Showing papers on "Craton published in 1984"
TL;DR: In this article, a quantitative procedure has been developed for calculating tectonic subsidence in fully lithified strata and has been applied to stratigraphic sections in the early Paleozoic miogeocline of the southern Canadian Rocky Mountains.
Abstract: A quantitative procedure has been developed for calculating tectonic subsidence in fully lithified strata and has been applied to stratigraphic sections in the early Paleozoic miogeocline of the southern Canadian Rocky Mountains. The results indicate that tectonic subsidence along the inner edge of the miogeocline was controlled mainly by thermal contraction of heated lithosphere. Comparison of a palinspastically restored cross section of the inner part of the miogeocline with a cross section constructed from a two-dimensional stretching model suggests that thinned continental crust was present beneath the inner miogeocline. These results support the passive-margin model that has been proposed for the miogeocline. The extensive transgression onto the craton east of the miogeocline in Cambrian time, however, cannot be explained by subsidence processes operating within a passive margin, and the transgression could be evidence for a eustatic rise of sea level. The form of the tectonic subsidence curves strongly implies that cooling of the heated lithosphere, which was initiated at the time of breakup, could not have begun earlier than the latest Precambrian or earliest Cambrian (555 Ma to 600 Ma). Ages of 800 Ma to 900 Ma that have been assumed previously for rifting in the miogeocline are too old to have led directly to continental breakup. Scattered occurrences of mafic volcanics interlayered with arkosic sediments have been reported in the latest Precambrian to earliest Cambrian Hamill Group exposed in the middle to outer part of the miogeocline. These deposits may record the phase of rifting that immediately preceded formation of the proto-Pacific margin in the southern Canadian Rockies.
521 citations
TL;DR: In this paper, the Junggar-Hegen suture is used to detect ophiolites and rare blueschists in the Cathaysian suture, and the presence of bluechists reveals evidence of large-scale subduction and tectonic exhumation during consolidation of the Eurasian plate.
Abstract: China is principally a part of the Eurasian plate, but the margins of the Indian and Philippine Sea plates are involved in the Himalayas and in the Coastal Range of Taiwan, respectively. Within the Eurasian plate, the Cathaysian paleoplate is separated from the Angaraian paleoplate by the Junggar-Hegen suture, which contains Paleozoic ophiolites and rare blueschists. The three microplates of the Cathaysian paleoplate consist of Precambrian cratons and/or Phanerozoic accretionary fold belts. These coalesced Precambrian cratons record at least six stages of intense orogeny before cratonization. The Paleozoic to Cenozoic accretionary fold belts of China can be correlated with similar events now found in west Pacific-, Andean-, and Atlantic-type active continental margins. Ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the Paleozoic to Cenozoic. The presence of blueschist in some of these Chinese sutures reveals evidence of large-scale subduction and tectonic exhumation during consolidation of the Eurasian plate. Cenozoic collision of the Eurasian and Indian plates produced deformation and uplift of the Himalayas, strongly influencing the tectonics of western China. In contrast, Mesozoic-Tertiary evolution of eastern China is typical basin-range geology, similar to that of the western United States, which included development of deep sedimentary basins along with calc-alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow. The complicated tectonic evolution of China is greatly illuminated by the presence of ophiolites and blueschists in Proterozoic to Tertiary convergent boundaries. These petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in China.
481 citations
TL;DR: In this article, reycled Cretaceous and Cenozoic marine microfossils have been recovered from samples of the Pliocene Sinus Formation, collected from outcrops in the Reedy, Beardmore, and Ferrar glacier areas of the Transantarctic Mountains between lat 77° and 86°S.
