Geochronology and geochemistry of the Bashikaogong S-type granitic rocks: a record of Early Paleozoic subduction and collision in North Altun, Northwestern China

We have examined some of the presumed Precambrian basement metamorphic and granitic rocks in Japan, through radiometric dating as well as on field evidence, and have found that mineral ages of about 175 to 250 m.y. are abundant in the Hida area, northwestern part of central Japan, that a number of thrust rocks in southwestern Japan show ages of 400 to 450 m.y., and that the oldest of the measured samples is about or somewhat over 500 m.y. Little evidence is available to support a view that the Pre-Sinian rocks, if ever existent, have remained unaltered under such a polycyclic orogenic zone as that represented by Japan, although remnants of the youngest Precambrian to Early Paleozoic cycle can be detected.

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Early Paleozoic granitic rocks of the South Qiangtang Terrane, northern Tibetan Plateau: Implications for subduction of the Proto- (Paleo-) Tethys Ocean

Journal of Asian Earth Sciences ◽

10.1016/j.jseaes.2020.104579 ◽

2020 ◽

Vol 204 ◽

pp. 104579

Author(s):

Haitao Wang ◽

Qingguo Zhai ◽

Peiyuan Hu ◽

Lingsen Zeng ◽

Yue Tang ◽

...

Keyword(s):

Tibetan Plateau ◽

Granitic Rocks ◽

Early Paleozoic ◽

The South ◽

Northern Tibetan Plateau ◽

Tethys Ocean ◽

Qiangtang Terrane

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Paleomagnetism of Siluro-Devonian and Cambrian granitic rocks from the Avalon zone in Cape Breton Island, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e81-112 ◽

1981 ◽

Vol 18 (7) ◽

pp. 1187-1210 ◽

Cited By ~ 11

Author(s):

K. V. Rao ◽

M. K. Seguin ◽

E. R. Deutsch

Keyword(s):

Granitic Rocks ◽

High Coercivity ◽

Early Paleozoic ◽

Early Devonian ◽

Cape Breton Island ◽

Polar Wander ◽

Cape Breton ◽

Northern Latitudes ◽

Two Generations ◽

Radiometric Ages

As part of a major study of the Avalon zone in Cape Breton Island, we describe the paleomagnetism of radiometrically well-studied granitic rocks of two generations, representing the Acadian (350–450 Ma) and the Avalonian (520–580 Ma) Orogenies, respectively. Detailed alternating field (AF) and thermal experiments performed on the younger granites indicate that they are characterized by three different mean directions of magnetization in the 10–60 mT coercivity spectra: SE (D = 149°, I = +70°; K = 160, N = 4 sites); NE-1 (D = 72°, I = −70°; K = 320, N = 3 sites); and NE-2 (D = 31°, I = −24°; K = 67, N = 3 sites) with corresponding paleopole positions at CB-1 (16°N, 41°W; δp, δm = 6°, 7°); CB-2 (32°N, 97°W; δp, δm = 7°, 8°); and CB-3 (27°S, 96°W; δp, δm = 6°, 11°). The radiometric ages of these three remanence directions do not differ from each other by more than 50 Ma; these remanences are also present as low coercivity (5–25 mT) magnetizations in the Avalonian granites (10 sites). Antipole CB-3 agrees with other recently reported Early Devonian paleomagnetic results from the northern Appalachians. In contrast, the two other antipoles (CB-1 and CB-2) are located in southerly latitudes but do not differ significantly from poles of contemporaneous rocks in New Brunswick and Newfoundland. The "aberrancy" of southerly located Siluro-Devonian poles with respect to those in northern latitudes is discussed in the context of possible transcurrent motion of the "Acadia" displaced terrain with respect to cratonic North America. Presently available paleomagnetic data are not conclusive and cannot confirm or negate this possibility. The CB-1, CB-2, and CB-3 poles are interpreted as representing rapid apparent polar wander with respect to Cape Breton Island during Siluro-Devonian time.In the older Cambrian granites, pole CB (37°N, 176°E; δp, δm = 2°, 3°), derived from a high coercivity (20–70 mT) mean remanence direction NW (D = 318°, I = +15°; K = 298, N = 10 sites), probably corresponds to the Avalonian Orogeny. Further results are needed to interpret the paleogeographic setting of the Avalon microcontinent in early Paleozoic time.

