Andrew Parsons

University of Plymouth | UoP · School of Geography, Earth and Environmental Sciences

This study presents the first use of high-angular resolution electron backscatter diffraction (HR-EBSD) to quantitatively characterise geometrically necessary dislocations in quartz subgrain structures. HR-EBSD exploits cross-correlation of diffraction patterns to measure intragranular misorientations with precision on the order of 0.01° with well-...

In this study, we integrate bedrock datasets, observations of subducted slabs in the mantle, and plate kinematic constraints, to constrain models for the India-Asia collision and the central Tethys oceans. To accomplish this, we review: (1) the post-Triassic bedrock record of subduction in Tibet; (2) seismic tomographic imaging of subducted slabs i...

Ultrahigh‐pressure (UHP) metamorphism observed in continental terranes implies that continental crust can subduct to ~40 kbar before exhuming to the surface. This process is one of the least understood and widely debated parts of the orogenic cycle. The dominantly felsic composition of UHP continental terranes means that many petrology‐based techni...

Plain Language Summary To understand the links between plate tectonics and mantle processes, researchers must determine how tectonic plates have moved with respect the evolving mantle through geological time. To overcome this problem, recent studies use the locations of subducted slabs in the deep mantle to reconstruct plate motions, based on the h...

The tectonic assembly of the Northern Cordillera is currently disputed and directly impacts Paleozoic-to-recent paleogeographic and plate tectonic reconstructions of North America. In this study, we present new U-Pb zircon geochronology from the allochthonous Yukon-Tanana terrane and the parautochthonous Cassiar terrane of the Northern Cordillera f...

Ophiolite complexes are an important component of oceanic terranes in the northern Cordillera during Cordilleran orogenesis. Despite their tectonic importance, few systematic studies of these complexes have been conducted. Detailed studies of the pseudostratigraphy, age, geochemistry, and structural setting of ophiolitic rocks in the northern Cor...

West-central Yukon and eastern Alaska are characterized by widespread metamorphic rocks that form part of the allochthonous, composite Yukon-Tanana terrane and parautochthonous North American margin. Structural windows through the Yukon-Tanana terrane expose parautochthonous North American margin in that broad region, particularly as mid-Cretaceous...

Distributions of slabs within Earth’s mantle are increasingly used to reconstruct past subduction zones, based on first-order assumptions that slabs sink vertically after slab break-off, and thus delineate paleo-trench locations. Non-vertical slab motions, which occur prior to break-off, represent a potentially significant source of error for slab-...

The India-Asia collision is one of the most globally significant tectonic events of the Cenozoic era. It is widely cited as providing a unique natural laboratory for studying collisional tectonics, offering invaluable insights of processes associated with continental collision across a multitude of scales. Yet despite its importance, significant de...

Alaska is made up of a mosaic of terranes that have enigmatic origins. Several plate restorations for the assembly of Alaska have been proposed, but their validity remains debated, partly due to the removal of vast volumes of oceanic plate material via subduction at the accretionary margins. The position, depth and volume of this subducted lithosph...

The Western Gneiss Region (WGR) of Norway, part of the Caledonian Orogenic Belt, is one of the largest and best studied examples of exhumed ultra-high pressure (UHP) continental terrains in the world. This makes it an ideal candidate for studying the poorly understood processes that facilitate and control the exhumation of UHP continental material....

Ultrahigh-pressure (UHP) metamorphism observed in continental terranes implies that continental crust can subduct to ~40 kbar before exhuming to the surface. This process is one of the least understood and widely debated parts of the orogenic cycle. The dominantly felsic composition of UHP continental terranes means that petrology-based techniques...

The Earth as a planetary system has experienced significant change since its formation c. 4.54 Gyr ago. Some of these changes have been gradual, such as secular cooling of the mantle, and some have been abrupt, such as the rapid increase in free oxygen in the atmosphere at the Archean-Proterozoic transition. Many of these changes have directly affe...

The Western Gneiss Region (WGR) of Norway is one of the largest and most studied high pressure (HP) and ultrahigh pressure (UHP) continental terranes on the planet. During the Caledonian orogeny, the WGR formed as a result of the collision of Baltica and Laurentia on closure of the Iapetus Ocean (Terry & Robinson, 2003). Baltica subducted below Lau...

The Western Gneiss Region (WGR) of Norway is one of the largest and best studied examples of exhumed ultra-high pressure (UHP) continental terrains in the world. It is part of the Caledonian Orogenic Belt, which formed during the collision of Baltica with Laurentia after the closure of the Iapetus Ocean in the Cambro-Ordovician. The WGR is situated...

The India-Asia collision is one of the most well-studied orogenic events on Earth; it recorded the terminal stages of the central Tethys ocean basins and offers invaluable insight into the geological processes associated with continental collision. In this study, we integrate bedrock datasets, observations of subducted slabs in the mantle, and plat...

Powerpoint file containing all figures from Palin et al. (2020) Earth Science Reviews "Secular change and the onset of plate tectonics on Earth" (doi: 10.1016/j.earscirev.2020.103172)

This file provides additional information and data sources to supplement and support our summary of Mesozoic to Cenozoic subduction in the south Tibetan crustal block presented in Section 5.1 and Figure 5 of the main article. A database of published geochronology used to build Figure 4 can also be found in Supplementary Materials 04.

Database of geochronology used to build Figure 3 in main article. Sheet 1 displays geological 'Events' displayed in Figure 3. Sheet 2 displays individual data sources used to constrain each 'Event' in Sheet 1. Data sources and 'Events' are linked by catalogue numbers.

Supplementary Materials 01 - Figures and maps of Tibet and the Himalaya

Supplementary Materials 02 - ArcGIS files of point, line, polygon and raster layers used in Figures 1, 2, 8, 21, and 23 (follow link in PDF to download).

