Volume 22, Issue No. 2, 1997

Geochemistry of metamorphosed mafic rocks _from Naxos (Greece): The pre-Cenozoic history _of the Cycladic crystalline belt

G. Pe-Piper* and C.N. Kotopouli**

** Department of Geology, Saint Maryâs University, Halifax, N.S. B3H 3C3, Canada,  ** Department of Geology, University of Patras, 261 10 Patras, Greece.

Keywords: Hercynian amphibolites, continental basalt, Mesozoic amphibolite, ophiolite, rift-related volcanites, core complex. Naxos, Greece.

ABSTRACT

The extensional core complex in Naxos preserves three main groups of metamorphosed mafic rocks (amphibolites). (1) Mafic enclaves in partially migmatised Hercynian granitoid basement, geochemically similar to high-Ti continental flood basalt. These rocks are very similar to Hercynian basement rocks exposed in Thessaly. (2) Mesozoic ophiolitic rocks, particularly MORB/IAT transitional rocks, similar to those of the Pindos ophiolite. (3) Amphibolites interlayered with terrigenous metasediments and marbles that are geochemically similar to Triassic rift-related elsewhere in Greece. Most amphibolites have entirely metamorphic textures, but a few with a Mesozoic protolith have remnant idiomorphic plagioclase of labradoritic composition, in contrast to oligoclase in the entirely metamorphic rocks. Amphibolites with a Mesozoic protolith have amphiboles with >0.07 Ti, whereas Hercynian amphibolites have low-Ti amphiboles. The geochemical consistency of the three groups of amphibolites and the close similarity of those with a Mesozoic protolith to unmetamorphosed rocks elsewhere in Greece suggests that their bulk geochemistry has not been significantly changed by metasomatism. One Hercynian sample shows substantial enrichment in HREE, Y and LILE, attributed to metasomatism. The occurrence of high- and low-Ti amphiboles in rocks of similar metamorphic grade within the metamorphic dome of Naxos may indicate that the Mesozoic cover rocks were tectonically juxtaposed with Hercynian basement metamorphosed at higher pressure prior to development of the thermal dome.