Academic literature on the topic 'Accretion prism'

The paper presents a review of processes of subduction or tectonic erosion at the Pacific-type convergent margins (PTCM) including definition of “tectonic erosion”, its triggers, driving forces and consequences. We review examples of tectonic erosion at the Circum-Pacific PTCMs and at the fossil PTCMs of the Paleo-Asian Ocean (PAO) currently hosted by the Central-Asian Orogenic Belt (CAOB). Recent geological and stratigraphic studies have shown two types of PTCMs: accreting and eroding. Accreting PTCMs consist of older deposits of accretionary and frontal prisms and grow oceanward, i.e. the trench retreats. Eroding PTCMs are characterized by the destruction of the prism, approaching arc and trench and typically form during shallow-angle and fast subduction of an oceanic slab with oceanic floor topographic highs. The mechanism of tectonic erosion includes destruction of oceanic slab, island arcs, accretionary prism, fore-arc and related prism. Tectonic erosion is a common phenomenon at many Circum-Pacific PTCMs, e.g., in South America, Tonga and Nankai troughs, Alaska. Accretion and subduction of oceanic rises contributes greatly to the processes of formation, transformation and destruction of continental crust at PTCM. The episodes of tectonic erosion can be also reconstructed for an ancient ocean, for example, for the PAO, which evolution and suturing formed the CAOB. Many CAOB foldbelts (Altai, Tienshan, eastern Kazakhstan, Transbaikalia, Mongolia) carry signs of disap-pearance of big volumes of continental crust (arcs). Studying processes responsible not only for the formation of continental crust, but also for the disappearance of big volumes of crustal mate-rial is important for correct evaluation of the nature of intra-continental orogenic belts, e.g., CAOB, and development of reliable tectonic models.

The Mesoarchean Târtoq greenstone belt, southern West Greenland, consists of tectonically imbricated slices of metamorphosed basalt, gabbro, peridotite, and sedimentary rocks and is intruded by felsic rocks (now mylonites) with well-preserved duplex structures, representing a relict accretionary prism. The Târtoq greenstone belt is a remnant of a supra-subduction zone ophiolite that originated as back-arc basin oceanic crust. Following the initiation of intra-oceanic subduction, the back-arc oceanic crust accreted to the overriding plate, forming an accretionary prism. The felsic mylonites are compositionally akin to Archean tonalite–trondhjemite–granodiorite suites. Field observations, along with geochemical and zircon U–Pb age data, indicate that the protoliths of the felsic mylonites were derived from partial melting of back-arc basalts in the accretionary prism and emplaced along thrust faults between 3012 ± 4 and 2993 ± 6 Ma. It is proposed that the partial melting of the basalts likely occurred in response to ridge subduction. The Upper Cretaceous turbiditic greywackes of the Chugach – Prince William accretionary complex in southern Alaska are intruded by Paleogene felsic dykes. These felsic dykes appear to have been derived from partial melting of subducted and (or) accreted oceanic crust during slab window magmatism. Archean granitoid–greenstone terrains share many geological characteristics of Phanerozoic subduction–accretion complexes such as the Alaskan and Altaid subduction–accretion complexes, consistent with the operation of uniformitarian geological processes in the Archean. The Archean Earth might have been dominated by numerous smaller plates and greater ridge length than today that would have resulted in more frequent ridge-accretionary prism interactions and larger volumes of tonalite–trondhjemite–granodiorite generation in subduction–accretion complexes.

Abstract A grid of closely spaced, high-resolution multichannel seismic (MCS) reflection profiles was acquired in May 2012 over the outer accretionary prism up dip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (offshore Chile) to complement a natural-source seismic experiment designed to monitor the post-earthquake response of the outer accretionary prism. We describe the MCS data and discuss the implications for the response of the accretionary prism during the earthquake and for the long-term evolution of the margin. The most notable observation from the seismic reflection survey is a rapid north-to-south shift over a short distance from nearly total frontal accretion of the trench sediments to nearly total underthrusting of undeformed trench sediments that occurs near the northern edge of slip in the 2010 earthquake. Integrating our structural observations with other geological and geophysical observations, we conclude that sediment subduction beneath a shallow décollement is associated with propagation of slip to the trench during great earthquakes in this region. The lack of resolvable compressive deformation in the trench sediment along this segment of the margin indicates that the plate boundary here is very weak, which allowed the outer prism to shift seaward during the earthquake, driven by large slip down dip. The abrupt shift from sediment subduction to frontal accretion indicates a stepdown in the plate boundary fault, similar to the stepovers that commonly arrest slip propagation in strike-slip faults. We do not detect any variation along strike in the thickness or reflective character of the trench sediments adjacent to the change in deformation front structure. This change, however, is correlated with variations in the morphology and structure of the accretionary prism that extend as far as 40 km landward of the deformation front. We speculate that forearc structural heterogeneity is the result of subduction of an anomalously shallow or rough portion of plate that interacted with and deformed the overlying plate and is now deeply buried. This study highlights need for three-dimensional structural images to understand the interaction between geology and slip during subduction zone earthquakes.