Advances in plate-reconstruction modelling allow geological and geophysical datasets to be readily integrated within a plate kinematic framework; this enables development of regional tectonic models that are consistent with the bedrock record, deep mantle structure and global tectonic plate networks. In this study, we evaluate the constraints that...

The India-Asia collision is one of the most well-studied orogenic events on Earth; it recorded the terminal stages of the eastern Tethys ocean basins and offers invaluable insight into the geological processes associated with continental collision. A variety of different models to explain the India-Asia collisions are still debated; distinctions be...

The Earth’s inner core exhibits significant anisotropy in both seismic velocity and attenuation as well as hemispherical and depth variations. These observations point to an inner core that is both complex and dynamic. However, interpretation of these observations without knowledge of the attenuation processes active in the inner-core is difficult....

Evidence of transformation at UHP conditions is often lacking in felsic rocks due to incomplete transformation and/or overprinting by later metamorphism and deformation. In the absence of coesite, the distinctive microstructures formed by coesite breakdown (e.g. ‘palisade’ quartz) provide the only robust evidence of burial to UHP depths. Whereas ex...

Mineral boundaries play crucial although often poorly understood roles in many grain scale processes (e.g. diffusion , dislocation creep, dynamic recrystallization). Intragranular boundaries occur within individual grains and accommodate differences in crystallographic orientations of <10˚. As misorientations are typically defined by rotations that...

Evidence of transformation at UHP conditions is often lacking in felsic rocks due to incomplete transformation and/or overprinting by later metamorphism and deformation. In the absence of coesite, microstructures after coesite (e.g. ‘palisade’ quartz) provide the only robust evidence of burial to UHP depths. Low strain rocks provide a potential win...

Crystallographic preferred orientations (CPOs) in olivine are widely used to infer the mechanisms, conditions, and kinematics of deformation of mantle rocks. Recent experiments on water-saturated olivine were the first to produce a complex CPO characterised by bimodal orientation distributions of both [100] and [001] axes and inferred to form by co...

We present the first detailed structural analysis of the Yukon River shear zone (YRSZ), which forms an important structural break within the Yukon-Tanana terrane of the Northern Cordillera in Yukon (Canada). The YRSZ is a NW-SE–striking shear zone that juxtaposes Mississippian orthogneiss hanging-wall rocks (Simpson Range suite) against pre-Late De...

Seismic tomography may be used to identify slabs of oceanic lithosphere that have subducted into the upper and lower mantle. Correlation of this information with constraints from the bedrock geological record provides a means to test and develop new and existing paleogeographic and tectonic plate reconstruction models. Here, we present a visual sum...

Upper-plate and lower-plate settings within subduction zones have distinct geological signatures. Identifying and discriminating between these settings is crucial to the study of accretionary orogens. We applied this distinction to the Northern Cordillera in Yukon, British Columbia, and Alaska, and we focused on the identification of upper-plate an...

Upper plate and lower plate settings within subduction zones have distinct geological signatures. Identifying and discriminating between these settings is crucial to the study of accretionary orogens. We apply this distinction to the Northern Cordillera in Yukon, British Columbia and Alaska, and focus on the identification of upper plate and lower...

The Yukon Tanana (YTT) and Slide Mountain terranes (SMT) of the Cordillera in Canada and Alaska were interpreted in terms of opening and closing of a Late Devonian-Permian Japan Sea-style backarc basin behind a continental arc built upon YTT, which rifted from Laurentia during the Famennian-early Mississippian. Formation of Famennian transitional o...

The distinction of upper and lower plate processes in paleosubduction zones is critical for identification and interpretation of terrane sutures, subduction zone geometries and mechanisms of accretionary orogenesis. We utilize geochemical and geochronological analyses to challenge existing Paleozoic-Mesozoic tectonic models for the Northern Cordill...

This open file report outlines the 2017 field activities conducted in the Dunite Peak area of the Big Salmon Range, south central Yukon (Figure 1), as part of the Geo-mapping for Energy and Minerals (GEM2) program Cordillera project. Following from 2016 field activities in the same region, targeted bedrock geological mapping and sampling was conduc...

Fault block basins exposed along NE Greenland provide insights into the tectonic evolution of East Greenland and the Norwegian-Greenland Sea. We present a new geological map and cross sections of the Traill Ø region, NE Greenland, which formed the western margin of the Vøring Basin prior to Ceno zoic seafloor spreading. Observations support a polyp...

The author of a prize-winning paper published in Geochemistry, Geophysics, Geosystems describes new insights into crustal mechanics and the formation of the Himalaya.

Accretionary orogens such as the NW Cordillera are often long lived and represent a collage of terranes amalgamated through multiple phases of deformation. In order to understand the early development of these orogens, key crustal components present during these early stages must be identified and studied in detail to unravel present day structural...

The pericratonic Yukon-Tanana terrane (YTT) exhibits a complex and enigmatic history of extension, arc magmatism and deformation associated with its separation and re-accretion to the western North American margin by early Mesozoic time. The Yukon River Thrust (YRT) is a suggested compressional ductile shear zone between pre-late Devonian silicicla...

Understanding of the formation of accretionary orogens requires investigations of the timing, kinematics and mechanisms of terrane accretion. In the NW Cordillera, the Slide Mountain oceanic terrane (SMT) formed between Phanerozoic island arcs and the North American continent (NAC) during Devonian-Permian times and subsequently recorded multiple de...

The Dunite Peak area of the Big Salmon Range, south-central Yukon, exposes klippen of maficultramafic strata belonging to the Slide Mountain terrane that structurally overlie metasedimentary strata of the Yukon-Tanana terrane. Previous workers also infer the suture between the allochthonous Yukon-Tanana terrane and parautochthonous Cassiar terrane...