U-Th-Pb geochronology of zircon and monazite from syenite and pincinite xenoliths in Pliocene alkali basalts of the intra-Carpathian back-arc basin

作者：Hurai V^*; Paquette J L; Huraiova M; Konecny P

来源：Journal of Volcanology and Geothermal Research, 2010, 198(3-4): 275-287.

DOI：10.1016/j.jvolgeores.2010.09.012

• maar
• alkali basalt
• syenite
• pincinite
• zircon
• monazite
• Western Carpathians

Phreatomagmatic eruptions in the Lucenec Basin in Slovakia ejected fragments of igneous rocks of unknown age and ranging in composition from gabbro to syenite and orthopyroxene granodiorite - pincinite. Two kinds of syenites with different Fe3+ contents composed of anorthoclase and interstitial metaluminous trachyte-to-alkali rhyolite glass represent the final products of alkali basalt differentiation at depths of 10 and 15-18 km. Pincinite composed of plagioclase, quartz, orthopyroxene, ilmenite and interstitial peraluminous dacite glass is a quenched supersolidus anatectic melt formed at the depth of 17-20 km by high-temperature dehydration melting of biotite-bearing gneissic protolith.
Zircon from pincinite and syenite, and monazite from syenite were dated using excimer laser ablation ICP-MS. The obtained ages cluster at 5.8 +/- 0.1 and 5.4 +/- 0.1 Ma, thus corroborating the genetic link between the two rock-types and constraining the residence time of at least 300 +/- 100 ka of the parental basalt in the deep crustal magma storage zones. The inferred ages overlap the Upper Miocene-Pliocene boundary, and are considerably younger than spatially associated basaltic lava flows dated using the K/Ar method. Consequently, the fluviolacustrine Poltar Formation overlying the maar structure must have sedimented during the Pliocene and not during the Upper Miocene (Pontian) as previously assumed.

• 出版日期2010-12-15