Content uploaded by William Joseph Collins
Author content
All content in this area was uploaded by William Joseph Collins on May 24, 2018
Content may be subject to copyright.
A preview of the PDF is not available
Compressional intracontinental orogens: Ancient and modern perspectives
Abstract
Compressional intracontinental orogens are major zones of crustal thickening produced at large distances from active plate boundaries. Consequently, any account of their initiation and subsequent evolution must be framed outside conventional plate tectonics theory, which can only explain the proximal effects of convergent plate-margin interactions. This review considers a range of hypotheses regarding the origins and transmission of compressive stresses in intraplate settings. Both plate-boundary and intraplate stress sources are investigated as potential driving forces, and their relationship to rheological models of the lithosphere is addressed. The controls on strain localisation are then evaluated, focusing on the response of the lithosphere to the weakening effects of structural, thermal and fluid processes. With reference to the characteristic features of intracontinental orogens in central Asia (the Tien Shan) and central Australia (the Petermann and Alice Springs Orogens), it is argued that their formation is largely driven by in-plane stresses generated at plate boundaries, with the lithosphere acting as an effective stress guide. This implies a strong lithospheric mantle rheology, in order to account for far-field stress propagation through the discontinuous upper crust and to enable the support of thick uplifted crustal wedges. Alternative models of intraplate stress generation, primarily involving mantle downwelling, are rejected on the grounds that their predicted temporal and spatial scales for orogenesis are inconsistent with the observed records of deformation. Finally, inherited mechanical weaknesses, thick sedimentary blanketing over a strongly heat-producing crust, and pervasive reaction softening of deep fault networks are identified as important and interrelated controls on the ability of the lithosphere to accommodate rather than transmit stress. These effects ultimately produce orogenic zones with architectural features and evolutionary histories strongly reminiscent of typical collisional belts, suggesting that the deformational response of continental crust is remarkably similar in different tectonic settings.
... The ca. 360-330 Ma rapid-cooling episode is only recorded east of the MSZ (Figures 1 and 8). The timing of this cooling episode overlaps with the timing of the intracontinental Devonian-Carboniferous Alice Springs Orogeny, which is extensively documented in central Australia within the Aileron and Irindina Provinces as well as Amadeus Basin (e.g., [86][87][88][89]) and involved extreme basin inversion in these locations (e.g., [90,91]). The Alice Springs Orogeny (ASO) is thought to be the result of far-field stress propagation from plate boundaries interactions to the interior of the Australian continent (e.g., [86][87][88][89]). ...
... The timing of this cooling episode overlaps with the timing of the intracontinental Devonian-Carboniferous Alice Springs Orogeny, which is extensively documented in central Australia within the Aileron and Irindina Provinces as well as Amadeus Basin (e.g., [86][87][88][89]) and involved extreme basin inversion in these locations (e.g., [90,91]). The Alice Springs Orogeny (ASO) is thought to be the result of far-field stress propagation from plate boundaries interactions to the interior of the Australian continent (e.g., [86][87][88][89]). Although the main tectono-thermal signature is located in central Australia, several studies have recorded exhumation in both northern and southern Australia via low-temperature thermochronology (e.g., [2,8,66,68,[92][93][94][95][96][97]). ...
... To the east of the structure, early Carboniferous reactivation of the Bunburra, Border, and Palinar Shear Zones, coeval with the ASO, is interpreted as the cause of shallow crustal exhumation observed within the thermal models, where fastcooling correlates with increasing proximity to these structures. Preexisting east-west-striking structures have been identified in the regions where the ASO-related deformation is localized and where Carboniferous rapid-cooling is observed, such as the Aileron and Irindina Provinces [86][87][88][89]91] and Pine Creek Orogen [68], respectively. In contrast, in regions where east-westtrending structural features are absent, a slower and monotonic cooling is observed (e.g., [68]), as is the case for the western side of the MSZ. ...
Combined apatite Lu–Hf, U–Pb, and fission track (AFT) triple dating affords the opportunity to investigate the ~60 and 730°C thermal history of a study area. Here, we apply apatite triple dating to resolve the tempo of multiple thermo-tectonic events within the Precambrian basement rocks of the Coompana (COP) and Madura (MAP) Provinces, Western Australia. Apatite Lu–Hf dates for the western COP (~1.52 Ga) and MAP (~1.36 Ga) agree with published Mesoproterozoic magmatic crystallization ages. Younger apatite U–Pb dates (~1.16–1.12 Ga) for the western COP and MAP suggest isotopic decoupling and radiogenic-Pb loss by volume diffusion in response to metamorphism at that time. Further East in the COP, the apatite Lu–Hf, and U–Pb dates are within uncertainty of each other and are interpreted to reflect recrystallization at ~1.20–1.14 Ga, coinciding with the late Mesoproterozoic Maralinga thermomagmatic event. The imprints of such an event were more pervasive towards the eastern COP, resulting in a thermally weakened crust in this area. AFT results constrain the subsequent Phanerozoic low-temperature history which has contrasting thermal trajectories on either side of the Mundrabilla Shear Zone (MSZ). Thermal history modeling suggests an early Carboniferous rapid cooling pulse (~360–330 Ma) for the COP, east of the MSZ, that is contemporaneous with the intraplate Devonian–Carboniferous Alice Springs Orogeny. In contrast, the MAP, west of the MSZ, records a protracted monotonic cooling history since the Middle Devonian, implying long-term crustal stability. The differences in low-temperature thermal histories may be preconditioned by the extent of thermal weakening during the late Mesoproterozoic, as indicated by the Lu–Hf and U–Pb results. Here, we show the value of apatite triple dating applied to grains recovered from drill core samples, demonstrating opportunities for understanding other poorly accessible terranes.
