FLUID-INCLUSION EVIDENCE FOR AN UPPER-MANTLE ORIGIN FOR GREEN CLINOPYROXENES IN LATE CENOZOIC BASANITES FROM THE NOGRAD-GOMOR VOLCANIC FIELD, NORTHERN HUNGARY SOUTHERN SLOVAKIA/

Green clinopyroxenes with elevated Fe and Na contents coexist with ''n ormal'' clinopyroxene phenocrysts in alkali basalts from the Nograd-Go mor Volcanic Field (NGVF) of northern Hungary and southern Slovakia. T he coexistence of these clinopyroxenes with incompatible compositions in the same sample is often used as evidence for mixing between a mafi c and a more evolved melt. However, results of fluid-inclusion, textur al, and geochemical studies of samples from Tertiary basanites from th e NGVF suggest that the majority of the green clinopyroxenes could not have formed from magma mixing but, rather, are products of lithospher ic processes such as metasomatism or dynamic melt flow. Two distinct t ypes of green clinopyroxenes have been identified. Group 1 green clino pyroxenes are Al rich and contain CO2 inclusions; Group 2 green clinop yroxenes are Al poor and lack CO2 inclusions. On the basis of analysis of CO2 inclusions, the Group 1 clinopyroxenes, observed as xenocrysts and major constituents of clinopyroxenite xenoliths, were entrained i nto the host basanitic magmas in the uppermost mantle. These clinopyro xenes originally formed during a metasomatic event or as a result of d ynamic melt flow in the mantle. Group 2 clinopyroxenes likely represen t xenocrysts from disaggregated dioritic cumulates produced from melt( s) related to the host basanitic magmas.