ABSTRACT Avalonia and Ganderia are composite microcontinental fragments in the northern Appalachian orogen likely derived from Gondwanan sources. Avalonia includes numerous Neoproterozoic magmatic arc sequences that represent protracted and episodic subduction-related magmatism before deposition of an Ediacaran–Ordovician cover sequence of mainly siliciclastic rocks. We characterized the nature of the basement on which these arcs were constructed using zircon grains from arc-related magmatic rocks in Atlantic Canada that were analyzed for their Lu-Hf isotope composition. The majority of zircon grains from Avalonia are characterized by initial 176 Hf/ 177 Hf values that are more radiogenic than chondritic uniform reservoir, and calculated crust formation Hf T DM (i.e., depleted mantle) model ages range from 1.2 to 0.8 Ga. These data contrast with those from Ganderia, which show typically positive initial εHf values and Hf T DM model ages that imply magmatism was derived by melting of crustal sources with diverse ages ranging from ca. 1.8 to 1.0 Ga. The positive distribution of initial εHf values along with the pattern of Hf T DM model ages provide a clear record of two distinct subduction systems. Cryogenian–Ediacaran magmatism is interpreted to have resulted from reworking of an evolved Mesoproterozoic crustal component in a long-lived, subduction-dominated accretionary margin along the margin of northern Amazonia. A change in Hf isotope trajectory during the Ediacaran implies a greater contribution of isotopically evolved material consistent with an arc-arc–style collision of Ganderia with Avalonia. The shallow-sloping Hf isotopic pattern for Paleozoic Ganderian magmatism remains continuous for ~200 m.y., consistent with tectonic models of subduction in the Iapetus and Rheic Oceans and episodic accretion of juvenile crustal terranes to Laurentia.

Abstract The Elan Bank microcontinent was separated from East India during the Early Cretaceous break-up. The crustal architecture and rifting geometry of East India and the Elan Bank margins document that the early break-up between India and Antarctica was initiated in the eastern portions of the Cauvery and Krishna–Godavari rift zones, and in the southern portion of Elan Bank. However, the westwards break-up propagation along the Krishna–Godavari Rift Zone continued even after the break-up in the overstepping portion of the Cauvery Rift Zone. Eventually, the western propagating end of the Krishna–Godavari Rift Zone became hard-linked with the failed western portion of the Cauvery Rift Zone by the dextral Coromandel transfer fault zone. Consequently, the break-up location between India and Antarctica shifted from its initial to its final location along the northern portion of the Elan Bank formed by the western Krishna–Godavari Rift Zone. The competition between the two rift zones to capture continental break-up and asymmetric ridge propagation resulted in a ridge jump and the Elan Bank microcontinent release.

Abstract The study focuses on the role of wrenching-involved continental break-up in microcontinent release, drawing from a review of examples. It indicates that the main groups of release mechanisms in this setting are associated with ‘competing wrench faults’, ‘competing horsetail structure elements’, ‘competing rift zones’ and ‘multiple consecutive tectonic events’ controlled by different stress regimes capable of release. Competing-wrench-fault-related blocks are small, up to a maximum 220 km in length. They are more-or-less parallel to oceanic transforms. The competing horsetail-structure-element-related blocks are larger (up to 610 km in length) and are located at an acute angle to the transform. Competing-rift-zone-related blocks are large (up to 815 km) and are either parallel or perpendicular to the transform. The multiple-consecutive-tectonic-event-related blocks have variable size and are generally very elongate, ranging up to 1100 km in length. The role of strike-slip faults in release of continental blocks resides in: linking the extensional zones, where the blocks are already isolated, by their propagation through the remaining continental bridges and subsequent displacement; facilitating rapid crustal thinning across a narrow zone of strike-slip-dominated faults; and slicing the margin into potentially detachable fault blocks.

