K–Ar isochron age and paleomagnetism of diabase along the trans-Avalon aeromagnetic lineament—evidence of Late Triassic rifting in Newfoundland

1980 ◽  
Vol 17 (4) ◽  
pp. 491-499 ◽  
Author(s):  
J. P. Hodych ◽  
A. Hayatsu
Keyword(s):  
Nova Scotia ◽  
Early Jurassic ◽  
Late Triassic ◽  
The North ◽  
Two Samples ◽  
Avalon Peninsula

A prominent aeromagnetic lineament crosses the Avalon Peninsula of Newfoundland from 46°50.4′N, 53°45.9′W to 47°22.1′N, 52°30.0′W. It is shown to be at least partly caused by diabase dikes of Late Triassic and possibly Early Jurassic age which are probably related to the Shelburne diabase dike and the North Mountain basalt, both of Nova Scotia. All are thought to have resulted from rifting which preceded opening of the Atlantic.Unmetamorphosed diabase was found at three sites along the trans-Avalon aeromagnetic lineament: as narrow sills at site 1 (46°58.0′N, 53°25.4′W), as a narrow dike at site 2 (47°4.7′N, 53°7.6′W), and as large angular boulders at site 3 (47°11.0′N, 52°52.2′W).For sites 1 and 2, analyses of seven diabase samples fall on a single K–Ar isochron whose intercept on the 40Ar/36Ar axis is at 215 ± 45 and whose slope gives a Late Triassic age of 201.1 ± 2.6 Ma. Analyses of two diabase samples from the Shelburne dike fall close to this isochron suggesting a similar age. Paleomagnetism adds support; the virtual paleopole measured for sites 1 and 2, using 12 oriented diabase samples demagnetized in 300 Oe (23 880 A/m) alternating field (AF), falls at 87.8°E, 72.9°N (dp = 3.0°, dm = 4.3°), close to the virtual paleopole reported for the Shelburne dike.For site 3, analyses of two samples fall on the K–Ar isochron reported for the North Mountain basalt, tentatively suggesting that the intrusion at site 3 occurred about 10 Ma later than at sites 1and 2.

Geochemical discriminators and the palaeotectonic environment of the North Mountain basalts, Nova Scotia

1980 ◽  
Vol 17 (12) ◽  
pp. 1740-1745 ◽  
Author(s):  
J. M. Wark ◽  
D. B. Clarke
Keyword(s):  
Nova Scotia ◽  
Continental Crust ◽  
Early Jurassic ◽  
Late Triassic ◽  
Chemical Characteristics ◽  
Sea Floor ◽  
The North ◽  
Sea Floor Spreading

The late Triassic – early Jurassic North Mountain basalts of Nova Scotia have been analyzed for various elements believed to be useful in determining the palaeotectonic environment of eruption. The discriminant diagrams show these basalts to have within-plate affinities, with a possible indication of oceanic chemical characteristics. An oceanic environment, however, is at variance with the field relations, which show the within-plate environment to be continental; thus the oceanic chemical characteristics may suggest eruption through a continental crust that was thinning prior to the onset of active sea-floor spreading later in the Jurassic.

scholarly journals New insights on the early Mesozoic evolution of multiple tectonic regimes in the northeastern North China Craton from the detrital zircon provenance of sedimentary strata

Solid Earth ◽  
2018 ◽  
Vol 9 (6) ◽  
pp. 1375-1397 ◽  
Author(s):  
Yi Ni Wang ◽  
Wen Liang Xu ◽  
Feng Wang ◽  
Xiao Bo Li
Keyword(s):  
North China Craton ◽  
North China ◽  
Early Jurassic ◽  
Orogenic Belt ◽  
Detrital Zircons ◽  
Late Triassic ◽  
Early Triassic ◽  
The South ◽  
The North ◽  
Early Mesozoic

