Polyphase late Paleozoic tectonothermal evolution of the southwestern Meguma Terrane, Nova Scotia: evidence from 40Ar/39Ar mineral ages

1987 ◽  
Vol 24 (6) ◽  
pp. 1242-1254 ◽  
Author(s):  
R. D. Dallmeyer ◽  
J. D. Keppie
Keyword(s):  
Nova Scotia ◽  
Shear Deformation ◽  
Contact Metamorphism ◽  
Late Paleozoic ◽  
Metamorphic Rocks ◽  
Stress System ◽  
Northern Margin ◽  
South Mountain Batholith ◽  
Dextral Shear ◽  
Meguma Terrane

40Ar/39Ar incremental-release ages of hornblende, muscovite, and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late Paleozoic tectonothermal evolution for the southwestern Meguma Terrane. Regional D1 folding with cleavage formation under greenschist – lower amphibolite facies, M1 metamorphic conditions, occurred at ca. 400–410 Ma and was followed by emplacement of a series of granitic stocks ranging in age between ca. 375 and 315 Ma. These were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade. These are locally superposed on M1 regional metamorphic assemblages and result in a complex isograd pattern. 40Ar/39Ar mineral ages suggest episodes of contact metamorphism occurred at (1) 360–375 Ma (possibly related to emplacement of the South Mountain Batholith or temporal equivalents), (2) 350–356 Ma around the Port Mouton Pluton and northeastern Shelburne Pluton, (3) ca. 315–325 Ma near the Wedgeport Pluton and in several other isolated localities, and (4) ca. 287 Ma along the northern margin of a large, low gravity anomaly located off the southwestern coast of Nova Scotia (inferred to reflect a subsurface pluton). Dextral shear deformation was locally associated with all of these thermal events. It is suggested that the Meguma Terrane experienced a similar stress system throughout the Late Devonian – Permian, with shear deformation localized in areas where increased temperatures resulted in decreased viscosity.

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.

Syn-Acadian emplacement model for the South Mountain batholith, Meguma Terrane, Nova Scotia: Magnetic fabric and structural analyses

1997 ◽  
Vol 109 (10) ◽  
pp. 1279-1293 ◽  
Author(s):  
Keith Benn ◽  
Richard J. Horne ◽  
Daniel J. Kontak ◽  
Geoffrey S. Pignotta ◽  
Neil G. Evans
Keyword(s):  
Nova Scotia ◽  
Magnetic Fabric ◽  
The South ◽  
South Mountain Batholith ◽  
Meguma Terrane

scholarly journals Superposed Late Paleozoic thermal events in the southwestern Meguma Terrane, Nova Scotia

10.4138/1648 ◽  
1988 ◽  
Vol 24 (2) ◽  
Author(s):  
R. D. Dallmeyer ◽  
J. D. Keppie
Keyword(s):  
Nova Scotia ◽  
Late Paleozoic ◽  
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.

Rb–Sr age and geochemical distinctions between the Carboniferous tin-bearing Davis Lake complex and the Devonian South Mountain batholith, Meguma Terrane, Nova Scotia

1989 ◽  
Vol 26 (10) ◽  
pp. 2044-2061 ◽  
Author(s):  
Jean M. Richardson ◽  
Keith Bell ◽  
John Blenkinsop ◽  
David H. Watkinson
Keyword(s):  
Nova Scotia ◽  
Trace Element ◽  
Biotite Granite ◽  
Granitic Magma ◽  
Trace Element Geochemistry ◽  
Magmatic Differentiation ◽  
Element Geochemistry ◽  
South Mountain Batholith ◽  
Granitoid Rocks ◽  
Meguma Terrane

