40Ar–39Ar ages for detrital white mica in Meguma terrane, Nova Scotia, Canada: implications for provenance of the Goldenville and Halifax groups

2012 ◽  
Vol 49 (7) ◽  
pp. 781-795 ◽  
Author(s):  
P.H. Reynolds ◽  
C.E. White ◽  
S.M. Barr ◽  
C.M. Muir
Keyword(s):  
Nova Scotia ◽  
Source Region ◽  
White Mica ◽  
Source Rocks ◽  
Low Grade ◽  
Rock Formation ◽  
Step Heating ◽  
Single Grain ◽  
Meguma Terrane ◽  
Late Neoproterozoic

Single-grain 40Ar/39Ar ages are reported for detrital white mica, along with conventional step-heating data for whole rocks, from low-grade metasandstone samples from the Goldenville, Halifax, and Rockville Notch groups in the Meguma terrane of southern Nova Scotia. The majority (166) of single grains from 11 samples yielded ages between ca. 615 and 350 Ma, and the remaining 12 grains yielded ages between ca. 1900 and 870 Ma. The late Neoproterozoic–Paleozoic age distributions are consistent with derivation of sediments from the rapidly uplifted flanks of an active rift, where partial to complete resetting of white mica ages occurred at ca. 520–500 Ma, preceding sediment deposition. The ca. 615 Ma ages may be relics of the original detrital white mica that existed in the source rocks prior to the rifting event. Ages from the Upper Silurian White Rock Formation appear to reflect this same ca. 520–500 Ma event, suggesting that sediments in the White Rock Formation were recycled from the Goldenville and Halifax groups. The older Precambrian ages are inferred to represent white mica in the source region, likely Amazonia. The whole-rock age spectra are discordant, with pronounced age gradients and no well-defined age plateaus. Initial gas released from five of the samples at low laboratory extraction temperatures (ca. 450–500 °C) yielded ages of ca. 260–300 Ma, not seen in the single-grain data, whereas gas released at the highest extraction temperatures yielded ages in the range ca. 510–530 Ma, possibly reflecting the principal result obtained from the single-grain data.

scholarly journals Effects of fluid flow, cooling and deformation as recorded by 40Ar/39Ar, Rb–Sr and zircon fission track ages in very low- to low-grade metamorphic rocks in Avalonian SE Cape Breton Island (Nova Scotia, Canada)

2014 ◽  
Vol 152 (5) ◽  
pp. 767-787 ◽  
Author(s):  
ARNE P. WILLNER ◽  
SANDRA M. BARR ◽  
JOHANNES GLODNY ◽  
HANS-JOACHIM MASSONNE ◽  
MASAFUMI SUDO ◽  
...  
Keyword(s):  
Nova Scotia ◽  
Fission Track ◽  
White Mica ◽  
Low Grade ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Zircon Fission Track ◽  
Meguma Terrane ◽  
Fission Track Ages ◽  
Oriented Parallel

Abstract40Ar/39Ar in situ UV laser ablation of white mica, Rb–Sr mineral isochrons and zircon fission track dating were applied to determine ages of very low- to low-grade metamorphic processes at 3.5±0.4 kbar, 280±30°C in the Avalonian Mira terrane of SE Cape Breton Island (Nova Scotia). The Mira terrane comprises Neoproterozoic volcanic-arc rocks overlain by Cambrian sedimentary rocks. Crystallization of metamorphic white mica was dated in six metavolcanic samples by 40Ar/39Ar spot age peaks between 396±3 and 363±14 Ma. Rb–Sr systematics of minerals and mineral aggregates yielded two isochrons at 389±7 Ma and 365±8 Ma, corroborating equilibrium conditions during very low- to low-grade metamorphism. The dated white mica is oriented parallel to foliations produced by sinistral strike-slip faulting and/or folding related to the Middle–Late Devonian transpressive assembly of Avalonian terranes during convergence and emplacement of the neighbouring Meguma terrane. Exhumation occurred earlier in the NW Mira terrane than in the SE. Transpression was related to the closure of the Rheic Ocean between Gondwana and Laurussia by NW-directed convergence. The 40Ar/39Ar spot age spectra also display relict age peaks at 477–465 Ma, 439 Ma and 420–428 Ma attributed to deformation and fluid access, possibly related to the collision of Avalonia with composite Laurentia or to earlier Ordovician–Silurian rifting. Fission track ages of zircon from Mira terrane samples range between 242±18 and 225±21 Ma and reflect late Palaeozoic reburial and reheating close to previous peak metamorphic temperatures under fluid-absent conditions during rifting prior to opening of the Central Atlantic Ocean.