Abstract. To investigate the timing of deposition and provenance of early Mesozoic strata in the northeastern North China Craton (NCC) and to understand the early Mesozoic paleotectonic evolution of the region, we combine stratigraphy, U–Pb zircon geochronology, and Hf isotopic analyses. Early Mesozoic strata include the Early Triassic Heisonggou, Late Triassic Changbai and Xiaoyingzi, and Early Jurassic Yihe formations. Detrital zircons in the Heisonggou Formation yield  ∼ 58 % Neoarchean to Paleoproterozoic ages and  ∼ 42 % Phanerozoic ages and were sourced from areas to the south and north of the basins within the NCC, respectively. This indicates that Early Triassic deposition was controlled primarily by the southward subduction of the Paleo-Asian oceanic plate beneath the NCC and collision between the NCC and the Yangtze Craton (YC). Approximately 88 % of the sediments within the Late Triassic Xiaoyingzi Formation were sourced from the NCC to the south, with the remaining  ∼ 12 % from the Xing'an–Mongolia Orogenic Belt (XMOB) to the north. This implies that Late Triassic deposition was related to the final closure of the Paleo-Asian Ocean during the Middle Triassic and the rapid exhumation of the Su–Lu Orogenic Belt between the NCC and YC. In contrast,  ∼ 88 % of sediments within the Early Jurassic Yihe Formation were sourced from the XMOB to the north, with the remaining  ∼ 12 % from the NCC to the south. We therefore infer that rapid uplift of the XMOB and the onset of the subduction of the Paleo-Pacific Plate beneath Eurasia occurred in the Early Jurassic.

Biostratigraphic and biogeographic constraints on the Carboniferous to Jurassic Cache Creek Terrane in central British Columbia

2001 ◽  
Vol 38 (4) ◽  
pp. 551-578 ◽  
Author(s):  
M J Orchard ◽  
F Cordey ◽  
L Rui ◽  
E W Bamber ◽  
B Mamet ◽  
...  
Keyword(s):  
North American ◽  
Early Jurassic ◽  
Late Carboniferous ◽  
Middle Permian ◽  
Late Triassic ◽  
Fine Grained ◽  
North American Continent ◽  
The North ◽  
Carbonate Buildups ◽  
North American Craton

Conodonts, radiolarians, foraminiferids, and corals provide constraints on the geology and tectonics of the Nechako region. They also support the notion that the Cache Creek Terrane is allochthonous with respect to the North American craton. The 177 conodont collections, assigned to 20 faunas, range in age from Bashkirian (Late Carboniferous) to Norian (Late Triassic); 70 radiolarian collections representing 12 zones range from Gzhelian (Late Carboniferous) to Toarcian (Early Jurassic); 335 collections assigned to 11 fusulinacean assemblages (with associated foram-algal associations) range from Bashkirian to Wordian (Middle Permian); and two coral faunas are of Bashkirian and Wordian age. The fossils document a long but sporadic history of sedimentary events within the Cache Creek Complex that included two major carbonate buildups in the Late Carboniferous (Pope limestone) and Middle Permian (Copley limestone), punctuated by intervening Early Permian deepening; basaltic eruptions during the mid Carboniferous and mid Permian; the onset of oceanic chert sedimentation close to the Carboniferous–Permian boundary and its persistence through the Late Triassic (Sowchea succession); latest Permian and Early Triassic mixed clastics and volcanics (Kloch Lake succession); Middle and Late Triassic reworking of carbonates (Whitefish limestone), including cavity fill in older limestones (Necoslie breccia), and fine-grained clastic sedimentation extending into the Early Jurassic (Tezzeron succession). Tethyan, eastern Pacific, and (or) low-latitude biogeographic attributes of the faunas are noted in the Gzhelian (fusulines), Artinskian (conodonts, fusulines), Wordian (fusulines, corals, conodonts), and Ladinian (conodonts, radiolarians). The Cache Creek Terrane lay far to the west of the North American continent during these times.

Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

2002 ◽  
Vol 39 (6) ◽  
pp. 1013-1051 ◽  
Author(s):  
Cynthia Dusel-Bacon ◽  
Marvin A Lanphere ◽  
Warren D Sharp ◽  
Paul W Layer ◽  
Vicki L Hansen
Keyword(s):  
Early Cretaceous ◽  
Final Stage ◽  
Complex Interaction ◽  
Early Jurassic ◽  
Crustal Thickening ◽  
Late Triassic ◽  
East Central ◽  
The North ◽  
Plutonic Rocks ◽  
Lake George