The Davis Lake complex (DLC), composed of biotite monzogranite, leucomonzogranite, and cassiterite–topaz greisen, hosts the East Kemptville tin mine in southwestern Nova Scotia. The DLC monzogranite contains glomeroporphyritic biotite with ilmenite and many rare-earth-element (REE) bearing accessory minerals, zircon-bearing quartz phenocrysts, and xenoliths of biotite granite. Primary muscovite is rare. Major- and trace-element geochemical trends indicate well-defined, but limited, magmatic differentiation trends. REE patterns of the least-evolved granites are flat and show a Ce/Yb ratio of 10.The DLC was previously considered cogenetic with the Devonian South Mountain batholith (SMB) on the basis of its location, lithologies, and similarities in major- and trace-element geochemistry. However, new Rb–Sr whole-rock isotopic data indicate an Rb–Sr date of 330 ± 7 Ma (mean square of weighted deviates (MSWD) = 2.8) for the DLC, implying that it is at least 35 Ma younger than the SMB. The initial 87Sr/86Sr ratio of 0.727 ± 0.004 is significantly higher than those for other Meguma Terrane granites and is the highest yet reported from Appalachian granitoid rocks. Rb–Sr data from biotite indicate open-system behaviour between 260 and 240 Ma and provide more evidence for previously documented tectonothermal events after 300 Ma in the Meguma Terrane.The peraluminous nature of the DLC, its high Rb/Sr and high 87Sr/86Sr ratios, high P, F, and Sn contents, low Ca and B contents, and high differentiation indices indicate that the complex was derived from a highly evolved felsic source. Geochemical distinctions indicate that the DLC is neither derived from nor cogenetic with the SMB. A more probable source for the DLC magma is a dehydrated felsic granulite from which a previous H2O-, B-, Cl-, and Zn-rich granitic magma (perhaps the SMB) had been extracted. Such a source is analogous to that postulated for A-type granites and topaz rhyolites.The DLC shows more similarities to the "stitching" Carboniferous Appalachian volatile- and metal-rich granites than to Devonian Meguma granites. Unlike most of these Appalachian plutons, which occur marginal to terrane boundaries and were probably crystallized from locally generated, anatectic magmas, the DLC was emplaced in the centre of the most-outboard Meguma Terrane, adjacent to the Tobiatic shear zone.

The margins of Avalonia

1997 ◽  
Vol 134 (5) ◽  
pp. 627-636 ◽  
Author(s):  
L. R. M. COCKS ◽  
W. S. MCKERROW ◽  
C. R. VAN STAAL
Keyword(s):  
Nova Scotia ◽  
Cape Cod ◽  
The South ◽  
Cape Breton Island ◽  
Northern Margin ◽  
The North ◽  
Southern Margin ◽  
Iapetus Ocean ◽  
History Of ◽  
Meguma Terrane

During Cambrian and earliest Ordovician times, Avalonia was an area forming an integral part of the huge Gondwanan continent, probably along the northern margin of Amazonia, until in early Ordovician (late Arenig or Llanvirn) time it split off from Gondwana, leaving a widening Rheic Ocean to its south. Today, its southern margin with Gondwana extends northeast from east of Cape Cod, Massachusetts, through Nova Scotia north of the Meguma terrane, and thence below sea level to the south of Newfoundland. On the eastern side of the present Atlantic, the southern margin may separate southwest Portugal from the rest of the Iberian Peninsula; it can be traced eastwards with more certainty from the south Cornwall nappes to a line separating the Northern Phyllite Belt (on the southern margin of the Rhenohercynian terrane) and the Mid-German Crystalline High. There is no certain evidence of Avalonian crust to the northeast of the Elbe Line. The northern margin of Avalonia extends westwards from south of Denmark to the British Isles, where it merges with the Iapetus Ocean suture between Scotland and England. Traced westwards, it crosses Ireland and reappears in northern Newfoundland to the east of New World Island, where it may follow the trace of the Dog Bay Line and the Cape Ray Fault. Recent work suggests that the northern margin of Avalonia may clip the northern tip of Cape Breton Island in Nova Scotia, and then enter the North American mainland at the Bay of Chaleur; it may then be traced from north and west of the Popelogan and Bronson Hill arcs to Long Island Sound near Newhaven, Connecticut. The Cambrian to Devonian faunas reflect the history of Avalonia: initially they were purely Gondwanan but, as Ordovician time proceeded, more genera crossed firstly the Tornquist Ocean as it narrowed between Avalonia and Baltica to close in latest Ordovician and early Silurian times, and secondly the Iapetus Ocean, so that by the early Silurian most of the benthic shelly faunas, apart from the ostracods, were the same round the adjacent margins of all three palaeocontinents.

scholarly journals Late Paleozoic motions of the Meguma terrane, Nova Scotia: New paleomagnetic evidence

1984 ◽  
pp. 82-98 ◽  
Author(s):  
Dann J. Spariosu ◽  
Dennis V. Kent ◽  
J. Duncan Keppie
Keyword(s):  
Nova Scotia ◽  
Late Paleozoic ◽  
Meguma Terrane

