Showing papers on "Terrane published in 1989"

The origins of granulites: a metamorphic perspective

Abstract: Although many recent reviews emphasize a uniformity in granulite pressure–temperature (P–T) conditions and paths, granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation. A thorough survey of over 90 granulite terranes or occurrences reveals that over 50% of them record P–T conditions outside the 7.5 ± 1 kbar and 800 ± 50 °C average granulite regime preferred by many authors. In particular, an increasing number of very high temperature (900−1000 °C) terranes are being recognized, both on the basis of distinctive mineral assemblages and geothermobarometry. Petrogenetic grid and geothermobarometric approaches to the determination and interpretation of P–T histories are both evaluated within the context of reaction textures to demonstrate that the large range in P–T conditions is indeed real, and that both near-isothermal decompression (ITD) and near-isobaric cooling (IBC) P–T paths are important. Amphibolite–granulite transitions promoted by the passage of CO2-rich fluids, as observed in southern India and Sri Lanka, are exceptional and not representative of fluid-related processes in the majority of terranes. It is considered, on the contrary, that fluid-absent conditions are typical of most granulites at or near the time of their recorded thermal maxima.ITD granulites are interpreted to have formed in crust thickened by collision, with magmatic additions being an important extra heat source. Erosion alone is not, however, considered to be the dominant post-collisional thinning process. Instead, the ITD paths are generated during more rapid thinning (1−2 mm/yr exposure) related to tectonic exhumation during moderate-rate or waning extension. IBC granulites may have formed in a variety of settings. Those which show anticlockwise P–T histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion, with or without additional crustal extension. IBC granulites at shallow levels (< 5 kbar) may also be formed during extension of normal thickness crust, but deeper-level IBC requires more complex models. Many granulites exhibiting IBC at deep crustal levels may have formed in thickened crust which underwent very rapid (5 mm/yr) extensional thinning subsequent to collision. It is suggested that the preservation of IBC paths rather than ITD paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust, and that hybrid ITD to IBC paths should also be observed.Most IBC granulites, and probably many ITD granulites, have not been exposed at the Earth's surface as a result of the tectonic episodes which produced them, but have resided in the middle and lower crust for long periods of time (100−2000 Ma) following these events. The eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation.

Continental growth of northwest China

Abstract: The northwest corner of China is the most interior part of Central Asia and includes parts of the Siberian, Tarim, and Kazakhstan plates where the Junggar and Tarim basins are separated by the east-west trending Tianshan Range. A preliminary terrane map divides the area into thirteen separate areas which are classified into four types: (l) continental, (2) oceanic crust, (3) island arc, (4) composite. The boundaries for these terranes are faults that have been previously defined either by geologic mapping or Holocene activity. Passive consolidation of the southern margin of Paleo-Asia is marked by accretion and subduction of the Paleo-Tethys oceanic basins and by development of volcanic arcs. Paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the Permian or later. The stratigraphic record reveals development of intracontinental basins in the late Carboniferous followed by the Pan-Asian thermal event that gave rise to widespread intrusion of A-type granites of late Paleozoic age. The frontal collision of India along the southern border of Asia in the Paleocene reactivated nearly all of the older major strike-slip and thrust faults formed during the late Paleozoic consolidation of Paleo-Asia. The complex nature of the continental growth of Central Asia has produced and destroyed many varieties of sutures, and reconstruction of the original plate and terrane configurations therefore is enigmatic.

New tectonic divisions of the Grenville Province, Southeast Canadian Shield

Abstract: On the basis of geological, geophysical, and geochronological data, the Grenville Province has been divided into three first-order longitudinal belts, the Parautochthonous Belt (PB), Allochthonous Polycyclic Belt (APB), and Allochthonous Monocyclic Belt (AMB). These are set apart by three first-order tectonic boundaries, the Grenville Front (GF), Allochthon Boundary Thrust (ABT), and Monocyclic Belt Boundary Zone (MBBZ). The belts are subdivided into terranes based on internal lithological character. The GF separates the Archean to Proterozoic foreland northwest of the orogen from reworked equivalents to the southeast. Continuous at the scale of the orogen, its main characteristic is that of a crustal-scale contraction fault. The PB, although less clearly identified along the length of the orogen, in most places represents upgraded and tectonically reworked rocks of the adjacent foreland. The boundary between the PB and the APB to the southeast, the ABT, is most clearly delineated in the eastern half of the province. It is the locus of major crustal delamination along which high-grade, mostly middle Proterozoic, polycyclic terranes were tectonically transported northwest toward and onto the PB. The AMB comprises two separate areas underlain by the Wakeham Supergroup and what is currently known as the Grenville Supergroup, respectively; its basal contact, the MBBZ, is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks. This first-order zonation implies a tectonic polarity to the Grenville Province, superimposed on which are second-order features evident from contrasting tectonic styles and radiometric ages. These characteristics are consistent with a diachronous or oblique collisional model for the Grenville orogen.

