of earthquake slip vectors indicates that modern sliver terranes typically migrate at rates of 1–2 cm/yr. Tertiary transport of some forearc slivers by 1000 km or more is therefore expected as a consequence of normal subduction. Active arc-parallel strike-slip faulting occurs whenever interplate coupling is strong and convergence is somewhat oblique; strike-slip rate increases with greater convergence obliquity.
283 citations
TL;DR: In the case of the Porcupine Creek anticlinorium and the Selkirk fan structure, a reversal in vergence between the bottom and the top of a tectonic wedge has been observed.
280 citations
TL;DR: The 1985 Chinese/British expedition to the Tibetan Plateau attempted to solve the question of the origin of the very thick crustal rocks in this region as mentioned in this paper, but the results were unsatisfactory.
Abstract: The 1985 Chinese/British expedition to the Tibetan Plateau attempted to solve the question of the origin of the very thick crustal rocks in this region. Continuing northwards movement of the Indian plate over the past 38 Myr has given rise to severe folding and thrust faulting, causing crustal thickening by internal deformation. Previous collisions of microplate terranes derived from Gondwanaland occurred during Mesozoic times but the Kun Lun terrane of northern Tibet was already part of Laurasia by the Carboniferous
264 citations
TL;DR: In this paper, age and petrographic data from the buried basement of the midcontinent region of North America, integrated with information from exposed rocks and magnetic-and gravity-anomaly maps, allow much of the Proterozoic history of the region to be assembled.
Abstract: Age and petrographic data from the buried basement of the midcontinent region of North America, integrated with information from exposed rocks and magnetic- and gravity-anomaly maps, allow much of the Proterozoic history of the region to be assembled. The Superior craton may be traced into the subsurface on the basis of characteristic magnetic patterns and limited age data. The region between the Superior craton and the Wyoming craton to the west is evidently underlain by southerly extension of the Trans-Hudson orogen of Canada. The Penokean orogen formed on the southern margin of the Superior craton 1890–1830 Ma, but is not inferred west of northwestern Iowa in the subsurface. Between 1780 and 1720 Ma, a major orogen developed along the southern margin of the continent and is exposed in Arizona and Colorado. These rocks are volcanogenic and, for the most part, juvenile additions to the crust; they can be traced beneath the plains as far as eastern Kansas and Nebraska. Another orogen formed farther to the south about 1700–1630 Ma and is exposed in southern Arizona and New Mexico; rocks of this age and type have beer, traced as far east as central Missouri but may extend as far as central Michigan. A major geophysical feature of the midcontinent is a system of northwest-trending magnetic and gravity anomalies in Missouri, Kansas, and Nebraska; the origin of these is not currently understood. The tectonic history of the midcontinent between 1480 and 1340 Ma was dominated by extensional formation of two widespread granite-rhyolite terranes that evidently were formed from, and overlie, the orogenic provinces. The older, formed 1450–1480 Ma, underlies the eastern midcontinent, whereas the younger, formed 1340–1400 Ma, underlies the southwestern midcontinent. The latest Proterozoic events were the formation of the midcontinent rift system and the collisional Grenville and Llano provinces about 1100 Ma.
224 citations
TL;DR: In this article, the authors consider that there are two Proterozoic rifts of E-W trend in the northern margin of the North China Platform, and the Zhaertay Group and Baiyun'ebo Group of closed lagoon facies or neritic facies were deposited respectively in the two rifts.