Abstract The Australian continent records c. 1860–1800 Ma orogenesis associated with rapid accretion of several ribbon micro-continents along the southern and eastern margins of the proto-North Australian Craton during Nuna assembly. The boundaries of these accreted micro-continents are imaged in crustal-scale seismic reflection data, and regional gravity and aeromagnetic datasets. Continental growth ( c. 1860–1850 Ma) along the southern margin of the proto-North Australian Craton is recorded by the accretion of a micro-continent that included the Aileron Terrane (northern Arunta Inlier) and the Gawler Craton. Eastward growth of the North Australian Craton occurred during the accretion of the Numil Terrane and the Abingdon Seismic Province, which forms part of a broader zone of collision between the northwestern margins of Laurentia and the proto-North Australian Craton. The Tickalara Arc initially accreted with the Kimberley Craton at c. 1850 Ma and together these collided with the proto-North Australian Craton at c. 1820 Ma. Collision between the West Australian Craton and the proto-North Australian Craton at c. 1790–1760 Ma terminated the rapid growth of the Australian continent.

The distribution and tectonic settings of structurally complex domains of generally folded and thrust-faulted, commonly allochthonous, rock assemblages, recognized in the very large (250,000 km 2 ) Koryak Upland and Chukotka regions, support the conclusion that Late Jurassic, Early Cretaceous, and Late Cretaceous shortening and, at times, accretion resulted in incorporation of the terranes into a structural collage at the northeastern Asian continental margin. The main stages of accretion and continental growth took place in the late Mesozoic during the Middle–Late Jurassic, at the Early-Late Cretaceous boundary, and in late Maastrichtian time. The Late Jurassic was the emergence time of the Oloi and Uda-Murgal volcanic belts, extending along the convergent boundaries between Siberia and the proto-Arctic and Pacific Oceans, respectively. Convergence persisted until the end of the Early Cretaceous. In Chukotka, convergence ended with collision of the Chukotka microcontinent with the active margin of Siberia that hosted the Oloi volcanic belt. During this collision, the southern passive margin of Chukotka was overthrust by tectonic nappes composed of tectono-stratigraphic units of the South Anyui terrane. Greenschists with ages of 115–119 Ma are related to accretion of oceanic- and island-arc terranes incorporated into the frontal zone of the Uda-Murgal island-arc system. The subsequent growth of the continental margin resulted from accretion of terranes of the North Koryak fold belt in the late Maastrichtian.

The Mesoarchean Kola-Karelia continent in the eastern Fennoscandian Shield includes three tectonic provinces, Kola, Karelia and Belomoria, that were formed by the Paleoarchean and Mesoarchean microcontinents. Traces of Mesoarchean tonalite-trondhjemite-granodiorite (TTG)-type early crust were documented in all of the most ancient units of the Kola-Karelia continent. Ancient crust was revealed and dated in the Ranua and Iisalmi microcontinents, 3.5–3.4 Ga; Vodlozero and Khetolambina microcontinents, 3.25–3.15 Ga; Kuhmo-Segozero microcontinent, ~3.0 Ga; Murmansk and Inari-Kola microcontinents, 2.93 Ga; and Kianta microcontinent, 2.83–2.81 Ga. In the older (>3.0 Ga) tectonic units and microcontinents, the ancient crust was possibly formed in brief bursts of endogenic activity. In younger microcontinents (3.0–2.93 Ga), these processes could continue until 2.8 and even 2.72 Ga. The tectonic settings in which early TTG crust has been produced are largely uncertain. The primary melt glassy inclusions with a glass phase in cores of prismatic zircon crystals from TTG gneisses provide evidence for the volcanic origin of gneiss protolith. Suggested genetic modeling of TTG-type complexes assumes that felsic K-Na melts with positive Eu anomaly are a product of dry high-temperature partial melting of the previously formed mafic-to-felsic crustal rocks and/or