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PhD candidate studying the interplay of modern technology and traditional field techniques.

PINBOARD SUMMARY

Thermochronology allows us to understand the thermal evolution of our Earths surface.

In ten seconds? Low-temperature (<200°C) thermochronology can be used to model the timing of tectonic events, both in extensional provinces and orogenies.

Don't believe it? A study in southwest Alaska used (U-Th)/He thermochronology to understand the response of erosion to surface uplift. Using the same techniques another study modeled the evolution of a major detachment fault in southern Tibet.

So what else can influence these temperatures? Of course it's not only fault movement that can cause uplift of the Earths surface. Another major influence is erosion as it removes material causing the underlying material to "rebound" and cool in response. Understanding what is the driver of surface is key to using thermochronology in the first place.

So in what cases are these techniques best for unraveling tectonic history?

Regions of significant tectonic activity - Regions such as the Tibetan Plateau are highly studied as areas of rapid orogenic uplift. Areas of extension like the Aegean province are also ideal for using thermochronology to model their history.

Alongside estimates of erosion - Some of the most actively uplift regions in the world are also host to the highest erosion rates in the world. Therefore, it is important to place thermochronologic data in the context of tectonic-erosional feedbacks. In contrast to this, extensional provinces tend to be dominated by tectonics making the precision of erosion estimates less crucial.

On a smaller scale : Fault evolution - A recent study has shown that the linkage of previously segmented normal faults can be seen in thermochronologic data. Studies like these have the potential to illuminate how active fault systems evolve through time, potentially enhancing our understanding of major fault zones like the San Andreas and Walker Lane Belt of western North America.

10 ITEMS PINNED

Diachronous uplift and cooling history of the Menderes core complex, western Anatolia (Turkey), based on new Zircon (U-Th)/He ages

Abstract: New (U-Th)/He thermochronology data from the syn-extensional granitoids in the Central part of the Menderes Massif in western Turkey reveal a minimum slip rate of 12.5 km/myr along the Alasehir detachment (~ 14° dip angle) and denudation rates between 1.75 km/myr and 3.25 km/myr between 4 Ma and 2 Ma. These values suggest relatively fast exhumation of the Central sub-massif, associated with cooling rates between 53°C/myr and 128°C/myr, which are higher than the estimated footwall cooling rates (60°/myr to 120°C/myr) from the Northern sub-massif. Based on the initial crystallization ages of the syn-extensional granitoid intrusions and their exhumation–related cooling ages, our thermochronological findings suggest that the Central sub-massif in Menderes underwent accelerated uplift and faster exhumation in the latest Cenozoic than the Northern and Southern sub-massifs. This latest doming and rapid extension of the Central sub-massif was associated with the asthenospheric upwelling beneath the region and the related Na-alkaline, Kula volcanism. Our results indicate that the Menderes Massif has had a diachronous uplift and cooling history during its extensional tectonic evolution in the late Cenozoic. Thermal weakening of the young orogenic crust in western Anatolia via both lithospheric and asthenospheric melting episodes and magmatism produced higher than normal geothermal gradients and played a significant role in core complex formation.

Pub.: 05 Dec '16, Pinned: 23 Apr '17

Constraining provenance, thickness and erosion of nappes using low‐temperature thermochronology: the Northland Allochthon, New Zealand

Abstract: The Northland Allochthon, an assemblage of Cretaceous–Oligocene sedimentary rocks, was emplaced during the Late Oligocene–earliest Miocene, onto the in situ Mesozoic and early Cenozoic rocks (predominantly Late Eocene–earliest Miocene) in northwestern New Zealand. Using low‐temperature thermochronology, we investigate the sedimentary provenance, burial and erosion histories of the rocks from both the hanging and footwalls of the allochthon. In central Northland (Parua Bay), both the overlying allochthon and underlying Early Miocene autochthon yield detrital zircon and partially reset apatite fission‐track ages that were sourced from the local Jurassic terrane and perhaps Late Cretaceous volcanics; the autochthon contains, additionally, material sourced from Oligocene volcanics. Thermal history modelling indicates that the lower part of the allochthon together with the autochthon was heated to ca. 55–100°C during the Late Oligocene and Early Miocene, most likely due to the burial beneath the overlying nappe sequences. From the Mesozoic basement exposed in eastern Northland, we obtained zircon fission‐track ages tightly bracketed between 153 and 149 Ma; the apatite fission‐track ages on the other hand, generally young towards the northwest, from 129 to 20.9 Ma. Basement thermochronological ages are inverted to simulate the emplacement and later erosion of the Northland Allochthon, using a thermo‐kinematic model coupled with an inversion algorithm. The results suggest that during the Late Oligocene, the nappes in eastern Northland ranged from ca. 4–6‐km thick in the north to zero in the Auckland region (over a distance >200 km). Following the allochthon emplacement, eastern Northland was uplifted and unroofed during the Early Miocene for a period of ca. 1–6 Myr at the rate of 0.1–0.8 km/Myr, leading to rapid erosion of the nappes. Since Middle Miocene, the basement uplift ceased and the erosion of the nappes and the region as a whole slowed down (ca. 0–0.2 km/Myr), implying a decay in the tectonic activity in this region.