The Red Indian Line is the fundamental Iapetus suture zone in the Newfoundland Appalchians along which the main tract of the Iapetus Ocean was consumed. Despite being the site of the closure of a wide ocean, few vestiges of the Iapetus plate have been accreted along Red Indian Line. Ordovician rocks in the Notre Dame Bay area preserve the only evidence for accretion of a seamount in Newfoundland. The seamount is characterized by alkali basalt and hypabyssal rocks that are juxtaposed with Darriwilian peri-Laurentian volcanic arc rocks (466 ± 4 and 467 ± 4 Ma) along a major mylonite zone. The mylonite zone lacks sedimentary rocks suggesting that the seamount was accreted to the arc along a sediment-starved interface and that significant subduction erosion took place along the Laurentian margin. Identification of subduction erosion indicates that an accretionary prism did not exist outboard of Laurentia in Newfoundland, in contrast to the well developed accretionary prisms of the Caledonides.

Abstract In this study, we determined the variations of tidal flow field and tidal prism caused by human activities in Tongzhou bay and using MIKE 21 hydrodynamic model as analyzing tool. After the human activities, the hydrodynamic in sea area alongshore engineering is changed, the most obvious changes can reach over 0.1m/s; the tidal discharge decreases caused by the land accretion leading to the shrink of the area of Nantong near-shore waters, there is up to 12% reduction after planned reclamation during one spring tide period.

AbstractThe eastern Nankai accretionary prism toe was surveyed to evaluate the nature and deformation of its frontal thrust. According to the determined porosities and yield strengths, turbidites were successively buried down to depths of 250–300 m before accretion, and were then exposed at the prism toe by uplift along the Tenryu frontal thrust during 3.4–1.98 Ma. Consolidation tests provided reasonable estimates of burial depth and, when combined with exposed sediment dates, yield prism toe uplift rates of 0.74–2.27 m ka–1. The displacement along the frontal thrust is estimated to be 500–900 m and the slip rates are 1.47–4.55 m ka–1, corresponding to the highest class of active faults on land in Japan. During the surveys of the Tenryu frontal thrust zone, we discovered a new active fault scarp that was several tens of centimetres high, interpreted to be a protothrust located c. 100 m south of the frontal thrust. This scarp is associated with chemosynthetic biocommunities. The thrust might potentially be the result of displacement during the East Nankai (To-Nankai) earthquake (Mw 8.1) in 1944. These lines of evidence indicate that the Tenryu frontal thrust is still active and that displacement along the thrust might induce a tsunami during future Tokai or To-Nankai earthquakes.

Development of tectonic subprovinces as shear-bounded granite–greenstone and sediment-dominated terranes during the late Archaean is reviewed and interpreted from relationships between portions of the Wabigoon, Wawa, and Quetico subprovinces.Greenstone-dominated subprovinces (Wabigoon and Wawa) are complex successions of tholeiites, 2.76–2.70 Ga calc-alkaline volcanic centres, and derived sediments. Supracrustal rocks aggregated on a scale of tens of kilometres, forming homoclines, locally upright folded, intruded by granitoids, exhibiting variable fabric trends and strains, and cut by transcurrent shear zones. Small-scale (10–100 km) accretion juxtaposed these varied supracrustal sequences, which were engulfed granitoid magmas, to form greenstone belts.Sediment-dominated subprovinces (Quetico) are metamorphosed wacke sequences deposited during and after the volcanic climax in the period 2.70–2.69 Ga. Overthrust imbrication at both the Wabigoon–Quetico and the Quetico–Wawa contacts occurred along north-dipping shears, now vertical. Continued right-lateral convergence at subprovince margins induced progressive shortening within the Quetico Subprovince, producing a regional planar fabric. Abukuma–style metamorphism, migmatite formation, and S-type granite intrusions occurred during the period 2.67–2.65 Ga.Greenstone-belt developments, terminated during large-scale (100–1000 km) late neo-Archæan accretion, are preserved within elongate, batholith-dominated terranes separated by metasedimentary migmatite belts. Geochronological, lithotectonic, and metamorphic patterns on a scale of hundreds of kilometres are permissive of an accretionary model of greenstone terrane coalescence in which formation of long-lived, complex volcanic arcs and a complementary fore-arc accretionary prism culminated in large-scale accretion and the formation of stable continental crust.