Thermal history of the southwestern Meguma zone, Nova Scotia, from an 40Ar/39Ar and fission track dating study of intrusive rocks

1987 ◽  
Vol 24 (10) ◽  
pp. 1952-1965 ◽  
Author(s):  
P. H. Reynolds ◽  
P. Elias ◽  
G. K. Muecke ◽  
A. M. Grist
Keyword(s):  
Nova Scotia ◽  
Fission Track ◽  
Southern Region ◽  
Small Areas ◽  
South Mountain Batholith ◽  
Sedimentary Sequences ◽  
The North ◽  
Meguma Terrane ◽  
Fission Track Ages ◽  
Intrusive Activity

Two geologically distinct regions within the Meguma terrane have been studied in detail and are shown to have contrasting thermal histories. This conclusion is based on 31 new 40Ar/39Ar age spectra on micas, K-feldspars, and hornblendes from several of the plutons in southern Nova Scotia, which are satellites to the much larger South Mountain batholith (SMB). In addition, we report four K-feldspar age spectra from a locality in the northeastern part of the SMB and seven fission track ages from both the southern and northern areas.The complex age spectrum of hornblende from a mafic phase associated with the Barrington Passage pluton suggests a minimum intrusive age of 385 Ma, a result consistent with geologic evidence that this pluton represents an early, less evolved magmatic pulse. Later intrusive activity appears to have been coeval with the intrusion of the SMB at ca. 370 Ma ago. In the southern region, argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event. The cumulative geochronologic and geologic evidence constrains this event to 300–320 Ma ago. In the SMB, this Alleghanian/Hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization.K-feldspars from the southern plutons record an episode of argon loss 220–230 Ma ago, which is less evident in the SMB to the north. Upper Triassic dike injection in the southern region, associated with the initial rifting phase of the Canadian Atlantic margin, accompanied this milder thermal pulse.Apatites in the two regions record a mean fission track age of ca. 180 Ma, which we attribute to the final cooling of the terrane below about 100 °C. The timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the Maritime continental shelf.

scholarly journals Stratigraphy and depositional setting of the Silurian-Devonian Rockville Notch Group, Meguma terrane, Nova Scotia, Canada

2017 ◽  
Vol 53 ◽  
pp. 337-365 ◽  
Author(s):  
Chris E. White ◽  
Sandra M. Barr
Keyword(s):  
Nova Scotia ◽  
Volcanic Rocks ◽  
Rock Formation ◽  
Metasedimentary Rocks ◽  
South Mountain Batholith ◽  
Metavolcanic Rocks ◽  
Northwestern Margin ◽  
Meguma Terrane ◽  
Two Stages ◽  
Depositional Setting

 The Silurian–Devonian Rockville Notch Group occurs in five separate areas along the northwestern margin of the Meguma terrane of southern Nova Scotia. In each area, the lowermost unit of the group is the White Rock Formation, which unconformably overlies the Lower Ordovician Halifax Group. Early Silurian U–Pb (zircon) dates from metavolcanic rocks in the White Rock Formation indicate that the unconformity represents a depositional gap of about 25 Ma. The U–Pb ages are consistent with early Silurian (Llandovery) trace fossils and sparse shelly faunas in metasedimentary rocks interlayered with the metavolcanic rocks. The metasedimentary rocks locally contain phosphatic ironstone and Mn-rich beds, and are overlain by mainly metasiltstone with abundant quartzite and metaconglomerate lenses. Some of the latter were previously interpreted to be Ordovician tillite. The White Rock Formation is conformably overlain by the slate- and metasiltstone-dominated Kentville Formation, which contains Upper Wenlock to Pridoli graptolites and microfossils. The overlying Torbrook Formation consists of metalimestone, metasandstone and metasiltstone, interbedded with phosphatic ironstone and minor mafic metatuff, and contains Pridoli to early Emsian fossils. It is in part laterally equivalent to the New Canaan Formation in the Wolfville area, which is dominated by slate, pillowed mafic metavolcanic rocks and fossiliferous metalimestone. Volcanic rocks in the Rockville Notch Group are alkalic and formed in a within-plate setting, probably related to extension as the Meguma terrane rifted from Gondwana. This process may have occurred in two stages, Early Silurian and Early Devonian, separated by a hiatus in volcanic activity. Stratigraphic differences suggest that the Meguma terrane was not adjacent to Avalonia before emplacement of the South Mountain Batholith.

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