The most widespread blocks within the Cretaceous ophiolitic mélange (North Anatolian ophiolitic mélange) in Central Anatolia (Turkey) are pillow basalts, radiolarites, other ophiolitic fragments and Jurassic-Cretaceous carbonate blocks. The pillow basalts crop out as discrete blocks in close relation to radiolarites and ophiolitic units in Cretaceous ophiolitic mélange. The geochemical results suggest that analyzed pillow basalts are within-plate ocean island alkali basalts. The enrichment of incompatible elements (Nb, Ta, Light REE, Th, U, Cs, Rb, Ba, K) demonstrates the ocean island environment (both tholeiites and alkali basalts) and enriched MORB. Dated calcareous intrafills and biodetrital carbonates reveal an age span of Callovian-Early Aptian. The thin-shelled protoglobigerinids, belonging to the genus Globuligerina, in the calcareous intrafills between pillow basalt lobes indicates a Callovian-Barremian age interval, most probably, Valanginian to Late Barremian. The volcanic and radiolarite detritus-bearing orbitolinid-Baccinella biodetrital carbonates dated as Late Barremian-Early Aptian in age, were probably deposited around atolls and have a close relationship with the ocean island pillow basalts. The results collectively support the presence of a seamount on the Neo-Tethyan oceanic crust during the Valanginian-Late Barremian and atolls during the Late Barremian-Early Aptian interval. The presence of an oceanic crust older than that seamount along the Northern Branch of Neo-Tethys is conformable with the geodynamic evolution of the Tethys.

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S U M M A RY: The major and trace element geochemistry of the early to middle Proterozoic meta-igneous rocks of the Willyama Complex in the Broken Hill Block indicates that the basic rocks originated by partial melting of a depleted mantle source, followed by fractional crystallization along a trend of strong iron enrichment coupled with some crustal assimilation. At least some of the intermediate-acid rocks were derived from fractionation of these basic parents, but major crustal involvement may be necessary to explain the large quantities of felsic volcanics in the lower part of the Complex. The volcanic rocks in the Broken Hill mine area show an unusually high degree of primary iron enrichment (up to 25 wt % total iron as Fe203) and a lesser degree of bimodality than elsewhere. By analogy with Recent ferrobasalt provinces, this extreme iron enrichment may indicate an origin in a propagating rift where small, high-level magma chambers separated from the magma source. If so, the consequent high geothermal gradient and high fracture permeability may have provided the necessary conditions for genesis of the Broken Hill ore deposit.

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