Genesis of monzonoritic rocks in the Rogaland anorthositic Province (S. W. Norway)

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6610912

Demaiffe, D; Duchesne, J C; Hertogen, J; Weis, D

Monzonoritic rocks (=jotunites) related to late-Proterozoic massif type anorthosites in the Rogaland province (S.W.Norway) appear (i) as fine grained dykes crosscutting the large anorthositic bodies, (ii) as chilled margins related to leuconorites-norites (Hidra, Garsaknatt, Bjerkrem-Sokndal), (iii) as separated intrusions (Eia-Rekefjord, Apophysis) emplaced in the contact zones between the anorthosites and the metamorphic envelope or between two anorthositic bodies. The monzonorites show high Fe, Ti and P contents, rather low SiO/sub 2/. From occurrence to occurrence, they have variable Fe/Mg ratios, similar LREE enriched trends (La/Yb approx. = 7) with no Eu anomaly, low LIL (Rb, Th, U,...) contents and variable (0.705 to 0.708) /sup 87/Sr//sup 86/Sr isotopic ratios; the rather unradiogenic Pb isotopic composition point to an U depleted source region. These geochemical features preclude both direct derivation from the mantle and comagmatic relationships with the massif-type anorthosites. The data suggest an origin for the monzonorites by a partial melting of LIL depleted mafic material in the lower crust or contamination of a mantle derived magma by a deep crustal component, the necessary heat being provided by the high T/sup 0/ anorthositic diapirs.

• Research Organization: Univ. Libre de Bruxelles, (Belgium)
• OSTI ID: 6610912
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

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