Two Rb-Sr Hhole rock isochrons have been obtained from plutons In the Cobequid Highlands of Nova Scotia: the Debert River and Hart Lake-Byers Lake Plutons. The undeformed, unfoilated Debert River Pluton yielded an age of 596± 70 Ma and an Initial 87Sr/88Sr ratio of 0.7059 ± 0.0007. This age places an upper age limit on the detonation recorded In the Folly River Schist (youngest unit of the Bass River Complex), the d I or I tic Frog Lake Pluton, and the sedimentary rocks immediately north and east of the Debert River Pluton.
			
The Hart Lake-Byers Lake Pluton yielded anageof348±5Maandan Initial 87Sr/88Sr ratio of 0.7046 ± 0.0008. The similarity of this age to that of the adjacent felsic volcanics of the Byers Brook For nation suggests that they are comagmatic and confine that a Carboniferous igneous event forms an Important part of the geological history of the Cobequid Highlands. The Initial 87Sr/88Sr ratio and the blotite-hornblende content of the two granites suggest a mafic Igneous loner crustal source or possible untie component for the magma.
			
			R&#xC9;SUM&#xC9;
			Les plutons de Debert River et Hart Lake-Byers Lake dans les monts Cobequld en Nouvel le-&#xC9;cosse ont livre deux isochrones Rb-Sr de roche globale.  Il d&#xE9;form&#xE9; ni fell&#xE9;, le pluton de Debert River a donn&#xE9; un &#xE2;ge de 596± 70 Ma et un rapport 87Sr/88Sr initial de 0.7059 ± 0.0007. Ceci place une limite sup&#xE9;rieure sur l’&#xE2;ge de la d&#xE9;formation enregistr&#xE9;e dans le schiste de Folly River (L’unit&#xE9; la plus jeune du complexe de Bass River), le pluton diorltique de Frog Lake et dans les roches s&#xE9;dimentaires Jouxtant le pluton de Debert River au nord et &#xE0; l’est.
			
Le pluton de Hart Lake-Byers Lake &#xE0; produit un &#xE2;ge de 348 ± 5 Ma et un rapport isotopique 87Sr/88Sr initial de 0.7046 ± 0.008. Cet &#xE2;ge, similaire &#xE0; ceux des volcanites felslques adjacentes de la formation de Byers Brook, sugg&#xE9;re qu'lis sent comagnatiques, signe evident qu'un &#xE9;pisode ign&#xE9; carbonif&#xE8;re forme l’un des faits majeurs de L’histoire g&#xE9;ologique des monts Cobequid. Le rapport 87Sr/88Sr initial et la teneur en blotite et hornbIende de ces deux granites sugg&#xE9;rent une gen&#xE8;se crustale profonde du magma avec une possible contribution mantellique.
					
[Traduit par le journal

Donohoe, H. V.

Halliday, A. N.