40Ar/39Ar ages of detrital muscovite within Lower Cambrian and Carboniferous clastic sequences in northern Nova Scotia and southern New Brunswick: implications for provenance regions

1997 ◽  
Vol 34 (2) ◽  
pp. 156-168 ◽  
Author(s):  
R. D. Dallmeyer ◽  
J. D. Keppie ◽  
R. D. Nance
Keyword(s):  
Nova Scotia ◽  
New Brunswick ◽  
Lower Cambrian ◽  
Source Region ◽  
Regional Distribution ◽  
Coarse Grained ◽  
Cape Breton Island ◽  
Late Proterozoic ◽  
Cape Breton ◽  
Meguma Terrane

Detrital muscovite from lowermost Cambrian sequences exposed in the Avalon Composite Terrane in Nova Scotia and New Brunswick record 40Ar/39Ar plateau ages of ca. 625–600 Ma. These are interpreted to date times of cooling in source areas. The regional distribution of coarse-grained detrital muscovite in Lower Cambrian rocks of Avalonian overstep sequences suggests a source region of dimensions considerably larger than any presently exposed in Appalachian segments of the Avalon Composite Terrane. Late Proterozoic tectonic reconstructions locate the Avalon Composite Terrane adjacent to northwestern South America, thereby suggesting a possible source within Late Proterozoic PanAfrican – Brasiliano orogens. Detrital muscovite from clastic sequences of the proximally derived, Lower Carboniferous (Tournaisian) Horton Group and the more distal Upper Carboniferous (Westphalian D – Stephanian) Pictou Group in Nova Scotia records 40Ar/39Ar spectra that define plateau ages of ca. 390–380 Ma (Horton Group) and and ca. 370 Ma (Pictou Group). Finer grained fractions from samples of the Horton Group display more internally discordant age spectra defining total-gas ages of ca. 397–395 Ma. A provenance for the finer muscovite may be found in southern Nova Scotia where Cambrian–Ordovician turbidites of the Meguma Group display a regionally developed micaceous cleavage of this age. The ca. 390–380 Ma detrital muscovites probably were derived from granite stocks presently exposed in proximal areas of northernmost Cape Breton Island. A more distal source for the ca. 370 Ma detrital muscovites in the Pictou Group is suggested by its original extensive distribution, although a local, possibly recycled, source may also have been present. The presence of only 400–370 Ma detrital muscovite suggests a rapidly exhumed orogenic source with characteristics similar to those of crystalline rocks presently exposed in the Cape Breton Highlands and (or) the Meguma Terrane.

Offshore continuation of Meguma Terrane, southwestern Nova Scotia

1989 ◽  
Vol 26 (1) ◽  
pp. 176-191 ◽  
Author(s):  
Georgia Pe-Piper ◽  
Bosko D. Loncarevic
Keyword(s):  
South Carolina ◽  
Nova Scotia ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Magnetic Anomalies ◽  
Near Surface ◽  
Rock Formation ◽  
South Mountain Batholith ◽  
Granitoid Rocks ◽  
Meguma Terrane

Eight short drill cores have been examined from the continental shelf southwest of Nova Scotia. Four cores recovered granitoid rocks of two types. Ilmenite-bearing granitoid rocks petrographically and geochemically resemble granodiorites of the South Mountain Batholith and granites of the Seal Island Pluton. Magnetite-bearing granitoid rocks are also peraluminous but have no exact analogues onshore in Nova Scotia. Two cores recovered metamorphic rocks in a small area 50 km south of Seal Island. One consits of chlorite–muscovite–quartz schist, geochemically similar to rocks of the Halifax Formation. The second sampled epidote–chlorite–quartz schist similar to metavolcanic rocks of the White Rock Formation. One further core sampled quartzite, and another sampled a metavolcanic rock (possibly erratic).The regional extent of these lithotypes can be inferred from gravity and aeromagnetic data. Regional gravity data suggest the presence of a large granite body off southwestern Nova Scotia. In this area, magnetic anomalies are irregular, apparently reflecting the presence of magnetite-bearing granites. The layer-stripping method of analyzing the magnetic field shows that the area is underlain at depth by high magnetic anomalies. Large near-surface linear magnetic anomalies are used to map the extent of the volcanic rocks of the White Rock Formation. The area is cut by several northwest-trending faults that postdate Acadian folding but predate the earliest Jurassic magmatism of the Shelburne Dyke and North Mountain basalt. The unusual magnetic signature of the area off southwestern Nova Scotia may reflect a different basement; it is possible that Meguma rocks are thrust over the Avalon Terrane. Alternatively, it may be solely the result of magnetite-bearing granites. These granites may be related to a Permian thermal event in southwest Nova Scotia, and they have some petrographic similarity to young granites of the Piedmont Zone of South Carolina.

