Current Projects
Lower crustal and upper mantle xenoliths from the Rio Grande rift
HOW DOES CONTINENTAL RIFTING INITIATE?
Rifting controls the generation of juvenile oceanic crust, the breakup of continents and formation of sedimentary basins. However, it is unclear whether or not rifting typically initiates in response to processes occurring in the asthenosphere or in the lithosphere. We are undertaking a detailed thermochronological and petrochronological investigation of deep crustal and mantle xenoliths from the Rio Grande--a nascent continental rift system in the SW USA.
Lawsonite pseudomorphs in garnet crystal from the Voltri Massif, W Alps; false-colored for Mn concentration.
HOW ARE HIGH-PRESSURE METAMORPHIC ROCKS EXHUMED?
High-pressure metamorphic rocks provide the only direct record of sub-arc conditions. Despite their importance, the mechanisms responsible for their exhumation from mantle-depths to the Earth's surface are unclear. We are undertaking a detailed petrological, microtextural and geochronological investigation of eclogites and blueschists from the Voltri Massif--a piece of oceanic lithosphere that underwent subduction and exhumation during the Alpine orogeny. Reconstruction of high-resolution P-T-t paths for the Voltri rocks will enable us to differentiate between competing exhumation mechanisms (forced return flow in a channel, or underplating) and to better understand the geodynamics of syn-subduction exhumation.
Collaborators: Marco Scambelluri (UNIGE)
HOW DOES LOWER CONTINENTAL CRUST FORM?
Understanding the physical and chemical processes that form the Earth's lower continental crust--and how that material evolves--is central to understanding Earth structure, dynamics, chemistry and seismology. We are undertaking a detailed petrochronological investigation of the Ivrea-Verbano Zone--the archetypal section of lower continental crust.
Collaborators: Brad Hacker (UCSB)
Geological map of the Ivrea-Verbano Zone (after Brack et al 2010)
Cartoon of Earth's water cycle. Modified from Parai & Mukhopadhyay (2012).
CHARACTERIZING THE NOBLE GAS SYSTEMATICS OF SUBDUCTION
The release of volatiles during subduction is one of the most important processes to have shaped the Earth and it continues to mediate processes that sustain the planet’s long-term habitability. Water and gases released from subducting tectonic plates initiate magmatism, leading to explosive volcanic activity, metallogenesis and the formation of new continental crust. Remarkably, despite these important implications, the physical and chemical mechanisms responsible for processing volatiles during subduction are not understood. Owing to their unreactive nature, the noble gases have the potential to trace the pathways of volatile transport during subduction. Toward this aim, we are studying the noble gas systematics of metamorphic rocks exhumed from subduction zones. Such rocks provide unique insight into the physical and chemical processes that control the release and movement of fluids from the downgoing slab.
Collaborators: Rosie Jones, Chris Ballentine (Oxford)
Photomicrograph (XPL) of an eclogite-facies reaction selvage adjacent to a quartz vein in an eclogite from the Eastern Alps.
LENGTH AND TIME SCALES OF FLUID TRANSPORT AT SUB-ARC CONDITIONS
Dehydration of subduction slabs promotes a host of geodynamically significant processes and yet the length and time scales over which fluids move through the slab are poorly constrained. We are undertaking a combined petrological and geochemical investigation of a suite of eclogites from the Eastern Alps that presverve a pristine record of reactive flow under conditions of ~26 kbar. Results will have important implications for the mechanisms responsible for transport of trace elements from the slab to regions of sub-arc melting.
Thermal model of continental lithosphere undergoing simple shear
DEEP CRUSTAL METAMORPHISM AND EXTENSION
Extension of continental lithosphere can either lead to cooling or heating of the rocks in the deep crust. The relationship between the vertical distribution of strain during extension and metamorphism is unclear: depth-dependent thinning of the lithosphere has the potential to drive regional granulite facies metamorphism. We are undertaking a systematic modeling investigation of the potential P-T-t paths that can result from extension. This will provide a guide to better understand the nature of the middle and lower crust in regions of active extension, as well as interpreting the high-grade metamorphic rock record.
Collaborators: D. Oakley (SR)
False-color map of rutile crystal from a Slave craton xenolith showing ilmenite lamellae network.
U-PB SYSTEMATICS OF RUTILE
Pb is diffusively mobile through rutile under deep crustal conditions, rendering the U-Pb system in rutile a potentially powerful thermochronometer. However, diffusive profiles are rarely observed, indicating that alternative processes control the mobility of Pb in rutile in the lower crust. We are undertaking a systematic investigation of the U-Pb and trace element systematics of rutile from a suite of lower crustal xenoliths from the Slave craton, NW Canada. In particular, we are working to constrain the importance of ilmenite and zircon exsolution on Pb mobility. Results will have implications for the derivation of high-temperature thermal history information that underpin geodynamic models.
Collaborators: N. Roberts (NIGL), B.Davis (GSC)