thick older TTG crust. Positive Eu anomaly in the eutectic is directly related to the predominance of plagioclase and K-feldspar in the melt. TTG-type crust melted to produce granite-granodiorite (GG) rocks. Earliest microcontinents are separated by Mesoarchean greenstone belts (mainly 3.05–2.85 Ga, in some cases up to 2.75 Ga), which are fragments of paleo–island-arc systems accreted to their margins: the Kolmozero-Voronya, Central Belomorian, Vedlozero-Segozero, Sumozero-Kenozero, and Tipasjärvi-Kuhmo-Suomussalmi belts; and the mature island arcs (microcontinents): Khetolambina and Kovdozero. These structural units are characterized by significant extent, close to rectilinear trend, localization along the boundaries between Archean microcontinents, and a specific set of petrotectonic assemblages (basalt-andesite-rhyolite, komatiite-tholeiite, and andesite-dacite associations). The recently discovered Meso-Neoarchean Belomorian eclogite province that is structurally linked with the Central Belomorian greenstone belt contains two eclogite associations distributed within TTG gneisses: the subduction-type Salma association and the Gridino eclogitized mafic dikes. The protolith of the Salma eclogites is thought to have been a sequence of gabbro, Fe-Ti gabbro, and troctolite, formed at ca. 2.9 Ga in a slow-spreading ridge (similar to the Southwest Indian Ridge). The main subduction and eclogite-facies events occurred between ca. 2.87 and ca. 2.82 Ga. Mafic magma injections into the crust of the active margin that led to formation of the Grigino dike swarm were associated with emplacement of a mid-ocean ridge in a subduction zone, beginning at ca. 2.87 Ga. Crustal delamination of the active margin and subsequent involvement of the lower crust in subduction 2.87–2.82 Ga ago led to high-pressure metamorphism of the Gridino dikes that reached eclogite-facies conditions during a collision event between 2.82 and 2.78 Ga. This collision resulted in consolidation of the Karelia, Kola, and Khetolamba blocks and formation of the Mesoarchean Belomorian accretionary-collisional orogen. To date, the subduction-related Salma eclogites provide the most complete and meaningful information on the nature of plate tectonics in the Archean, from ocean-floor spreading to subduction and collision. The Kovdozero granite-greenstone terrain that separates the Khetolambina and Kuhmo-Segozero microcontinents is formed by TTG granitoids and gneisses hosting metasediments and metavolcanics of several greenstone belts, which belonged to the Parandovo-Tiksheozero island arc that existed from ca. 2.81 to 2.77 Ga. The Iringora greenstone belt includes the ophiolite complex of the same name with an age of 2.78 Ga. The collision of microcontinents resulted in the upward squeezing of the island arc and the obduction of its marginal portions onto surrounding structures.

The basement of the East European Platform corresponding to northeastern Sarmatia is known as the Voronezh Crystalline Massif (VCM). The Kursk microcontinent, which lies in northeastern Sarmatia, occupies the bulk of the Voronezh Crystalline Massif. The predominant portion of the Kursk microcontinent is a combination of sedimentary–volcanic complexes making up greenstone belts and granite-gneiss (granite-migmatite) associations of the granite-greenstone domain bearing the same name. The smaller Kursk–Besedino granulite-gneiss terrane is situated in the central part of the microcontinent. The following sequence of events may be proposed as a preliminary model of crustal evolution: (1) Paleo- to Mesoarchean: formation of granite-greenstone continental crust (3.7–3.1 Ga); (2) events related to the activity of a mantle plume 2.85–2.82 Ga ago: underplating by mantle-derived magmas; formation of an intracontinental depression; its rapid filling with sediments, including Fe-rich varieties; and metamorphism of granite-greenstone basement and the sedimentary fill of the depression; and (3) Neoarchean and/or Paleoproterozoic: collisional compression and transformation of the depression into a synformal tectonic nappe.