Detrital muscovite geochronology and the Cretaceous tectonics of the inner Scotian Shelf, southeastern Canada 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. 2Geological Survey of Canada Contribution 20120142.

2012 ◽  
Vol 49 (12) ◽  
pp. 1558-1566 ◽  
Author(s):  
Peter H. Reynolds ◽  
Georgia Pe-Piper ◽  
David J.W. Piper
Keyword(s):  
Nova Scotia ◽  
Lower Cretaceous ◽  
Special Issue ◽  
Scotian Shelf ◽  
Single Grain ◽  
Meguma Terrane ◽  
Maritimes Basin ◽  
Uplift And Erosion

Geochronology of detrital muscovite from the Lower Cretaceous of the central Scotian Basin has shown predominant supply of Meguma terrane detritus, including muscovite with Alleghanian (mid-Carboniferous to Permian) ages from the inner Scotian Shelf. In this study, 87 detrital muscovite grains from five wells in the eastern Scotian Basin, representing depositional ages from Tithonian to Early Albian, were dated by single-grain 40Ar/39Ar techniques. Previous work shows that the provenance of this sediment was different from wells in the central Scotian Basin. Compared with the central Scotian Basin, the muscovite age populations from the eastern Scotian Basin have more (20% versus 7%) pre-Devonian ages, derived from inboard terranes of the Appalachians. In both the central and eastern Scotian Basin, most old grains are found in the Tithonian and the Aptian–Albian, with fewer in the Valanginian and almost none in the Kimmeridgian and the Hauterivian–Barremian. These data suggest rapid unroofing of the Meguma terrane in the Kimmeridgian and Hauterivian–Barremian and greater supply of sediment from Newfoundland to the eastern Scotian Basin in the Tithonian and Aptian–Albian. Compared with the central Scotian Basin, which has most ages in the range 340–300 Ma, the muscovite age populations from the eastern Scotian Basin have a higher proportion of 420–340 Ma and in particular 300–260 Ma ages. Such late Alleghanian overprinting of argon ages is very rare on land in Nova Scotia, but in the Maritimes Basin, this was the time of uplift and erosion of strata.

scholarly journals Origin of sediments during Cretaceous continent—continent collision in the Romanian Southern Carpathians: preliminary constraints from 40Ar/39Ar single-grain dating of detrital white mica

2013 ◽  
Vol 64 (5) ◽  
pp. 375-382 ◽  
Author(s):  
Franz Neubauer ◽  
Ana-Voica Bojar
Keyword(s):  
Late Jurassic ◽  
Upper Cretaceous ◽  
Shear Zones ◽  
White Mica ◽  
Low Grade ◽  
Late Permian ◽  
Ductile Shear Zones ◽  
Single Grain ◽  
Ductile Shear ◽  
Southern Carpathians

Abstract Single grains of detrital white mica from the lowermost Upper Cretaceous Sinaia Flysch have been dated using the 40Ar/39Ar technique. The Sinaia Flysch was deposited in a trench between the Danubian and Getic microcontinental pieces after the closure of the Severin oceanic tract. The Danubian basement is largely composed of a Panafrican/Cadomian basement in contrast to the Getic/Supragetic units with a Variscan-aged basement, allowing the distinction between these two blocks. Dating of detrital mica from the Sinaia Flysch resulted in predominantly Variscan ages (329 ± 3 and 288 ± 4 Ma), which prove the Getic/Supragetic source of the infill of the Sinaia Trench. Subordinate Late Permian (263 ± 8 and 255 ±10 Ma), Early Jurassic (185 ± 4 and 183 ± 3 Ma) and Late Jurassic/Early Cretaceous (149 ± 3 and 140 ± 3 Ma) ages as well as a single Cretaceous age (98 ± 4 Ma) are interpreted as representing the exposure of likely retrogressive low-grade metamorphic ductile shear zones of various ages. Ductile shear zones with similar 40Ar/39Ar white mica ages are known in the Getic/Supragetic units. The Cretaceous ages also show that Cretaceous metamorphic units were already subject to erosion during the deposition of the Sinaia Flysch.

Sediment sources and dispersion as revealed by single-grain 40Ar/39Ar ages of detrital muscovite from Carboniferous and Cretaceous rocks in mainland Nova ScotiaGeological Survey of Canada contribution 20090289.