Keppie, J. Duncan

English

University of New Brunswick: Centre for Digital Scholarship Journals

Vol. 22Maritime Sediments and Atlantic GeologyAugust, 1986 No. 2Two R b-S r W hole Rock Isochron s  from  P lu to n s  In  th e  Cobequld  H ig h la n d s , Nova S c o t ia ,  CanadaH . V . Do n o h o e * , A.N. Halllday**, J. Duncan Kepple**** ***Department of Mines and Energy, P.0. Box 1087, HalifaxNova Scotia, Canada B3J 2X1 **ScottIsh Universities Research and Reactor Centre East Kilbride, Glasgow, Scotland, Great Britain, G75 OQUTwo Rb-Sr whole rock isochrons have been obtained from plutons in the Cobequid Highlands of Nova Scotia: the Debert River and Hart Lake-Byers Lake Plutons. The undeformed, unfoliated Debert RiverPluton yielded an age of 596 ± 70 Ma and an Initial 87Sr/86Sr ratio of 0.7059 ± 0.0007. This age places an upper age limit on the deformation recorded in the Folly River Schist (youngest unit of the Bass River Complex), the dioritic Frog Lake Pluton, and the sedimentary rocks immediately north and east of the Debert River Pluton.The Hart Lake-Byers Lake Pluton yielded an age of 348 ± 5 Ma and an initial 87Sr/86Sr ratio of 0.7046 ± 0.0008. The simlIiarity of this age to that of the adjacent felslc volcanics of the Byers Brook Formation suggests that they are comagmatlc and confirms that a Carboniferous igreous event forms an important part of the geological history of the Cobequid Highlands. The initial 87Sr/86Sr ratio and the biotlte-hornblende content of the two granites suggest a mafic igneous lower crustal source or possible mantle component for the magma.Les plutons de Debert River et Hart Lake-Byers Lake dans Ies monts Cobequid en Nouvelle-Ecosse ont llvrd deux isochrones Rb-Sr de roche globale. Ni d6form6 nI foIi6, le pluton de Debert River a donnd un 3ge de 596 ± 70 Ma et un rapport 87Sr/86Sr initial de 0.7059 ± 0.0007. Cecl place une llmite supdrleure sur l'8ge de la reformation enreglstrde dans le schists de Folly River (I'unitd la plus Jeune du compiexe de Bass River), le pluton dioritique de Frog Lake et dans les roches s6dImental res Jouxtant le pluton de Debert River au nord et a I'est.Le pluton de Hart Lake-Byers Lake a produit un age de 348 ± 5 Ma et in rapport isotopique 87Sr/88Sr initial de 0.7046 ± 0.008. Cet age, similalre a ceux des volcanites felsiques adjacentes de la formation de Byers Brook, suggSre qu'ils sont comagmatlques, signs evident qu'un episode IgnS carbon if6re forme I'un des fa its majeurs de I'hlstoire gbologlque des monts Cobequid. Le rapport 87Sr/88Sr initial et la teneur en blotite et hornblende de ces deux granites suggdrent une genSse crustale profonde du magma avec une possible contribution mantel IIque.INTRODUCTIONIn this study, two plutons In the Cobequid Highlands, the Debert River Pluton and the Hart Lake-Byers Lake Pluton were chosen for Rb-Sr Isotopic analysis (Fig. 1). These plutons and the geology of the Cobequid Highlands have been described by Donohoe andMARITIME SEDIMENTS AND ATLANTIC GEOLOGY 22, 148-154 (1986)0711-1150/86/020148-7$2.05/0Wallace (1980, 1982, 1985). The agedates allow limits to be set upon the ages of various sedimentary and volcanic units and deformat Iona I events. They also provide better definition of the ages of plutonlc events and the origin of the magma.TECHNIQUESRb-Sr isotopic analysis were per­formed at the Scottish UniversitiesLATE TRIASSICWOLFVILLE FORMATION: red, beigesandstone19LATE CARBONIFEROUSundifferentiated CANSO, RIVERSDALE, CUMBERLAND, and PICTOU GROUPS: sandstone, siltstone, conglomerate, coalEARLY CARBONIFEROUSFALLS FORMATION: red conglomerate,sandstonegranitedioriteWINDSOR GROUP: siltstoneNUTTBY FORMATION: red, grey sandstone,siltstoneMIDDLE DEVONIAN TO EARLY CARBONIFEROUS FOUNTAIN LAKE GROUP(13) undifferentiated FOUNTAIN LAKE GROUP: mafic and felsic volcanic rocks (12) DIAMOND BROOK FORMATION: basalt flows; red siltstones, sandstones;(11) BYERS