Paleomagnetic, Anisortopy of Magnetic Susceptibility, and structural Data Bearing on Magma Emplacement and the growth of the Miocene Hrad Trosky a Monogenic Strombolian Cinder Cone

The Hrad (castle) Trosky is a 14th century medieval castle located in NE Bohemia, Czech Republic built on top of a monogenic Strombolian cinder-spatter cone. The Hrad Trosky Volcano belongs to a relatively well-preserved set of middle Miocene scoria cones in the Jičín Volcanic field. Volcanic activity occurred in the form of scattered Strombolian eruptions from multiple volcanic centers producing basanitic magmas mostly erupted along an east-west trend associated with the Lusatian fault. Erosion of the Hrad Trosky Volcano resulted in exceptional three dimensional exposure of the magma feeder conduit system. In order to gain a better understanding of the magma emplacement and subvolcanic deformation processes at the Hrad Trosky volcano we collected samples for a detailed, paleomagnetic, anisotropy of magnetic susceptibility (AMS), and structural study. AMS data provides information on magma flow patterns and improve our understanding of the kinematics of magma flow. Paleomagnetic data will be compared to the late Miocene expected field direction to discern any subvocanic deformation associated with subsequent intrusions during the growth of the volcanic system. Structural data, such as basic field mapping, fracture patterns, Reidel shears, and other kinematic indicator, should provide additional constraints on the details of volcanic construction and/or deformation. To asses the evolution of the Hrad Trosky volcano, we collected twenty-one sampling sites with eight to fourteen sample collected at each sites. These include fifteen sites in the magma conduit, five sites in lava flows, and one site scoria. In addition, we conducted five baked-contact tests to evaluate the stability of the remanence and the antiquity of the magnetization. Preliminary results are encouraging with AMS data yielding high susceptibility resultsand well defined principal susceptibility axes. Paleomagnetic data show a relatively simple demagnetization behavior that likely reflects a primary thermoremanent magnetization. The results from the Hrad Trosky volcano provide a better understanding of the magma transport through the volcanic construct to the eruptive vent and critical insight into subvolcanic deformation processes.