Abstract: On the basis of recent investigations in southern Inner Mongolia the authors consider that there are two Proterozoic rifts of E–W trend in the northern margin of the North China Platform. The Zhaertay Group and Baiyun'ebo Group of closed lagoon facies or neritic facies were deposited respectively in the two rifts. The lead isotopic dating of carbonaceous limestone from the middle sequence of Baiyun'ebo Group yields an age of 1500 Ma. Along the rifts a series of alkaline volcanics and intrusions is scattered in the Yinshan Mountains and Yanshan Mountains. To the north of the rifts, four ophiolite belts and at least five accreted terranes of various ages have been recognized in the Paleozoic orogenic zone. The presence of the ophiolite suites and these accreted suspect terranes in Inner Mongolia indicates that probably there was an open ocean between Siberia and North China in Paleozoic times, when repeated subduction of the oceanic crust had occurred along both continental margins. The suture line between Cathaysia and Angaraland extends from Linxi to Solon Obo. In the late Permian, epicontinental mountain systems of the two converging continents collided with each other. From the analysis of the tectonic evolution of Inner Mongolia and adjacent areas we conclude that the evolution of the southern margin of the Siberian Platform is approximately the same as the history of activity of the trench-arc-basin system in the eastern Asian epicontinental areas during Mesozoic and Cenozoic times but the northern margin of the North China Platform is similar in evolution to the Cordilleran system in western North America.
192 citations
TL;DR: In this paper, eight Euler poles are considered to be reliable Jurassic reference poles for cratonic North America and they form a consistent chronological progression defining two arcuate tracks of apparent polar wander (APW) from Sinemurian through Tithonian time.
Abstract: Eight paleomagnetic poles are considered to be reliable Jurassic reference poles for cratonic North America. These poles form a consistent chronological progression defining two arcuate tracks of apparent polar wander (APW) from Sinemurian through Tithonian time (203–145 Ma). Combined with reliable Triassic and Cretaceous reference poles, the resulting path is well modeled by paleomagnetic Euler pole (PEP) analysis and is significantly different from previous APW compilations. These differences reflect differences in original data sets, modes of analysis, and geologic time scales and translate into substantial and important differences in paleolatitude estimates for cratonic North America. PEP analysis reveals two cusps, or changes in the direction of APW: one in the Late Triassic to Early Jurassic (Jl) and one in the Late Jurassic (J2). The Jl cusp represents the change in North American absolute plate motion associated with rifting of the central Atlantic and Gulf of Mexico, while the J2 cusp correlates temporally with the marine magnetic anomaly M21 plate reorganization and to various North American intraplate tectonomagmatic events (e.g., Nevadan Orogeny). Analysis of pole progression along the Jl to J2 and J2 to Cretaceous APW tracks indicates constant angular plate velocity of 0.6°–0.7°/m.y. from 203 to 150 Ma followed by significantly higher velocity from 150 to 130? Ma. Late Triassic-Jurassic reference poles indicate more southerly paleolatitudes for cratonic North America than have previous compilations requiring modification of displacement scenarios for suspect terranes along the western Cordillera.
176 citations
TL;DR: The Tintina trench-northern Rocky Mountain trench (TT-NRMT) and the Fraser River-Straight Creek (FR-SC) fault zones are separate, en echelon, concentric, small circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the Canadian Cordillera, from the outboard part of a tectonic collage of accreted foreign terranes in the south into the North American preaccretionary continental margin in the north as discussed by the authors.
Abstract: The Tintina trench-northern Rocky Mountain trench (TT-NRMT) fault zone and the Fraser River-Straight Creek (FR-SC) fault zone are separate, en echelon, concentric, small-circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the Canadian Cordillera, from the outboard part of a tectonic collage of accreted foreign terranes in the south into the North American preaccretionary continental margin in the north. Most of the 450 km of right-hand slip on the TT-NRMT fault zone was transformed southward during the Late Cretaceous and Paleocene into oblique convergence in the southern Canadian Rockies; the remainder, probably comprising less than 100 km, was transformed southwestward during early and middle Eocene time via a zone of distributed shear and east-west crustal stretching into right-hand slip on the en echelon FR-SC fault zone. These interpretations, based on regional systematic mapping of geologic structures, are in conflict with interpretations of paleomagnetic measurements that call for more than 1000 km of post-mid-Cretaceous, right-hand displacement along the general locus of the TT-NRMT fault zone, involving foreign terranes and the parts of North America to which they had been accreted. This paradox must be resolved.