BROOK FORMATION: felsic ignimbrites, ash falls;12SILURIANundifferentiated WILSON BROOK and EARLTOWN FORMATIONS: grey sandstone siltstone;felsic volcanic rocksMIDDLE TO LATE ORDOVICIANunnamed green volcaniclastic rocksLATE HADRYNIAN (TO EARLY CAMBRIAN)(6) WARWICK MOUNTAIN FORMATION:I mafic meta-volcanic rocks I (5) unnamed red, grey siltstones, sandstones--- 1 (8) granite toS granodiorite '(7) dioriteEARLY HADRYNIAN OR OLDERBASS RIVER COMPLEX(3) FOLLY RIVER SCHIST: green maficmeta-volcanic rocks(2) GAMBLE BROOK SCHIST: quartzite,biotite schist(1) GREAT VILLAGE RIVER GNEISS: grey, white orthogneisses; paragneissgranite gneissFigure 1. Geological map of the Cobequid Highlands (modified from Donohoe and Wallace, 1980) with sample locations.TV 13 30HONOQM A R IT IM E  SEDIMENTS AND A TLA N TIC  GEOLOGY 150Research and Reactor Centre using stan­dard techniques described in detail elsewhere C Ha 11i day ai at.. 1979,1983). Sample powders spiked with 87Rb and 84Sr enriched isotopic tracers were dissolved using HF, HNO3 and HC1 acids. Rb and Sr were separated using conven­tional cation exchange resins. Isotopic analyses were performed on a fully automated V.G. Isomass 54E mass spectrometer. Ratios of 87Sr/88Sr are reported normalized to 88Sr/88Sr 8.37521. The average 87Sr/86Sr for NBS987 on this machine was 0.71027±1 (2a mean, N»79) at the time of analysis. Regression followed the method of York (1969). The decay con­stant for 87Rb used is 1.42x10-11y“ 1 • The uncertainty in 87Rb/88Sr Is estimated to be ±1 .0% (2a).DEBERT RIVER PLUTONThe Debert River Pluton is located in the Bass Terrane (Keppie, 1982) between the Cobequid and Rockland Brook Faults (Fig. 1). On Its west side, it is intrusive Into the Folly River Schist which forms the upper part of the Bass River Complex. A minimum age for the Bass River Complex of 642 ± 15 Ma is provided by preliminary Rb-Sr data from granite gneisses intruding the Bass River Complex (Gaudette et a I.. 1983, 1984). On its east side,the pluton Intruded and contact meta­morphosed sedimentary rocks which have been correlated Iithostratigraphleally with the Devono-Carboniferous Nuttby Formation by Donohoe and Wallace (1980, 1982). To the south, it intruded the undated Frog Lake dioritic pluton. The undated Gain Brook Pluton intruded the Debert River Pluton along its northern margin.The Debert River Pluton is a fresh, light grey to pale tan grey, medium to coarse grained,hypldiomorphic granular monzogranite to granodlor Ite. It consists ofoligoclase (40-55%), quartz (20-30%), potassium-feldspar (5-30%), accessory biotite and hornblende, and traces of sphene, zircon, epldote and opaques.The pluton is not foliated although local shear zones are present. The pluton contains foliated xenoliths of green, metavolcanlc rocks and quartz- biotite schist derived from the Folly River Schist and the Gamble Brook Schist respectively, both units of the Precambrian Bass River Complex. It also contains xenoliths of other Plutonic rocks such as biotite monzogranite, biotite granodiorite and dior ite.Seven whole rock samples of the Debert River Pluton were analyzed for Rb-Sr and the results are given in Table 1 and plotted on a conventional isochron diagram In Figure 2. The data scatter about a best fit line corresponding to an age of 596 Ma. The "scatter error" (York, 1969) for this determination is ± 70 Ma (2a). The initial 87Sr/88Sr so determined is 0.7059 ± 7 (2a) (MSWD - 82).The age of 596 ± 70 Ma is consistent with all the geological constraints described above except for its intrusive relationship with sedimentary rocks previously correlated with the Devono-CarbonIferous Nuttby Formation (Donohoe and Wallace, 1980; 1982). These new data Indicate that these sedimentary rocks are not correlatives of the Nuttby Formation. They may be correlatives of the (?)Late Precambrian Warwick Mountain Formation and/or Jeffers