Models of large, hot orogens containing a collage of reworked and accreted terranesThis article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent.

Abstract

We describe a classification scheme for orogens using Temperature-Magnitude (T-M) diagrams and use this framework for modelling large, hot orogens that evolve in continents comprising cratonic nuclei bordered by a series of juvenile accreted, reworked, and metamorphosed terranes. Modelling the complete evolution of an orogen is difficult, particularly large orogens with multiple orogenic phases. Early phases during which a continent is assembled produce a tectonic and metamorphic fabric that needs to be taken into account when modelling the main collisional orogeny. This inherited fabric is represented in a simple way in models described here by a series of lower crustal blocks that are arranged to be systematically stronger toward the cratonic continental interiors. We investigate how this fabric influences the development of the model orogen during the main collisional phase using upper-mantle-scale (UMS) and crustal-scale (CS) finite element models. The models exhibit a diachronous three-phase evolution: crustal thickening, thermal incubation, and lower crustal indentation. The UMS and CS models are shown to give comparable results in regard to crustal deformation. The UMS models exhibit additional features including single-and double-slab breakoffs and corresponding episodes of uplift and gravitational spreading within the orogenic crust. Protracted postconvergent gravitational spreading of the hot, decoupled crust is also demonstrated. Lastly, we demonstrate the application of this type of model to natural orogens, the Grenville orogen in western Ontario and the southern Canadian Cordillera, and in terms of the T-M diagram.Résumé : Le présent article décrit un système de classification des orogènes basé sur des diagrammes température-magnitude et nous utilisons ce cadre pour modéliser de gros orogènes chauds qui ont évolué dans les continents qui comportaient des noyaux de cratons délimités par une série de terranes juvéniles, accrétés, retravaillés et métamorphosés. Il est difficile de modéliser l'évolution complète d'un orogène, surtout les gros orogènes comportant de multiples phases orogéniques. Les premières phases durant lesquelles un continent est assemblé produisent une fabrique tectonique et métamorphique dont il faut tenir compte lors de la modélisation de l'orogène principale de collision. Cette fabrique héritée est représentée d'une manière simple dans les modèles décrits ici par une série de blocs dans la croûte inférieure qui sont arrangés pour être systématiquement plus forts vers l'intérieur des cratons continentaux. Nous étudions comment cette fabrique influence le développement de l'orogène modèle au cours de la principale phase de collision en utilisant des modèles aux éléments finis à l'échelle du manteau supérieur et à l'échelle de la croûte. Les modèles présentent une évolution en trois phases diachroniques, un épaississement de la croûte, une incubation thermique et une indentation de la croûte inférieure. Les modè-les à l'échelle du manteau supérieur et à l'échelle de la croûte donnen...

Prolonged Partial Melting of Garnet Amphibolite from the Eastern Himalayan Syntaxis: Implications for the Tectonic Evolution of Large Hot Orogens

“…During the Early Miocene from 20 to 10 Ma, the weak lower crust extruded by channel flow between the MCT and STD systems with an opposite shear sense to form the migmatitic HP granulites and leucogranites of the HHC in the Himalayan orogenic core (Figure 15b). It is likely, therefore, that many hot orogens have experienced prolonged partial melting and tectonic evolution process similar to that documented in the Himalayan orogen, as proposed by previous works (Beaumont et al, 2006(Beaumont et al, , 2010Cottle et al, 2015;Maierová et al, 2016;Rivers, 2009;Schulmann et al, 2008).…”

“…The role of weak layers in the lithosphere during the evolution of large hot orogens has become a focus for modern tectonics research (Clark & Royden, 2000;Cottle et al, 2015;Law et al, 2006). The Himalayan-Tibetan orogen is a typical large hot orogen and has a molten and thickened lower crust (Beaumont et al, 2006(Beaumont et al, , 2010. Many models of crustal dynamics implicate the flow of hot, weak middle to lower crust as a major control on orogenic architecture, with the Indo-Asian collision being the type example (Beaumont et al, 2001;Clark & Royden, 2000;Cottle et al, 2015;Kohn & Corrie, 2011).…”

“…The Himalayan-Tibetan orogen formed due to India-Asia continental collision, which initiated at ca. 55-50 Ma (Ding et al, 2016;Guillot et al, 2003;Meng et al, 2012;Najman et al, 2010;Yin & Harrison, 2000;Zhang et al, 2019;Zhu et al, 2015), and is typical of large hot orogens (Beaumont et al, 2006(Beaumont et al, , 2010. Available studies have shown that ultrahigh pressure (UHP) and high-pressure (HP) metamorphic rocks occur in the western Himalaya (Ahmad et al, 2006;Guillot et al, 2008;Kaneko et al, 2003;Kouketsu et al, 2015;Lanari et al, 2013;O'Brien, 2019;O'Brien et al, 2001) and HP granulites and retrogressed eclogites occur throughout the central Himalaya (Chakungal et al, 2010;Cottle，Jessup, et al, 2009;Groppo et al, 2007;Kohn, 2014;Li et al, 2018;Lombardo et al, 2016;Lombardo & Rolfo, 2000;Wang et al, 2017), whereas only HP granulites are exposed in the eastern Himalayan syntaxis (EHS) (Booth et al, 2009;Ding et al, 2001;Guilmette et al, 2011;Liu & Zhong, 1997;Peng et al, 2018;Su et al, 2012;Tian et al, 2016;Xu et al, 2010;Zhang et al, 2010;Zhu et al, 2015).…”

Whither the supercontinent cycle?

“…excursions). Given the unprecedented scale of orogenesis associated with the assembly of Rodinia (Beaumont et al, 2010), the lack of signifi cant changes in the Sr seawater and ε Hf (zircon) suggests that relatively juvenile crust was recycled during its amalgamation, compatible with evidence that the eastern fl ank (modern coordinates) of Laurentia was a Pacifi c-type margin for nearly 0.8 g.y. prior to collision, and produced abundant juvenile crust between 1.7 and 1.3 Ga (e.g., Åhäll, and Gower, 1997;Dickin, 2000).…”

Logan Medallist 2. Geophysics and Geology: An Essential Combination Illustrated by LITHOPROBE Interpretations–Part 1, Lithospheric Examples

“…One was the continuing development of computer simulation capabilities to enable modelling of more realistic and complex processes that have been active in tectonic evolution (e.g. Beaumont et al 2010;Pysklywec et al 2010; and references within these papers). The second component was application of geodynamic modelling to fundamental tectonic processes inferred within transects and comparisons of interpreted structures and characteristics with those determined from modelling (e.g.…”