Orogenic Welt Research Articles

The geological history of the Istria ‘Depression’, Romanian Black Sea shelf: tectonic controls on second-/third-order sequence architecture

Abstract The Istria ‘Depression’ or sub-basin of offshore Romania lies at the intersection of the trans-European Tornquist–Teisseyre ‘Zone’ and the Black Sea back-arc basin, just outboard of the East Carpathian orogenic welt. Its Late Mesozoic–Cenozoic succession records an extraordinary polyphase history of subsidence and sedimentation, interrupted by several quite spectacular second-/third-order erosional unconformities, reflecting the interplay between these tectonic domains. The unconformities divide the succession into a number of stratigraphic sequences. The sub-basin first developed as a transtensional rift in the Triassic–Early Jurassic, evolving into a narrow oceanized trough in the later Jurassic. This was tilted west during the Early Cretaceous, and the residual Late Jurassic topography was filled and buried by a west-facing clastic–evaporite wedge. Following Late Aptian–Albian(?) rifting, post-rift subsidence and spreading in the Western Black Sea imposed a strong easterly tilt, encouraging the partial evacuation of its Early Cretaceous sedimentary fill by gravity-driven mass wastage. The incised valley topography was subsequently infilled and buried during the later Cretaceous and Early Cenozoic. During the mid-Late Cenozoic, the Black Sea Basin experienced intermittent periods of partial to complete isolation from the world ocean and significant base-level drawdown. The first major sea-level fall occurred in the Eocene when the Istria ‘Depression’ was deeply incised, to be healed by Oligocene shales during the subsequent rise. Yet another period of drawdown and exposure occurred in the mid-Miocene, with extensive shelf-margin mass wastage and erosion, followed by re-flooding and deposition of a transgressive backstepping sequence in the middle-late Miocene. Messinian drawdown in the Mediterranean caused a further period of isolation and falling base level. The shelf margin was again exposed, and experienced widespread mass wastage and slumping. Rising sea level eroded the earlier slumped sequence and the margin was healed by a lowstand prograding wedge in the late Miocene–early Pliocene. This was followed by shelf sedimentation in the Plio-Pleistocene periodically interrupted by canyon-incision events, testifying to continued climatically or tectonically imposed base-level fluctuations. Several direct and indirect tectonic factors were responsible for valley/canyon incision within the Istria Depression and erosion of the Romanian Black Sea shelf margin. These include: (1) the local structural framework; (2) direct tectonic uplift and tilting; and (3) more indirect tectonically imposed isolation encouraging significant base-level falls.

Orogenesis without collision: Stabilizing the Terra Australis accretionary orogen, eastern Australia

The Neoproterozoic to end-Paleozoic Terra Australis orogen extended along the Gondwana margin of the paleo–Pacific Ocean, and it now provides a detailed record of orogenic activity and continental stabilization within an ongoing convergent, accretionary plate margin. New geochronological data from end-Paleozoic plutonic and volcanic rocks associated with the Gondwanide orogeny in the New England region of eastern Australia, integrated with information on the nature and timing of associated sedimentation, deformation, and metamorphism, allow resolution of a high-fidelity record of orogenesis. At the end of the Carboniferous, around 305 Ma, convergent margin magmatism, which had been active along the western margin of the New England region, terminated and was followed by a short pulse of regional compressional deformation and metamorphism, marking the commencement of the Tablelands phase of Gondwanide orogenesis. Deformation was almost immediately followed by the onset of clastic sedimentation and local calc-alkaline volcanism, dated at 293 Ma, in the extensional Barnard Basin. Emplacement of the two New England S-type granitic suites, the Bundarra and the Hillgrove suites, along with localized high-temperature, low-pressure metamorphism, was essentially contemporaneous, ranging in age from 296 to 288 Ma, and overlapped in time with I-type magmatism and the switch from regional compression to extension and Barnard Basin rifting. The Hunter-Bowen phase of the Gondwanide orogeny commenced with contractional deformation, resulting in termination of sedimentation in the Barnard Basin and regional deformation and metamorphism across New England and into the Sydney and Gunnedah basins to the west at around 265–260 Ma. Contractional loading of the Sydney and Gunnedah basins resulted in their conversion from extensional to foreland basins, which received ongoing pulses of sediment from the New England orogenic welt until 230 Ma. The Hunter-Bowen phase was associated with widespread I-type plutonism and volcanic activity in New England that ceased around 230 Ma, marking the termination of Gondwanide orogenesis. Orogenesis occurred in an evolving convergent plate-margin setting. S- and I-type magmatic activity ranging in age from ca. 300 to 230 Ma represents a stepping out of arc magmatism from the western margin of New England (prior to 305 Ma) into the preexisting arc-trench gap. There is no evidence that deformation was related to the collision of the convergent margin with a major lithospheric mass, and the widespread development of extensional basins in the eastern third of Australia in the Early Permian indicates control by phenomena acting on a continental scale, probably changing plate kinematics associated with the amalgamation of Pangea.

