Browsing by Author "Thurner, Sally"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Ongoing lithospheric removal in the western Mediterranean: Evidence from Ps receiver functions and thermobarometry of Neogene basalts (PICASSO project)(American Geophysical Union, 2014) Thurner, Sally; Palomeras, Imma; Levander, Alan; Carbonell, Ramon; Lee, Cin-TyThe western Mediterranean tectonic system consists of the Betic Mountains in southern Spain and the Rif Mountains in northern Morocco curved around the back-arc extensional Alboran basin. Multiple tectonic models have been developed to explain the coeval compressional and extensional tectonic processes that have affected the western Mediterranean since the Oligocene. In order to provide constraints on these evolutionary models, we use Ps teleseismic receiver functions (RF), thermobarometric analyses of post-Oligocene basalts, and previous teleseismic tomography images to investigate the lithospheric structure of the region. Ps RFs were calculated using seismic data from 239 broadband seismic stations in southern Iberia and northern Morocco and thermobarometric analysis was performed on 19 volcanic samples distributed throughout the region. The RF images reveal a highly variable Moho depth (∼25 to ∼55 km), as well as a strong positive, sub-Moho horizon between ∼45 and ∼80 km depth beneath the central Betic and Rif Mountains, which we interpret to be the top of the previously imaged Alboran Sea slab. Thermobarometric constraints from magmas in the eastern Betics and Rif indicate mantle melting depths between 40 and 60 km, typical of melting depths beneath mid-oceanic ridges where little to no lithosphere exists. Together, the RF and thermobarometric data suggest ongoing and recent slab detachment resulting from delamination of the continental lithosphere.Item Seismic Array Study of the Western Mediterranean and the United Stats Great Plains: Insight into the Modification and Evolution of Continental Lithosphere(2014-11-17) Thurner, Sally; Levander, Alan; Niu, Fenglin; Lee, Cin-Ty; Pu, HanNumerous tectonic processes are responsible for the modification and evolution of continental lithosphere. The continents, however, are generally resilient through geologic time and keep a record of Earth’s tectonic activity, both past and present. The focus of this work is to better understand the modification and evolution of continental lithosphere associated with continent-continent collisions. We do this by studying two orogenic systems: the Alpine Orogeny, associated with the ongoing collision between the African and Eurasian plates, and the Trans-Hudson Orogeny, associated with the initial formation of the North American craton during the Precambrian. This research focuses on the westernmost edge of the Alpine system in the western Mediterranean, where subduction and slab rollback have caused significant extension and Africa-Iberia convergence has caused simultaneous contraction. Here we calculate Pds receiver functions to constrain the discontinuity structure. Additionally, we jointly invert Pds receiver functions and Rayleigh wave phase velocity dispersion data to create a 3-D shear velocity model. These results show a deep Moho around the western portion of the Gibraltar Arc. Below this deep Moho we see the Alboran Slab extending down to ~250 km. In the eastern Gibraltar Arc, there is a very shallow Moho where the slab has detached from the surface and removed continental lithosphere. In the Trans-Hudson Orogen we use receiver functions and gravity data to determine the discontinuity and density structure of the shallow lithosphere. This analysis reveals crustal-scale thrusting associated with the Wyoming-Superior suture zone. We also find a relatively low Moho density contrast throughout the Trans-Hudson and northern Yavapai Province. This low Moho density contrast is associated with a deep Moho (>50 km) and is interpreted to be evidence of a dense lower crustal layer resulting from mafic underplating. Finally, we investigate the contribution that this dense thick crust may have played in the isostatic stabilization of the North American craton as well as other cratons around the world. We find that the lithospheric mantle must provide a negative component to cratonic lithospheric buoyancy in order to account for the low elevations observed along with thick crust in the cratons.