The Appalachian-Ouachita Orogen in the United States

Abstract: Includes 14 chapters on the Appalachian orogen, 15 of the Ouachita orogen, and a chapter on the connection between them beneath the eastern Gulf Coastal Plain. The Appalachian chapters synthesize the geologic development of the orogen by tectonostratigraphic intervals (pre-orogenic, Taconic, Acadian, Alleghanian, and post-Alleghanian), and also treat Paleozoic paleontologic control, regional geophysics, thermal history of the crystalline terranes, parts of the orogen buried beneath the Atlantic and eastern Gulf coastal plains, regional geomorphology, mineral and energy resources; an integration chapter also is included. The Ouachita chapters cover physical stratigraphy and biostratigraphy of the Paleozoic rocks, structural geology, a synthesis of the subsurface geology beneath the western Gulf Coastal Plain, a review of the mineral and energy resources, regional geophysics, and a tectonic synthesis. Twelve excellent plates provide four-color geologic maps, structural cross sections, tectonic syntheses, and geophysical maps; a black-and-white synthesis of Appalachian mineral deposits, and a reflection seismic cross section.

Late Paleozoic to Jurassic silicic magmatism at the Gondwana margin: Analogy to the Middle Proterozoic in North America?

Abstract: A vast region of upper Paleozoic to Middle Jurassic (300-150 Ma) silicic magmatic rocks that erupted inboard of the Gondwana margin is a possible Phanerozoic analogue to the extensive Middle Proterozoic (1500-1350 Ma) silicic magmatic province that underlies much of the southern mid-continent of North America. Like the North American rocks, the Gondwana silicic magmas appear to be melts of crust that formed about 200-300 m.y. earlier. In the North American case, this older crust formed and was accreted to the continent during a major period of crustal formation (1700-1900 Ma), whereas in the Gondwana case, the crust that melted consisted mainly of magmatic are terranes accreted to the continental margin during the Paleozoic. In both cases, basic to intermediate magmatic rocks are extremely rare and magmatism is less abundant in regions that contain older (and previously melted) crust. The similarities between the North American and Gondwana silicic rocks suggest that both suites formed in extensional settings where basaltic magmas, ponded at the base of the preheated crust, caused extensive crustal melting that inhibited upward passage of the basalts. In both cases, silicic volcanism occurred after major assembly of a supercontinent by subduction and accretion processes, and before breakup of the supercontinent. By analogy with the polar wander curves for Gondwana, the granite-rhyolite provinces may have formed during a period of very slow motion of the supercontinents relative to the poles.

Cretaceous geotectonic patterns in the New Zealand Region

Abstract: In the mid-Cretaceous, around 105±5 Ma, the tectonic regime in New Zealand changed significantly. From the Permian to the Early Cretaceous most rocks formed under the influence of convergent margin tectonics and comprise incomplete remnants of magmatic arcs, forearc basins, trench slope basins, and accretionary complexes. This tectonic pattern was ended by the approach and collision of the spreading ridge between the Phoenix and Pacific plates. Crustal extension, leading eventually to fragmentation of the continental crust, commenced immediately after ridge collision. Precollisional and syncollisional events deformed and thickened the accretionary prism, with concurrent folding and thrusting of more arcward elements. Cretaceous granulites in southwest New Zealand are thought to result from the closure of a small backarc basin or marginal sea slightly earlier than the main ridge collision. Postcollisional block faulting led to thick nonmarine sedimentation in new basins that cut across old terrane boundaries, except in the outboard area where a thick wedge of marine rocks was deposited over the subsiding accretionary prism. After oblique ridge trench collision along the New Zealand margin, the Phoenix-Pacific Ridge propagated to the southwest to link with zones of incipient spreading in the Tasman Sea and south of Australia. Subsequently, the eastern part of the ridge continued to migrate south with increasing offset along the Udinsev Fracture Zone. In the Late Cretaceous a duplicate ridge developed. The southern branch continued to move southward and collided with the trench west of the Antarctic Peninsula in the Cenozoic. The northern branch is the extant East Pacific Ridge.