Abstract: Recycled Cretaceous and Cenozoic marine microfossils have been recovered from samples of the Pliocene Sinus Formation. Samples were collected from outcrops in the Reedy, Beardmore, and Ferrar glacier areas of the Transantarctic Mountains between lat 77° and 86°S. The glaciogene sediments contained diatoms, foraminifera, calcareous nannoplankton, silicoflagellates, radiolarians, sponge spicules, palynomorphs, and ostracodes of Late Cretaceous, Paleocene, Eocene, late Oligocene, late Miocene, and Pliocene age. This suggests the presence of open marine basins on the East Antarctic craton during late Mesozoic and Cenozoic time. The apparent absence of early Oligocene and early through middle and earliest late Miocene assemblages suggests either that marine regression exposed the basin floors or that ice filled the basins during these times. The high-elevation setting of Sirius Formation outcrops suggests one of two hypotheses for their origin: (1) They are in situ Pliocene glaciomarine deposits that were uplifted 1,750–2,500 m with the Transantarctic Mountains to their present elevation; (2) the Sirius Formation deposits are a mixture of derived sediments stripped from sub-ice intracratonic basins and subsequently redeposited by ice flowing up the inland slope of the Transantarctic Mountains. We favor the second hypothesis, with transport to sites sometime within the past 3 m.y.
272 citations
TL;DR: The Himalaya orogen is closely connected with the development of the present-day Andaman-Nicobar-Indonesia island arc-subduction system in the southeast and the Makran Ranges-Oman Trench in the southwest as mentioned in this paper.
226 citations
TL;DR: The Cheyenne belt of southeastern Wyoming is a major shear zone which separates Archean rocks of the Wyoming province to the north from 1800-1600 Ma old eugeoclinal gneisses to the south as discussed by the authors.
210 citations
TL;DR: In this paper, the total strength of different lithospheres is compared by integrating the limits of lithospheric stress with depth, and it is shown that continental lithosphere is weaker than oceanic lithosphere by about a factor of three.
Abstract: Lithospheric rifting, while prevalent in the continents, rarely occurs in oceanic regions. To explain this preferential rifting of continents, the total strength of different lithospheres is compared by integrating the limits of lithospheric stress with depth. Comparisons of total strength indicate that continental lithosphere is weaker than oceanic lithosphere by about a factor of three. Also, a thickened crust can halve the total strength of normal continental lithosphere. Because the weakest area acts as a stress guide, any rifting close to an ocean-continent boundary would prefer a continental pathway. This results in the formation of small continental fragments or microplates that, once accreted back to a continent during subduction, are seen as displaced terranes. In addition, the large crustal thicknesses associated with suture zones would make such areas likely locations for future rifting episodes. This results in the tendency of new oceans to open along the suture where a former ocean had closed.
198 citations
TL;DR: In the Cordilleran region of the western United States, Mesozoic and Tertiary peraluminous granitic rocks display regional variations in initial 143Nd/144Nd (eNd) values.
Abstract: In the Cordilleran region of the western United States, Mesozoic and Tertiary peraluminous granitic rocks display regional variations in initial 143Nd/144Nd (eNd); eNd = −10 to −12 in southern Arizona, − 17 to −19 in the northern Great Basin (NGB), and −30 in the northern Rocky Mountains. Initial 87Sr/86Sr values are between 0.710 and 0.721 and show no regional pattern. Metaluminous granitic rocks have a wider range of eNd values extending from values similar to those of the peraluminous granites to much higher values. The 87Sr/86Sr values are mostly fairly low, between 0.705 and 0.710 except in the NGB where values as high as 0.7157 are observed. No systematic differences between the eNd or 87Sr/86Sr values of Cu- or Mo-mineralized and Unmineralized granite were discerned, except for Cu-mineralized granite in eastern Nevada and Mo-mineralized granite in Colorado, which have eNd values higher (∼0) and lower ( ∼−10.0), respectively, than Unmineralized granite in the same region. Comparison to eNd values of exposed Precambrian rock suggests that the peraluminous granite, and the Mo granite in Colorado, were derived exclusively from felsic Precambrian basement rocks and that the regional variations in the eNd values reflect the regional variation in the average crustal age. The Nd data confirm that the Precambrian basement underlying the NGB and eastern California is isotopically distinct from Precambrian crust in the remainder of the western United States. The similarity between the eNd values of peraluminous granite and Precambrian crust also suggests that the high 147Sm/144Nd (>0.13) and the low total light rare earth element (LREE) abundances characteristic of peraluminous granite in southern Arizona were imposed during the chemical evolution of the magmas. Metaluminous granite are interpreted to have formed via mixing of mantle-derived magma and large proportions of low 87Sr/86Sr (granulite facies) lower crust, except in the eastern NGB where the mantle magmas mixed with a lower crustal source with a significantly higher 87Sr/86Sr ratio. REE abundance patterns for metaluminous granite in the NGB are characterized by extreme LREE enrichment, which supports the proposed origin for these rocks by mantle/crust mixing or by remelting of the lower crust alone. No systematic difference exists between the sources of Cu- or Mo-mineralized and Unmineralized metaluminous granite, but the data suggest that the Cu sources are in the mantle and the Mo sources are in preexisting crust. Overall, the Nd data indicate that continental interior granite in the western United States was primarily derived from preexisting crust, and although changes in the thermal structure of the continental mantle may have triggered magma formation, the resulting granites do not represent significant juvenile additions to the continental crust.
