Electron-probe studies of the earlier pyroxenes and olivines from the Skaergaard intrusion, East Greenland

Hypersthene-ilmenite(/magnetite) symplectites in coronitic olivine-gabbronorites

“…In crystal portions which are .optically homogeneous, without exsolutions, by repeated point analysis, and i~ crystal portions showing exsolutions by a moving defocussed beam giving an integrated composition of matrix and exsolved augite. Both methods give very similar results with an average of Wo,~ ~En57 tFs33.t,, which conforms very well to the compositions reported by Nwe (1976) f~::~r the Skaergaard gabbro (Fig. 3).…”

“…The Ca-rich pyroxene composition has been determined with a moving defoeussed beam giving a composition of approximately Wo35.lEn44.3Fs20.~, in san lple 742:59, and Wo35.gEn45.0Fs19.1 in 75Z1C,9. These compositions are somewhat Ca-poorer than those reported by Nwe (1976) for the Skaergaard gabbro. The tie-line between the main magmatic Ca-rich and Ca-poor pyroxenes for sample 74Z54 conforms to those given by Nwe (1976), but that for sample 75Z109 is less steep (see Fig.…”

“…These compositions are somewhat Ca-poorer than those reported by Nwe (1976) for the Skaergaard gabbro. The tie-line between the main magmatic Ca-rich and Ca-poor pyroxenes for sample 74Z54 conforms to those given by Nwe (1976), but that for sample 75Z109 is less steep (see Fig. 3).…”

Evidence of mingling between contrasting magmas in a deep plutonic environment: the example of Várzea Alegre, in the Ribeira Mobile Belt, Espírito Santo, Brazil

“…These trends are close to the sub-solidus trend from Skaergaard CPX-crystals (Brown & Vincent 1963, Nwe 1970. Analytical scanning of several CPX exsolution lamellae in OPX-grains and individual CPXgrains of OPX-gabbros points towards a second variation trend, from salite to sub-calcic augite.…”

Complex Pyroxene Assemblages of Proterozoic Dolerites, S.E. Greenland

“…Greenland have been described in a previous report (Hall et al, 1986). Although the successive generations of these dykes are progressively Ferich, their pyroxenes do not show a simple sequential Fe-enrichment trend, such as that defined by successively differentiated units of layered intrusions and typified by the Skaergaard pyroxene evolution trend (Wager and Brown, 1968;Nwe, 1976). Although there is a slight shift in average pyroxene composition from one generation of dykes to another (Hall et aI., 1985), this is very largely outweighed by the extremely wide ranges of pyroxenes occurring in individual dyke samples.…”