A prograded clastic wedge, represented by formation- to group-scale units of metasedimentary strata in the Beardmore–Geraldton Terrane, developed in a transitional zone at the southern margin of a volcanic arc between the Onaman–Tashota Terrane, part of the Wabigoon Subprovince to the north, and the Quetico Subprovince, an accretionary prism to the south. Megasequences or couplets with lower basaltic and upper clastic sedimentary parts are now exposed as regionally metamorphosed mafic volcanic and sedimentary belts, outlining thrust slices. Relatively proximal facies (belts) are juxtaposed on top of more distal ones, forming a regional stratigraphy of repetitive volcanic–sedimentary megasequences produced in an imbricate thrust stack. A variety of minor and regional structural features illustrate accretion and subsequent transpression. Isoclinal folding associated with dip-slip, overthrust shearing was followed by inhomogeneous ductile strain of dextral sense along weak lithologies and existing shear zones. Possible subduction-related accretion added a monotonous sequence of arc-derived wacke turbidites to the underside of the thrust-imbricated arc-margin succession. Post-tectonic melting in the northern section of this tectonically thickened accreted sediment gave rise to S-type granites.

Les données GPS indiquent que la subduction accumule des contraintes qui devraient être libérées lors de futurs séismes, Makran potentiel sismogénique est très mal contraint. J’ai d’abord construit une carte structurale le long de la partie iranienne de la mer d'Oman. Ensuite, j’ai contraint la pression de fluide interstitiel et les propriétés de friction du prisme à partir de la théorie du prisme critique et de l'analyse limite. Les résultats montrent que le long des profils Est et Ouest, une transition d'une friction très faible à une friction extrêmement faible est nécessaire pour activer la grande faille normale côtière. Pour propager la déformation vers le front, une augmentation de la friction le long de la zone imbriquée est necessaire. Les modèles Makran sont calibrés les paramètres thermiques et les conditions aux limites des simulations à l'aide de la profondeur des réflecteurs du plancher océanique et du fond marin et des quelques données de puits disponibles. En considérant deux décollements: -le sous-plaquage est associé à une déformation visqueuse, -la déshydratation et la transition smectite/illite permettent de produire des segments à trois pentes comme observés dans les prismes. -la subduction d'un grand mont sous-marin est accompagnée de grandes failles normales. Dans le cas d’un comportement sismogénique du décollement, la limite inférieure de la zone sismogénique correspondra au début du sous-plaquage. En supposant que la limite supérieure des aspérités sismiques soit corrélée à la transition smectite-illite, une aspérité sismique peut donc s'étendre de cette transition, jusqu'au début du sous-plaquage, et correspondre à une topographie relativement plate<br>Makran has a largely unconstrained seismogenic potential although GPS data indicate the subduction is accumulating some strain to be released during future earthquakes. I first build a structural map along the Iranian part of the Oman Sea which indicates three segments. Then, I retrieve the pore fluid pressure and the frictional properties of the wedge with the critical taper theory and the limit analysis. The results show that along the eastern and western profiles, a transition from very low to extremely low friction is required to activate the large coastal normal fault. To propagate the deformation to the front, an increase of friction along the imbricated zone is necessary.The Makran Models are calibrated the thermal parameters and boundary conditions of the numerical simulations using seafloor and bottom sea reflector depth and few available well data. Considering two décollements, the results show that, -underplating is associated to viscous deformation -dewatering and smectite/illite transition permit to produce three slope segments observed in accretionary prisms but this friction drop is not sufficient for formation of normal faults. - the subduction of a large