Formation, which implies that a discontinuity is present between these rocks and the dated Nuttby Formation (Fig. 1). However, the age error limits also allow the possibility that the intruded sedimentary rocks could be Cambrian in age.The age of the Debert River Pluton agrees with the 575 ± 22 Ma age of the McCallum Settlement granite pluton (Gaudette el al.. 1983, 1984) which Is located Just to the east (Fig. 1). The Intrusive contact of the undeformed Debert River Pluton with the dlorltlc Frog Lake Pluton Indicates an older episode of dioritic plutonism. Elsewhere In the Cobequid Highlands this episode is represented by the Jeffers Brook DiorIte (K-Ar on biotite:151 DONOHOE ET ALTable 1. Analytleal and stat 1st leal data for the Debert River Pluton.Letter Sample Rb Sr Rb/Sr 87Sr/86Sr 87Sr/86Sr ± 2 aM *on Fig. 1 Number (ppm) (ppm) (Weight) (atomic) (atomic)A JS75-46 91.00 190.4 0.4779 1.384 0.71733 + 3B E11-4569 46.09 321 .4 0.1434 0.4150 0.70931 ± 3c E11-4570 66.12 294.2 0.2247 0.6504 0.71195 ± 6D E11-4571 52.94 190.4 0.2781 0.8050 0.71309 ± 3E E11-4573 75.42 248.2 0.3039 0.8796 0.71326 ± 3F E11-4574 85.37 238.1 0.3586 1 .038 0.71454 ± 4*2aM - two standard errors of the meanAge t 20 a priori (scatter error) Ma - 596 ± 7 (70) Ma(87Sr/86Sr) initial i 20 a priori (scatter error) - 0.70593 ± 9 (73)SUMS - 326 (SUMS - sum of the squares of the residuals)MSWD - 81.6 (MSWD - mean squared weighted deviates)Figure 2. Rb-Sr whole rock isochron for the Debert River pluton.544 ± 22 Ma, 564 ± 22 Ma, 585 ± 23 Ma; and K-Ar on hornblende, 616 ± 28 Ma and 628 ± 28 Ma; Wanless fii a I.. 1973,recalculated by Kepple and Smith, 1978, using the decay constants proposed by Steiger and Jager, 1977; and a Rb-Sr blotlte Isochron, 541 ± 25 Ma, Cormier, 1979, using 1.42 x 10-11y-1 for the 87Rb decay constant).The initial 87Sr/86Sr ratio of0.7059 ± 0.0007 indicates that themagma had a crustal component. The mafic mineralogy suggests that the Debert River Pluton has an l-type nature and therefore that the source may have been mafic and igneous. A mantle-derived component could also be involved but its significance cannot be assessed without knowing the exact nature of the lower crust and a more complete petrologic study of the pluton.HART LAKE-BYERS LAKE PLUTONThis granitoid pluton occurs in the Cobequid Terrane (Kepple, 1982) lying north of the Rockland Brook Fault (Fig. 1). It has intruded and contact metamorphosed the fossiI Iferous Silurian Wilson Brook Formation and the Devono-Carboniferous Byers Brook Formation (Donohoe and Wallace, 1982) along Its northeastern contact. Felsic volcanic rocks of the Byers Brook Formation have recently yielded a whole rock Rb-Sr isochron age of 341 ± 4 Ma (Cormier, 1982). The Hart Lake-Byers Lake Pluton is also intrusive into the diorltlc Folly Lake Pluton to the southwest. It is cut and my Ion I zed by lateral movement on the Rockland Brook Fault to the south and unconformably overlain by Late Carboniferous rocks to the north.The Hart Lake-Byers Lake Pluton isM A R IT IM E  SEDIMENTS AND A TLA N TIC  GEOLOGY 152a pale pink, hypldlomorphic granular, occasionally porphyrltic, hornblende biotlte syenogranite to alkali feldspar granite. It consists of potassium- feldspar (35-50%), quartz (20-35%), alblte-olIgoclase (10-15%), hornblende (5-10%) and traces of biotlte, riebecklte, fluorite, sphene, zircon, apatite, a I Ian Ite and opaques. No internal fo11 at ion was observed.Rb-Sr Isotopic analyses of eight whole rock samples from the Hart Lake- Byers Lake pluton are given in Table 2 and plotted in Figure 3. All eightsamples define a reasonable linear array but sample JS76-57 plots slightly further off than the others. A best fit line for all eight samples gives an age of 355 ± 18 Ma (MSWD - 91) and exclusion of sample JS76-57 yields a better fit corresponding to an age of 348 ± 5 Ma with an initial 87Sr/88Sr of0.7046 ± 8 (MSWD - 5.8). We accept