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Geochemistry of mafic noncumulate and volcanic rocks in the ophiolites from the lherzolite province of the Central Dinaride

The geochemistry and the petrological characteristics of the mafic noncumulate and volcanic rocks in the lherzolite province of the Central Dinaride are shown on the basis of about 170 rock and 100 mineral analyses. The noncumulate rocks comprise microgabbro, dolerite and typical diabase, whereas the volcanic rocks are represented exclusively by spilites. All this rocks differ in their modal mineralogical composition and in the content of the major, trace and rare earth elements. Dolerites contain mostly primary amphibole, rarely augite, and zoned plagioclase of intermediate to more sodium rich composition. Diabases are composed of Ti-augite, partly Ti-amphibole and low basic plagioclase, whereas spilites consist of Ti-augite and albite. Spilites never contain amphibole. Low to intermediate hydrothermal alteration of the noncumulate rocks is often. In general, clinopyroxenes of spilites are characterized by higher Ti-, Al-, Ca- and Na-content than diabase ones, indicating different chemical and pressure conditions of crystallization. Dolerites, diabases and spilites have the similar ranges of SiO_2, Al_2O_3 and sum of Fe-oxides, but spilites have higher TiO_2-content. In comparation to the noncumulate rocks spilites have also lower Al_2O_3/TiO_2 ratio, lower Mg number and Cr- and Ni-content and remarkably higher values of incompatible elements (La, Ce, Zr, Y, Nb). All mafic rocks have tholeiitic character and belong to high aluminium (H-Al) and moderately to high titanium (M-Ti to H-Ti) basic rocks. They show similarities with the rocks formed in the embryonic (E-MORB) or marginal oceanic basins (BABT). They are probably derived from the same mantle reservoir, but with different degree of partial melting. Dolerites, diabases and spilites are the parts of the highly desintegrated ophiolite suite. Dolerites and diabases occur either in the form of veins cutting peridotites, cumulate rocks, associated garnet pyroxenites and amphibolites or as small stocks having an extent of less than 10 km^2. Spilites occurs as massive flows or as pillows. On the basis of the available data it is not possible to make definite conclusions about the systematic composition variations of the mafic magmatic rocks in the lherzolite province. This province, extending 400 km, is characterized by highly fertile spinel lherzolite of a subcontinental type. The radiometric absolute age of dolerites and diabases ranges between 170 and 160 Mio years.

mafic noncumulate rocks; volcanic rocks; ophiolites; lherzolite province; Central Dinaride

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