PRECAMBRIAN GREENSTONE BELTS AS DIFFERENT OPHIOLITE TYPES

Phanerozoic ophiolites can be linked to subduction-related and –unrelated settings. Ophiolites generated in these environments represent two main types that can be subdivided further into several subtypes that exhibit different crustal construction, and in which a sheeted dike complex may or may not be developed [1]. The geochemistry of the metabasalt of lavas and/or dikes from the two main ophiolite types show pronounced differences in the concentration of elements that are sensitive to subduction processes, i.e. Cs, Pb, Rb, K, Ba, Th, U and LREE, and thus define contrasting patterns with respect to element-element -, element ratio -, and multi-element diagrams. We apply this geological and geochemical classification [1] to some well-preserved, 2.0 – 3.8 Ga greenstone belts. The metabasalts of the Isua (Greenland) [2, 3] and Barberton (South Africa) [4] greenstone belts, 3.8 and 3.5 Ga, respectively, show geochemical signatures comparable with those of Phanerozoic subduction-related ophiolites. The 2.7 Ga Wawa greenstone belt (Superior Province, Canada) [5] and the 1.95 Ga Jormua Complex (Finland) [6], on the other hand, show subduction-unrelated geochemical patterns, and can be related to plume- and continental margin type ophiolites, respectively.

[1] Dilek & Furnes (2011) GSA Bull 123, 387-411. [2] Polat et al. (2002) Chem. Geol. 184, 231-254. [3] Furnes et al. (2009) Lithos 113, 115-132. [4] Furnes et al. (in prep.). [5] Polat et al. (1999) Precamb. Res. 94, 139-173. [6] Peltonen et al. (1996) Jour. Petrol. 37, 1359-1383.