174 citations
TL;DR: In this article, a revision of previous models of Proterozoic crustal accretion in the southwestern U.S. is presented, based on the more extensive data now available.
Abstract: A revision of previous models of Proterozoic crustal accretion in the southwestern U.S. is presented, based on the more extensive data now available. Five Early Proterozoic predominantly volcanic supracrustal terranes are recognized, with ages of 1760-1800 Ma, 1730-1740 Ma, 1720 Ma, 1680-1700 Ma, and 1650 Ma. In some areas they are overlain by a sixth, comprised chiefly of quartzite-pelite. In the oldest three terranes mafic volcanic rocks of largely submarine origin are more abundant than felsic. In the 1680-1700 Ma and 1650 Ma terranes felsic rocks exceed mafics, volcanics are mixed submarine and subaerial, and non-volcanogenic sediments are important. Least mobile incompatible element distributions in basalts from the 1760-1800 Ma and 1720 Ma terranes are similar to those in basalts from evolved oceanic arcs and associated back-arc basins. Basalts from the other terranes resemble those from continental-margin arcs and associated back-arc basins at early stages of opening. Incompatible element ratios in...
167 citations
TL;DR: In this paper, the authors present two balanced cross-sections of the Canadian Cordillera, based on available structural, petrologic, geophysical and geochronologic data.
165 citations
TL;DR: In this paper, the authors present an alternative model, in which low-P/high-T metamorphism (prograde reactions at pressures near or below the Al2SiO5 triple point) results from contact effects near sill-like igneous intrusions at intermediate crustal levels.
Abstract: Wickham and Oxburgh1 recently proposed that low-pressure/high-temperature (low-P/high-T) metamorphism in the eastern Pyrenees, and possibly all low-P/high-T metamorphic belts, resulted from anomalously high mantle heat flow brought about by rifting. Their model is largely constrained by the presence of nearby synmetamorphic rift-related sedimentary rocks and the interpretation that the migmatites and granites are the product of in situ melting in the presence of an anomalously steep geotherm. Here we present an alternative model, in which low-P/high-T metamorphism (pro-grade reactions at pressures near or below the Al2SiO5 triple point) results from contact effects near sill-like igneous intrusions at intermediate crustal levels. Low-P/high-T conditions can be achieved through this process in regions of continent–continent collision with normal mantle heat flux as well as in zones of extension. Our model is based on studies of the low-P/high-T metamorphic terrane in the New England Appalachians.
TL;DR: In this article, the authors model the tectonic evolution of the Arabian Shield in terms of the classic pattern of Phanerozoic plate tectonics (the Wilson cycle) and interpret it as follows: during the first stage of evolution (900-630 Ma), plutonism was dominated by intermediate plutonic rocks (diorite, quartz diorites, tonalite and trondhjemite) and involved a progressive evolution from primitive tholeiitic series are rocks to mature calc-alkaline series rocks.
TL;DR: U-Pb isotope analysis of zircon, titanite, monazite and rutile extracted from 15 different Grenville Province rocks in eastern Labrador reveals: 1) major crust formation through magmatism between 1,710 and 1,630 Ma ago; no evidence of older crustal material was found as mentioned in this paper.
Abstract: U-Pb isotope analysis of zircon, titanite, monazite and rutile extracted from 15 different Grenville Province rocks in eastern Labrador reveals: 1) major crust formation through magmatism between 1,710 and 1,630 Ma ago; no evidence of older crustal material was found. 2) Pegmatite and gabbro intrusions between 1,500 and 1,400 Ma ago, probably related to incomplete rifting of the earlier formed crust. 3) Granite and syenite plutonism, presumably anorogenic, circa 1,300 Ma ago. 4) High grade metamorphism and anatexis during the Grenvillian Orogeny, causing Pb-loss in primary zircon and new growth of zircon, titanite and monazite at circa 1,030 Ma ago in the south (Lake Melville and Mealy Mountains terranes) and circa 970 Ma ago in the north (Groswater Bay Terrane and Trans-Labrador Batholith); geochronological distinction of these large-scale crustal segments substantiates their juxtaposition along deeply rooted, intracontinental ductile thrust zones during Grenvillian Orogeny. 5) Late Grenvillian growth of rutile in gabbros circa 925 Ma ago.