169 citations
TL;DR: In the early Proterozoic time (Aphebian Period) much of the southwestern Churchill province of the Canadian shield was covered by a sea, called the Manikewan Ocean as discussed by the authors, and the highly deformed and metamorphosed rocks that represent its evolution and final closure over an area of at least 6 × 105 km2.
148 citations
TL;DR: In the case of the Papuan ultramafic belt, there is evidence that emplacement was preceded by development of a secondary rupture in the down-going plate, at some distance from the subduction zone, and was followed by extension, buoyant emergence, and reversed movement of the ophiolite as discussed by the authors.
Abstract: Summary The major ophiolite complexes of Papua New Guinea lie on the northeastern margin of the Australian craton and are flanked, externally, by Palaeogene volcanic arcs. The ophiolites are segments of oceanic lithosphere which occupied the forearc zone prior to arc-continent collision. In the case of the easternmost ophiolite, the Papuan ultramafic belt, there is evidence that emplacement was preceded by development of a secondary rupture in the down-going plate, at some distance from the subduction zone, and was followed by extension, buoyant emergence, and reversed movement of the ophiolite. The westernmost ophiolite (April ultramafics) has more complex structure and probably developed as a series of thrust sheets in a subduction system; the thrust sheets were subjected to renewed deformation and thrusting by continued convergence after arc-continent collision.
140 citations
TL;DR: In this article, the Pongola supergroup and Usushwana Intrusive Suite (UIS) were used for the first time to date the pyroxenites of the UIS.
139 citations
TL;DR: In this paper, the formation of these basins involved a dense pattern of pre-existing faults and Hydroplastic slickensides, which affect nonlithified sediments, help identify not only dip-slip but also strikeslip faults, together with other tectonic and sedimentary structures.
Abstract: Upper Triassic sandstone- and siltstone-infilled basins in the “Massif Ancien” of the High Atlas (Morocco) are distributed along a complex east-northeast trough at the boundary between the Hercynian orogen and the West African craton. The formation of these basins involved a dense pattern of pre-existing faults. Hydroplastic slickensides, which affect nonlithified sediments, help identify not only dip-slip but also strike-slip faults, together with other tectonic and sedimentary structures. The directional distribution of these faults leads to a model in which extension varies from north-northwest (during lower unit sandstone infilling) to northwest (during upper unit siltstone infilling). The latter direction is compatible with the formation of the lower Liassic intrusional doleritic dikes of the Anti-Atlas.
TL;DR: The Southern Province in the Lake Huron area of Ontario, and the Penokean Fold Belt of Minnesota, Wisconsin, and Michigan have the earmarks of a collisional orogen.
Abstract: The Southern Province in the Lake Huron area of Ontario, and the Penokean Fold Belt of Minnesota, Wisconsin, and Michigan have the earmarks of a collisional orogen. The Huronian Supergroup, a southerly facing passive margin sequence, was deposited during early Aphebian (Early Proterozoic) crustal stretching (and ocean basin formation?) along the southern margin of the Superior Province Archean craton. It accumulated as four unconformity-bounded, northerly tapering, onlapping clastic wedges (megacycles). The thickness and facies variations reflect syndepositional down-to-the-basin (south) normal faulting that controlled the accumulation and preservation of the lower three Huronian megacycles. These are overlapped northward by the youngest megacycle, an extensive sheet of clastic sediments recording post-stretching regional subsidence of the cratonic margin due to cooling and thermal contraction. Soft-sediment folds in the rocks of the youngest megaycycle to the extreme south probably indicate southward slu...
