Himalayan-Tibetan Orogen

3D Strain and Structures in Arcuate Orogenic Wedges

Integrating surface geologic data, I constructed the first 3D structural model of major shear zones for the central-western Himalaya, revealing the significant along-strike variations in strain accumulated in the mid-lower crust of the orogen (Fan and Murphy, 2021).  Comparing this geometry model with the published megathrust coupling model, channel steepness, micro-seismicity, thermochronologic data, metamorphic pressure-temperature condition estimations and topography, I discussed the mechanical effects of oblique convergence in an arcuate orogen, a complex 3D geometry of megathrust ramps, and rheologic changes in both dip and strike directions of the megathrust. Invoking these factors, I reconciled the coeval development of orogen-parallel extensional features (supra-detachment basin, metamorphic core complex and transtensional active fault system), orogen-normal shortening features (thrust faults and duplexes), and along-strike tectonic segmentation in central-western Himalaya (expressed as a structural-topographic embayment). 

The discussion in this paper conceptually proposes many ideas that form the foundation for hypotheses explored in my subsequent projects in geodynamics, thermochronology and thermokinematics, active tectonics, and tectonic geomorphology! It summarises my answer to "How do the deep megathrust 3D geometry and rheology of an orogenic wedge affect upper-plate strain accumulation and partitioning, rock exhumation, orogenic wedge morphology, and active fault systems? "

Thermokinematic Models Revealing Deep Structures

Although many studies suggest along-strike variations in the geometry of the megathrust in Nepal Himalayan (MHT), the specific geometry is not well understood, especially in western Nepal. Fan and Murphy (2021) attempt to propose a conceptual 3D megathrust geometry model and its evolution and further suggest its critical influences on rheology, orogenic wedge growth, tectonic segmentation, and strain partitioning. To quantitatively test the geometry and kinematic models of the MHT, I conduct low-temperature thermochronology analyses coupled with inversions of 3D thermokinematic modeling. Comparing the modeling result, thermochronology, and other geologic observations along the strike, the study proved that the along-strike variations in megathrust rheology are primarily controlled by its 3D geometry, especially the mid-lower crustal ramps. The study further suggests active crustal accretion on a mid-lower crustal ramp at or below the rheological transition, revealing the deep cause of the regional topographic embayment of the hinterland orogenic plateau and the associated drainage system evolution across the Himalaya. The work is published on Tectonics (Fan et al., 2022) and featured as a research spotlight on EOS (science news by AGU).

The work was presented at the AGU Fall Meeting 2021. Below is the recorded talk.

Structures Accommodating a Continental Sliver

I am working on an NSF-supported project investigating the bedrock structures of the Western Nepal Fault System (WNFS), which is proposed and interpreted to be the boundary fault of a "forearc" (continental) sliver in the western Himalaya by Murphy et al (2014). The WNFS is a trans-extensional fault system accommodating strain partitioning caused by oblique convergence in the western Himalaya (see Murphy et al., 2014; Sliver et al., 2015). My mapping focuses on the geometry, kinematics, propagation, and linkage of the fault segments of the WNFS (in prep.). I also collaborate with research groups focusing on paleoseismology and tectonic geomorphology of this fault system.

University of Houston EAS Newsletter (Spring 2023): Students and Faculty Assess Hazards of Active Faults in The Himalayas