NATURE OF THE MAGMA SOURCE OF THE SZARVASKÖ COMPLEX (NE-HUNGARY): PETROLOGICAL AND GEOCHEMICAL CONSTRAINTS

Abstract

The Szarvaskö complex exposes a rare fragment of Jurassic mafic and ultramafic igneous rocks that have been described as a dismembered portion of a Mesozoic ophiolitic sequence, formed in a setting related to the opening of a narrow basin of the Vardar ocean. These magmatic rocks are mainly extrusive pillow basalts, along with gabbroic sills intruded into terrigenous shales, and minor ultramafic and plagiogranite bodies. The basalts and some of the gabbros have fractionated N-MORB-like trace element patterns, but low eNd values, indicating a possible enriched source component as well. Other gabbros as well as the ultramafic rocks have the lowest REE patterns and are regarded as cumulates. The plagiogranites on the other hand, show inverse patterns with overall high trace element contents, and remarkable Eu anomalies. This suite of samples cannot be related solely by fractional crystallization to a common parental magma. Rather, they represent a combination of processes where the originally N-MORB-like magmas fractionated variable amounts of olivine+plagioclase+ clinopyroxene±chromite and then assimilated terrigenous sediments abundantly present in the area. There is no reliable evidence for a subduction-related component in these rocks.