INSIGHTS INTO TECTONOSTRATIGRAPHIC ZONE IDENTIFICATION IN SOUTHWESTERN NEWFOUNDLAND BASED ON ISOTOPIC (ND, O, PB) AND GEOCHEMICAL DATA

Plutonic and supracrustal rocks sampled from various tectonostratigrap hic divisions in southwestern Newfoundland exhibit a large range in Si O2 (49 to 77 wt.%), K2O (0.9 to 4.2 wt.%), epsilon(Nd) (T) (-9.2 to +8 .1), delta(18)O (+6.3 to +12.7 parts per thousand), and Pb isotopic ra tios. In general, isotopic plus geochemical data are either compatible with, or substantiate, structurally and lithologically based correlat ions between southwestern Newfoundland and the Central Mobile Belt fat her north. Such data can thus represent a robust terrane identificatio n tool in highly telescoped or segmented portions of orogenic belts, s uch as southwestern Newfoundland, and can also provide significant ins ights into orogen evolution. For example, the Port aux Basques granite (tonalite), which is characterized by MORE-like epsilon(Nd) (+8.1) an d delta(18)O (+7.5 parts per thousand) and radiogenic Pb (Pb-207/Pb-20 4 = 15.818), is interpreted as a Late Ordovician partial-melt of a juv enile source added to the Gander Zone during Early Ordovician opening of the Exploits back-are basin. Strongly negative epsilon(Nd) (T), man tle-like delta(18)O, variable Pb isotopic ratios and metaluminous char acteristics of Ordovician plutonism in the Notre Dame are suggest deri vation from Paleoproterozoic or older infracrustal sources. The data i ndicate formation in an Andean-type continental are formed on the edge of the Laurentian margin.