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40Ar/39Ar ages of detrital muscovite within early Paleozoic overstep sequences, Avalon composite terrane, southern New Brunswick: implications for extent of late Paleozoic tectonothermal overprint

Canadian Journal of Earth Sciences ◽

10.1139/e90-128 ◽

1990 ◽

Vol 27 (9) ◽

pp. 1209-1214 ◽

Cited By ~ 11

Author(s):

R. D. Dallmeyer ◽

R. D. Nance

Keyword(s):

New Brunswick ◽

Coarse Grained ◽

Granitic Rocks ◽

Late Paleozoic ◽

Low Grade ◽

Early Paleozoic ◽

Late Precambrian ◽

Pelitic Schist ◽

Gas Fractions ◽

Thermal Overprint

Concentrates of coarse-grained detrital muscovite from the Ratcliffe Brook Formation (lowermost Cambrian) display internally discordant 40Ar/39Ar age spectra. Gas fractions evolved at intermediate and high experimental temperatures record apparent ages of ca. 610–620 Ma. These are interpreted as dating initial cooling through temperatures appropriate for intracrystalline retention of 40Ar and may indicate derivation from mylonite zones developed within proximal late Precambrian granitic rocks. Gas fractions evolved at lower experimental temperatures record patterns of spectra discordance that suggest the constituent grains experienced partial, intracrystalline diffusive loss of 40Ar during a late Paleozoic, low-grade thermal overprint. A muscovite concentrate from pelitic schist beneath the allochthonous, latest Precambrian Cranberry Head granite records a 40Ar/39Ar plateau age of 318 ± 1 Ma. This is interpreted as closely dating Late Carboniferous thrust emplacement of the allochthon.

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Geochronology and tectonic implications of magmatism and metamorphism, southern Kootenay Arc and neighbouring regions, southeastern British Columbia. Part I: Jurassic to mid-Cretaceous

Canadian Journal of Earth Sciences ◽

10.1139/e83-178 ◽

1983 ◽

Vol 20 (12) ◽

pp. 1891-1913 ◽

Cited By ~ 77

Author(s):

D. A. Archibald ◽

J. K. Glover ◽

R. A. Price ◽

E. Farrar ◽

D. M. Carmichael

Keyword(s):

British Columbia ◽

North America ◽

Regional Metamorphism ◽

Granitic Rocks ◽

Early Paleozoic ◽

Small Bodies ◽

Western Margin ◽

The North ◽

Windermere Supergroup ◽

Igneous Activity

K–Ar dates and U–Pb zircon dates define three periods of igneous activity in the southern Kootenay Arc: (1) emplacement of late-synkinematic to post-kinematic granodioritic plutons in mid-Jurassic time (170–165 Ma) accompanying amphibolite-facies regional metamorphism; (2) emplacement of post-kinematic granitic plutons in mid-Cretaceous time (~100 Ma); and (3) emplacement of small bodies of syenite in Eocene time (~50 Ma) in the western part of the area. Micas from mid-Jurassic plutons that yield the oldest K–Ar dates (158–166 Ma) also yield plateau-shaped 40Ar/39Ar age spectra. Age spectra for biotites younger than these but older than 125 Ma reflect thermal overprinting.In southeastern British Columbia, the Kootenay Arc marks the transition from the North American rocks of the Cordilleran miogeocline to the tectonic collage of allochthonous terranes that have been accreted to it.Deformation, metamorphism, and plutonism recorded in rocks of the southern Kootenay Arc commenced in mid-Jurassic time as a composite allochthonous terrane was accreted to and overlapped the western margin of North America. The geochronology and metamorphic geothermobarometry show that in less than 10 Ma between 166 and 156 Ma: (1) rocks as young as the late Proterozoic Windermere Supergroup and the early Paleozoic Lardeau Group were carried rapidly to depths of 20–24 km while being deformed and intruded by granitic rocks of a hornblende–biotite suite that were also being emplaced at a much shallower level in the overriding allochthonous terrane; and (2) the miogeoclinal rocks of the Windermere Supergroup in the southern Kootenay Arc were then uplifted by more than 7 km at an estimated rate of 2 mm/year, and thrust over the allochthonous terrane prior to being intruded by post-kinematic granitic rocks, many of which belong to the two-mica suite of mid-Cretaceous age..

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