The LHCb tracking system

The LHCb detector is being constructed to measure CP-violation parameters and rare B decays. The LHCb tracking system consists of silicon micro-strip detectors and straw chambers. The system is composed of four major sub-detectors: the Velo (Vertex Locator), TT (Trigger Tracker), IT (Inner Tracker) and OT (Outer Tracker). The Velo uses silicon micro-strip detectors which are placed at 8 mm from the beam, and that can be retracted during injection. The TT is a four-layer silicon strip detector that covers the full acceptance of the experiment at the entrance of the spectrometer dipole magnet. The fringe field of the magnet allows the transverse momentum of tracks to be measured by their deflection between the Velo and TT detectors for use in the trigger. The IT and OT detectors measure the tracks behind the magnet. The IT is a silicon strip detector which covers the region close to the beam pipe, while the OT is a straw tube detector which covers the rest of the acceptance. All of the detectors are currently under construction and will be ready for installation before the end of 2006. The expected performance for the tracking system is as follows; the tracking efficiency is larger than 95% and the ghost rate is smaller than 7%, for tracks with a momentum larger than 12 GeV. The momentum resolution ranges from 0.35% to 0.5% and the IP resolution reaches 14 mm for tracks with a large transverse momentum

New insight in the Hawaiian plume swell dynamics from scaling laws

The formation and shape variation of the Hawaiian plume swell is re-examined numerically. Scaling laws for the plume buoyancy flux and swell width and height help gaining new insight in relationships between swell formation and relevant model parameters, like plume temperature and size, and mantle rheology. A scaling law for the plume buoyancy F = Aη0 −1.2 R p 3.5ΔT p 2.2 exp(1.3 × 10−8 EΔT p ), with background mantle viscosity η0, plume radius R p , plume excess temperature ΔT p , and activation energy E fits numerical flux measurements within 8%. Scaling laws for the swell width and height have similar forms, and their multiplication resembles the buoyancy flux scaling law within 10%. These scaling laws suggest that the background mantle viscosity plays a significant role, and that the increased Hawaiian plume intensity ∼25 Ma ago is due to a plume excess temperature increase of 50%

The Bs -> Ds pi and Bs -> Ds K selections

The decay channels Bs->Dspi and Bs->DsK will be used to extract the physics parameters $\Delta m_s$, $\Delta\Gamma_s$ and $\gamma + \phi_s$. Simulation studies based on Monte Carlo samples produced in 2004 and 2005 show that a total of 140k Bs->Dspi and 6.2k Bs->DsK events are expected to be triggered, reconstructed and selected in $2fb^{-1}$ of data ($10^7s$ of data taking at a luminosity of 2\times 10^{32}\unit{cm^{-2}s^{-1}}). The combinatorial background-over-signal ratio originating from inclusive bb events is expected to be $B/S Dspi whereas, for Bs->DsK, the limit is$B/S < 0.18~\at~90\%$~CL

Repeat ridge jumps associated with plume‐ridge interaction, melt transport, and ridge migration

Repeated shifts, or jumps, of mid-ocean ridge segments toward nearby hot spots can produce large, long-term changes to the geometry and location of the tectonic plate boundaries. Ridge jumps associated with hot spot–ridge interaction are likely caused by several processes including shear on the base of the plate due to expanding plume material as well as reheating of lithosphere as magma passes through it to feed off-axis volcanism. To study how these processes influence ridge jumps, we use numerical models to simulate 2-D (in cross section) viscous flow of the mantle, viscoplastic deformation of the lithosphere, and melt migration upward from the asthenospheric melting zone, laterally along the base of the lithosphere, and vertically through the lithosphere. The locations and rates that magma penetrates and heats the lithosphere are controlled by the time-varying accumulation of melt beneath the plate and the depth-averaged lithospheric porosity. We examine the effect of four key parameters: magmatic heating rate of the lithosphere, plate spreading rate, age of the seafloor overlying the plume, and the plume-ridge migration rate. Results indicate that the minimum value of the magmatic heating rate needed to initiate a ridge jump increases with plate age and spreading rate. The time required to complete a ridge jump decreases with larger values of magmatic heating rate, younger plate age, and faster spreading rate. For cases with migrating ridges, models predict a range of behaviors including repeating ridge jumps, much like those exhibited on Earth. Repeating ridge jumps occur at moderate magmatic heating rates and are the result of changes in the hot spot magma flux in response to magma migration along the base of an evolving lithosphere. The tendency of slow spreading to promote ridge jumps could help explain the observed clustering of hot spots near the Mid-Atlantic Ridge. Model results also suggest that magmatic heating may significantly thin the lithosphere, as has been suggested at Hawaii and other hot spots