TL;DR: Heat flow has been determined at 314 separate sites, many of which include several separate boreholes or probe casts, within the continental area of Canada, including the continental shelves as discussed by the authors.
TL;DR: In this article, the authors used the Bullard predrift reconstruction for the southern Atlantic to delineate the upper Proterozoic shield boundary and put forward an evolutionary model for late Precambrian time.
TL;DR: In this paper, it is suggested that the first primitive felsic magmas were generated at subduction zones, giving rise to komatiitic magmas, and that the increase in the rate of sedimentation during the Archaean tectonics resulted from increased crustal buoyancy.
TL;DR: In this article, a complex pattern of provenances is displayed by 15 formations in the northern Apennines composed chiefly of turbidites that were deposited during the Alpine orogenesis.
Abstract: A complex pattern of provenances is displayed by 15 formations in the northern Apennines composed chiefly of turbidites that were deposited during the Alpine orogenesis. Q-F-L and Qp-Lv-Ls values can be used to characterize specific source areas that existed in the Apennine region from Cretaceous through Miocene time. Whereas sandstone mineralogy can be used to infer plate-tectonic setting, such an approach must make allowances for both the size of the area studied and the tectonic framework that existed prior to sandstone deposition.
In an early stage of the compressive phase of the Tethys (Late Cretaceous), both arkose and litharenite were derived from cratonic blocks, whereas volcanic sandstone was derived from uplifted oceanic sediments and lavas.
Sediments recording the main Oligo-Miocene collisional tectonic phases accumulated in two principal tectonic settings: (1) intermontane (successor) basins, and (2) foreland basins. In the first case, individual formations exhibit a wide provenance variability. Arkosic-lithic sandstone (recycled orogen), volcanic sandstone (magmatic arc), and arkose were deposited simultaneously. In the second case, basins filled with thick turbidite sequences composed of arkose and lithic arkose, which were supplied by basement rocks uplifted along the edge of the European craton and/or by the nascent orogenic belt.
TL;DR: In this paper, the southwestern margin of the Baltic Shield was formed after the Svecokarelian orogenic event (2.2-1.8 Ga), and granitoid rocks intruded the southwest margin and simultaneously also the already cratonized part of the shield.
Abstract: Contrary to earlier opinions, the southwestern margin of the Baltic Shield was formed after the Svecokarelian orogenic event (2.2-1.8 Ga). During the initial stages of its formation (1.7-1.6 Ga), granitoid rocks intruded the southwestern margin and simultaneously also the already cratonized part of the shield. Among these granitoids, the most important chemical difference is between calc-alkalic differentiated granitoids to the west and alkalicalcic more evolved granites to the east of an intraorogenic “suture” (the Mylonite Zone). The chemical differences between alkali-calcic granites found on both sides of the interorogen boundary proper (the Protogine Zone) are less significant. As yet, a final choice cannot be made between wholly actualistic and non-actualistic, possibly intracratonic(?) variants of precursory plate-tectonic processes.
TL;DR: In this article, microtectonic observations of dominant sets of extension and conjugate hybrid joints are used to infer regionally significant extension directions and the origin of the macrostructures.
Abstract: The eastern part of the Saudi Arabian craton is a platform underlain by gently tilted and horizontal Mesozoic-Cenozoic sedimentary rocks everywhere more than 250 km distant from the Zagros deformation front. Despite its tectonic simplicity, the platform contains several laterally extensive, but subdued, structures and lineaments belonging to more than one system of fault zones and flexures. New microtectonic observations of dominant sets of extension and conjugate hybrid joints permit regionally significant extension directions to be inferred and the origin of the macrostructures to be assessed. The central Arabian arch, the E-W crest of which coincides with an axis of Mesozoic subsidence, developed during the Late Cretaceous to Eocene when the basin inverted as a consequence of the emplacement of ophiolite-bearing nappes on the Zagros and Oman margins. During arching, there was strike-parallel elongation of beds. At the same time as the arch amplified, the central Arabian graben system evolved as a result of the northward displacement of an East Arabian block or sheet that became detached across an arcuate separation zone, which in the south is coincident with the crest of the arch. An important Neogene response in the Arabian platform to NE-SW shortening in the Zagros ranges was the formation of a swarm of NE striking master joints and lineaments. These structures reflect the diffuse and peripheral expansion of the foreland beyond the Zagros deformation front.