Coolwater culmination: Sensitive high‐resolution ion microprobe (SHRIMP) U‐Pb and isotopic evidence for continental delamination in the Syringa Embayment, Salmon River suture, Idaho

During dextral oblique translation along Laurentia in western Idaho, the Blue Mountains superterrane underwent clockwise rotation and impinged into the Syringa embayment at the northern end of the Salmon River suture. Along the suture, the superterrane is juxtaposed directly against western Laurentia, making this central Cordilleran accretionary‐margin segment unusually attenuated. In the embayment, limited orthogonal contraction produced a crustal wedge of oceanic rocks that delaminated Laurentian crust. The wedge is exposed through Laurentian crust in the Coolwater culmination as documented by mapping and by sensitive high‐resolution ion microprobe U‐Pb, Sri, and ɛNd data for gneisses that lie inboard of the suture. The predominant country rock is Mesoproterozoic paragneiss overlying Laurentian basement. An overlying Neoproterozoic (or younger) paragneiss belt in the Syringa embayment establishes the form of the Cordilleran miogeocline and that the embayment is a relict of Rodinia rifting. An underlying Cretaceous paragneiss was derived from arc terranes and suture‐zone orogenic welt but also from Laurentia. The Cretaceous paragneiss and an 86‐Ma orthogneiss that intruded it formed the wedge of oceanic rocks that were inserted into the Laurentian margin between 98 and 73 Ma, splitting supracrustal Laurentian rocks from their basement. Crustal thickening, melting and intrusion within the wedge, and folding to form the Coolwater culmination continued until 61 Ma. The embayment formed a restraining bend at the end of the dextral transpressional suture. Clockwise rotation of the impinging superterrane and overthrusting of Laurentia that produced the crustal wedge in the Coolwater culmination are predicted by oblique collision into the Syringa embayment.

Cenozoic Crustal Evolution and Mantle Dynamics of Post-Collisional Magmatism in Western Anatolia

Post-collisional magmatism in western Anatolia followed a continental collision event in the Early Eocene, and occurred in discrete pulses that appear to have propagated from north to south over time. The first episode occurred during the Eocene and Oligo-Miocene and was subalkaline in nature, producing medium-to high-K calc-alkaline granitoids and mafic to felsic volcanic rocks. Partial melting and assimilation-fractional crystallization of enriched subcontinental lithospheric mantle-derived magma(s) were important processes in the genesis and evolution of the parental magmas, which experienced decreasing subduction influence and increasing crustal contamination through the Early Eocene-Early Miocene. This magmatic episode coincided with continued regional compression and development of a thick orogenic crust, and was influenced by an influx of asthenospheric heat and melts provided by lithospheric slab break-off. Extensional tectonics replaced the regional compression by the Middle Miocene, following the initial collapse of the western Anatolian orogenic welt, and resulted in the development of metamorphic core complexes and horst-graben structures. The second main episode of magmatism occurred during the Middle Miocene (16-14 Ma) and produced mildly alkaline rocks that show a decreasing amount of crustal contamination and subduction influence through time. Although melting of a subduction-modified lithospheric mantle continued, an asthenospheric mantle-derived melt contribution played a major role in the generation of these mildly alkaline magmas. The inferred asthenospheric melt contribution was a result of delamination of the lowermost part of the lithospheric mantle and/or partial convective removal of the sub-continental lithospheric mantle (SCLM). The third episode of post-collisional magmatism started around ~12 Ma and continued through the Late Quaternary. The main melt source for this phase carried no subduction component and was generated by the decompressional melting of asthenospheric mantle, which flowed in beneath the attenuated continental lithosphere in the Aegean extensional province. Lithospheric-scale extensional fault systems acted as natural conduits for the transport of uncontaminated alkaline magmas to the surface. Post-collisional magmatism in western Anatolia thus displays compositionally distinct episodes controlled by slab break-off, lithospheric delamination, and asthenospheric upwelling and decompressional melting, reflecting the geodynamic evolution of the eastern Mediterranean region throughout the Cenozoic. These events and the associated processes in the mantle took place primarily in response to the plate tectonic evolution of the region and collectively constitute a time-progressive template for the mode and nature of the post-collisional magmatism common to most alpine-style orogenic belts.