TL;DR: In this article, a new tectonic map based on geophysical information, which includes aeromagnetic, gravity, seismic refraction, multi-channel seismic reflection and electromagnetic induction data, is used to extend our knowledge of the Canadian Shield beneath the Phanerozoic Williston basin of south-central Canada and the north-central United States.
TL;DR: U-Pb isotopic analyses of zircons from a distinctive suite of previously undated granulite facies metaplutonic rocks, here termed the Western Fiordland Orthogneiss (WFO), in New Zealand, indicate synkinematic magmatic emplacement between ∼120 and 130 Ma ago.
Abstract: U-Pb isotopic analyses of zircons from a distinctive suite of previously undated granulite facies metaplutonic rocks, here termed the Western Fiordland Orthogneiss (WFO), in Fiordland, southwest New Zealand, indicate synkinematic magmatic emplacement between ∼120 and 130 Ma ago. These rocks were previously interpreted as possibly being of Precambrian age. Initial Pb and Sr ratios are consistent with arc/subduction related magmagenesis with little or no involvement of ancient continental crust. Subsequent high pressure (>12 kb) metamorphism of the WFO may reflect a major collision event involving crustal thickening by overthrusting of a >15 km thick sequence. Metamorphism ceased ≤116 Ma ago based on206Pb/238U ages of zircon from a retrogressed granulite. U-Pb isotopic analysis of apatite, along with previously published Rb/Sr mineral ages, indicate that final uplift and cooling to <300–400° C was largely completed by ∼90 Ma. The average uplift rate during this period is inferred to have been in excess of 1 mm/yr. Unmetamorphosed gabbronorites of the Darran Complex in eastern Fiordland, inferred by some investigators to be the granulite protolith, yield concordant U/Pb zircon ages of 137±1 Ma. U-Pb ages of apatite, and previously published K/Ar mineral ages indicate that these rocks experienced a rapid and simple cooling history lasting only a few million years. The high-grade WFO and unmetamorphosed Darran Complex are now separated by a profound structural break. However, the ages and similarities in initial Pb and Sr isotopic ratios suggest that both suites are products of the same Early Cretaceous cycle of subduction-related magmatism. The timing of Early Cretaceous magmatism and metamorphism, collision and resultant crustal thickening, and subsequent great uplift and erosion in Fiordland has important implications for terrane accretion and the evolution of relative plate motions along the New Zealand segment of the Gondwana margin.
TL;DR: In this article, the authors examined the biogeography of North American Pliensbachian faunas to provide constraints on the tectonic movement of suspect terranes along the western margin of the craton.