2010 ◽  
Vol 47 (7) ◽  
pp. 957-970 ◽  
Author(s):  
Peter H. Reynolds ◽  
Georgia Pe-Piper ◽  
David J.W. Piper
Keyword(s):  
Nova Scotia ◽  
Early Cretaceous ◽  
Early Carboniferous ◽  
Metamorphic Rocks ◽  
Sediment Sources ◽  
The South ◽  
Lower Carboniferous ◽  
South Mountain Batholith ◽  
Single Grain ◽  
Meguma Terrane

Single-grain ages of detrital muscovite from 15 sand(stone) samples from the Lower Carboniferous Horton Group and the Lower Cretaceous Chaswood Formation of central Nova Scotia were used to infer the nature of the Early Carboniferous unroofing of the Meguma terrane and the reworking of Carboniferous rocks in the Early Cretaceous. In the western Windsor Basin, a sample from the oldest Horton Group rocks yielded ages principally between ca. 400 and 380 Ma, suggesting that most of the muscovite present came from the metamorphic rocks of the Meguma terrane but was variably reset by the intrusion of the South Mountain Batholith at ca. 380 Ma. Other samples in this part of the basin show partial post-depositional resetting. Younger Horton Group metamorphic rocks in the eastern Windsor Basin contain many grains with ages of ca. 370–360 Ma, suggesting derivation from the central core of the South Mountain Batholith or the Musquodoboit Pluton. Horton Group sandstones from the western part of the St. Marys Basin contain muscovite derived from the Liscomb Complex along with metamorphic muscovite variably reset by the intrusion of this complex. In general, our data suggest predominant northward dispersion of muscovite from the Meguma terrane to the Horton Group and a lack of axial transport along the Horton grabens through central Nova Scotia, a pattern compatible with tectonic models in which the Meguma terrane is ramped over the Avalon terrane. Muscovite ages obtained for the Chaswood Formation compare well with those from the Horton Group rocks in the western St. Marys Basin. These rocks may have been exposed to rapid erosion by reactivation of the Cobequid–Chedabucto fault zone in the Early Cretaceous and the resulting sediments were perhaps transported to depositional sites along northeast-trending faults. Unlike the detrital monazites in these rocks, there is no evidence that any of the detrital muscovites came from distal sources outside the Meguma terrane.

Meguma terrane orocline: U-Pb age and paleomagnetism of the Silurian Mavillette gabbro, Nova Scotia, Canada

2020 ◽  
Author(s):  
Halima Sadia Warsame ◽  
Phil J.A. McCausland ◽  
Chris E White ◽  
Sandra M. Barr ◽  
Greg R. Dunning ◽  
...  
Keyword(s):  
Nova Scotia ◽  
North America ◽  
Tectonic Evolution ◽  
Volcanic Rocks ◽  
Late Carboniferous ◽  
Early Devonian ◽  
Rock Formation ◽  
Metasedimentary Rocks ◽  
Meguma Terrane ◽  
New Evidence

Paleomagnetic results and a U-Pb baddeleyite age from the Silurian Mavillette gabbroic sill in southwest Nova Scotia provide new evidence about the Paleozoic tectonic evolution of the Meguma terrane. The Mavillette gabbro sill intruded ca. 440-430 Ma bimodal rift-related metavolcanic and metasedimentary rocks of the White Rock Formation in the Silurian-Devonian Rockville Notch Group. The 426.4±2.0 Ma Mavillette gabbro age is notably younger than the ca. 440 Ma magmatism, but is part of a geochemically-defined suite of within-plate sills and volcanic rocks of the Rockville Notch Group with ages as young as Early Devonian. Paleomagnetic investigation of thirteen sites distributed along the Neoacadian (ca. 390 Ma) synclinal limbs of the Mavillette sill reveal magnetization directions that fail a fold test and therefore postdate Silurian emplacement of the gabbro. The post-folding remanence has a mean direction of D=153.4, I=17.1°; α95=6.5° (n=12 sites), with corresponding paleopole 31.9°S, 325.2 E; dp=3.5°, dm=6.7° that resembles a pervasive Late Carboniferous Kiaman overprint magnetization in North America, but is rotated significantly 22.2°±8.1° counter-clockwise (CCW). Mavillette remanence acquisition likely occurred in concert with fluid mobilization related to Alleghanian deformation, recorded locally by ca. 320 Ma muscovite 40Ar-39Ar ages. Previously published paleomagnetic results from the Meguma terrane also have Carbonifereous remanence directions with similar ~24° CCW discordance. The regional CCW rotation of the southwest Meguma terrane post-dates this ca. 320 Ma tectonothermal remanence acquisition event, likely recording the development of an oroclinal bend of the Meguma terrane during Alleghanian orogeny.