Movement and mineralization in the Tyndrum Fault Zone, Scotland and its regional significance

Major and minor fracture analysis of the Tyndrum Fault Zone, Scotland, reveals a late Silurian history of transtensional deformation with opening across the zone as well as left-lateral strike-slip movements. The extensional phases are characterized by hydrothermal quartz veins and breccias associated with the early stages of precious-metal mineralization. The strike-slip movements are characterized by cataclastic textures and are associated with the later stages of the precious-metal mineralization. Further transtensional deformation in the Carboniferous is indicated by right-lateral strike-slip movements, associated with fractures throughout the zone containing both cataclastic and extensional hydrothermal quartz veins: the quartz veins are associated with base-metal mineralization. The pre-Devonian, WSW–ENE-directed, transtensional deformation of the zone is extrapolated to the whole Dalradian Terrane, the driving force being the gravitational collapse of the orogenic welt parallel to the tectonic trend. The necessary area increase is signified by the intrusion of the end-Caledonian granitic magmas and quartz-veins. The Carboniferous right-lateral movements resulting from N-S extension are related to similar movements, also transtensional, on the Great Glen Fault Zone and in the Midland Valley; the associated mineralization is related to a broader Dinantian base-metal mineralizing event.

Latest Cretaceous-Tertiary Tectonic Evolution of Northern Yukon and Adjacent Arctic Alaska

Regional crustal shortening in northern Yukon and northeastern Alaska occurred episodically from the latest Cretaceous to the late Miocene, with a major culmination occurring in the Paleocene to middle Eocene, and a secondary culmination in the late Miocene. Structural trends are predominantly north to northeastward in northern Yukon and adjacent east-central Alaska, and generally east-west along the Brooks Range. The early Tertiary trend is strongly arcuate in the Beaufort fold belt and adjacent onshore areas. The continuity of structures southward from the Beaufort Sea region through northern Yukon and east-central Alaska supports the interpretation that the structures north of 65°N form a single orogenic entity. The Beaufort Sea region is 1000 km from the nearest plate margin. Northward shortening across Arctic Alaska and the northern Canadian cordillera reflects the convergent component of Kula (later, Pacific)-North America interactions throughout the Tertiary. North- to northeast-trending structures of latest Cretaceous to early Tertiary age in northern Yukon and east-central Alaska accommodate shortening of 180-240 km, and reflect Eurasia-North America convergence. The strongly arcuate offshore Beaufort fold belt and similar structures in adjacent northernmost Yukon and northeast Alaska were formed by the complex interplay of three factors: shortening of northern Yukon between Arctic Alaska and the craton to produce a north-trending orogenic welt; northward displacements propagated from the Kula plate margin; and local boundary conditions imposed by lithology and crustal structure, which aided lateral escape of the deforming supracrustal succession northward into the Beaufort Sea. In central Alaska, any kinematic linkage between the Kaltag fault in the west and the Tintina fault of the northern cordillera is more complex than was previously assumed. A new regional tectonic reconstruction of northern Yukon-Alaska quantifies the tectonic shortening in central Alaska south of the Kaltag and Tintina faults in an area where tectonic shortening is difficult to quantify due to complex geology. Complex deformation accommodated by folding, thrust and strike-slip faulting, and/or tectonic rotations accounts for an estimated 460 km of crustal shortening, approximately equivalent in magnitude to the total Tintina fault displacement of at least 450 km. The foreland of the Brooks Range, the Beaufort fold belt, and the northern cordillera contain proven petroleum basins. This regional synthesis validates a model of orogenic shortening for the Beaufort fold belt and provides a unifying tectonic setting for oil and gas plays throughout the region. The latest Cretaceous-Tertiary structural evolution of the Brooks Range, Beaufort, and northern Yukon fold belts is a case study of the temporally and kinematically complex far-field deformation arising from the convergence of four major tectonic plates.