seamount is accompanied by large normal faults, while their location migrates through time. If the brittle décollements have a seismogenic behavior, the down-dip limit of the seismogenic zone will correspond to the onset of underplating. By assuming that the up-dip limit of seismic asperities correlates with smectite-illite transition, then a seismic asperity may extend from this transition, down to the onset of underplating, and correlate with a relatively flat topography<br>منشور برافزايشي مكران به راحتي در دسترس نيست، بنابراين و بويژه در بخش خشكي به خوبي موردبررسي قرار نگرفته است. پتانسيل لرزه اي مكران به درستي شناسايي نشده است. اين در حالي است كه دادههاي جي پي اس تجمع استرين را نشان مي دهد كه در طول زلزله هاي محتمل آتي آزاد شود. در اينجامطالعه دگرشكلي غرب منشور برافزايشي مكران بر پايه ي داده هاي ساختاري جديد، پروفيل هاي لرزه اي بههمراه پروفيل هاي توموگرافي پيشنهاد شده است. اين رساله با به كارگيري مدل سازي مكانيكي وترمومكانيكي، تكامل ساختاري منطقه و تحليل خطر لرزه اي در امتداد سه سكشن دريايي و دو سكشنخشكي در مقياس پوسته اي را مطرح كرده است.( ابتدا نقشه ساختاري در امتداد قسمت ايراني درياي عمان تهيه گرديد كه نشانگر سه بخش است؛ ( ١منطقه راندگي همپوشان در قسمت پيشاني؛ ( ٢) منطقه دياپيري با منشا كم عمق در بين منطقه راندگيهمپوشان و ساحل؛ ( ٣) گسل هاي نرمال فعال در قسمت هاي شرقي و غربي منطقه كه به نظر ميرسند ازلايه ديتچمنت ريشه گرفته اند. در مقابل گسل نرمال در امتداد قسمت مركزي جايي كه كوه دريايي واردفرورانش ميشود، شناسايي نشد. سپس فشار سيالات منفذي و مشخصات اصطكاكي گوه بر طبق تئوري گوههاي بحراني و آناليز محدود بدست آمد. نتايج نشان مي دهد براي فعال شدن گسل نرمال كاهش اصطكاك از٠,٠٠٣ ) در امتداد پروفيل شرقي و غربي لازم است. براي انتشار - ٠,٠٦ ) به ناچيز ( ٠,٠١٢ - مقادير كم ( ٠,٠١٠,٠٣١ ) ضروري است. - دگرشكلي به جلو، افزايش اصطكاك در امتداد منطقه راندگي همپوشان ( ٠,٠١٧شيب توپوگرافي بسيار كم متناسب با مقدار اصطكاك ناچيز ميتواند به عنوان منطقه قفل شده لرزه اي درطول تراست اصلي، كه به صورت اپيزودي با نرخ لغزش ديناميكي دگرشكل شده، يا رفتار خزش شكل پذيرديتچمنت تفسير شود. براي مطالعه انتقال رفتار شكننده- ويسكوز بر شيب توپوگرافي و دگرشكلي، مدل سازيدو بعدي ترمومكانيكي با ثابت كردن جريان حرارتي در انتهاي مدل كه منجر به افزايش دما با افزايش عمقمي شود، انجام گرفت. ابتدا شبيه سازي هاي ساده در جهت بررسي تاثير جريان حرارتي كف، گرمايش برشي،روپوشش دمايي رسوبات و ضخامت رسوبات ثانويه انجام شد. نتايج نشان دهنده سه بخش متناسب با سه رفتاردگرشكلي متفاوت است؛ ( ١) گوه كاملا شكننده با شيب توپوگرافي ثابت پيش بيني شده با تئوري گوه هايبحراني در بخش جلويي؛ ( ٢) نشيب بسيار ناچيز به همراه ديتچمنت و توالي ويسكوز، نزديك به حصار پايانيمدل؛ و ( ٣) در ميان اين دو، افزايش محلي نشيب به عنوان مشخصه انتقال شكننده- ويسكوز همراه باديتچمنت شكننده و دگرشكلي ويسكوز. هيچ يك از اين مدل ها منجر به شكل گير گسل نرمال نشد.براي بازسازي ويژگي هاي مكران، پيچيدگي مدل افزايش يافت و مشخصه هاي دمايي و شرايط مرزيكف دريا و داده ي چاه سنجيده شد. با در نظر گرفتن دو لايه ديتچمنت ،bsr مدل با استفاده از عمق بازتابندهنتايج بيان ميكند كه:١- زير راندگي متناسب با دگرشكلي ويسكوز است.٢- آبدهي و انتقال اسمكتيت- ايليت منجر به شكل گيري سه توپوگرافي متفاوت مشاهده شده در گوههاي برافزايشي مي شود اما اين كاهش اصطكاك براي شكل گيري گسل نرمال كافي نيست.٣- فرورانش كوه دريايي با شكل گيري گسل هاي نرمال بزرگ همراه است، در حالي كه مكان آنها درطول زمان تغيير مي كند.اگر ديتچمت شكننده رفتار لرزه اي داشته باشد، حد پاييني منطقه لرزه زا با شروع زيرراندگي تطابقخواهد داشت. با فرض كنترل حد بالايي منطقه لرزه زا با انتقال اسمكتيت- ايليت، پس پتانسيل لرزه اي ازاين انتقال تا شروع زيرراندگي كه معرف توپوگرافي مسطح است، گسترش مي يابد. اين مكان سازگار با مدلمحل وقوع زلزله ٨,١ ريشتري ١٩٤٥ پاكستان و پيشينه ي كم عمق لرزه اي در امتداد خشكي ،gps سازيو بخش شكننده راندگي ها و نه در امتداد عميق ساختاري است.در طول پروفيل شرقي، اگرچه شكل گيري گسل نرمال ممكن است مرتبط با زيرراندگي يا فرورانش كوهدريايي باشد، گسل نرمال در حال حاضر در بالاي منطقه زيرراندگي درنتيجه انتقال شكننده - ويسكوز قرارگرفته است.پروفيل مركزي نشان دهنده دوپلكس هاي عميق در مناطق ساحلي و با حضور زون دياپيري طويل است.از آنجايي كه توپوگرافي مسطح و محل گل فشان ها احتمالا آشكار كننده پنجره انتقالي اسمكتيت- ايليتاست، اگر اين پنجره معرف زون لرزه زا باشد، اين منطقه نيز پتانسيل لرزه زايي دارد. به هر صورت اين مناطقبا پتانسيل لرزه زايي وسعت كمي دارند و بزرگاي زلزله فقط به گسترش جانبي آن بستگي دارد