The first broad Russian experiment aimed at the study of the deep structure of Earth's crust and upper mantle by the common midpoint (CMP) method along the 1-EU geotraverse and cross-traverse 4B was realized in 1995–2008 in the territory of the East European Platform under the Russian Federal Program on Development of the State Geotraverse Network and Deep and Superdeep Boreholes. At the same time, the EGGI profile, geotraverses TATSEIS, ESRU 2003–2005, and DOBRE in Ukraine, as well as the system of profiles under the FIRE project in the adjacent territory of Finland were acquired. Integration of the existing geological maps and available geological (in the widest sense: structural, geochemical, geochronological, and so forth) data with results of geological interpretation of seismic images of the crust and upper mantle have led to a three-dimensional (3D) model of the deep crustal structure of the East European craton and a significant revision of previous ideas on the deep structure and Early Precambrian evolution of the region. In the geological interpretation of seismic data, we attached particular significance to the direct tracing of geological boundaries and fault zones recognized on the seismic-reflection pattern and the section of effective acoustic impedance toward the present-day surface and to their correlation with mapped geological and tectonic units. Comparison of the seismic image geometry with the geology of the eastern Fennoscandian Shield at the present-day erosion level shows that the reflection pattern matches the general trends of compositional layering, gneissic banding, and schistosity. The roughly homogeneous structural domains of the crust correspond to relatively large tectonic sheets, 3–5 km thick. Their inner structure commonly is not discernible in reflection patterns. The 3D model of deep structure in the Kola-Lapland region is based on correlation of tectonostratigraphic complexes depicted in the geological-tectonic map with structural subdivisions recognized as a result of interpretation of seismic crust images and their tracing to depth. In addition to the geological section along the 1-EU geotraverse, the model includes the section along the FIRE-4–4a profile that crosses the western part of the region studied in Finland. The 3D model shows the Paleoproterozoic tectonic structures (Lapland granulite-gneiss belt and its structural and evolutionary relationships with lower-crustal granulites, the structure and tectonic position of the Tana belt) and Archean tectonic structural units (the Central Kola granulite-gneiss belt, the Inari-Kola granite-greenstone domain, and the boundary zone between the Kola craton and the Belomorian orogen). The detailed 3D model of the crust and uppermost mantle in the Karelian-Belomorian region is also based on correlation between the exposed geological structure and geological interpretation of seismic images along the 1-EU geotraverse and cross-traverse 4B. The geological interpretation of the seismic crust image along the FIRE-1 profile serves as the additional basis for the Svecofennian accretionary orogen and its boundary with the Kola-Karelia continent. The model of the crust in the Karelian-Belomorian region contains the Paleoproterozoic tectonic structures (East Karelian imbricate thrust belt, Svecofennian accretionary orogen, and Onega Depression) and also Archean tectonic structures (Kuhmo-Segozero and Kovdozero microcontinents, and Chupa granulite-gneiss belt). The deep structure of the platform basement beneath the Moscow syneclise is an immediate extension of the Fennoscandian Shield. The basement structure in this area was controlled by Paleoproterozoic processes resulting in formation of the Lapland–Mid-Russia–South Baltia intracontinental orogen. The 3D model shows the marginal Totma and Aprelevka volcanic-sedimentary belts, and a synformal structure for the upper crust in the central domain of the orogen. The rock complexes of the Zubtsov-Diakonovo granulite-gneiss belt in the northwest and the Dmitrov-Galich belt in the southeast make up a distinctly outlined stage in the synform section. These complexes are underlain by gneiss-migmatite-amphibolite associations of the Bologoevo