Pacific‐type orogeny revisited: Miyashiro‐type orogeny proposed

Abstract The concept of Pacific‐type orogeny is revised, based on an assessment of geologic data collected from the Japanese Islands during the past 25 years. The formation of a passive continental margin after the birth of the Pacific Ocean at 600 Ma was followed by the initiation of oceanic plate subduction at 450 Ma. Since then, four episodes of Pacific‐type orogeny have occurred to create an orogenic belt 400 km wide that gradually grew both oceanward and downward. The orogenic belt consists mainly of an accretionary complex tectonically interlayered with thin (<2 km thick), subhorizontal, high‐P/T regional metamorphic belts. Both the accretionary complex and the high‐P/T rocks were intruded by granitoids ∼100 million years after the formation of the accretionary complex. The intrusion of calc‐alkaline (CA) plutons was synchronous with the exhumation of high‐P/T schist belts. Ages from microfossils and K‐Ar analysis suggest that the orogenic climax happened at a time of mid‐oceanic ridge subduction. The orogenic climax was characterized by the formation of major subhorizontal orogenic structures, the exhumation of high‐P/T schist belts by wedge extrusion and subsequent domed uplift, and the intrusion‐extrusion of CA magma dominantly produced by slab melting. The orogenic climax ended soon after ridge subduction, and thereafter a new Pacific‐type orogeny began. A single Pacific‐type orogenic cycle may correspond to the interaction of the Asian continental margin with one major Pacific oceanic plate. Ophiolites in Japan occur as accreted material and are not of island‐arc but of plume origin. They presumably formed after the birth of the southern Pacific superplume at 600 Ma, and did not modify the cordilleran‐type orogeny in a major way. Microplates, fore‐arc slivers, intra‐oceanic arc collisions and the opening of back‐arc basins clearly contributed to cordilleran orogenesis. However, they were of secondary importance and served only to modify pre‐existing major orogenic components. The most important cause of cordilleran‐type orogeny is the subduction of a mid‐oceanic ridge, by which the volume of continental crust increases through the transfer of granitic melt from the subducting oceanic crust to an orogenic welt. Accretionary complexes are composed mainly of recycled granitic sediments with minor amounts of oceanic material, which indicate that the accretion of oceanic material, including huge oceanic plateaus, was not significant for orogenic growth. Instead, the formation and intrusion of granitoids are the keys to continental growth, which is the most important process in Pacific‐type orogeny. Collision‐type orogeny does not increase the volume of continental crust. The name ‘Miyashiro‐type orogeny’ is proposed for this revised concept of Pacific‐type or cordilleran‐type orogeny, in order to commemorate Professor A. Miyashiro's many contributions to a better understanding of orogenesis.