Ce travail de thèse est une étude des relations entre les fluides et les déformations dans le prisme d'accrétion de Nankai. Ce travail s'appuie entre autres sur les résultats des deux campagnes de forage récentes Leg Ocean Drilling Program 190 et 196. L'étude des relations entre la mise en place de déformations et les circulations de fluides est plus particulièrement centrée sur le décollement, au front du prisme. Nous présentons d'abord une estimation de la surpression de fluides dans les formations sédimentaires autour du décollement à partir de l'étude des profils de porosité. Ceci nous permet de montrer que le décollement n'est pas une barrière pour les surpressions de fluides et de proposer que le saut de porosité au niveau du décollement résulte d'une discontinuité de l'état de contrainte au travers du décollement. Nous étudions ensuite l'anomalie de chlorinité présente dans les fluides interstitiels de la formation dans laquelle se développe le décollement. Nous montrons que l'on peut rendre compte de cette anomalie en ne considérant que les processus de compaction des argiles et de transformation des smectites en illites. Par ailleurs, nous avons mesuré la perméabilité d'échantillons du prisme sous contraintes avec une presse triaxiale, nécessaire pour la réalisation de simulations numériques de circulation de fluides dans le prisme. Les perméabilités mesurées sont comprises entre 10-18 et 10-19 m2. La rupture des échantillons entraîne une augmentation de la perméabilité à faible pression de confinement mais pas de modification de la perméabilité à une pression de confinement correspondant à la contrainte verticale de l'échantillon en place. Dans une autre partie, nous comparons les mesures de porosité des échantillons et la porosité calculée dans la formation in situ à partir d'un log de résistivité. Cela nous permet de montrer que la zone de décollement présente à la fois des déformations compactantes et dilatantes. Nous estimons la dilatance de fracture du décollement entre 2 et 8 %, et nous proposons un modèle incrémentiel de propagation du décollement par couplage entre des transferts transitoires de surpression de fluides et la déformation mécanique en tête de décollement. Enfin, nous présentons une étude numérique en 2D de la propagation d'ondes de surpression de fluide le long du décollement en supposant que la perméabilité dépend de la pression effective. Les ondes peuvent se propager rapidement le long du décollement. Le couplage hydromécanique entre l'état de contrainte dans la séquence subduite et la pression de fluide dans le décollement est proposés comme un mécanisme possible d'initiation et d'entretien de l'onde de pression.

