MAGMA EMPLACEMENT PROCESSES OF THE OLIGOCENE ZÁKUPY AND THE MIOCENE MĚRUNICE DIATREMES, CZECH REPUBLIC REVEALED VIA FIELD RELATIONS, PETROGRAPHIC, ANISOTROPY OF MAGNETIC SUSCEPTIBILITY, PALEOMEGNETICS, AND GROUND MAGNETOMETERY

Emplacement of silica-undersaturated magma in continental rift volcanoes remain important but poorly understood because the roots of these systems are not often accessible. The Měrunice and Zákupy diatremes, Czech Republic are located within and on the SE shoulder of the Eger Rift and present a unique opportunity to conduct a comparative emplacement study, in near 3-dimensions, of sub-volcanic magma plumbing systems. Here we report preliminary data on how varying degrees of alkaline magma generation paired with a dynamic stress regime yielded unique emplacement mechanisms of presumed monogenetic rift diatremes. Studies across the rift reveal that magma compositions show a temporal evolution trend that coincides with three rift phases: melilitic-nephelinites during pre-rift (79-49 Ma); two magmas, weakly alkaline olivine basalts and strongly alkaline nephlelinite-tephrite-phonolites during syn-rift (42-16 Ma), and olivine foidites during late rift (16-0.3 Ma). Field observations and laboratory data at both diatremes indicate multiple emplacement and eruptive events, as shown by variation in eruptive materials and cross cutting relationships between dikes and sills that differ in composition and emplacement dynamics. Anisotropy of magnetic susceptibility (AMS) data from 25 Zákupy diatreme sites yield primarily oblate with some prolate magnetic flow fabrics showing magma moving up to and laterally away from the suspected main conduit. In addition, ground magnetometry data indicate that the main conduit is likely located at the center of the quarry as shown by a magnetic low with a magnetic high radiating around the probable conduit. Curie point estimates reveal that the magnetic mineral phases carrying the characteristic remanent magnetization are moderate to high titanomagnetite as well as ilmenite forming inclusions in clinopyroxene. AMS and rock magnetic experiments on 27 Měrunice diatreme sites are underway to examine emplacement and magnetic mineralogy. Petrographic analysis will further determine the composition of the intrusive and extrusive rocks and their effect on the emplacement style of the diatremes. The results from this multidisciplinary study reveal that these presumed monogenetic systems display characteristics that are better described by a polygenetic emplacement model.