Granitic rocks comprising the eastern half of the main batholith of southwestern Nova Scotia have been studied. The granitic rocks intrude Lower Paleozoic metasediments of the Meguma Group. Field work, the chemistry and petrology of the granitic rocks, and Rb–Sr whole-rock isochron dates indicate that there were at least two episodes of granite emplacement, the earlier about 415 m.y. ago and the later about 350 m.y. ago. Samples from a much smaller pluton some 65 mi (104 km) away from the study area were also dated and are correlated with rocks in the main batholith.
Zircons from biotite monzogranite of the Wedgeport Pluton, intrusive into deformed metasediments of the Cambrian(?) Goldenville Formation in the southwestern Meguma Tenane of Nova Scotia, yield concordant U-Pb ages of 316 + 5 Ma. This is interpreted as the time of intrusion and crystallization. Within the error limits, the 323 f 12 Ma Rb-Sr whole-rock isochron age is identical and gives an initial 87Sr/86Sr ratio of 0.7137 f 0.0056. Rb-Sr analyses of mineral separates of biotite, potassium feldspar, and quartz -plagioclase from several samples yield subparallel, internal isochrons with an average age of 257 f 8 Ma. Initial ratios of the internal isochrons range from 0.716 to 0.759. A slow-cooling model for these latter data is discarded because the mineral data fall on straight lines. Instead, a reheating event related to plutonism ca. 257 Ma ago, which was sufficient to cause local grain-to-grain migration and reequilibration of strontium and rubidium but not large-scale redistribution, is invoked. This reheating is also inferred to be responsible for the hydrothermal alteration and Sn-U mineralization concentrated along the northwestern margin of the pluton. A dextral northeast-southeast shear zone cutting the pluton is also inferred to be ca. 257 Ma old. It may be related to the last stages of westward obduction of the Meguma Terrane.These results provide a clear example of Permo-Carboniferous plutonism in the southwestern Meguma Terrane and suggest a similar interpretation may apply to other anomalously young ages recorded in this area. In light of these results, the Permo-Carboniferous age of the large East Kemptville tin deposit and its location in a dextral shear zone suggest that the association of younger plutonism and shear zones may be a significant factor for economic mineralization.Les zircons d'un monzogranite ii biotite du pluton de Wedgeport, lequel recoupe les m6tas6dim~nts d6formts de la Formation de Goldenville du Cambrien(?), dans la partie sud-ouest du tenane de Meguma, en Nouvelle-Ecosse, fournissent des Lges U -Pb concordants de 316 f 5 Ma. Cette date est considtke comme indiquant le moment de la mise en place de l'intrusion et de la cristallisation. En considkrant les limites d'erreur, on peut affirmer que 1' Age isochrone de 323 f 12 Ma obtenu par la m6thode Rb-Sr sur roche totale est identique, et le rapport initial B7Sr/86Sr est de 0,7137 f 0,0056. Les analyses Rb-Sr de concentks de biotite, feldspath potassique et quartz -plagioclase provenant de plusieurs tchantillons fournissent des courbes isochrones internes subpalalleles avec un Lge moyen de 257 f 8 Ma. Les rapports initiaux de ces isochrones internes varient de 0,716 0,759. Le modtle d'un refroissement lent pour expliquer ces derniers ksultats ne peut &re applique car les d6terminations B partir de ces mintraux tombent sur des lignes droites. I1 faut plut6t faire appel ? i un tv6nement de kchauffement associt au plutonisme apparu il y a environ 257 Ma et suffisant pour produire une migration grain-a-grain et une d6quilibration du...
Deformed strata, of early Devonian age in southwestern New Brunswick and adjacent Maine are intruded by the post-orogenic St. George pluton and simiZnr intnisions in Maine. A Rb-ST whole-rock isochron age of 394 2 20 m.y. obtained from lhe St. George pEuton defines an Early Devonian age for the pluton. The 8ge of this post-orogenic intrusive event is supported by other radiometric dates. Therefore, the Acadian deformation in this area occurred in Early Devonian time. --Des couches dCformees du DCvonien inferieur dans le sud-ouest du Nouveau-Brunswick et I'adjacent Maine sont pCnCtrCes par le pluton post-orogknique de St. Georges et par d'autres intrusions similaires dans le Maine. Un isochrone PgC de 394 f 20 m.y. de Rb-Sr sur la roche totale du pluton St. Georges nous donne 1'Pge du Devonien infkrieur. L'Pge de cette intrusion post-orogknique est soutenu par d'autres datations radiomttriques. Donc, la deformation Acadienne dans cette region est survenue au temps du DCvonien ~nferieur.[Traduit par le journal]
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