Abstract: A diversity gradient and endemic patterns that are a function of latitude are evident in the ammonoid biogeography of the Pliensbachian. High diversity, Tethyan faunas are dominated by the families Hildoceratidae and Dactylioceratidae whereas the less diverse faunas of the northern part of the Northern Hemisphere are dominated by the Amaltheidae and Liparoceratidae. The biogeography of North American Pliensbachian faunas is examined quantitatively to provide constraints on the tectonic movement of suspect terranes along the western margin of the craton. Standards of reference by which to measure displacement are provided by low-diversity, autochthonous Borealfaunas on the craton as far south as southern Alberta, and higher diversity, Tethyanfaunas on the Sonomia terrane in western Nevada, which was accreted in Triassic time. Diversity and similarity coefficients are high for Sonomia and three suspect terranes (Wrangellia, Stikinia, and Quesnellia); this reflects their mutual Tethyan affinities and the pervasive presence of the east Pacific ammonite Fanninoceras. Much weaker, but still signifcant similarity coefficients between the faunas on the suspect terranes and the Boreal Craton fauna result from the gradational area of BorealTethyan overlap passing across the northern regions of the suspect terranes. These biogeographic data constrain the latitudinal position of the suspect terranes with respect to the North American continent and also indicate that the suspect terranes were in the Northern rather than the Southern Hemisphere and in the eastern rather than the western Pacific during the Pliensbachian. Evident migration of various molluscs between the eastern Pacific and western Tethyan oceans suggests the presence of a rifted seaway, the Hispanic Corridor, through the Caribbean and along the North Atlantic, that preceded spreading and the formation of oceanic crust.
TL;DR: The Upper Triassic Chinle Formation of the Colorado Plateau contains voluminous volcanic detritus evidently derived from a source to the south as discussed by the authors, but the source terrane for the Chinle has not been identified.
Abstract: The Upper Triassic Chinle Formation of the Colorado Plateau contains voluminous volcanic detritus evidently derived from a source to the south. Volcanic rocks exposed in southern Arizona and northern Sonora have been assumed to represent this source terrane, but U-Pb isotopic geochronology and regional stratigraphic correlations indicate that these volcanic rocks are distinctly younger than the Chinle, and thus not a source for the volcanic detritus in the Chinle. Igneous rocks of known or possible Late Triassic age in Nevada, California, or northeastern Mexico are possible sources, but a clearly defined source terrane for the volcanic detritus in the Chinle has not been identified. Tectonic removal of the source terrane by rifting or strike-slip offset, though not proven, is a possibility.
TL;DR: In this paper, the authors suggest that in the Philippines some originally vertical strike-slip boundaries may have evolved into shallow-dipping sutures marked by fold and thrust systems.
Abstract: Concepts of allochthonous terrane transport and emplacement are dominated by the assumption that most terranes originate on the subducting plate, collide with the upper plate, and are emplaced there. Movement of terranes along the convergent margin is recognized but is generally attributed to postcollision slip. In the northern Philippines, allochthonous terranes originate primarily within the arc system, have been translated along it by strike-slip faults, and were emplaced by cessation of that slip. The authors suggest that in the Philippines some originally vertical strike-slip boundaries may have evolved into shallow-dipping sutures marked by fold and thrust systems. This mode of terrane evolution may be more common than generally appreciated, particularly in orogenic belts developed in response to oblique convergence.
TL;DR: The history of the Lachlan fold belt involves terrane translation and accretion of discrete allochthonous fragments as discussed by the authors, and four major terranes developed adjacent to the Gondwana continental margin and were overthrust in the Middle Devonian to form a partly composite crust for southeastern Australia.
Abstract: The Paleozoic history of the Lachlan fold belt involves terrane translation and accretion of discrete allochthonous fragments. Four major terranes developed adjacent to the Gondwana continental margin and were overthrust in the Middle Devonian to form a partly composite crust for southeastern Australia.
TL;DR: In this paper, the authors reviewed the Celtic 9Province9 and concluded that each of the island faunas should be treated separately (since many have links with adjacent continents), rather than together as a province.
Abstract: The shallow-water benthos of cratonic areas distinguish different continents, and the closure of the Iapetus Ocean during the Ordovician and Silurian can be monitored by the faunas which crossed the ocean at different geological times. Brachiopod and trilobite distributions carry different palaeobiological evidence than, for example, contemporary conodont provinces, which probably reflected a combination of temperature differences and water depths. The Celtic 9Province9 is reviewed, and it is concluded that each of the island faunas should be treated separately (since many have links with adjacent continents), rather than together as a province. In Newfoundland, faunas help to locate the site of the main Iapetus closure at the Reach Fault, although a substantial island arc in the Notre Dame Bay area accreted on to America in early Caradoc times. In the late Ordovician and early Silurian of Newfoundland fossils assist in the dating of quite local fault-controlled marginal basins, some of which include large olistostromes; undisturbed assemblages of brachiopods in life position give indications of the depth of water in some basins.