the latter as the best estimate of the age of the pluton.The Hart Lake and Byers Lake Plutons were previously dated by Cormier (1979), using Rb-Sr techniques,Table 2. Analytical and statistical data for the Hart Lake-Byers Lake PlutonNumber (on Fig. 1)Samp Ie NumberRb(ppm)Sr(ppm)Rb/Sr(Weight)87Rb/86Sr(atomic)87Sr/88Sr ± (atomic)20M *1 JS75-22 308.7 129.8 2.378 6.900 0.73831 ± 302 JS75-23 286.4 19.78 14.48 42.75 0.91707 + 33 JS75-32 161.8 22.71 7.122 20.80 0.80524 ± 64 JS75-33 207.9 113.0 1 .840 5.335 0.73117 + 35 JS75-37 191.8 9.811 19.55 58.15 0.99391 ± 166 JS75-57 225.5 35.85 6.291 18.38 0.80684 ± 37 JS75-58 166.1 14.33 11.59 34.08 0.87452 ± 38 JS75-59 234.6 23.36 10.04 29.46 0.85036 ± 42+ JS75-23 293 20.1 14.58 43.0 0.91275+ JS75-37 195 12.6 15.48 45.6 0.9179*2o m  - two standard errors of +Data from Cormier (1979) calculations In this paper)the mean for compar Ison (these data are not used In ageSuitesAge ± 20 a.p. (87Sr/86Sr)|N1 (s.e) (Ma)2 ± 20 a.p.(s.e)2 SUMS3 MSWD4Hart Lake Byers Lake8 355 ± (± 18)2 0 .70419 ± 32 (± 306)546 91ditto minus 76 - 57 7 348 ±  ( ±  5)2 0..70457 ±  30 ( ±  76)29 5.81. N -  number of samples used In calculations of age 87Sr/86Sr2. ±  2 0 a.p. (s.e.) -  ±  two standard errors a priori3. SUMS -  sum of the squares of the residuals4. MSWD «  mean squared weighted deviatesand intlal (scatter error)153 DONOHOE ET ALand yielded results of 331 ± 17 Ma (Initial 87Sr/86Sr ratio- 0.7076 ± 0.0096) and 331 ± 27 Ma (initial 87Sr/88Sr ratio - 0.7097 ± 0.0093), respectively. The errors were sufficiently large that is was impossible to determine whether the plutonism correlates with the widespread Late Devonian (375-360 Ma) granitoid plutonism in the Meguma Terrane of Nova Scotia (Clarice and Halllday, 1980), or represents a later Carboniferous thermal event. The result from the present study (348 ± 5 Ma) suggests that the plutonism is part of a Carboniferous event.The sample suite for this study Includes two samples previously analyzed by Cormier (1979) whose results are Included In Table 2 for comparison. Discrepancy between the two laboratories for sample JS75-23 Is only 0.6% but Is larger for the other sample (JS75-37) (8% for 87Sr/86Sr, and 25% for 87Rb/86Sr). Analysis of a standard (NBS987) along with these samples at the Scottish Universities Research and Reactor Centre Indicates an analytical uncertainty of ± 0.1% (a) for 87Rb/86Sr in this laboratory. Cormier (1979) does not report analysesof a standard run along with his samples so it is impossible to assess the source of the large discrepancies. Two possibilities are inaccurate analyses by Cormier (1979) or inhomogeneity in sample JS75-37. The fact that the ages and initial ratios derived from the two laboratories agrees within the reported errors may suggest than the latter possibility Is more I ikely.The 348 i 5 Ma age of the Hart Lake-Byers Lake Fluton is similar to the age of 339 + 4 Ma obtained from granitoid rocks in drill core just north of the Hart Lake-Byers Lake Pluton (Cormier, written communication, 1984). Furthermore, the similar ages of the Hart Lake-Byers Lake Pluton and the Juxtaposed felslc volcanics of the Byers Brook Formation (341 ± 4 Ma, Cormier, 1982; and 343 ± 5 Ma, Cormier, written communication, 1984) suggests that they are comagmatlc.The low Initial 87Sr/88Sr ratio of 0.7047  ^ 0.0010 suggests a possible lower crustal or mantle source for the magma. More detailed petrologic studies of the Plutonic and volcanic rocks are necessary In order to Interpret their petrogenesls.154M A R IT IM E  SEDIMENTS AND A TLA N TIC  GEOLOGYCONCLUSIONSThe 596 ± 70 Ma age of the Debert River Pluton Indicates that LatePrecambrlan-Cambrlan plutonism was more widespread In the Cobequid Highlands than formerly known (Donohoe and Wallace, 1980; 1982). It places anupper limit on the age of the rocks It Intrudes and on the age of deformation observed In the Bass