Journal Article•
TL;DR: In this paper, the spatial and temporal relationships between mid-Proterozoic, intracratonic sedimentation in the Cuddapah Basin and earlier basic dyke swarms are analyzed in the context of thermal and mechanical models for crustal doming, erosion and subsidence.
Abstract: The spatial and temporal relationships between mid-Proterozoic, intracratonic sedimentation in the Cuddapah Basin and earlier Proterozoic basic dyke swarms are analyzed in the context of thermal and mechanical models for crustal doming, erosion and subsidence. The dyke orientations imply that the Archaean crust of South India was thermally warped into an elliptical dome with a roughly E-W axis, under varying regional tectonic conditions. Thermal relaxation of this dome, after erosion and crustal thinning, laid the basis for sedimentation in the Cuddapah Basin, whose deepest part lay to the SW of its present outcrop. Late-Proterozoic sedimentation of the Kurnool rocks must have been initiated by a later, separate thermal event.
TL;DR: The early Proterozoic history of the Baltic Shield in Fennoscandia provides evidence of fragmentation of a late Archaean craton, continental sedimentation and then back-arc spreading, interpreted as being associated with the uprise of a mantle diapir as mentioned in this paper.
TL;DR: A new aeromagnetic survey of a part of southern Alabama reveals that magnetic signatures of the Appalachian Piedmont are truncated by a major magnetic lineament beneath the Gulf Coastal Plain this paper.
Abstract: A new aeromagnetic survey of a part of southern Alabama reveals that magnetic signatures of the Appalachian Piedmont are truncated by a major magnetic lineament beneath the Gulf Coastal Plain. Mylonitic rocks have been recovered from a drillhole along this lineament, which is probably a fault zone of late Paleozoic and/or Triassic-Jurassic age. We suggest that this fault zone may initially have been the Alleghanian convergent suture between the North American craton and accreted terranes to the southeast. The zone may have been locally reactivated as part of an extensive buried Triassic-Jurassic graben system.
TL;DR: In the Eromanga Basin, the seismic velocity boundaries within the crust are sharp compared with the transitional nature of the boundaries under the North Australian and Lachlan provinces.
TL;DR: The Gibeon cluster of Namibian kimberlites is emplaced into the Orange River Belt which has accreted to the Kaapvaal Craton.
Abstract: The Gibeon cluster of Namibian kimberlites is emplaced into the Orange River Belt which has accreted to the Kaapvaal Craton. These “offcraton” kimberlites lack diamonds and are younger than the diamondiferous “on-craton” kimberlites. The Hanaus-I and Louwrensia kimberlites each contain a bimodal suite of upper-mantle-derived garnet lherzolite xenoliths characterized by a coarse granular or mosaic porphyroclastic texture. The Louwrensia pipe in addition contains garnet harzburgites. Deformed lherzolites are not iron-enriched relative to the coarse types. Conditions of equilibration calculated by the Wells-Wood method are 841–1,013° C at 25.6–36.3 kbars, and 869–1,195° C at 23.9–39.4 kbars, for coarse lherzolites from Louwrensia and Hanaus respectively, and from 1,080–1,112° C at 31.6–34.5 kbars, and 983–1,228° C at 24.7–35.2 kbars, for mosaic porphyroclastic types from Louwrensia and Hanaus respectively. The coarse varieties from both localities have similar equilibration conditions to coarse lherzolites from “on-craton” kimberlites and define the lower limb of a perturbed geotherm. The upper high temperature limb of the Namibian geotherm is considered to be an apparent geotherm generated by the deformation and metasomatism of the upper mantle by a rising diapir. Such geotherms, being the result of kimberlite-xenolith interactions, provide no stratigraphic or thermal information concerning the site of kimberlite or diamond formation.
TL;DR: The Ailao Shan fault zone in West Yunnan represents a suture boundary between South China and Indosinian Cratons as mentioned in this paper, and preliminary paleomagnetic results from three sites in Sichuan, Guichou, and Yunnan Provinces reveal a 14° northward migration of South China Craton between Late Permian and Middle Triassic.