Bedrock geology and tectonic evolution of the Wrangellia, Peninsular, and Chugach Terranes along the Trans‐Alaska Crustal Transect in the Chugach Mountains and Southern Copper River Basin, Alaska

Abstract: The Trans-Alaskan Crustal Transect in the southern Copper River Basin and Chugach Mountains traverses the margins of the Peninsular and Wrangellia terranes, and the adjacent accretionary oceanic units of the Chugach terrane to the south The southern Wrangellia terrane margin consists of a polymetamorphosed magmatic arc complex at least in part of Pennsylvanian age (Strelna Metamorphics and metagranodiorite) and tonalitic metaplutonic rocks of the Late Jurassic Chitina magmatic arc The southern Peninsular terrane margin is underlain by rocks of the Late Triassic (?) and Early Jurassic Talkeetna magmatic arc (Talkeetna Formation and Border Ranges ultra-mafic-mafic assemblage) on Permian or older basement rocks The Peninsular and Wrangellia terranes are parts of a dominantly oceanic superterrane (composite Terrane II) that was amalgamated by Late Triassic time and was accreted to terranes of continental affinity north of the Denali fault system in the mid- to Late Cretaceous The Chugach terrane in the transect area consists of three successively accreted units: (1) minor greenschist and intercalated blueschist, the schist of Liberty Creek, of unknown protolith age that was metamorphosed and probably accreted during the Early Jurassic, (2) the McHugh Complex (Late Triassic to mid-Cretaceous protolith age), a melange of mixed oceanic, volcaniclastic, and olistostromal rocks that is metamorphosed to prehnite-pumpellyite and lower greenschist facies that was accreted by middle Cretaceous time, and (3) the Upper Cretaceous Valdez Group, mainly magmatic arc-derived flysch and lesser oceanic volcanic rocks of greenschist facies that was accreted by early Paleocene time A regional thermal event that culminated in early middle Eocene time (48–52 Ma) resulted in widespread greenschist facies metamorphism and plutonism

Accretion of the Archean Slave province

Abstract: Continental rift models have long been applied to the Archean Slave province of northwestern Canada. A reassessment of these models shows them to be incompatible with observed geological relations and suggests that contractional tectonic models may be more appropriate than extensional ones. Regions composed of different rock suites (e.g., orthogneisses vs. mafic volcanics) are separated by high-strain zones recording large displacements. It is proposed that the high-strain zones separate four distinct terranes that have been juxtaposed during collisional orogenesis. From west to east, these include the Anton terrane, interpreted as an Archean microcontinent; the Sleepy Dragon terrane, possibly an exhumed more eastern part of the Anton terrane; the Contwoyto terrane, a westward-verging fold and thrust belt containing tectonic slivers of greenstone volcanics; and the Hackett River volcanic terrane, interpreted as an Archean island arc. The Contwoyto and Hackett River terranes represent a paired accretionary prism and island-arc system that formed above an east-dipping subduction zone. These collided with the Anton microcontinent, producing a basement nappe, expressed as the Sleepy Dragon terrane, during the main accretion event within the Slave province. The whole tectonic assemblage was intruded by late-kinematic to postkinematic granitoids.

Origin of Granulite Terranes and the Formation of the Lowermost Continental Crust

Abstract: Differences in composition and pressures of equilibration between exposed, regional granulite terranes and suites of granulite xenoliths of crustal origin indicate that granulite terranes do not represent exhumed lowermost crust, as had been thought, but rather middle and lower-middle crustal levels. Application of well-calibrated barometers indicate that exposed granulites record equilibration pressures of 0.6 to 0.8 gigapascal (20 to 30 kilometers depth of burial), whereas granulite xenoliths, which also tend to be more mafic, record pressures of at least 1.0 to 1.5 gigapascals (35 to 50 kilometers depth of burial). Thickening of the crust by the crystallization of mafic magmas at the crust-mantle boundary may account for both the formation of regional granulite terranes at shallower depths and the formation of deep-seated mafic crust represented by many xenolith suites.

Evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the Canadian cordillera

Abstract: Sm–Nd and Rb–Sr isotopic studies of several Phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked, pre-existing continental crust. In contrast, isotopic data collected from two of the largest terranes in the Canadian Cordilleran orogenic belt, the Alexander and Stikine terranes, show that these tectonic fragments are composed of mantle-derived continental crust. In many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some Proterozoic crustal regions

Impact production of CO2 by the Cretaceous-Tertiary extinction bolide and the resultant heating of the Earth

Abstract: Evidence at the Cretaceous/Tertiary boundary suggests that the proposed 'extinction' bolide struck a continental or shallow marine terrane. This evidence includes: shocked quartz and feldspar grains found in the boundary layer inherited from a range of rock types; a high ^(87)Sr/^(86)Sr ratio in some planktonic fossils which could reflect continental-derived Sr(ref.5); and evidence that the platinum-group-element-rich clay layer is underlain (at some localities) by a deposit of possible tsunamic origin. These observations and data demonstrate that sea level at the end of the Cretaceous was ~150-200 m higher than at present, suggesting the possibility that the extinction bolide struck a shallow marine carbonate-rich sedimentary section. Here we show that the impact of such a bolide (~5km in radius) onto a carbonate-rich terrane would increase the CO_2 content of the atmosphere by a factor of two to ten. Additional dissolution of CO_2 from the ocean's photic zone could release much larger quantities of CO_2. The impact induced release of CO_2, by itself, would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 K to 10 K for periods of 10^4 to 10^5 years.

The Evolution of the Pacific Ocean margins

Abstract: Part 1 Oceanic plates and the Pacific Ocean margins Oceanic plateaus and the Pacific Ocean margins, A. Mur and Z . Ben - Avraham Terrane trajectories and plate interactions along continental margins in the North Pacific Ocean basin, A. Cox, et al Terrain analysis: A circum-Pacific overview, G.G.Howell and D.L.Jones. Part 2 The Northeast Pacific Ocean margins: The North American sector of the circum-Pacific, P.J.Coney Paleomagnetic evidence for the relative terrane motion in Western North America, D.P.Stone and M.McWilliams. Part 3 The Northwest Pacific Ocean margins: Mesozoic and cenozoic evolution of Asia, S.Maruyama et al Accretion tectonics and evolution of Japan, A.Taira et al The mesozoic and cenozoic tectonism in Eastern China, Zh.M.Zhanq et al. Part 4 The equatorial and Southwest Pacific Ocean margins: Speculations on the late mesozoic and cenozoic evolution of the Southeast Asia margin, R.McCabe and J.Cole Displace terranes of the Southwest Pacific, C.S.Hutchison Mesozoic-cenozoic ocean floor/continent interaction and terrain configuration, Southwest Pacific Area around New Zealand, K.B.Spoorli and P.F.Ballance. Part 5 The Southeast Pacific Ocean margins: Tectonic evolution of the late cenozoic centras Andes, T.E.Jordan and M.Gardeweq The evolution of the Pacific Ocean margin in South America north of the Arica Elbow, F.Meqard.

Early Paleozoic terranes of New Zealand

Abstract: Lower Paleozoic rocks of New Zealand comprise two major assemblages each with their own distinct sedimentary tectonic, metamorphic and igneous history; they thus represent two distinct tectono-stratigraphic terranes. In Nelson-Westland, the western, or Buller, terrane consists of the Western Sedimentary Belt, together with Ordovician paragneiss at Charleston and in Victoria Range. The sedimentary sequence, ranging in age from basal to Upper Ordovician, comprises continentderived quartz-rich turbidites with black shales inferred to have been deposited in submarine fans and slope basins. The eastern, Takaka terrane (Central and Eastern Sedimentary Belts) is much more varied in lithofacies, composition and age (Cambrian to Silurian) and itself comprises several tectonic, probably thrust, slices. Volcanics, volcaniclastics, siliceous and calcareous siltstone, conglomerate and turbidites dominate the Cambrian part of the sequence and indicate proximity to a Cambrian island arc. The oldest sediments ar...

Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen

Abstract: The Early Proterozoic Penokean Orogen developed along the southern margin of the Archean Superior craton. The orogen consists of a northern deformed continental margin prism overlying an Archean basement and a southern assemblage of oceanic arcs, the Wisconsin magmatic terranes. The south-dipping Niagara fault (suture) zone separates the south-facing continental margin from the accreted arc terranes. The suture zone contains a dismembered ophiolite.The Wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure. The northern Pembine–Wausau terrane contains a major succession of tholeiitic and calc-alkaline volcanic rocks deposited in the interval 1860–1889 Ma and a more restricted succession of calc-alkaline volcanic rocks deposited about 1835 – 1845 Ma. Granitoid rocks ranging in age from about 1870 to 1760 Ma intrude the volcanic rocks. The older succession was generated as island arcs and (or) closed back-arc basins above the south-dipping subducti...

Evolution and assembly of Archean Gneiss Terranes in the Godthåbsfjord Region, southern west Greenland: Structural, metamorphic, and isotopic evidence

Abstract: The Godthabsfjord region of southern West Greenland comprises several terranes that were assembled between 2750 and 2550 Ma and folded during amphibolite facies metamorphism. The terranes, which are dominated by gneisses of different ages and show different preassembly metamorphic and structural histories, are (1) the Faeringehavn terrane containing the 3820–3600 Ma Amitsoq gneisses, with granulite facies metamorphism at circa 3600 Ma, (2) the Akia terrane containing the 3070–2940 Ma Nuk gneisses, with granulite-amphibolite facies metamorphism at circa 2980 Ma, (3) the Tasiusarsuaq terrane containing circa 2900 Ma gneisses, with granulite facies metamorphism at circa 2800 Ma, and (4) the Tre Brodre terrane containing the 2800–2750 Ma Ikkattoq gneisses, with amphibolite facies metamorphism at 2800–2750 Ma. Metamorphic assemblages and structures formed prior to terrane assembly, were variably overprinted during amphibolite facies metamorphism and heterogeneous strain associated with assembly. Recognition of the region as consisting of several terranes indicates that the anatomy of some Archean high-grade gneiss complexes may resemble that of orogens of Proterozoic and Phanerozoic age that formed as a consequence of plate tectonic processes.

Correlations between Nazca/Farallon Plate kinematics and forearc basin evolution in Ecuador

Abstract: The Tertiary evolution of the forearc basins of Ecuador shows a close correlation between the changing convergence rate of the Farallon, and later Nazca, oceanic plates and continental South America. The correlation occurs during the subduction of a relatively young slab and, in the Late Miocene, onset of the subduction of the Carnegie aseismic ridge. The Ecuador forearc basins lie on a basement of oceanic crust known as the Pinon terrane. The accretion of this terrance occurred in the Paleocene as the leading edge of the Farallon plate, the Macuchi island arc, collided with South America. In the Middle Eocene this forearc terrane was the site of major pull-apart basin formation and turbiditic sedimentation, coincident with a phase of very rapid convergence between chron 21 and chron 13 (48–37 Ma). This deformation was bounded by the trench and a major dextral strike-slip fault zone and resulted in the northward translation of the forearc with respect to continental South America. During the Oligocene a phase of extension normal to the trend of the active margin occurred, coincident with a phase of relatively slow convergence (chron 13 to chron 6, 37–20 Ma). This extension was followed in the Middle Miocene by inversion of most of the forearc basins, coincident with a return to relatively fast convergence from chron 6 (20 Ma) to the present day. Subduction of the Carnegie aseismic ridge occurred during this period (circa 8 Ma to present) and may have enhanced the compressive event. Further, northward translation of the forearc silver accompanied this later deformation. The relationships outlined for the forearc may be modeled in terms of a dynamic orogenic wedge which responds directly to changes in convergence rate at the subduction zone. The convergence rate appears to be an important control on the coupling between the downgoing slab and overriding continental plate.