Pub.: 30 Dec '15, Pinned: 22 Apr '17

Thermochronologic constraints on the slip history of the South Tibetan detachment system in the Everest region, southern Tibet

Abstract: North-dipping, low-angle normal faults of the South Tibetan detachment system (STDS) are tectonically important features of the Himalayan–Tibetan orogenic system. The STDS is best exposed in the N–S-trending Rongbuk Valley in southern Tibet, where the primary strand of the system – the Qomolangma detachment – can be traced down dip from the summit of Everest for a distance of over 30 km. The metamorphic discontinuity across this detachment implies a large net displacement, with previous studies suggesting >200 km of slip. Here we refine those estimates through thermal–kinematic modeling of new (U–Th)/He and 40Ar/39Ar data from deformed footwall leucogranites. While previous studies focused on the early ductile history of deformation along the detachment, our data provide new insights regarding the brittle–ductile to brittle slip history. Thermal modeling results generated with the program QTQt indicate rapid, monotonic cooling from muscovite 40Ar/39Ar closure (ca. 15.4–14.4 Ma at ca. 490 °C) to zircon (U–Th)/He closure (ca. 14.3–11.0 Ma at ca. 200 °C), followed by slower cooling to apatite (U–Th)/He closure at ca. 9–8 Ma (at ca. 70 °C). Although previous work has suggested that ductile slip on the detachment lasted only until ca. 15.6 Ma, thermal–kinematic modeling of our new data suggests that rapid (ca. 3–4 km/Ma) tectonic exhumation by brittle–ductile to brittle fault slip continued to at least ca. 13.0 Ma. Much lower modeled exhumation rates (≤0.5 km/Ma) after ca. 13 Ma are interpreted to reflect erosional denudation rather than tectonic exhumation. Projection of fault-related exhumation rates backward through time suggests total slip of ca. 61 to 289 km on the Qomolangma detachment, with slightly more than a third of that slip occurring under brittle–ductile to brittle conditions.

Pub.: 01 Dec '16, Pinned: 22 Apr '17

Thermochronology constraints on Miocene exhumation in the Central Range Mountains, Trinidad

Abstract: The Central Range fault zone is a continental transform that accommodates most of the present-day slip between the Caribbean and South American plates in Trinidad. Global positioning system data and paleoseismic work suggest that this zone is active today and has been active for at least the past several thousand years. The modern fault zone overprints a middle Miocene fold-and-thrust belt; therefore, the strain recorded in the Central Range fault zone is the sum of both middle Miocene and more recent events. Thermochronology data from Eocene and Oligocene sandstones in the Central Range were collected to evaluate the timing of exhumation driven by crustal shortening and thickening. (U-Th)/He zircon analysis of subhedral zircons collected from eight samples indicated that the burial temperatures of these sedimentary rocks did not exceed ~180 °C, suggesting that these grains record detrital (U-Th)/He dates. Apatite fission-track (AFT) analysis of 10 samples yielded mixed results, with cooling ages ranging from 30 to 15 Ma; however, most sites failed the 2 test, suggesting that multiple age cohorts are present. Pooled AFT ages suggest that rocks presently at the surface were exhumed through their AFT closure temperature ca. 11–18 Ma. Cooling and exhumation thus most likely resulted from middle Miocene shortening across the fold-and-thrust belt in response to early oblique convergence between the Caribbean and South America plates. Post-Miocene deformation associated with more recent transform tectonics has therefore resulted in more limited (

Pub.: 28 Dec '16, Pinned: 22 Apr '17

Thermal history and differential exhumation across the Eastern Musgrave Province, South Australia: Insights from low-temperature thermochronology

Abstract: Multi–method geo- and thermochronological data obtained for Palaeo- and Mesoproterozoic granitoids traversing the main structural architecture of the eastern Musgrave Province within South Australia reveal multiphase cooling histories. Apatite U-Pb dating on six samples yield consistent ages of ~ 1075–1025 Ma, suggesting a thermal reset coinciding with mantle-derived magmatism of the greater Warakurna Large Igneous Province (~ 1080–1040 Ma). Apatite fission track (AFT) analysis indicate that four discrete thermal events affected the study area, inducing cooling through the AFT partial annealing zone (~ 60–120 °C), supported by apatite and zircon (U-Th-Sm)/He data. Late Neoproterozoic cooling from deep crustal levels to temperatures < 200 °C was discerned, which is thought to be related to exhumation and denudation during the Petermann Orogeny. Subsequent cooling events at ~ 450–400 Ma (Silurian–Devonian) and ~ 310–290 Ma (Late Carboniferous) are interpreted to represent exhumation associated with the Alice Springs Orogeny. The latter event exhumed the sampled plutons to shallow crustal depths. An additional Triassic – early Jurassic thermal event, likely recording elevated geothermal gradients at that time, was observed throughout the study area, however, more data is needed to further support this interpretation. The high sample density across the structural architecture of the study area furthermore reveals patterns of fault reactivation and resulting differential exhumation, indicating shallower exhumation levels in the centre and deeper exhumation towards the margins of the sampled transect. The observed differential exhumation patterns match with existing seismic data and fit a model of an inverted graben system for the Phanerozoic evolution of the eastern Musgraves.

Pub.: 07 Mar '17, Pinned: 22 Apr '17