River Complex. In contrast, the 348 ± 5 Ma age of the Hart Lake-Byers Lake Pluton clearly documents the existence of Carboniferous plutonism in theCobequid Highlands which corroborates the 339 ± 22 Ma age for the CapeChlgnecto pluton in the western Cobequid Highlands (Cormier, 1979). This Carboniferous plutonism wassynchronous with adjacent felslc voI can ism suggesting that they are comagmatIc.ACKNOWLEDGMENTSThe authors would like to thank Drs. P.S. Giles, R.F. Cormier and H.E. Gaudette for critically reviewing the manuscript, S. Saunders and B. MacDonald for typing the paper and Nova Scotia Department of Mines and Energy draftsmen for drafting the figures.CLARKE, D.B. and HALL IDAY, A.N. 1980. Strontium isotope geology of the South Mouitain Batholith, Nova Scotia. Geochlmica et Cosmochimica Acta, 44, pp. 1045-1058. CORMIER, R.F. 1979. Ribidlum/Strontlim isochron ages of Nova Scotia granitoid plutons. Nova Scotia Department of Mines Report 79-1, pp. 143-148.CORMIER, R.F. 1982. Rb/Sr age data for the Fountain Lake Group volcanics. Nova Scotia Department of Mines and Energy Report 82-1, pp. 114-115.DONOHOE, H.V., JR. and WALLACE, P.I. 1980. Structure and stratigraphy of the Cobequid Highlands, Nova Scotia; Geological Association of Canada-Mlneraloglcal Association of Canada, Halifax '80, Field Guide to Trip 19, 64 p.DONOHOE, H.V., JR. and WALLACE, P.I. 1982. Geological Map of the Cobequid Highlands, Nova Scotia. Scale 1:50,000. Halifax, Nova Scotia, Canada.DONOHOE, H.V., JR. and WALLACE, P.l. 1985. Repeated orogeny, faulting, and stratigraphy In the Cobequid Highlands, Avalon Terrane of North-western Nova Scotia;Field Excursion 3. Geological Association of Canada/Mineraloglcal Association of Canadian Annual Meeting, university of New Brunswick, Fredericton, New Brunswick, 77 p.GAUDETTE, H.E., OLSZEWSKI, W.J., JR. and DONOHOE, H.V., JR. 1983. Age and origin of basement rocks, Cobequid Highlands, Nova Scotia. Geological Society of America Abstracts with Programs 15, p. 138.GAUDETTE, H.E., OLSZEWSKI, W.J., JR., and DONOHOE, H.V., JR. 1984. Rb/Sr isochrons of Precambrian age from Plutonic rocks In the Cobequid Highlands, Nova Scotia. Jn Mines and Minerals Branch Report of Activities 1983, Nova Scotia Department of Mines and Energy Report 84-1, pp. 285-292.HALL IDAY, A.N., AFTALION, M., VAN BREEMEN, 0. and JOCELYN, J. 1979. Petrogenetic significance of Rb-Sr and U-Pb isotope systems In the c.400 Ma old British Isles granitoids and the hosts. Jn Harris, H.L., Holland, C.H. and Leake, B.E. (Editors). TheCaledon ides of the British Isles - reviewed. Special Publication of the Geological Society of London, pp. 653-661.HALL IDAY, A.N., FALLICK, A.E., DICKIN, A.P., MACKENZIE, A.B., STEPHENS, W.E. and HILDRETH, W. 1983. Theisotopic and chemical evolution of Mount St. Helens. Earth and Planetary Science Letters, 63, pp. 241-256.KEPPIE, J.D. 1982. Tectonic Map of Nova Scotia. Scale 1:500,000. Nova Scotia Department of Mines and Energy, Halifax, Nova Scotia, Canada.KEPPIE, J.D. and SMITH, P.K. 1978. Compilation of isotopic age data of Nova Scotia. Nova Scotia Department of Mines and Energy Report 78-4.STEIGER, R.H. and JAGER, E. 1977. Subcommission on geochronology: convention on the use of decay constants in geo- and cosmochronology; Earth and Planetary Science Letters, 36, pp. 359-362.WANLESS, R.K., STEVENS, R.D., LACHANGE, G.R., and DELABI0, R.N. 1973. Age determinations and geological studies: Geological Survey of Canada Paper 73-2, 139 p.YORK, D. 1969. Least squares fitting of a straight line with correlated errors. Earth and Planetary Science Letters, 5, pp. 320-324.

Two Rb-Sr Whole Rock Isochrons from Plutons In the Cobequid Highlands, Nova Scotia, Canada

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Two Rb-Sr Whole Rock Isochrons from Plutons In the Cobequid Highlands, Nova Scotia, Canada

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