scholarly journals Tectonothermal history of the basement rocks within the NW Dinarides: new40 Ar/39 Ar ages and synthesis

2012 ◽  
Vol 63 (6) ◽  
pp. 441-452 ◽  
Author(s):  
Šoštarić Sibila Borojević ◽  
Neubauer Franz ◽  
Handler Robert ◽  
Palinkaš Ladislav A.
Keyword(s):  
New Age ◽  
White Mica ◽  
Low Grade ◽  
Vardar Zone ◽  
Basement Rocks ◽  
Metamorphic Basement ◽  
Step Heating ◽  
History Of

Abstract Very low-grade and low-grade metamorphosed basement rocks from distinct inliers of the Africa-derived northwestern Dinarides (Medvednica Mts and Paleozoic Sana-Una Unit, respectively) have been studied with the multigrain step-heating 40Ar/39Ar technique in order to compare and reveal their tectonothermal history. 40Ar/39Ar ages from detrital white mica of the very low-grade basement rocks of the Paleozoic Sana-Una Unit gave a Variscan age of ~335 Ma. The new age is in agreement with 40Ar/39Ar ages from the very low-grade basement exposed at Petrova and Trgovska Gora of the NW Dinarides. Within low-grade metamorphic basement rocks from the Medvednica Mts, we found no Variscan ages. White mica from phyllitic basement rocks of the Medvednica Mts gives predominantly early Alpine ages ranging between 135 and 122 Ma and younger Alpine ages of ~80 Ma. The early Alpine ages of 135 and 122 Ma are interpreted as the date to the onset of ductile nappe stacking predating the formation of Gosau-type collapse basins. The late early Alpine event of ~80 Ma can be traced in the entire Cretaceous-aged orogen of the Circum- Pannonian Region and is synchronous with subsidence of the Gosau-type basins and opening and closure of the neighbouring Sava-Vardar Zone.

The Cer massif in the internal Dinarides: Exhumation triggered as a far-field effect of the Carpathian slab roll-back

2021 ◽  
Author(s):  
Georg Löwe ◽  
Susanne Schneider ◽  
Blanka Sperner ◽  
Philipp Balling ◽  
Jörg Pfänder ◽  
...  
Keyword(s):  
Shear Zone ◽  
Late Cretaceous ◽  
Pannonian Basin ◽  
Structural Data ◽  
Shear Zones ◽  
White Mica ◽  
Step Heating ◽  
Type Granite ◽  
Single Grain ◽  
Internal Dinarides

<p>Extension across the southern Pannonian Basin and the internal Dinarides is characterized by the occurrence of a chain of Oligo-Miocene metamorphic core complexes (MCCs) exhumed along mylonitic low-angle extensional shear zones which in part represent former suturing thrusts. Cer MCC at the transition between the internal Dinarides and the Pannonian Basin occupies a structural position within the distal-most Adriatic thrust sheet and originates from two different tectonic processes: Late Cretaceous-Paleogene nappe-stacking during continent-continent collision between Adria and fragments of European lithosphere with Adria residing in a lower plate position, followed by Miocene exhumation. Structural data and a balanced cross section through the Cer massif show that the exhuming shear zone links to a breakaway fault, which reactivated the early Late Cretaceous most internal nappe contact between the two distal-most Adriatic thrust sheets. At Cer MCC, Paleozoic greenschist- to amphibolite-grade lithologies surround a polyphase intrusion composed of I- and S-type granites. These lithologies were exhumed along the shear zone by top-N transport. Thermobarometric analyses indicate an intrusion depth of 7-8 km of the Oligocene I-type granite; cooling below ~500°C occurred at 25.4±0.6 Ma (1σ) yielded by <sup>40</sup>Ar/<sup>39</sup>Ar dating of hornblende. Biotite and white mica from this intrusion as well as from the mylonitic shear zone yield <sup>40</sup>Ar/<sup>39</sup>Ar ages of 17-18 Ma independent of the used techniques (in-situ laser ablation, single-grain total fusion, single-grain step heating, and multi-grain step heating). White mica from the S-type granite yield an <sup>40</sup>Ar/<sup>39</sup>Ar age of 16.7±0.1 Ma (1σ). Associated dikes intruding the shear zone were also affected by N-S extension, indicating that deformation was still ongoing at that time. Our data suggests that exhumation of the MCC was related to the opening of the Pannonian back-arc basin in response to the Carpathian slab-rollback and triggered extensional reactivation of thrusts in the internal Dinarides.</p>

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