and Ivanovo-Sharya belts and are overlain by similar rocks of the Tver and Bukalovo belts. Lastly, the Kashin synformal granulite-gneiss belt is localized in the upper part of the section. The alternation of rocks of differing metamorphic grade clearly indicates the tectonic or tectonized stratigraphic character of the section in the Nelidovo synform. The crust sandwiched between the southward-plunging Totma and Aprelevka belts is characterized by rough layering. The reflections and boundaries of crustal sheets outlined in agreement with this pattern plunge southward beneath the Archean Sarmatia and Volgo-Uralia continental blocks. The deep crustal structure of the Voronezh Crystalline Massif is determined by a succession of geodynamic settings and Archean and Paleoproterozoic tectonic events that resulted in the formation of the Archean crust in the Kursk granite-greenstone domain and probably in the Khopior microcontinent, the Middle Paleoproterozoic East Voronezh orogen, and the Late Paleoproterozoic North Voronezh orogen. The 3D model applies particularly well to the Middle Paleoproterozoic East Voronezh orogen. The orogen is localized in the area of collision of the Kursk and Khopior microcontinents, which differ markedly in crustal structure and composition. The crocodile-type tectonic structure of the East Voronezh orogen is clear evidence for collisional compression. The countermotion of microcontinents resulted in the wedge-shaped structure of the Kursk microcontinent extending for 150 km, delamination of crust in the Khopior microcontinent, and counterdisplacement of tectonic sheets coherently thrust over and under the Kursk microcontinent. The tectonic structure of the central and western Volgo-Uralia continent to a depth of 15–20 km is characterized by sections of 3D models of effective density and magnetization. The second block of information on the Volgo-Uralia continent deep structure comes from results of seismic profiling along the TATSEIS, ESRU 2003–2005, and URSEIS geotraverses. The TATSEIS geotraverse crosses a significant part of the Volgo-Uralia continent from southeast to northwest. The seismic crust images along this geotraverse not only create the basis for interpretation of regional deep structure, but also robustly link the crustal models of the western and southeastern parts of the Volgo-Uralia continent. The data along the ESRU 2003–2005 geotraverse played an important role in ascertaining the deep structure of the Krasnoufimsk ovoid, which is overlapped by sedimentary fill of the Ural foredeep. Additional evidence was provided by the URSEIS geotraverse. The Archean crust, slightly modified in the Paleoproterozoic, which forms the East European Platform basement in the Volgo-Uralia continent, is made up of mafic granulites, khondalite, mafic-ultramafic intrusions, and granitoid plutons. The 3D model of the crust based on the TATSEIS geotraverse demonstrates the deep structure of the Vetluga synform in the Tokmov ovoid and of the interovoid domain. Ovoids play a crucial role in the Volgo-Uralia continent structure and occupy no less than 60% of the crust. In 3D representation, they are bowl-shaped blocks, round or oval in outline, and 300–600 km in diameter at the basement surface, and with a base at the level of the crust-mantle interface, i.e., at a depth of 60 km. The thickness of crust of the interovoid domain does not commonly exceed 50 km. Two types of elongated oval synforms are distinguished: the interovoid ovals (Verkhnevyatka, North Tatar, Almetevsk), up to 200–300 m long, with aspect ratio of 2:1–3:1, and the interovoid belts (Usovo, Vyatka, Kilmez, Elabuga-Bondyuga, Tuma-Penza, as well as Zhiguli-Pugachev homocline), 300–400 km in extent, with aspect ratio of 4:1–5:1. The bottom of the largest interovoid oval crossed by the TATSEIS profile reaches 25 km in depth. In crustal section, the structural elements of the interovoid domain are underlain or partly crosscut by acoustically transparent layers composed of the Bakaly-type granitoids. The lower crust of the interovoid domain is ~35 km in thickness and is composed of tectonic sheets plunging toward the northwestern end of the geotraverse and penetrating into the mantle.

