TRANSPORT RATE OF MAGMATIC EPIDOTE AND 40AR/39AR AGE OF GRANITOIDS FROM NE BRAZIL

Magmatic epidote-bearing granitoids (mEpG) are known from five terranes in the Borborema province, NE Brazil. They are calc-alkalic, high K calc-alkalic, shoshonitic to trondhjemitic plutons mostly emplaced at 630-650Ma, showing εNd = -1 to -4 and TDM between 1.1 and 1.4 Ga. Plutons with similar petrological/geochemical features, emplaced at 590-570Ma, are mEp-free. ⁴⁰Ar/³⁹Ar analysis of coexisting bi and hbl from high K-calc alkalic plutons reveals that hbl from the Brejinho pluton is significantly older (572 ± 2 Ma) than bi, which is 509.6 ± 1.1 Ma old, while in the Tavares pluton, hbl is 604 ± 7Ma old and bi is 538.1 ± 1.6Ma. These data suggest that these two plutons solidified at relatively great depth and remained at depth for long period of time. Hbl from a calc-alkalic pluton yielded age of 618.8 ± 2.7 Ma and bi 603.8 ± 1.7Ma (Dallmeyer et al., 1987). Hbl from a mEp-free calc-alkalic pluton yields an age of 613.3 ± 2.0 Ma and bi, an age of 608.7 ± 1.7Ma, suggesting rapid cooling at ca. 610-615 Ma. Al-in-hbl barometry indicates that hbl in mEpG solidified at 5 to 7 Kbar (3-4 Kbar outside the Transversal Domain). When in contact with mc, mEp is less corroded than when in contact with/hosted by plag. In a pluton of the Seridó terrane, mEp was transported upward at ~1200m.year-1 with avg. dissolution time of ~15 years. In the Cachoeirinha terrane, mEp underwent corrosion during 15-35 years and has been transported upward at 450-1300 m.year-1, whereas in six plutons in the Alto Pajeú terrane rates of upward migration were 650-1050 m.year-1 and time of dissolution, 10-25 years. In a pluton of the Macururé terrane, mEp was transported at ~1800m.year-1 with shorter dissolution time (~10 years). Plutons display shape suggesting transport by dikes or products of inflation, at lower pressure, of dike-transported magmas.

REFERENCES Dallmeyer, D.R., Sial, A.N., Long, L.E., and McMurry, J., 1987. GSA Ann. Meeting, Phoenix, Arizona: 634.