Paleogeography and Depositional History of the Middle and Upper Devonian in Central Idaho

Middle and Upper Devonian rocks of central Idaho were deposited in a foreland basin east of the Antler orogenic welt' and west of a positive feature that extends along the central Idaho-Montana border. Upper Devonian rocks are anomalously thick (more than 700 m) in central Idaho, relative to the carbonate platform (300 m) in southwestern Montana. West of the Antler orogenic welt' Lower to Upper Devonian siliciclastic and carbonate rocks of the western Milligan Formation were deposited in an inner arc basin. East of the Antler orogenic welt' intertidal to subtidal deposition of the lower black dolomite unit of the Jefferson Formation occurred from Givetian to late Frasnian time. Restricted conditions suggest the Antler orogenic welt' was periodically an effective barrier to circulation as early as Givetian time. Stratigraphic variation in the upper Jefferson Formation is associated with subaerial exposure along the Antler orogenic welt' and increased foreland basin subsidence during the late Frasnian. Shallowing to supratidal and intertidal, siliciclastic channels and eolian sand probably are derived from early Paleozoic rocks along the Antler orogenic welt.' Conformably overlying the Jefferson Formation is the Famennian Trident Member of the Three Forks Formation, which contains a garnet-bearing argillaceous limestone, suggesting that erosionmore » along the Antler orogenic welt' had reached Precambrian basement rocks. Middle Famennian flysch deposition suggests increased subsidence in the foreland prior to the unconformity over which Early Mississippian rocks were deposited.« less

Uplift of deep crust during orogenic extensional collapse: A model based on field studies in the Sogn‐Sunnfjord Region of western Norway

The Western Gneiss Region (WGR) in Norway experienced high‐pressure metamorphism during Silurian‐Devonian continent‐continent collision. The eclogite‐bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen; formation of the Devonian basins is related to the extension. The footwall of the detachment zones comprises three structural and metamorphic zones. The upper zone, zone 1, is characterized by penetrative homogeneous down‐to‐the‐west simple shear developed under retrograde greenschist‐facies metamorphism. Zone 2 suffered inhomogeneous simple shear of the same polarity. Petrography and mineral chemistry data from the lower zone, zone 3, show a record of initial eclogite facies metamorphism at 600°C and >16 kbar, which was decompressed almost isothermally to amphibolite‐facies conditions at 550°C and 10–12 kbar. Both the eclogite‐ and amphibolite‐facies metamorphism developed in a regime of pure shear with vertical shortening. The rapid decompression records an approach of approximately 20 km to the surface, related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere. The pure shear regime, which developed initially in the lower crust, was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels. Extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear. The shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust. A considerable amount of tectonic stripping of the orogenic welt predates deposition of the Devonian sedimentary basins.

Contributions to the tectonic history of the Innuitian Province, Arctic Canada

The Innuitian Tectonic Province contains the record of a Phanerozoic mobile belt in northern Greenland and the Canadian Arctic Archipelago. Two fundamentally different phases in its development were separated by the Devonian–Carboniferous Ellesmerian Orogeny. The first contribution focuses on the early Paleozoic history of a key area, the second summarizes the Carboniferous to Cenozoic history of most of the Canadian part of the province.(1) The early Paleozoic architecture of the mobile belt is apparent only in Ellesmere Island, where exposures extend from the Canadian Shield through Arctic Platform and Franklinian basin into the Pearya orogenic welt. The Franklinian basin comprised the deep but ensulic Hazen Trough and two unstable shelves bordering it on the northwest and southeast. The northwestern shelf was a site of felsic to intermediate volcanism, mainly in the Ordovician Period. Pearya, a site of granitic plutonism in the Devonian Period, supplied much of the clastic basin fill. Its core consisted of a metamorphic complex, about 1.0 Ga old, exposed in basement uplifts in nor thernmost Ellesmere Island. Both basin and welt essentially formed part of the North American Plate, although rifting, evident from mafic and ultramafic intrusions, probably occurred in Early Devonian (or latest Silurian) time. The history of this part of the province is tentatively interpreted as response to the opening and closure of an ocean, connected with lapetus, that separated northern Ellesmere Island and Greenland from the sialic crust of the present Lomonosov Ridge and Barents Shelf. The Lomonosov Ridge still seems to be attached to the shelf off northeasternmost Ellesmere Island.(2) Deep subsidence and filling of Sverdrup Basin dominated the Innuitian region from Early Carboniferous through Late Cretaceous time. Large halokinetic diapirs and mafic dikes and sills intruded axial parts of the basin succession through Mesozoic time. Steep faults along the northwestern margin of the basin are Middle Cretaceous and older. Part of the northwestern rim of Sverdrup Basin sagged in latest Cretaceous time, becomingpart of the Arctic continental terrace. In the Late Cretaceous and early Tertiary a system of large grabens developed through the southern part of the Innuitian region, linking Canada Basin with Baffin Bay; about the same time, uplift formed some large arches in the northeastern part of the region. Middle Eocene and older rocks were laterally compressed by a phase of pre-Miocene folding and faulting. Some uplift took place in Oligocene or Miocene time on Axel Heiberg Island. The distribution of recent earth quakes does not indicate the presence of modern active plate margins.