... According to plate tectonics theory, orogenic settings are usually associated with plate boundaries and their immediate vicinity, resulting from interactions between rigid lithospheric plates [1]. However, in the last 50 years, with advances in plate tectonic research, it has been widely accepted that major deformations are not exclusive to plate boundaries but can also occur within plate interiors [2]. In the absence of local plate margin interactions, the deformation must be controlled either by the transmission of horizontal far-field stress from a plate boundary or vertical intraplate stresses via processes such as viscous dripping and delamination or interactions between large igneous provinces at the surface [2,3]. ...
... However, in the last 50 years, with advances in plate tectonic research, it has been widely accepted that major deformations are not exclusive to plate boundaries but can also occur within plate interiors [2]. In the absence of local plate margin interactions, the deformation must be controlled either by the transmission of horizontal far-field stress from a plate boundary or vertical intraplate stresses via processes such as viscous dripping and delamination or interactions between large igneous provinces at the surface [2,3]. ...
... Orogenic belts are primarily distributed along the plate boundaries and their immediate vicinity, where the interaction of rigid lithospheric plates results in intense crustal deformation and the uplift of mountains (Dewey & Bird, 1970). However, it is increasingly recognized that the compressional stress may also transfer a considerable distance away from the collision front and result in deformation in the continent's interior, which is commonly referred to as intracontinental orogens (Aitken et al., 2013;Cunningham, 2005;Raimondo et al., 2014). Geodynamic numerical modeling studies have previously emphasized the role of rheological heterogeneity in the continental lithosphere as a crucial factor in intracontinental deformation (Dyksterhuis & Müller, 2008;Gao et al., 2023;Huangfu et al., 2022Huangfu et al., , 2023. ...
Compressive stress generated at collision fronts can propagate over long distances, inducing deformation within the continent's interior. Nevertheless, the factors governing the partitioning of intracontinental deformation remain enigmatic. The Altai Mountains serve as a type‐example of ongoing intracontinental deformation. Here, we investigate the crustal architecture of the Chinese Altai Mountains, using receiver functions obtained from newly deployed dense seismic nodal arrays. The new seismic results reveal distinct crustal features, including (a) a negative polarity discontinuity beneath Chinese Altai Mountains, suggesting a low‐velocity layer; (b) a north‐dipping mid‐crustal structure beneath the suture zone between East Junggar and Chinese Altai, indicating underthrusting of East Junggar's lower crust beneath the Chinese Altai Mountains; (c) a double Moho structure beneath East Junggar, revealing a high‐velocity lower crustal layer. In conjunction with constraints from previous multi‐disciplinary regional studies, the double Moho structures are interpreted as mafic restite from Late Paleozoic magma underplating. The addition of mafic materials can significantly enhance the rheological strength of East Junggar's crust, causing it to function as an indenter that thrust beneath the Chinese Altai Mountains during the subsequent convergence process. As a consequence, significant deformation occurs in the Chinese Altai region, resulting in the emergence of decollements, as evident by the negative polarity discontinuity. The presence of pre‐existing decollements makes the Altai Mountains region more susceptible to deformation, thereby facilitating the concentration of intracontinental deformation. These findings illuminate the evolution history of the Chinese Altai Mountains and highlight the great impacts of ancient tectonics on intracontinental deformation partitioning.