In this chapter, the available seismic and geological data are integrated and applied to the East European craton as a whole. The deep structure and seismic characteristics of the granite-greenstone crust in the Archean microcontinents vary significantly. The unevenly distributed and vaguely oriented short reflections are occasionally gathered into packets. The intensely reflecting bodies with high acoustic impedance correspond to greenstone belts reaching many tens of kilometers in extent. The oval acoustically transparent domains in the middle-crustal level are composed of moderately dense rocks that correspond to granitoid plutons. The total thickness of the crust in granite-greenstone domains can vary from 40 km in the Kola-Karelia continent to 50 km in the Kursk microcontinent. The Archean granulite-gneiss complexes form the delineated belts localized in the upper crust. These are synformal tectonic nappes, the vertical thickness of which reaches 15 km. A special case is the Volgo-Uralia continent, the crust of which is completely composed of granulite-gneiss rocks partly replaced by retrograde metamorphic assemblages. The granulite-gneiss crust is distinguished by significant thickness (~60 km; maximum 65–70 km). The lower-crustal “layer,” ~35 km thick, consists of inclined tectonic sheets plunging in a northwestern direction and penetrating the upper mantle. The interface between upper and lower crust is replaced by acoustically transparent granitoid crust 10–20 km in thickness. The Middle Paleoproterozoic East Voronezh intracontinental collisional orogen between the Archean Kursk and the Khopior microcontinents is represented by a “crocodile-jaw” structure. The structural pattern in the seismic image of the crust clearly indicates a Paleoproterozoic age of lower-crustal layer and shows the absence of the Paleoproterozoic lower-crustal complex at the base of the Kursk craton proper. The Late Paleoproterozoic intracontinental Lapland–Mid-Russia–South Baltia orogen surrounds in a wide arc the Karelian craton in the northeast, east, south, and southwest. The upper crust in the inner zone of the orogen in the Mid-Russia sector is composed of alternating granulite-gneiss and gneiss-migmatite-amphibolite tectonic sheets 5–10 km thick, deformed in gentle synformal folds. The marginal zones consist of south-plunging tectonic sheets of the Totma belt in the north and the Aprelevka belt in the south. The Totma sheet, reaching 10 km in thickness and dipping at a mean angle of 5°–10°, is traced by reflectors from the basement surface (interval 1700–1800 km) to the crust-mantle interface (interval 2000–2200 km). These parameters, along with composition of the rocks, allow interpretation of the Totma belt as a suture zone, separating the synformal structural assemblage from the lower crust. In the Paleoproterozoic Svecofennian accretionary orogen, interpretation of the FIRE-1 profile shows that the Central Finland granitoid massif is a nearly horizontal, sheetlike intrusive body that conceals an accretionary complex—a succession of tectonic sheets, 10–20 km thick, which plunges northeast at angles of 10°–12° down to the crust-mantle interface at a depth of 65 km and can be traced beneath the margin of the Karelian craton for more than 150 km. The lower-crustal layer, often called a reflectivity zone, is always present at the base of the Lapland–Mid-Russia–South Baltia orogen and the Archean cratons surrounded by this arcuate orogen. This layer was formed in the Early Paleoproterozoic as a result of under- and interplating of mantle melts accompanied by granulite-facies metamorphism. The increase in thickness of the lower-crustal layer is related to hummocking (mutual over- and underthrusting and wedging) of tectonic sheets at the base of the crust. The lower-crustal layer of the Kola-Karelia continent was formed before the main collisional events, which took place in the Late Paleoproterozoic. The structure of the crust depicted by seismic reflectors indicates in some cases that the crust-mantle interface has remained unchanged since the time of crust formation, whereas in other situations, this boundary is younger than the bulk crust. The crust-mantle interface beneath the East European craton reveals manifold deviations from its persistent near-horizontal outline due to bending, plunging, and apparent dissolution of lower-crustal sheets in the mantle. The underlying upper mantle reveals a number of indistinct reflectors imaged as dashed lines, which trace lower-crustal structural elements incorporated into the mantle. These domains are regarded as crust-mantle