Feedbacks between chemical and mechanical processes in the lithosphere
Fluid infiltration ± deformation are important catalysts for metamorphism and chemical alteration. However, the exact nature and feedbacks between syndeformational metamorphism and metasomatism remains poorly constrained and has important implications for the behavior of currently deforming crust within inaccessible portions of the earth.
Some of our recent work on fluid infiltration, deformation and metamorphism, at scales from the μm to the craton include:
What is the environment of deep episodic tremor and slow slip?
Recent geodetic and seismological techniques have revealed a host of enigmatic fault zone behaviors (e.g., episodic tremor and slip [ETS]) within conditionally stable portions of subduction interfaces directly below the locked seismogenic zone. Fluid migration and high pore fluid pressures may play an important role in producing these poorly understood behaviors.However, little is known about the geologic cause of tremor or slow slip, in part due to the inaccessibility of this portion of the subduction interface in currently subducting regions.
My work tackles this problem from a variety of perspectives, including:
(1) field observations of exhumed subduction terranes from just below the paleo-subduction seismogenic zone
(2) thermodynamic modeling of the metamorphic environment of ETS
Check out our recent paper in EPSL - Condit et al., 2020
(3) integration of field and petrologic observations with deformation experimental constraints on ETS mechanisms - French and Condit, 2019
Deformation mechanisms and rheology of the lithosphere
Lithospheric rheology, or the constitutive relationship between stress and strain within a rock, is both vital for understanding the long term strength of the lithosphere during deformation and difficult to constrain.
From the natural rock record, I reconstruct the conditions of deformation and how this deformation is accommodated through coupled thermobarometry/thermodynamic modeling and microstructural analysis. Then, using deformation experimental constraints, I am able to estimate the absolute strength during deformation.
This work requires a combination of a robust field context for the style of deformation, detailed microstructural and petrologic analysis, and appropriate laboratory constraints from deformation experiments.
I have become particularly excited about the mineral amphibole, which may accommodate significant amounts of deformation in the deep crust (e.g., Condit and Mahan, 2018). However, we currently lack fundamental laboratory constraints on it's rheology. My NSF-EAR Postdoctoral Research Fellowship at MIT's Rock Deformation Laboratory was aimed at providing preliminary constraints on amphibole deformation.