TL;DR: A marine seismic reflection line across the northeast extremity of the Canadian Appalachians in Newfoundland indicates a collisional suture(?) in the lower crust beneath the central ophiolitic Dunnage terrane as mentioned in this paper.
Abstract: A marine seismic reflection line across the northeast extremity of the Canadian Appalachians in Newfoundland indicates a collisional suture(?) in the lower crust beneath the central ophiolitic Dunnage terrane. The thrust and fold belt (miogeocline) above the Grenville basement, and the Dunnage and Gander tectonostratigraphic terranes all appear to be allochthonous with respect to lower crustal basement. The Gander-Avalon terrane boundary to the east is a near-vertical feature that penetrates the crust. The data also suggest that the ancient passive margin of North America extends eastward under the Dunnage terrane for about 70 km. The Newfoundland deep seismic experiment indicates major tectonic differences compared to results for the southern Appalachians.
TL;DR: A suspect terrane exists along the western flank of the Central Cordillera in the Colombian Andes as mentioned in this paper, which consists of sea floor of Late Jurassic or Early Cretaceous age that was accreted onto the continental edge at about 125-130 Ma, along the Romeral fault zone, during a pause between the Jurassic and cretaceous cycles of plutonism.
Abstract: A suspect terrane exists along the western flank of the Central Cordillera in the Colombian Andes. It consists of sea floor of Late Jurassic or Early Cretaceous age that was accreted onto the continental edge at about 125–130 Ma, along the Romeral fault zone, during a pause between the Jurassic and Cretaceous cycles of plutonism.
TL;DR: In this article, age and structural data have been used for reconciliation of previously conflicting models for Late Jurassic genesis of the Josephine, Smartville and Coast Range ophiolites, and the Nevadan orogeny in the Klamath Mountains and Sierra Nevada.
Abstract: Recently published age and structural data allow the reconciliation of previously conflicting models for Late Jurassic genesis of the Josephine, Smartville and Coast Range ophiolites, and the Nevadan orogeny in the Klamath Mountains and Sierra Nevada. The resulting model is consistent with the mode of initiation, location and geometry of the Great Valley forearc basin, and with the lack of a significant forearc basin west of the Klamath Mountains. The Coast Range ophiolite formed by backarc spreading west of an east-facing intraoceanic arc. Soon thereafter, a remnant arc was calved off the west side of this arc, and the Smartville ophiolite formed by backarc (interarc) spreading. During this time, the Sierran phase of the Nevadan orogeny began as the intraoceanic arc encountered the west-facing continental-margin arc of North America. An east-west-trending calcalkaline dike swarm in the Sierra Nevada foothills may mark the trajectory of the colliding arcs at the initiation of the collision. Simultaneously, a new subduction zone was initiated west of the collision (suture) zone, and this new trench propagated southward, thus trapping the Coast Range ophiolite in the new forearc area south of the Klamath area. Intense deformation in the Sierran region resulted from this collision, and both magmatic arcs became inactive as the last remnant of intervening oceanic crust was subducted. Continued westward relative movement of the North American arc was permitted north of the Sierra Nevada owing to the lack of a colliding intraoceanic arc. The result was the westward rifting of the continental-margin arc by intraarc spreading, which formed the Josephine ophiolite in the Klamath area. The Klamath phase of the Nevadan orogeny resulted from contraction of the west-facing intraoceanic arc and Josephine backarc basin beneath the continental margin. Basal sediments of the Great Valley forearc basin were derived primarily from the sutured arc/ophiolite terranes, and were deposited on top of the Coast Range ophiolite, the southern edge of the Klamaths, and the western side of the Sierra Nevada. A new (late Mesozoic) magmatic arc was superposed across the previously accreted terranes, and formed the primary sediment source for the Cretaceous forearc basin.