Abstract: The Ailao Shan fault zone in West Yunnan represents a suture boundary between South China and Indosinian Cratons. Preliminary paleomagnetic results from three sites in Sichuan, Guichou, and Yunnan Provinces reveal a 14° northward migration of South China Craton between Late Permian and Middle Triassic. The two cratons were separated by about 20° latitudes during the Early Triassic. The tectonic setting of East Asia during the Triassic was probably analogous to the present Indonesian region.
TL;DR: In this paper, it is argued that the predominantly biomodal volcanic suites of Archaean greenstone belts and the genetically related tonalite-trondhjemite-granite plutons did not originate through growth on intra-oceanic island arcs or in Andean-type arcs and marginal basins but in intracontinental rift settings.
Abstract: Modern plate tectonic processes do not appear to be very efficient in continent-building since they have contributed little to the total volume of the continental lithosphere over the last 900 Ma. The much higher crust-formation rate in the Archaean cannot be ascribed to faster plate motion or frequent collision of many small plates during that time but appears to be related to extensive melting in the upper mantle and underplating of dense magmas that could not penetrate the overlying continental crust. These magmas provided a reservoir for most of the typical Archaean magmatic rock associations found in greenstone-grainite-gneiss terrains. It is argued that the predominantly biomodal volcanic suites of Archaean greenstone belts and the genetically related tonalite-trondhjemite-granite plutons did not originate through growth on intra-oceanic island arcs or in Andean-type arcs and marginal basins but in intracontinental rift settings. Magmatic underplating led to non-linear growth and differentiation of Archaean continental crust and is also seen as the prime cause for early lithospheric thickening and stabilization, allowing large intracontinental basins to form since 3.5 Ga ago. The end-Archaean global crust-forming event generated the first large cratons whose subsequent stability may be the result of subcrustal lithospheric thickening through melt extraction and depletion, underplating and carbonic granulite metamorphism in the lower crust. Magmatic underplating continued to remain an important process in the generation of volcanic sequences in the Lower Proterozoic intracontinental basins although there appears to be first evidence for local horizontal crustal accretion in magmatic arcs at about 2 Ga ago. Most of the widespread Proterozoic mobile belts lack typical Wilson-cycle signatures and are interpreted by a model involving extensive crustal thinning, subcrustal lithosphere delamination and crust restacking during basin closure and orogeny. New and fertile, but initially mechanically weak lithosphere is accreted to the crust from below during this process. By the end of the Precambrian horizontal accretion of juvenile continental crust became widespread, but vertical accretion may still be important in Phanerozoic crust-forming events. It is concluded that vertical rather than horizontal growth of lithosphere has dominated global evolution during the first 3.5 Ga of earth's history and that this mechanism also accounts for the observed magmatic rock assemblages as well as for lithospheric stabilization and cratonization of continental crust.
Book•
01 Jan 1984
TL;DR: In this article, the authors studied the geochemical properties of the early Archaean Mafic-Ultramafic Xenolith patterns and their relation to the composition of the Archaean Continental Crust.
Abstract: Mantle Chemistry and Accretion History of the Earth.- Geochemical Characteristics of Archaean Ultramafic and Mafic Volcanic Rocks: Implications for Mantle Composition and Evolution.- Archaean Sedimentary Rocks and Their Relation to the Composition of the Archaean Continental Crust.- Spatial and Temporal Variations of Archaean Metallogenic Associations in Terms of Evolution of Granitoid-Greenstone Terrains with Particular Emphasis on the Western Australian Shield.- Magma Mixing in Komatiitic Lavas from Munro Township, Ontario.- Oxygen Isotope Compositions of Minerals and Rocks and Chemical Alteration Patterns in Pillow Lavas from the Barberton Greenstone Belt, South Africa.- Petrology and Geochemistry of Layered Ultramafic to Mafic Complexes from the Archaean Craton of Karnataka, Southern India.- Pressures, Temperatures and Metamorphic Fluids Across an Unbroken Amphibolite Facies to Granulite Facies Transition in Southern Karnataka, India.- Origin of Archaean Charnockites from Southern India.- Radiometric Ages (Rb-Sr, Sm-Nd, U-Pb) and REE Geochemistry of Archaean Granulite Gneisses from Eastern Hebei Province, China.- The Most Ancient Rocks in the USSR Territory by U-Pb Data on Accessory Zircons.- Age and Evolution of the Early Precambrian Continental Crust of the Ukrainian Shield.- Significance of Early Archaean Mafic-Ultramafic Xenolith Patterns.
