Abstracts
Abstract
The New Cornwall syenogranite is a 1.7 km2 intrusion at the southern margin of the Whale Lake mon7ogranitc of the South Mountain Batholilh of southwestern Nova Scotia- It has a mean SiO> content of 75 8%, and contains accessory amounts of tourmaline, andalusite, and primary muscovitc. Ratios such as A-'CNK (- 1.25). Rb/K (-215), and NbH'a (- 3.5) show that the syenogranitc is not highly fractionated. Although binary clement plots for some elements show the same regular trend for both monzogranite and syenogranite, variations in trace elements such as Rb, Ha, Th and LRI'E show that the syenogranite is not derived from the monzogranite by fractional crystalli7ation, as the syenogranite has lower Eu and HREE compared with the monzogranite. Similarities in LREI', Nd isotope composition (eNJ - -2) and other geochemical indicators between monzogranite and syenogranitc suggest that they were derived by partial melting of a common source Both the Whale Lake monzogranite and the New Cornwall syenogranite then evolved independently by fractional crystallization and late fluids played only a minor role in the further evolution of the syenogranitc. This represents a third mode of development of mineralized Icucogranitc m the South Mountain Batholith, in addition to the previously recognized "associated" and "independent" Icucogranitc
RESUME
Lc syenogranitc de New Cornwall constituc une intrusion de 1.7 kilometre carre" sur la limitc meridionale du granite monzonitique du lac Whale, lequcl fait panic du batholithe du mont South, dans lc sud-oucst dc la Nouvclle-Fcossc. II a une tcneur moyenne en Si02 de Ti.8 %, et renferme dcs quantitcs accessoires dc tourmaline, d'andalousite ct de muscovitc primairc. Lcs rapports d'A/CNK (- 1,25), de Rb'K (- 215) et dc Nb-Ta (- 3,5) revclcnt que le syenogranite n'est pas extrcmement fractionnc. Memc si lcs rcprcsenlaiions graphiqucs dcs elements binaires dc certains elements rcvclent la memc tendance reguliere dans le cas du granite mon/onitique ct du syenogranitc, lcs variations dcs elements traces commc lc Rb, lc Ba, lc Th ct les elements de terrcs rates legers signalcnt que le syenogranite nc provicnl pas du granite monzonitique par cristallisation fractionnairc, car lc syenogranitc possede dcs tencurs moindres en Fu ct en elements de terres rares lourds comparativement au granite mon/onitique Lcs similantes cxistantes en ce qui conccme les elements de terrcs rares legers, la composition en isotopes de Nd (i:»,j - -2) et d'autres mdicatcurs geochimiques entrc lc granite mon/onitique ct lc syenogranitc pcrmettent dc supposer qu'ils provienncnt d'unc fontc particlle d'unc source commune. Lc granite monzonitique du lac Whale ct le syenogranite dc New Cornwall ont ensuitc tous deux cvolue independamment par cristallisation fractionnairc et lcs fluidcs tardifs ont seulcment jouc un role secondaire dans ('evolution ultcneure du syenogranite. 11 s'agit la d'un troisieme mode dc developpemcnt du leucogranitc mineralise dans lc batholithe du mont South, qui s'ajoute aux leucogranites assoacs » et < independants » deja rcconnus
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