mixtures. The crust images along the seismic lines exhibit widely varying structural features and degrees of contrast (sharpness) of the crust-mantle interface. The following structural and morphological types of the crust-mantle interface are distinguished beneath the East European craton: (1) a smooth, generally flat or horizontal or slightly sloping boundary with an abrupt decrease in number of reflectors at the lower edge of intensely reflecting layered lower crust; (2) a boundary similar to the previous type but periodically interrupted at sites where the sheetlike fragments of the lower crust sharply bend and sink into the mantle and acoustically as if they dissolve therein; (3) a serrated boundary in the regions of consecutive plunging lower-crustal tectonic sheets into the mantle; these domains are commonly conjugated: reverse-thrust assemblages in the upper crust rise in the same direction as the lower-crustal sheets plunge; (4) a serrated boundary confining from below the ensemble of inclined tectonic sheets that form the crust completely or partly; (5) a diffuse crust-mantle interface that is observed where a distinct lower-crustal reflectivity zone is absent; and (6) a phantom (disappearing) crust-mantle interface that separates acoustically transparent crustal and mantle domains that can be detected by seismic-refraction exploration. Integration of the entire body of information allowed us to simulate the 3D deep structure of the Early Precambrian crust of the East European craton as a whole using sections along the 1-EU geotraverse, cross-traverse 4B, TATSEIS regional profile, and FIRE-1 and FIRE-4 profiles. The 3D deep structure of the East European craton is represented by the tectonically delaminated Early Precambrian crust with a predominance of gently dipping boundaries between the main tectonic subdivisions and a complexly built crust-mantle interface. The integral model includes Archean granite-greenstone domains and granulite-gneiss areas and Paleoproterozoic accretionary and intracontinental collisional orogens.

The earliest events in the geological history of the Early Precambrian crust of the East European craton (3.5–2.93 Ga) resulted in the emergence of spatially separate and genetically independent areas of continental crust (continental embryos), the dimensions of which rarely exceeded a few hundred kilometers across. The period between 3.05 Ga and ca. 2.75 Ga was a time of mainly plate-tectonic development: origin, evolution, and accretion of ancient island-arc systems, and collision of microcontinents. The Vedlozero-Segozero and Sumozero-Kenozero systems of greenstone belts, Tipasjärvi-Kuhmo-Suomussalmi and Central Belomorian greenstone belts in Karelia, and the Kolmozero-Voronya greenstone belt in the Kola Peninsula are interpreted as accretionary systems transformed in collisional orogens. The Belomorian eclogite province is structurally linked with the Central Belomorian greenstone (suture) belt. The Kovdozero granite-greenstone terrane is formed by granitoids and gneisses hosting metasediments and metavolcanics of several greenstone belts, which belonged to the Parandovo-Tiksheozero island arc. The amalgamation of the continental domains that made up the bulk of the Archean crust in the growing East European composite craton took from 2.82 to 2.66 Ga, but the main events had terminated by 2.75 Ga. During the period from 2.79–2.55 Ga, specific areas of intracontinental thermal and tectonic activity (hot regions) developed in the inner portions of the recently formed continent: Karelian-Belomorian and Kola areas in the eastern Fennoscandian Shield and extensive Volgo-Uralia granulite-gneiss area in the eastern part of the East European craton. These processes marked a principally new evolutionary episode in the Early Precambrian history of the East European craton. Widespread high-temperature magmatic and metamorphic processes and the development of synformal structures and linear sedimentary basins testify to an anorogenic extensional environment and a significant influx of heat to the crust, i.e., a significant event of mantle-plume type. During the Paleoproterozoic (2.53–1.87 Ga), a number of intracontinental collisional orogens were produced within the East European craton. The largest of them are the Lapland–Mid-Russia–South Baltia intracontinental orogen and the Svecofennian accretionary orogen. The Lapland–Mid-Russia–South Baltia orogen surrounds the Karelian craton as a wide arc, separating it from Volgo-Uralia and Sarmatia. The orogen extends for more than 3000 km; its width in the northern and central