A partir de nouvelles observations structurales, nous proposons un nouveau modèle cinématique pour la Zone Houillère Briançonnaise, située au-dessus du front briançonnais (structure majeure des Alpes occidentales). Ce modèle est conforté par l'inversion des données de déformation finie, interpolées et visualisées à l'aide du modeleur 3D GOCAD (ENSG-LIAD Nancy). Les données de déformation finie ont été acquises par l'utilisation d'algorithmes d'analyse d'images, semi-automatisées au cours de ce travail. L'inversion a été effectuée à l'aide du logiciel FaultPack (Université Rennes 1). Le modèle cinématique qui résulte de ce travail se décompose en trois évènements principaux suivis d'un épisode extensif. L'évènement D1 traduit très probablement la subduction de l'océan piémontais au cours de laquelle, restant dans le prisme d'accrétion tectonique, la Zone Houillère subit un écaillage vers L'ouest alors qu'une partie de la Vanoise est entrainée dans la subduction. Au cours de D2, la subduction de la Vanoise se bloque et cette zone est alors charriée sur la Zone Houillère puis elle l'emboutit. L'évènement D3 est associé à l'indentation de la croûte européenne par le poinçon adriatique. Cette indentation est, entre autre, la cause de la surrection des Massifs cristallins externes qui réactive une surface correspondant au Front Briançonnais originel (décollement précoce D1 et/ou structure D2) en faille normale. Le rebroussement résultant de la surrection des Massifs cristallins externes produit une structure de type roll-over. L'évènement extensif D4, continuum plus superficiel de D3, provoque alors le basculement de tout l'édifice vers l'Ouest

Sediments incorporated into accretionary prisms experience significant changes in physical properties, grain fabric, and diagenesis. The record of such changes is preserved in sediment microstructures. Scanning electron microscopy (SEM) analyses were carried out on sediments collected from within and seaward of the Nankai accretionary prism to document microstructural changes with depth, lithology, and discrete deformation during the earliest stages of tectonic deformation. Clay mineral preferred orientations (CPOs) increased with depth due to burial, inclined CPOs were evident adjacent to discrete deformation structures and within the accretionary prism, reflecting the influence of sub-horizontal tectonic stress with accretion. Mineralogical and microstructural contrasts across the decollement and the seaward proto-decollement suggest strength differences that may help to localize the fault at this location.

ABSTRACT Many of the hallmarks of modern plate-tectonic processes first occurred in the Paleoproterozoic Era, indicating that the mechanical, thermal, and compositional parameters of Earth’s lithosphere had evolved to approximately modern ranges of values by that time. The core of Laurentia preserves widespread examples of both convergent and divergent tectonic processes in the time span from 2.2 to 1.7 Ga, particularly within the Trans-Hudson composite orogen. Large continental masses or supercontinents previously accreted during the Neoarchean Era began to break up between 2.4 and 2.0 Ga, leading to the deposition of widespread passive-margin sedimentary prisms and locally voluminous emplacement of mafic magma in radiating dike swarms. Further rifting and drifting led to the formation of incipient (e.g., Bravo Formation) to fully developed oceanic crust (e.g., Manikewan Ocean). Plate convergence beginning ca. 1.92 Ga heralded the demise of the Manikewan Ocean ~150 m.y. after its postulated opening. Protracted subduction of oceanic lithosphere over a period of ~90 m.y. produced a series of island arcs, some of which (Lynn Lake, Flin Flon, Snow Lake) host world-class volcanogenic massive sulfide (VMS) ± Au deposits. Plate convergence also led to progressive southeastward (present-day coordinates) accretion of microplates on a pre-amalgamated core consisting of the Slave craton and the Rae and Hearne “Provinces,” forming the Churchill plate. Following the formation of the Churchill plate collage ca. 1.86 Ga, subduction of oceanic lithosphere organized along an ~4000-km-long, north-dipping subduction zone along the southeastern edge of the Churchill plate, producing voluminous continental arc magmas in an Andean-type setting. The final phase of tectonic evolution involved collision of the Superior and North Atlantic cratons with the Churchill plate and intervening juvenile oceanic arc terranes. That phase was strongly influenced by the irregular shape of the indenting Superior craton, favoring the development of oroclines and leading to escape tectonics and lateral extrusion of continental microplates. For the most part, the Trans-Hudson was a hot but not necessarily thick orogen, perhaps reflecting a higher geothermal gradient during the Paleoproterozoic Era.