Subsidence of the West Siberian Basin: Effects of a mantle plume impact

Comparison of modeling results with observed subsidence patterns from the West Siberian Basin provides new insight into the origin of the Siberian Traps, and constrains the temperature, size, and depth of an impacting mantle plume head during and after the eruption of the Siberian Traps at the Permian-Triassic boundary (250 Ma). We compare subsidence patterns from one-dimensional conductive heat flow models to observed subsidence from backstripping studies of wells in the basin. This results in a best-fit scenario with a 50-km-thick initial plume head with a temperature of 1500 °C situated 50 km below the surface, and an initial regional crustal thickness of 34 km, in agreement with published values. Backstripping and modeling results agree very well, including a 60–90 m.y. delay between the rifting phase and the first regional sedimentation. Regional subsidence patterns indicate that the plume head was present across a minimum area of ∼2.5 × 106 km2. These results re-emphasize the viability of a mantle plume origin for the Siberian Traps, provide important constraints on the dynamics of mantle plume heads, and suggest a thermal control for the subsidence of the West Siberian Basin

Deformation driven by deep and distant structures : Influence of a mantle lithosphere suture in the Ouachita orogeny, southeastern United States

Heron is grateful for funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement 749664 and a DIFeREns2 COFUND Junior Research Fellowship. We thank the editor, D. Harry, E. Hopper, R. Keller, and anonymous reviewers for their helpful comments. Pysklywec acknowledges support from a Natural Sciences and Engineering Research Council of Canada Discovery Grant and and SciNet HPC Consortium (Loken et al., 2010). We thank the Computational Infrastructure for Geodynamics which is funded by the U.S. National Science Foundation under awards EAR-0949446 and EAR-1550901 for supporting the development of ASPECT. Figure 1A was generated using Generic Mapping Tools (Wessel et al., 2013).Peer reviewedPublisher PD

Relamination of mafic subducting crust throughout Earth’s history

Earth has likely cooled by several hundred degrees over its history, which has probably affected subduction dynamics and associated magmatism. Today, the process of compositional buoyancy driven upwelling, and subsequent underplating, of subducted materials (commonly referred to as “relamination”) is thought to play a role in the formation of continental crust. Given that Archean continental crust formation is best explained by the involvement of mafic material, we investigate the feasibility of mafic crust relamination under a wide range of conditions applicable to modern and early Earth subduction zones, to assess if such a process might have been viable in an early Earth setting. Our numerical parametric study illustrates that the hotter, thicker-crust conditions of the early Earth favour the upward relamination of mafic subducting crust. The amount of relaminating subducting crust is observed to vary significantly, with subduction convergence rate having the strongest control on the volume of relaminated material. Indeed, removal of the entire mafic crust from the subducting slab is possible for slow subduction (∼2 cm/yr) under Archean conditions. We also observe great variability in the depth at which this separation occurs (80–120 km), with events corresponding to shallower detachment being more voluminous, and that relaminating material has to remain metastably buoyant until this separation depth, which is supported by geological, geophysical and geodynamical observations. Furthermore, this relamination behaviour is commonly episodic with a typical repeat time of approximately 10 Myrs, similar to timescales of episodicity observed in the Archean rock record. We demonstrate that this relamination process can result in the heating of considerable quantities of mafic material (to temperatures in excess of 900 °C), which is then emplaced below the over-riding lithosphere. As such, our results have implications for Archean subduction zone magmatism, for continental crust formation in the early Earth, and provide a novel explanation for the secular evolution of continental crust

