Volcanism near the N.America-Eurasisa Plate boundary

We propose a petrologic, geochemical and geochronologic study of several key regions of the Late Neogene volcanoes from North Eastern Russia to evaluate the hypothesis that magmatism in the area was triggered by rift- related decompression, but also facilitated in part by presence of volatiles introduced by ancient slab-window paleo-Pacific subduction zone along the continental margins. We also intend to estimate the volumes, intensity and cyclicity of Late Cenozoic volcanism in the region. This is a collaborative study with Dr. V. Akinin of the NE Interdisciplinary Scientific Research Institute (Russian Academy of Sciences, Magadan). Major oxide and trace element concentrations will be measured to model the degree of melting and geochemical character of the source, both vital to understanding what causes the eruptions. We will use the more commonly utilized standard element partition models, employing modal batch melting formulations but also equations for the dynamic melting model, which are likely to be more representative of mantle melting scenarios. Comprehensive 40Ar/ 39Ar and 14C geochronology programs are proposed to refine our understanding of the eruption history of the province, and also to provide a chronologic framework for follow-up isotopic determinations. We will determine the Nd, Sr, and Pb isotopic compositions of the samples for a detailed assessment of source characteristics and modeling mixing relationships. Volcanic rocks provide an excellent opportunity to study eruption history as fresh rocks are abundant, the rocks are in many cases represented by undifferentiated, often mantle xenolith-bearing basaltic flows that have not experienced shallow magma chamber fractionation, and the rocks include recently erupted materials, which eliminates concerns about post-emplacement evolution of the radiogenic isotope ratios by radioactive decay of the parent nuclides. Mantle-derived Xenoliths from the area will be studied in order to decipher the nature of the Lithospheric mantle the degree of depletion in basaltic components, the nature and the time of possible metasomatic processes, the age of the Lithosphere and its relationships to the overlain Crust. The nature of metasomatic melts/fluids as well as their reaction and stabilization mechanisms in the lithospheric mantle sections, will be in detail studied as they place important constraints on the composition of basic magmas generated in intra-plate geodynamic settings like the proposed for study area. The combined study of host basalts and mantle xenoliths will contribute to our understanding the plate tectonic development of the region close to two sets of plate boundaries (North America-Eurasia and Pacific - North America), recognized to be an important boundary condition for other studies including climate change, environmental change and life/lithosphere interactions.

Alkaline basalts (lavas poor in Silica and rich in Sodium) in NE-Russia are basanites and nephelinites that carry earth mantle xenoliths. Both lavas have been formed in the asthenosphere, which is the less rigid and deeper part of the upper mantle. The shallower and rigid part of the upper mantle is the lithosphere. The nephelinites have been formed at depths greater than 110 km after low degrees of partial melting of an asthenosphere and the basanites at depths around 110 km after higher degrees of partial melting of an asthenosphere. The calculated temperatures during the formation of the melts were high (~1500C) but high enough that it could be attributed to convective upwelling of hot material (plume), which increased the ambient upper mantle temperature causing partial melting in that way. The reason for the melt production underneath NE-Russia is pressure decrease as a result of lithospheric attenuation. Lithospheric attenuation is a common process that takes place when margins of two tectonic plates collide or separate. During the collision of an oceanic with a continental plate the oceanic plate that is colder and denser, dives underneath the continental plate causing extensive volcanism at the collision front, e.g. Andes. As response to this process the continental lithosphere attenuates initiating partial melting in the upper mantle. On their way to the surface the basaltic lavas are able to transport very fast - within few days -unmolten fragments (xenoliths) from the lithosphere (the most rigid and shallow part of the upper mantle). Such fragments provide highly detailed information about the lithospheric mantle at the time the samples were extracted and brought to the surface by the host basalt. The detailed study of such fragments (xenoliths) from NE-Russia has shown that the ambient temperatures of these fragments were between 900 and 1000 C in depth of around 60 km. These fragments have been partly affected by the presence of unique melt droplets rich in coexisting carbonate and Sodium-rich silicate melt. Such melts could only coexist after entering the xenolith if the xenolith was transported to the surface at a very fast rate. Such melt droplets are very rare and they prove the existence and percolation of Carbon in the lithosphere. Projects most important results (scientific advances) from the project leaders point of view should be presented on a single page (DIN A4, 11 pt type, line spacing 1.5) in a way that is accessible to the general public. It is important to use as few technical terms as possible, so that the text is interesting and understandable to people not familiar with the field. The main point should be placed at the start of the summary. Please keep descriptions of the issues addressed and results obtained short and succinct. Please describe the integration of the domestic (sub) project into the collaborative research project. Possible applications to or implications for social, cultural, ecological, medical, economic or technological areas should be briefly mentioned.