We present new 40Ar/39Ar ages for hornblende, muscovite, and biotite from metamorphic and plutonic rocks from the Yukon–Tanana Upland, Alaska. Integration of our data with published 40Ar/39Ar, kinematic, and metamorphic pressure (P) and temperature (T) data confirms and refines the complex interaction of metamorphism and tectonism proposed for the region. The oldest metamorphic episode(s) postdates Middle Permian magmatism and predates the intrusion of Late Triassic (215–212 Ma) granitoids into the Fortymile River assemblage (Taylor Mountain assemblage of previous papers). In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by ~188–186 Ma 40Ar/39Ar plateau ages for hornblende from plutons that intrude the Fortymile River assemblage, and for metamorphic minerals from the Fortymile River assemblage and the structurally underlying Nasina assemblage. We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages. Although a few metamorphic samples from the Lake George assemblage yield Jurassic 40Ar/39Ar cooling ages, most yield Early Cretaceous 40Ar/39Ar ages: hornblende ~135–115 Ma, and muscovite and biotite ~110–108 Ma. We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.

Palaeomagnetism, North China and South China collision, and the Tan-Lu fault

1990 ◽  
Vol 331 (1620) ◽  
pp. 589-598 ◽  
Keyword(s):  
South China ◽  
North China ◽  
Eastern China ◽  
Early Jurassic ◽  
Late Triassic ◽  
Polar Wander ◽  
The North ◽  
Indosinian Orogeny ◽  
North And South ◽  
Transcurrent Faults

Refined Apparent Polar Wander (APW) paths for the North and South China Blocks (ncb and scb) are presented and the collision between the NCB and SCB discussed. We suggest that the amalgamation of the NCB and SCB was completed in the late Triassic-early Jurassic, during the Indosinian Orogeny. This proposed timing is based on an analysis of palaeomagnetic signatures relating to continental collisions, such as the convergence of palaeolatitude, deflections of declination, hairpin-like loops in and superposition of APW paths. Like the Cenozoic India—Eurasia collision, the Mesozoic NCB- SCB collision reactivated ancient faults in eastern China, converting some of them into transcurrent faults, of which the Tan-Lu fault is the most famous.

A geodynamic model for some structures within and adjacent to the Okanagan Valley, southern British Columbia

1981 ◽  
Vol 18 (10) ◽  
pp. 1581-1598 ◽  
Author(s):  
John V. Ross
Keyword(s):  
Volcanic Rocks ◽  
High Heat ◽  
Early Jurassic ◽  
Late Triassic ◽  
Second Phase ◽  
The North ◽  
Open Structures ◽  
International Boundary ◽  
Radiometric Ages ◽  
Okanagan Valley

Detailed and reconnaissance mapping of areas along the east and west sides of the Okanagan Valley, from the International Boundary in the south to Kamloops in the north, has revealed a similarity in structural sequence and geometry in rocks ranging in age from Pennsylvanian (Harper Ranch, Anarchist, Kobau, Old Tom, and Shoemaker Groups) through Late Triassic – Early Jurassic (Nicola, Sicamous, and Slocan Groups).Earliest recognizable folds, F1, have northerly trending axes, are isoclinal in form, and are disrupted on all scales by a strongly penetrative second phase of deformation, F2. This second phase is characterized by northerly and southerly verging isoclinal folds having east–west axes that are very nearly parallel with a well-developed stretching lineation, L2. Mylonitic lamination is developed parallel with these F2 axial surfaces. A third phase of folding, F3, comprising more unright open structures having a consistent southerly vergence, deforms the earlier F1 and F3 structures. Later phases of deformation, F4 and F5, almost coeval, have produced the present foliation configuration outlining basins and domes and associated northerly trending normal faults.Progressive metamorphism accompanied F1, F2, and F3 deformations and peaked during F2. F4 and F5 are associated with a thermal event resulting in resetting of most radiometric ages within the region.F1 deformation is probably Permo-Triassic in age and associated with lower greenschist metamorphism, whereas F2 and F3, associated with a much higher metamorphism up to amphibolite facies, affect all the sedimentary rocks within the region and apparently terminated by about 178 Ma (K–Ar on hornblende), Triassic – Early Jurassic. The latest movements, F4 and F5, involve volcanic rocks whose age of crystallization is set radiometrically at about Eocene.A plate model involving easterly obduction during the Permo-Triassic, followed by easterly dipping subduction with associated dextral transform movement during the Late Triassic – Early Jurassic, is proposed to explain the observed geometry. A mantle diapir below the region is rationalized to explain the localized high heat flow during Eocene time.