segments is 400–700 km and increases to 1000 km in the southwest. The Lapland sector of the orogen is characterized by spatial distribution of tectonic belts composed of low-grade metavolcanic-metasedimentary rocks and belts of high-grade metamorphic rocks, including granulite-gneiss complexes. The former are localized along the orogen boundaries; in turn, the axial zone of the orogen is mainly formed by alternation of low-angle tectonic sheets varying in thickness from a few to 20–25 km: sheets composed of Paleoproterozoic granulite-gneiss complexes with a predominance of metamorphosed juvenile intrusive and volcanic bodies and sedimentary rocks alternate with the sheets of Archean granite-greenstone and amphibolite-gneiss complexes. The Paleoproterozoic evolution of the Kola-Karelia continent and, accordingly, the Lapland–Mid-Russia–South Baltia orogen, is subdivided into four episodes: (1) ca. 2.53–2.3 Ga: failed rifting of the Archean continent; (2) 2.3–2.1 Ga: quiescent within-plate activity and diffuse rifting that can be regarded as “failed attempts” to break the supercontinent; (3) 2.1–1.95 Ga: rifting of the Kola-Karelia continent; and (4) 1.95–1.87 Ga: origin of the intercontinental collisional orogens. The Paleoproterozoic pulse of tectonic activity, which transformed the Neoarchean Kola-Karelia continent, continued for more than 600 m.y. Globally speaking, Early Paleoproterozoic magmatic and thermal activities were largely constrained within the ancient continent that then included North America and most of the eastern European continent, including the Fennoscandian Shield (Lauroscandia). Analysis of the extensive data leads us to distinguish a new type of tectonic structure: the intracontinental oval orogen formed in the inner portions of continents under the effect of large mantle plumes. It is an oval-shaped tectonic ensemble of regional rank with diameters from 600–1000 to 2500–3000 km, of which at least a part is characterized by concentric structure and metamorphic zonation or which contains bowl-shaped crustal structures. Intracontinental orogens contain granulite-gneiss complexes, derivatives of juvenile (though crust-contaminated) mafic magmas (gabbro-anorthosites and layered mafic-ultramafics), intrusions of “dry” high- temperature, within-plate–type granites, enderbites, and charnockites, and low-grade sedimentary-volcanic belts. The oval or oval-concentric structure excludes the possibility that intracontinental orogens originated as a result of processes at convergent plate boundaries. Their size and morphology and the evidence of a vast influx of mantle heat make intracontinental orogens comparable to oceanic plateaus and large igneous provinces on the continents. The fundamental changes in Earth's geological evolution that occurred at the Mesoarchean-Neoarchean boundary (ca. 2.75 Ga) can be related to the transition from Archean “microplate tectonics” to Paleoproterozoic “supercontinent tectonics” (or “microocean tectonics,” with regard to the limited size of the Red Sea–type oceans that were formed within the partly fractured supercontinent). The origin of Earth's first supercontinent, a landmass covering much of Earth's surface, by 2.80–2.76 Ga, should have played an extremely important role in restyling the system of convection cells in the underlying mantle. The style of tectonic processes and the geodynamic environment of plate tectonics in the Neoarchean–Paleoproterozoic differ from those in both the Archean and the Phanerozoic: the Archean tectonics of multiple “miniplates” was much more similar to Phanerozoic plate tectonics than to the Neoarchean–Paleoproterozoic “tectonics of supercontinents.”

Abstract Reconnaissance 2D seismic reflection data intended to investigate the petroleum potential of New Zealand’s marine territories have contributed many insights into the geological evolution of the large continental block that surrounds New Zealand. These include: definition of a back-thrust system to the Mesozoic Gondwana subduction margin along the Northland–Reinga Basin and the transition to back-arc rifting; the development of a Mesozoic back-arc rift system through the present New Caledonia and probably the Bounty troughs; the Early Cretaceous cause, at least locally, of the cessation of subduction along the New Zealand sector of the Gondwana margin; evidence for anticlockwise rotation of eastern New Zealand relative to the west in Late Eocene time; an explanation for the development of the Alpine Fault and the South Island compressional strike-slip margin between the Pacific and Australian plates through South Island.