Thrust tectonics along the north-western continental margin of Sabah/Borneo

Abstract: Widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north-west continental margin of Sabah. In contrast, interpretation of reflection seismic data acquired by BGR shows an autochthonous continental terrane comprising an Oligocene to Early Miocene carbonate platform being progressively overthrust by an allochthonous rock complex. Progressive compression resulted in the development of four structural zones: Imbricated thrust sheets (Zone III); two thrust sheet systems one on top of the other (Zone IV); a complex zone with multiphase deformation (Zone V); and piercement ridges (Zone VI).

The Alberta foreland basin: relationship between stratigraphy and Cordilleran terrane-accretion events

Abstract: A foreland-basin sequence resulting from accretion of a terrane to a continental passive margin ideally should be unconformity bounded, with a shallowing-upward pattern, like the classic Flysch to Molasse sequence of Alpine foreland basins. The basal unconformity is cut as the peripheral bulge associated with lithospheric flexure migrates cratonward ahead of the basin and the advancing overthrusts. The shallowing occurs because sediment supply at first is low – early stages of accretion near the continental slope generate little or no topography above sea level; later stages result in significant tectonic uplift, and much sediment is shed into the foreland, filling the basin. The upper unconformity is cut as lithospheric bending stresses are relaxed following overthrusting, and reduction of the flexural load on the lithosphere through erosion and (or) tectonic denudation of the overthrusts causes regional uplift or basin "rebound". Actual sequences show differences from this idealized version in that (i) ...

Nd Isotopes and the Origin of Grenville-Age Rocks in Texas: Implications for Proterozoic Evolution of the United States Mid-Continent Region

Abstract: Nd isotopic data were obtained for Precambrian Grenville-belt rocks in Texas. The samples represent most components of the crust of the Llano, Van Horn, and Franklin Mountains exposed terranes. Almost all Precambrian igneous, metamorphic, and sedimentary rocks from the three regions document addition to North America of mantle-derived crustal materials in the 1.6-1.0 Ga interval. The exception is a quartzite from the westernmost (Franklin Mountains) exposure, which was derived from {approximately}1.8 Ga crust of the southwestern United States. The initial {epsilon}{sub Nd} values of all rocks except the quartzite lie in the +1 to +6 range for igneous/metamorphic ages of 1.37 to 1.06 Ga. These results can be interpreted in two ways: (1) as documenting 0-20% additions of older crustal material to mantle-derived products 1.4-1.0 Ga ago; or (2) as documenting derivation of the Grenville exposures by recycling of older crustal protoliths separated from the mantle 1.6-1.3 Ga ago. The Nd data in isolation do not resolve these two interpretations. The model mantle separation ages (T{sub DM}) of the rocks are very similar to published values of granulites in Mexico and Virginia: all these regions of the United States and Mexico show a strong peak of T{sub DM} around 1.4more » Ga ago. If the ages represent older crustal protoliths, then they would have formed coevally with the 1.5-1.3 Ga Granite-Rhyolite Terranes of the continental interior USA. This would imply that the Granite-Rhyolite Terranes were formed during orogenic/accretionary processes in the adjoining Grenville Belt, and are not anorogenic in association, as conventionally assumed.« less

Tectono-stratigraphic terranes in Cape Breton Island, Nova Scotia: Implications for the configuration of the northern Appalachian orogen

Abstract: Cape Breton Island is divided into four terranes on the basis of contrasts in pre-Carboniferous geology. The Blair River Complex in the north is an exposure of North American Grenvillian basement, analogous to the Humber zone basement in Newfoundland. Ordovician to Devonian metavolcanic, metasedimentary, gneissic, and granitic rocks of the Aspy terrane are correlative with parts of the Gander terrane of Newfoundland and New Brunswick. The Bras d9Or terrane, characterized by low-pressure gneisses, a carbonate-clastic platform sequence, and late Precambrian-Early Cambrian plutons, may be correlative with units previously included in the Gander terrane in southern Newfoundland and the Avalon terrane in southern New Brunswick. The Mira terrane in southeastern Cape Breton Island, including late Precambrian to Early Cambrian volcanic and sedimentary sequences and fossiliferous Cambrian-Ordovician units, is clearly part of the Avalon terrane. Therefore, with the exception of the Dunnage terrane, which is not represented in Cape Breton Island, the terranes of Newfoundland continue through Cape Breton Island. They are offset to the northwest to the mainland part of the Appalachian orogen in New Brunswick.