Paleomagnetism and K–Ar isochron dates of Early Jurassic basaltic flows and dikes of Atlantic Canada

1988 ◽  
Vol 25 (12) ◽  
pp. 1972-1989 ◽  
Author(s):  
J. P. Hodych ◽  
A. Hayatsu
Keyword(s):  
Nova Scotia ◽  
Recent Time ◽  
Early Jurassic ◽  
Eastern North America ◽  
Bay Of Fundy ◽  
Atlantic Canada ◽  
North Shore ◽  
The North ◽  
Boundary Date ◽  
Newark Supergroup

K–Ar isochron dates of 193 ± 2, 189 ± 3, and 191 ± 2 Ma are reported for the Shelburne dike of Nova Scotia, the Avalon dike of Newfoundland, and the Caraquet dike of New Brunswick, respectively. These major tholeiitic dikes agree in radiometric date with the North Mountain Basalt of Nova Scotia and with other tholeiitic flows of the Newark Supergroup that have been paleontologically assigned to the Hettangian. However, further work is needed to resolve the discrepancy between the Triassic–Jurassic boundary date of 193 ± 6 Ma suggested by the Newark Supergroup flows and the boundary dates of 204–213 Ma adopted in recent time scales.The North Mountain Basalt flows at nine sites on the north shore of the Bay of Fundy are shown to have likely magnetized during initial cooling, yielding an Hettangian virtual paleopole at 66°N, 72°E (dp = 9°, dm = 14°). New paleomagnetic results are also reported for the Caraquet and Avalon dikes.The virtual paleopoles from Hettangian flows and dikes of Atlantic Canada lie on average ~11 °north of the virtual paleopoles from Hettangian flows of the northeastern United States. This discrepancy is likely due to insufficient averaging out of paleosecular variation and demonstrates that caution is needed in paleomagnetically correlating among the Early Jurassic flows and intrusions of eastern North America.

Mesozoic–Cenozoic paleomagnetism of the Intermontane and Yukon–Tanana terranes, Canadian Cordillera

2005 ◽  
Vol 42 (6) ◽  
pp. 1163-1185 ◽  
Author(s):  
D TA Symons ◽  
M J Harris ◽  
P JA McCausland ◽  
W H Blackburn ◽  
C JR Hart
Keyword(s):  
Early Jurassic ◽  
Late Triassic ◽  
Canadian Cordillera ◽  
Geological Evidence ◽  
Polar Wander ◽  
The North ◽  
Apparent Polar Wander Path ◽  
The Pacific ◽  
North American Craton ◽  
Made In

Lithoprobe Slave – Northern Cordillera Lithospheric Evolution (SNORCLE) transect support enabled 24 paleomagnetic collections (536 sites, 6547 specimens) to be made in the northern Cordillera. Paleopoles from 16 studies are integrated with other published paleopoles to present a tectonic synthesis for the Intermontane Belt (IMB) and Yukon–Tanana (YT) terranes since 215 Ma. It shows that the YT terrane has been parautochthonous with the North American craton at least since the Early Jurassic. Since 54 Ma the IMB terranes have rotated steadily clockwise at 0.29° ± 0.11°/Ma on top of the YT terrane and craton or by 16° ± 6° clockwise. Between 102 ± 14 and 54 Ma, the IMB terranes rotated another 35° ± 14° clockwise, probably during Paleocene collision with the craton, and were translated 8.3° ± 7.0° (2σ) (915 ± 775 km) northward, probably during the Late Cretaceous on the Kula plate. The 915 km estimate is much less than most paleomagnetic estimates for "Baja BC" but agrees with the geological evidence. These post-Jurassic estimates are used to reconstruct the position of the Late Triassic – Jurassic cratonic apparent polar wander path for the IMB. The resulting IMB path is found to be concordant with the Cache Creek and Quesnellia terrane poles, indicating that these terranes were together and close to the craton in the Early Jurassic. These results place the IMB terranes close to the Pacific coastline of the northern USA and southern Canada but rotated 35° ± 14° counterclockwise, in the Jurassic and Early Cretaceous.