Tectonic controls of late Cretaceous sedimentation, western interior, USA

Anomalous subsidence of continental crust occurred during the Late Cretaceous in a region centred about Colorado, southern Wyoming and eastern Utah. The amount of subsidence is greater than can be explained by eustatic sea level rise and supracrustal loading by water and sediment. Analysis of thickness and distribution of Upper Cretaceous strata of the Western Interior Seaway, USA, shows two distinct basinal trends. The subsidence of the earliest (100–80 Myr BP) is attributed partly to isostatic flexure in front of the rising orogenic welt. The subsidence of the later (80-70 Myr BP) is attributed to subcrustal loading induced by a shallowly subducted plate.

Ordovician (Trenton to Richmond) depositional patterns of New York State, and their relation to the Taconic orogeny

Research Article| December 01, 1978 Ordovician (Trenton to Richmond) depositional patterns of New York State, and their relation to the Taconic orogeny GREGORY J. ZERRAHN GREGORY J. ZERRAHN 1Shell Oil Company, P.O. Box 60775, New Orleans, Louisiana 70160 Search for other works by this author on: GSW Google Scholar Author and Article Information GREGORY J. ZERRAHN 1Shell Oil Company, P.O. Box 60775, New Orleans, Louisiana 70160 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1978) 89 (12): 1751–1760. https://doi.org/10.1130/0016-7606(1978)89<1751:OTTRDP>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation GREGORY J. ZERRAHN; Ordovician (Trenton to Richmond) depositional patterns of New York State, and their relation to the Taconic orogeny. GSA Bulletin 1978;; 89 (12): 1751–1760. doi: https://doi.org/10.1130/0016-7606(1978)89<1751:OTTRDP>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A regional stratigraphic synthesis employing subsurface and outcrop data was conducted on a regressive sequence of Middle (Trenton) to Late (Richmond) Ordovician terrigenous rocks in New York and northern Pennsylvania. The sequence is divided into three conformable units: (1) basal shale, (2) medial siltstone, and (3) upper sandstone. Isopachous and lithologic trends of these units reflect tectonic evolution associated with the Taconic orogeny. These trends, coupled with paleocurrent data, suggest that two diachronous source areas influenced Taconic sedimentation: an eastern area (Green Mountain axis) uplifted during Middle Ordovician time, and a southeastern area in Pennsylvania (ancestral Piedmont?) during Late Ordovician time.Accepting a cordilleran-type model for the Taconic orogeny, it appears that the eastern source was an elongate low-relief orogenic welt resulting from thermal and isostatic disequilibrium. Subsurface trends, however, indicate that the southeastern uplift was of a more rugged relief and limited areal extent, suggesting that it may have resulted from a collision-type mechanism. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Similar Folds, Recumbent Folds, and Gravity Tectonics in Ice and Rocks

Under steady state flow in glaciers, a banding will form and tend towards parallelism with the flow lines in basal regions of high shear. A simple mathematical model shows that departures from the steady state cause a reorientation of the flow lines such that they depart from parallelism with the banding. If a suitable bedrock ridge is present, the banding will subsequently become deformed into subsimilar folds, whose axial surfaces are very nearly parallel to the direction of maximum extension of the associated strain. The cleavage pattern, geometry, and orientation of many folds in rocks suggest a similar origin during gravitationally-induced flow away from an orogenic welt. In some cases buckling may be a secondary response, resulting in non-similar folds.