The Yangtze Craton hosts significant Zn-Pb deposits in Neoproterozoic to Carboniferous carbonates (> 60 Mt Pb + Zn metals), accounting for 30% of China's Zn-Pb resources. However, determining the timing of zinc and lead mineralization in these reservoirs is challenging. This study employs LA-ICP-MS U-Pb geochronology on calcites to date Zn-Pb deposits hosted in Lower Cambrian limestone in the Huayuan orefield. Three generations of calcite formation were dated: the first recorded the pre-ore deposition of Lower Cambrian limestone at 517 ± 10 Ma, the second marked a hydrothermal event linked to stratiform sphalerite ore formation at 501.4 ± 8.4 Ma, and the third was associated with discordant breccia-hosted Zn-Pb mineralization at 397.5 ± 9.6 Ma. Our results indicate that Paleozoic carbonate-hosted Pb-Zn mineralization in the Yangtze Craton is linked to (1) the final assembly of Gondwana in the late Cambrian-early Ordovician (520 − 480 Ma); and (2) the intracontinental orogeny response to Jiangnan Uplift (420 − 400 Ma). This study highlights the spatial-temporal relationship between low temperature carbonate-hosted mineralization and orogenic events that are consistent with classic Mississippi Valley-type models worldwide. Furthermore, it demonstrates the potential of in situ U-Pb calcite geochronology to date ore deposits lacking syn-ore minerals suitable for traditional dating methods.
Epidote group minerals, including allanite, clinozoisite and epidote are common in a range of metamorphic, igneous and hydrothermal systems, and are stable across a wide range of pressure–temperature (P–T) conditions. These minerals can incorporate substantial amounts of rare earth elements (REEs) during their crystallisation, making them potential candidates for Lu–Hf geochronology to provide age constraints on various geological processes. Here we report on a first exploration into the feasibility of in situ Lu–Hf geochronology for epidote group minerals from various geological settings and compare the results with age constraints from other geochronometers. Magmatic allanite samples from pegmatites and monzogranites in the Greenland anorthosite complex, Coompana Province and Qingling Orogen provided dates consistent with magmatic events spanning from c. 2660 to 1171 Ma. In the Qingling pegmatites, a younger phase of hydrothermal allanite was dated at c. 215 Ma, consistent with the timing of regional REE mineralisation. Allanite from the Yambah Shear Zone, Strangways Metamorphic Complex, yielded Lu–Hf age of c. 430 Ma. It predates the garnet and apatite growth at c. 380 Ma, suggesting the Lu–Hf system can be preserved in allanite during prograde amphibolite-facies metamorphism. Additionally, Lu–Hf dates for hydrothermal clinozoisite and epidote are consistent with the timing of hydrothermal alteration and mineralisation in a range of settings, demonstrating the utility of the technique for mineral exploration. Despite the current lack of matrix-matched reference materials, the successful application of laser ablation Lu–Hf geochronology to epidote group minerals offers valuable geochronological insights into various geological processes that can be difficult to access through other geochronometers.
We investigated highly mature sedimentary rocks exposed along both sides of the Fram Strait in the northern North Atlantic using apatite fission track and (U‐Th)/He thermochronology to obtain information on the thermal imprint of rifting and continental breakup processes along a sheared margin. Our data showed that the conjugate margins experienced several heating episodes, which we explain as resulting from heat transfer along segments of the De Geer Fracture Zone, a large continental transform system which connected magmatic centers north and south of the Fram Strait. Heating occurred prior to and during the Eurekan intraplate orogeny, which occupied the position of the present‐day Fram Strait during the Eocene. Heat transfer may have caused or contributed to lithospheric weak zones, which focussed deformation during intraplate orogeny. Movements along the transform fault system continued during the Oligocene, after the end of the Eurekan Orogeny, causing further structural weakening of pre‐existing fault zones. These were exploited during the final continental breakup leading to the opening of the Fram Strait. No unambiguous thermal signature associated with this latest stage of breakup was detected. Our data underline recent studies on the importance of structural inheritance and continental transform faults for the prolonged and complex processes of continental rifting and breakup.
Gravity anomalies from geological features in the upper crust are masked by large amplitude long wavelength gravity variations from isostatic roots. An isostatic residual (IR) gravity anomaly grid of onshore Australia has been produced by Geoscience Australia which has these long wavelength features removed. This gravity map reveals more clearly the density distributions of geological interest within the upper crust.
The depth to mantle model and subsequent isostatic corrections were produced using a modified version of the USGS program AIRYROOT provided by Intrepid Geophysics. Geoscience Australia’s 2009 Bathymetry and Topography Grid was used to calculate the depth to crustal bottom following the Airy-Heiskanen crustal-root model. The isostatic corrections were then applied to the complete Bouguer anomalies to produce the Isostatic Residual Gravity Anomaly Grid of Australia.
The aim of this chapter is to present an overview of the behaviour of fluids during the metamorphic cycle, i.e. from sedimentation and diagenesis through metamorphism to post-metamorphic cooling, uplift and cratonization of an orogenic belt. In particular, the chapter will attempt to put metamorphic fluids, in the sense of those fluids actually generated in situ from metamorphic devolatilization reactions, in the context of other fluid inputs into the metamorphic pile before, during and after metamorphism. In the course of this review, there are three issues to which particular attention will be drawn: the role of original sedimentary fluids in dictating the character of subsequent metamorphic fluids; the rates at which the fluids may be released by reaction; and the extent to which fluids may be drawn down from high crustal levels into crystalline rocks during post-metamorphic uplift.