scholarly journals New insights on the early Mesozoic evolution of multiple tectonic regimes in the northeastern North China Craton from the detrital zircon provenance of sedimentary strata

2018 ◽  
Author(s):  
Yi Ni Wang ◽  
Wen Liang Xu ◽  
Feng Wang ◽  
Xiao Bo Li
Keyword(s):  
Detrital Zircon ◽  
North China Craton ◽  
North China ◽  
Early Jurassic ◽  
Orogenic Belt ◽  
Late Triassic ◽  
Early Triassic ◽  
The South ◽  
The North ◽  
Early Mesozoic

Abstract. To investigate the timing of deposition and provenance of early Mesozoic strata in the northeastern North China Craton (NCC), and to reconstruct the early Mesozoic tectono-paleogeography of the region, we combine LA–ICP–MS detrital zircon U–Pb dating, Hf isotopic data. Early Mesozoic strata include the Early Triassic Heisonggou, Late Triassic Changbai and Xiaoyingzi, and Early Jurassic Yihe formations. Detrital zircons in the Heisonggou Formation comprise ~ 58 % Neoarchean to Paleoproterozoic and ~ 42 % Phanerozoic grains that were sourced from areas to the south and north of the basins within the NCC. This indicates that Early Triassic deposition was controlled primarily by southward subduction of the Paleo-Asian oceanic plate beneath the NCC, and collision between the NCC and the Yangtze Craton (YC). Approximately 88 % of sediments within the Late Triassic Xiaoyingzi Formation were sourced from the NCC to the south, with the remaining ~ 12 % from the Xing'an–Mongol Orogenic Belt (XMOB) to the north. This implies that Late Triassic deposition was related to the final closure of the Paleo-Asian Ocean during the Middle Triassic and the rapid exhumation of the Su–Lu Orogenic Belt between the NCC and YC. In contrast, ~ 88 % of sediments within the Early Jurassic Yihe Formation were sourced from the XMOB to the north, with the remaining ~ 12 % from the NCC to the south. We therefore infer that rapid uplift of the XMOB and the onset of subduction of the Paleo-Pacific Plate beneath Eurasia occurred in the Early Jurassic.

Initial rifting and breakup between Nova Scotia and Morocco: insight from new magnetic models 1This article is one of a series of papers published in this CJES Special Issue on the theme of Mesozoic–Cenozoic geology of the Scotian Basin. 2Earth Sciences Sector Contribution 20120024.

2012 ◽  
Vol 49 (12) ◽  
pp. 1385-1394 ◽  
Author(s):  
Sonya A. Dehler
Keyword(s):  
Nova Scotia ◽  
Magnetic Anomaly ◽  
Late Triassic ◽  
Magnetic Data ◽  
Supporting Evidence ◽  
The North ◽  
New Models ◽  
Basin Geometry ◽  
Thinned Continental Crust ◽  
High Degree

New models of magnetic data are presented that provide insight into the early stages of rifting and breakup between Morocco and Nova Scotia. The margins, which began forming during the Late Triassic rifting and Middle Jurassic separation of the North American and African plates, display considerable variability in deeper crustal structure, faulting style, and basin geometry along their length. The central and northeastern portions of the Nova Scotia margin show characteristics of a magma-poor margin, with a high degree of crustal thinning and a complex ocean-continent transition zone with little direct evidence of volcanism. In contrast, the margin to the southwest of Nova Scotia has clearly recognized characteristics of a volcanic-style rifted margin, including seaward-dipping reflector (SDR) sequences that are interpreted as rift-related volcanic flows overlying basement. These SDRs are coincident with a strong linear magnetic anomaly, the East Coast Magnetic Anomaly (ECMA), which shares many characteristics with the West African Coast Magnetic Anomaly (WACMA). Both magnetic anomalies change character and diminish in amplitude northward along the margins. The new models show the expected decrease in magnetic source material towards the northeastern end of the margin and suggest that modest amounts of igneous material, emplaced at or near the edge of the thinned continental crust, will satisfy the observed anomalies in this magma-poor section of the margin. These new interpretations and supporting evidence indicate volcanism was a factor along much of the margin during early rifting between Nova Scotia and Morocco.

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