My research
Ph.D. Geology at University of Otago, New Zealand (in progress): "Comparative Fault Mechanics in Quartzofeldspathic, Mafic and Ultramafic Protoliths: a Study of the Alpine Fault Zone in South Westland" under Virginia Toy, Richard Norris, Alan Cooper and external advisor Simon Cox
Alpine Fault exposure at Martyr River:
The study area is roughly defined by a strip between the Alpine Fault (AF) and Livingstone Fault Zones (LFZ), extending from the Arawhata River near Jacksons Bay, south to Milford Sound where the AF continues offshore. Through this region the AF transitions from a dextral reverse strike-slip fault, characteristic of the classic West Coast AF exposures (e.g. Gaunt Creek, Hare Mare Creek), to a subvertical-dipping, primarily strike-slip fault to the south. This region is also of interest because it is where the majority of New Zealand basement terranes converge onto the AF, resulting in a more diffuse plate boundary including the AF, reactivated terrane-related faults and new faults created by the current AF regime. Despite its many obvious interests to the geologist, the AF in this region has been seldom visited, largely due to the remoteness of the area. Some of the more detailed studies of the AF in this region include work by K. Berryman, R. Sutherland, R. Norris and H. Campbell.
The three main aspects of my project include:
Interpretation at lower Cascade River:
View looking north from near Woodhen Creek towards the lower Cascade River
The diversity of rock types present in the same tectonic regime (including brittle / brittle-ductile / ductile deformed rocks with quartzose, quartzofeldspathic, pelitic, tuffaceous, carbonitic, mafic and ultramafic petrologies) are, in essence, a natural laboratory experiment allowing a comparative study of the deformation of geologic materials. The implications of this research could be readily applied to fault zones around the world and help characterize seismicity, seismic potential and properties of deformation purely as a function of rock type.
Distance to foreground: Haast Schist, Caples Group, Dun Mountain Ultramafics (red), Livingstone Group, Maitai Group
Take a virtual tour of the Alpine Fault here
M.S. Geological Sciences at UCSB: "Strain within the Ultrahigh-Pressure Western Gneiss Region of Norway Recorded by Quartz LPOs" under Brad Hacker
The Nutshell
I used the exciting new technique of Electron Backscatter Diffraction (EBSD) at UCSB to study strain recorded in quartz and feldspar microstructures from the Western Gneiss Region (WGR) of Norway. Lattice preferred orientations (LPOs) can be used to tell the active slip system, deformation temperature, distortion (plane strain vs. flattening vs. constriction), vorticity (simple shear vs. pure shear) and sense of shear in a rock sample. I constructed a database of over 100 quartzite and quartzofeldspathic gneiss samples from all across the WGR so that I could better understand the exhumation of the Western Gneiss Region of Norway, one of the world’s two giant ultra-high pressure terranes (>50,000km2).
Map of the Western Gneiss Region of Norway:
Abstract
Ultrahigh-pressure (UHP) metamorphism is a fundamental component of continental
orogenesis, but the exhumation of UHP rocks remains poorly understood. The Western
Gneiss Region (WGR) of Norway, the root zone of the Scandinavian Caledonides, is one of two giant UHP domains worldwide. Several conflicting exhumation hypotheses for the Western Gneiss Region have been proposed based on geochronologic, thermobarometric and petrologic data.
This study uses quartz lattice-preferred orientation (LPO) data (collected using
electron backscatter diffraction) from over 100 samples across the WGR to assess deformation mechanisms (e.g. slip systems), deformation temperatures, distortion, fabric strength, vorticity and sense of shear. Quantitative quartz LPO data were then used to construct a pseudo-Flinn plot and to create interpolated maps of strain and LPO properties across the WGR. The data were used to test previous WGR exhumation hypotheses and develop a new exhumation model.
The principal findings are: 1) The sense of shear is predominantly top-W in the
western half of the study area and top-E in the east. 2) There are distinct domains of plane strain and apparent constriction that trend NE-SW parallel to km-scale folds: these domains may represent different structural levels. 3) The activated slip systems (basal <a> and prism <a> slip) correlate inversely with peak metamorphic temperature. 4) Fabric strength correlates inversely with peak metamorphic temperature: the hottest
regions (NW) have the weakest fabrics. 5) Vorticity values of 0.85–1.00, indicate a
dominance of simple shear. 6) No evidence of flattening was observed.