TL;DR: The tectonic evolution of Northeastern Asia is outlined through recognition of tectonostratigraphic terranes and their lateral zonations of island arc and continental margin affinities.
TL;DR: In this article, the authors show that the Late Triassic subduction-related rocks are exposed in two discontinuous belts that lie east and west of the Cache Creek terrane in Canada and correlative melange terranes farther south.
Abstract: Igneous rocks of Late Triassic age are widespread in the Cordillera of western North America and, except in Wrangellia, consist of subduction-related plutonic and volcanic suites. Many of these, including those in the Stikinia, Quesnellia, Rattlesnake Creek, and Jackson terrenes and in southern California, are clinopyroxene rich and belong to high-potassium and shoshonitic rock series, features that are generally absent from older and younger igneous rocks in the same terranes. The Late Triassic subduction-related rocks are exposed in two discontinuous belts that lie east and west of the Cache Creek terrane in Canada and correlative melange terranes farther south. Stratigraphic and structural data suggest that these belts were spatially separate magmatic arcs in Late Triassic time. Tectonic implications of this analysis include an explanation of Middle Jurassic Cordilleran deformation as the result of collision of the western with the eastern belt, absence of Late Triassic links between Stikinia and Quesnellia, disassociation of Stikinia with terranes in northwestern Nevada, and tentative correlation of the Wallowa (Seven Devils) terrane with Stikinia rather than Wrangellia.
TL;DR: The Mt Windsor Subprovince encompasses the dismembered remnants of a thick volcanic and sedimentary succession predominantly of Late Cambrian and Early Ordovician age located within the northern part of the Tasman Orogenic Zone.
Abstract: The Mt Windsor Subprovince encompasses the dismembered remnants of a thick volcanic and sedimentary succession predominantly of Late Cambrian and Early Ordovician age located within the northern part of the Tasman Orogenic Zone. The succession is divided into four formations which together comprise the Seventy Mile Range Group. Its lower part, Puddler Creek Formation, comprises immature terrigenous clastic strata lacking in volcanics but hosting numerous penecontemporaneous dolerite sills and dykes. Its upper part, Mt Windsor Volcanics, Trooper Creek Formation and Rollston Range Formation, is dominated by acid and intermediate volcanics and volcaniclastics. The group has been dismembered, deformed and in part metamorphosed by emplacement of the Middle Ordovician Ravenswood Granodiorite Complex which is regarded as having been diapirically emplaced. Stratigraphic relationships and reconnaisance geochemistry suggest that the volcanics comprise a consanguineous series ranging from basaltic andesite to rhyoli...
TL;DR: A detailed examination of the boundary between Peach and Home's (1899) Northern and Central Belts, in the Lower Palaeozoic rocks of the Southern Uplands of Scotland and their Irish continuation in Longford-Down, demonstrates it to be a major Caledonian sinistral wrench fault as discussed by the authors.