TL;DR: The early Proterozoic shows evidence of crustal stability and rigidity in the form of aulacogens, dyke swarms, kimberlites (diamonds), and linear/arcuate orogenic belts bordering older cratons.
TL;DR: In this article, the results of a recent regional stratigraphical and sedimentological study on the ∼2770-yr old lower Fortescue Group were presented, which was previously classified lithologically as Proterozoic and referred to as Archaean.
Abstract: The stabilization of continental crust to form cratons represents one of the major features of Earth history1. Major structural, geochemical2,3 and, to a lesser extent, sedimentological changes4 associated with the development of stable crustal blocks are recorded mainly around 2,500 Myr ago1. This change, however, appears to have been globally diachronous and cratonic sequences as old as 3,100 Myr are recorded5. I now present the results of a recent regional stratigraphical and sedimentological study on the ∼2770 Myr old lower Fortescue Group6,7 (previously classified lithologically as Proterozoic8, but following the recent recommendation of a 2,500-Myr Archaean/Proterozoic chronological boundary9 is referred to as Archaean) in the Pilhara Block10, Western Australia. A major stabilization of the underlying granitoid–greenstone terrain appears to have pre-dated Fortescue basin formation. This event, which available geochronology suggests was relatively rapid, marked a major changing point in the tectonic evolution of the Pilhara Block.
TL;DR: In this article, it was shown that palaeolatitudes derived palaeomagnetically from Upper Devonian and Lower Carboniferous rocks of cratonic North America are 15-20° more northerly than those of Acadia and Europe.
Abstract: Kent and Opdyke1 have argued that during the late Devonian and early Carboniferous, the eastern part of the northern Appalachians (Acadia) was situated ∼1,500 km further south relative to cratonic North America than it is at present, and that it moved to its present position sometime later in the Carboniferous (Fig. 1). Van der Voo and Scotese2 proposed an even greater displacement of 2,000 km which they attribute to motion between cratonic North America and Europe, Acadia being attached to Europe (Fig. 1). The argument is that palaeolatitudes (λp) derived palaeomagnetically from Upper Devonian and Lower Carboniferous rocks of cratonic North America are 15–20° more northerly than those of Acadia and Europe. The proposed shear zone passes through central Newfoundland. Using palaeomagnetic results from eastern and western Newfoundland we show here that no such motion occurred. We also show that Kiaman (late Carboniferous and Permian) overprinting is widespread in Newfoundland, and that these secondary magnetizations agree (with two exceptions attributed to dextral rotation of the Colorado Pleateau) with observations from late Devonian and early Carboniferous rocks of the North American craton, confirming the proposal3 that magnetizations of the cratonic early Carboniferous rocks are Kiaman, not early Carboniferous in age. Our results also enable us to extend this proposal3 to late Devonian rocks of the craton. Hence the palaeolatitudinal offset of Fig. 1 is almost certainly not tectonic, but is an artefact of the wrong assumption of the equivalence of rock and magnetization ages.
TL;DR: In this paper, the 198 Ma Lower Jurassic Copper Mountain intrusions outcrop in the Quesnellia Subterrane of Terrane I in the Canadian Cordillera, and the resulting pole position of 11.8°E, 57.3°N (δp = 2.7°, δm = 4.4°) is discordant for the North American craton and reflects 39 ± 6° of clockwise rotation and 9 ± 5° of northward translation.
Abstract: The 198 Ma Lower Jurassic Copper Mountain intrusions outcrop in the Quesnellia Subterrane of Terrane I in the Canadian Cordillera. Thermal demagnetization at 550 ± 10°C defines a single stable remanence component of 25.9°, 41.2° (α95=3.6°) in 11 reliable sites. The resulting pole position of 11.8°E, 57.3°N (δp = 2.7°, δm = 4.4°) is discordant for the North American craton and reflects 39 ± 6° of clockwise rotation and 9 ± 5° of northward translation. Combined with previous paleomagnetic and geologic data, a consistent model for the geotectonic evolution of Quesnellia and Terrane I emerges.