These findings imply that the exhumation of the WGR through crustal levels occurred
via a combination of plane strain and constriction, with a shift from plane strain to
constriction (and increasing top-W sense of shear) during cooling from amphibolite facies conditions to greenschist-facies conditions. Granulite-facies quartz LPOs predating peak metamorphism are rare, but generally indicate top-E shear sense and conditions approaching plane strain.
Interpolated map of Pn values (calculated from quartz LPOs). High Pn values (red) indicate regions dominated by plane strain while low Pn (blue) indicates constriction:
Ultrahigh-Pressure Metamorphism
The formation and exhumation of ultrahigh-pressure (UHP) rocks are intrinsic to a number of Earth processes including the generation and collapse of mountain belts, crust-mantle material exchange, and the creation of continental crust. The occurrence of multiple temporally-spaced UHP events in many of the best-known orogens indicate that UHP processes are fundamental to collisional orogenesis. Exposure of UHP rocks (with deep origins and perhaps frequently incompletely exhumed) may lead to a significant underestimate of the prevalence of UHP processes in Earth’s evolution.
Western Gneiss Region
The Western Gneiss Region, a root of the Scandinavian Caledonides, is considered by many to be the best-exposed UHP terrane in the world and is thus a prime locale to study UHP processes associated with collisional orogenesis. A late-stage amphibolite facies overprint prevalent throughout the WGR has obscured any higher-temperature structural boundaries that may define (U)HP terranes. The Western Gneiss Region (WGR) of Norway has ultrahigh-pressure minerals that indicate subduction to depths greater than 100 km and subsequent exhumation. Gathering evidence shows that ultrahigh-pressure (UHP) and high-pressure (HP) metamorphism are a fundamental component of continental orogenesis worldwide, but the exhumation processes of UHP and HP rocks remain poorly understood. Numerous models have been proposed, but there are few comprehensive field-based datasets. Several exhumation hypotheses have been proposed for the WGR.
Lattice Preferred Orientations
Quartz lattice preferred orientations represent a useful tool in this regard because they are reset by relatively small strains and should therefore not be as complicated as the hand-sample to orogen-scale structure, which record the cumulative effects of the long (c. 1 Ga) deformation history of the WGR. High-temperature deformation can produce mineral lattice-preferred orientations (LPOs). These preferred orientations can arise from dislocation glide along particular crystallographic slip systems in individual crystals as they deform. Electron Backscatter Diffraction (EBSD) can be used to efficiently and reliably map mineral textures and orientations in thin sections and determine mineral LPOs.
Here is a figure showing the range of LPOs common in the Western Gneiss Region:
Here is a nice example of a prism <a> slip amphibolite-facies LPO intermediate between constriction and plane strain. The textural map below is colored based on quartz orientations (other grains are feldspars and mica). Notice the large feldspar delta clast showing top-left shear sense, consistent with the LPO.
See also my advisor Brad Hacker's website for related research
B.S. Geological Sciences at UCSB, Senior Thesis: "Geology of the South Branch of the Pareora and Otaio Rivers Region, Hunter Hills, Canterbury, New Zealand"
As an undergraduate I conducted a Senior Thesis project on the Hunter Hills of the South Island of New Zealand, while studying at the University of Otago, New Zealand. The study primarily focused on an inversion tectonic study of the range-front Hunters Fault and a reinterpretation of the type locality of the so-called "Marshall Paraconformity." Other studies included lithology, structure, petrography, macrofossil assemblages, hydrogeology, geomorphology, geological hazards and economic geology. Geologic mapping and cross sections constructed at 1:5,000.
Here's a excerpt from my mapping and a cross section:
My advisor for this project was Rick Sibson
I am also deeply interested in the feasibility of Enhanced Geothermal Systems (EGS)
Copyright © 2010 Nicolas C. Barth. All Rights Reserved.