Abstract: A detailed examination of the boundary between Peach and Home's (1899) Northern and Central Belts, in the Lower Palaeozoic rocks of the Southern Uplands of Scotland and their Irish continuation in Longford–Down, demonstrates it to be a major Caledonian sinistral wrench fault. Maps and descriptions of outcrops of the fault at Slieve Glah in County Cavan, at Orlock Bridge on the NE coast of Down, at Cairngarroch on the Rhinns of Galloway and at Garvald, 11 km SW of Dunbar, are presented. A distinctive fault fabric, clearly the result of repeated sinistral slip at the first three localities, characterises these outcrops along the 400 km trace. The fabric elements include: (1) lenticular shearing of arenites in the fault protolith, (2) a fault-associated phyllonitic fabric, with abundant pressure-solution seams, overprinting the regional S1, (3) numerous foliation-parallel quartz segregations, (4) refolding of the regional S1 cleavage, segregation veins and the phyllonitic fabric in at least two generations of steeply plunging, sinistrally-verging folds, (5) a non-penetrative crenulation cleavage, (6) a locally developed sinistral S–C fabric, and (7) typical protomylonite, mylonite and ultramylonite textures in thin sections of the fault rocks. The zone of fault-associated deformation varies from a few metres across at Garvald to over 1 km at Slieve Glah. The fault thus differs from other tract-defining faults in the Southern Uplands, particularly in its clear evidence of ductile, quasi-plastic, deformation at depth, in its lack of associated imbrication, in its significant refolding and overprinting of the regional S1 cleavage and in its uniquely large stratigraphic effects.The main fabric-generating movement postdates the regional, accretion-related, S1 cleavage but predates minor Caledonian (c. 400 Ma) intrusions. For its entire length the fault separates the Northern Belt, with proof only of Upper Ordovician turbidites, and the Central Belt, where turbidite deposition began in the Silurian. The age of the base of the turbidites decreases southward by some six graptolite zones at the fault trace. The fault thus either (a) excises the equivalent of four tracts from a single accretionary-prism terrane, or (b) juxtaposes two distinct terranes, one of late Ordovician and the other of Silurian age. In either event the sinistral slip is probably in excess of 400 km.
TL;DR: Geologic, seismic, gravity, and magnetic data from the northern Chugach Mountains and southern Copper River Basin, Alaska, indicate that the composite Peninsular/Wrangellia terrane (PET/WRT) are thin (< 10 km), rootless sheets bounded on the south by north-dipping thrust faults that sole into a shallow, horizontal, low-velocity zone as discussed by the authors.
Abstract: Geologic, seismic, gravity, and magnetic data from the northern Chugach Mountains and southern Copper River Basin, Alaska, indicate that the Chugach terrane (CGT) and the composite Peninsular/Wrangellia terrane (PET/WRT) are thin (< 10 km), rootless sheets bounded on the south by north-dipping thrust faults that sole into a shallow, horizontal, low-velocity zone. The CGT has been thrust at least 40 km beneath the PET/WRT along the Border Ranges fault system (BRFS). Adjacent to the BRFS, uplift and erosion of 30-40 km since Jurassic time have exposed blueschist-facies rocks in the CGT and mafic and ultramafic cumulate rocks in the PET/WRT. Four paired north-dipping layers of low and high seismic velocities extend beneath the northern CGT and southern PET/WRT and may be slices of subducted oceanic crust and upper mantle; the upper two pairs may now be joined to the continental plate. 15 references, 5 figures.
TL;DR: In this paper, a plot of age versus distance across strike shows that the diachronous migration of these phenomena across the foreland proceeded at rates of 2 to 3 cm/yr; they regard this as the plate convergence rate during the latter part of the Taconic Orogeny.
Abstract: The rate of plate convergence during arc-continent collision can be estimated from the rate at which the secondary effects of subduction move across the underriding plate in advance of the plate boundary. The following sequence of events is typical: (I) shoaling and/or emergence of the continental shelf, presumably caused by lithospheric flexure; (2) rapid subsidence, by a combination of normal faulting and trenchward tilting; and (3) a change from platformal to flysch sedimentation. Such a sequence has been recognized in the Taconic foreland basin in eastern New York and interpreted as being the result of collision between the ancient passive margin of North America and an island arc terrane at an east-dipping subduction zone during Medial Ordovician times. A plot of age versus distance across strike shows that the diachronous migration of these phenomena across the foreland proceeded at rates of 2 to 3 cm/yr; we regard this as the plate convergence rate during the latter part of the Taconic Orogeny. Our result is comparable with modern rates of plate motion and also agrees with an earlier estimate for the Taconic, which was based on the rate at which a series of locations on the outer trench slope passed through fossil-defined isobaths.