Modelling fluid flow in complex natural fault zones. Implications for natural and human-induced earthquake nucleation

Pore fluid overpressures in active fault systems can drive fluid flow and cause fault weakening and seismicity. In return, deformation accommodated by different modes of failure (e.g. brittle vs. ductile) also affects fault zone permeability and, hence, fluid flow and pore fluid pressure distribution. Current numerical simulation techniques model how fluid flow controls fault reactivation and associated seismicity. However, the control exerted by pore fluid pressure on the transition from slow aseismic fault sliding to fast seismic sliding, during the earthquake nucleation phase, is still poorly understood. Here, we model overpressured, supercritical CO2 fluid flow in natural faults, where non-linear, complex feedback between fluid flow, fluid pressure and fault deformation controls the length of the nucleation phase of an earthquake and the duration of the interseismic period. The model setup is an analogue for recent seismic source events in the Northern Apennines of Italy (e.g. Mw 6.0 1997-98 Colfiorito and Mw 6.5 2016 Norcia earthquakes). Our modelling results of Darcy fluid flow show that the duration of the nucleation phase can be reduced by orders of magnitude, when realistic models of fault zone architecture and pore pressure- and deformation-dependent permeability are considered. In particular, earthquake nucleation phase duration can drop from more than 10 years to a few days/minutes, while the seismic moment can decrease by a factor of 6. Notably, the moment of aseismic slip (M0=109Nm) obtained during the nucleation phase modelled in our study is of the same order as the detection limit of local strain measurements using strain meters. These findings have significant implications for earthquake early warning systems, as the duration and moment of the nucleation phase will affect the likelihood of timely precursory signal detection. Interestingly, aseismic slip has been measured up to a few months before some recent large earthquakes, although in a different tectonic context than the model developed here, rekindling interest in the nucleation phase of earthquakes. In addition, our results have important implications for short and long term earthquake forecasting, as crustal fluid migration during the interseismic period may control fault strength and earthquake recurrence intervals

Plate rotation during continental collision and its relationship with the exhumation of UHP metamorphic terranes: Application to the Norwegian Caledonides

Lateral variation and asynchronous onset of collision during the convergence of continents can significantly affect the burial and exhumation of subducted continental crust. Here we use 3-D numerical models for continental collision to discuss how deep burial and exhumation of high and ultrahigh pressure metamorphic (HP/UHP) rocks are enhanced by diachronous collision and the resulting rotation of the colliding plates. Rotation during collision locally favors eduction, the inversion of the subduction, and may explain the discontinuous distribution of ultra-high pressure (UHP) terranes along collision zones. For example, the terminal (Scandian) collision of Baltica and Laurentia, which formed the Scandinavian Caledonides, resulted in the exhumation of only one large HP/UHP terrane, the Western Gneiss Complex (WGC), near the southern end of the collision zone. Rotation of the subducting Baltica plate during collision may provide an explanation for this distribution. We explore this hypothesis by comparing orthogonal and diachronous collision models and conclude that a diachronous collision can transport continental material up to 60 km deeper, and heat material up to 300°C hotter, than an orthogonal collision. Our diachronous collision model predicts that subducted continental margin material returns to the surface only in the region where collision initiated. The diachronous collision model is consistent with petrological and geochonological observations from the WGC and makes predictions for the general evolution of the Scandinavian Caledonides. We propose the collision between Laurentia and Baltica started at the southern end of the collisional zone, and propagated northward. This asymmetric geometry resulted in the counter clockwise rotation of Baltica with respect to Laurentia, consistent with paleomagnetic data from other studies. Our model may have applications to other orogens with regional UHP terranes, such as the Dabie Shan and Papua New Guinea cases, where block rotation during exhumation has also been recorded