Architecture, kinematics, and lithospheric processes of a compressional intraplate orogen | RESEARCH The architecture, kinematics, and lithospheric processes of a compressional intraplate orogen occurring under Gondwana assembly: The Petermann orogeny, central Australia Alan R.A. Aitken1,*, Peter G. Betts1, and Laurent Ailleres1 1SCHOOL OF GEOSCIENCES, MONASH UNIVERSITY, WELLINGTON ROAD, CLAYTON, VICTORIA 3800, AUSTRALIA ABSTRACT We ally aeromagnetic interpretation with constrained three-dimensional (3D) gravity inversion over the Musgrave Province in central Aus- tralia to produce a 3D architectural and kinematic model of the ca. 550 Ma compressional intraplate Petermann orogeny. Our model is consistent with structural, metamorphic, and geochronological constraints and crustal-scale seismic models. Aeromagnetic interpretation indicates that divergent thrusts at the margins of the province are cut by transpressional shear zones that run along the axis of the orogen. Gravity inversion indicates that the marginal thrusts are crustal-scale and shallow-dipping, but that the transpressional shear zones of the axial zone are more steeply dipping, and penetrate the crust-mantle boundary, accommodating offsets of 10–25 km. This thick wedge of mantle within the lower crust has been in isostatic disequilibrium for more than 500 Ma, and we suggest that this load may be supported by local lithospheric strengthening resulting from the emplacement of relatively strong lithospheric mantle within the relatively weak lower crust. Other orogenic processes inferred from the model include: probable inversion of relict extensional architecture; crustal-scale strain partitioning leading to strain accommodation by the vertical and lateral extrusion of relatively undeformed crustal blocks; and escape tectonics directed toward the relatively free eastern margin of the orogen. These processes are consistent with the concept that mechani- cal and thermal heterogeneities in the lithosphere, and the resulting feedbacks with deformation, are the dominant controls on intraplate orogenesis. This model also demonstrates that the architecture and kinematics of the Petermann orogeny require modifi cation of leading models of Gondwana assembly. LITHOSPHERE; v. 1; no. 6; p. 343–357. doi: 10.1130/L39.1 INTRODUCTION et al., 2003) and Altai (Cunningham, 2005) inlier (e.g., Collins and Shaw, 1995; Sandi- regions of central Asia. These studies highlight ford, 2002). The architecture and kinematics of oro- the diverse range of settings for intraplate com- The initiation of these orogens has been the genic belts have been the topic of many stud- pressional deformation, and also the variety of topic of much study, and several quite different ies, mostly focused on actively deforming or lithospheric processes that can occur. How- models may explain the initiation and some of recently deformed plate margins, such as the ever, one fi nding that is common to all studies the main features of these orogens (cf. Braun Himalaya (e.g., Molnar, 1988; Yin, 2006) or the is the importance of thermal and mechanical and Shaw, 2001; Camacho et al., 2002; Neil European Alps (e.g., Bruckl et al., 2007; Ebbing heterogeneities in the continental lithosphere and Houseman, 1999; Neves et al., 2008; San- et al., 2001; Luschen et al., 2004). In contrast, as a control on crustal architecture (e.g., Cun- diford et al., 2001). A detailed regional-scale compressional intraplate orogens have been the ningham, 2005; Dickerson, 2003; Hand and model of the 3D architecture and kinematics subject of comparatively few studies. Sandiford, 1999; Sandiford and Hand, 1998; of these orogens is lacking. This is important To date, studies of the structure and kine- Ziegler et al., 1998). because it may indicate the orientation and matics of intraplate compression have concen- Late Neoproterozoic to Devonian tectonic intensity of the forces driving the system and trated on the inversion of extensional basins in reworking of central Australia is interpreted characterize the feedback processes that con- both backarc-hinterland and forearc-foreland to refl ect intraplate compressional orogenesis trol the interaction between crustal architecture settings (e.g., Dickerson, 2003; Sandiford, (e.g., Betts et al., 2002; Camacho and Fanning, and the dynamics of the orogen. 1999; Turner and Williams, 2004; Ziegler et al., 1995; Camacho et al., 2002; Hand and Sandi- In addition, these orogens provide a record 1995), with others studying the dynamic evolu- ford, 1999; Sandiford and Hand, 1998). Two of intraplate continental lithospheric deforma- tion of the currently active intraplate compres- discrete orogens are recognized: the ca. 600– tion under the infl uence of one of Earth’s most sional orogens of the Tien Shan (Burov et al., 500 Ma Petermann orogeny that reworked the dramatic periods of tectonism associated with 1990; Tapponnier and Molnar, 1979; Zhao Mesoproterozoic Musgrave Province (e.g., the assembly of Gondwana, and their architec- Major and Conor, 1993; Wade et al., 2008) ture and kinematics may help to recognize the *Corresponding author e-mail: alan.aitken@sci. and the ca. 450–350 Ma Alice Springs orog- most (and least) credible of many competing monash.edu.au. eny that reworked the Paleoproterozoic Arunta tectonic models (e.g., Boger and Miller, 2004; For permission to copy, contact [email protected] | © 2009 Geological Society of America 343 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/1/6/343/3037640/i1941-8264-1-6-343.pdf by guest on 02 October 2021 AITKEN et al. Cawood, 2005; Collins and Pisarevsky, 2005; deus and Offi cer basins, defi ning the extent of collision of Gondwana, resulting in the suturing Jacobs and Thomas, 2004; Meert and Van Der the ca. 1200 Ma Musgravian-Albany-Fraser of Australia, east Antarctica, and the Kalahari Voo, 1997; Meert, 2003; Rino et al., 2008; orogeny (Aitken and Betts, 2008). craton, onto the remainder of Gondwana, which Veevers, 2003). Subsequent to the Musgravian orogeny, the was previously assembled during the ca. 750– A combination of aeromagnetic data and voluminous mafi c intrusions of the Giles Com- 620 Ma east African orogen (Meert, 2003). gravity data can be used to image architecture plex and coeval mafi c dikes and granitoids were However, a lack of accreted arc fragments or from the near surface to crust-mantle bound- emplaced within the Musgrave Province dur- continental blocks and the limited extent of its ary geometry (e.g., Williams and Betts, 2007), ing the extensional Giles event at ca. 1080 Ma component terranes led Squire et al. (2006) to and therefore these data provide the ideal tool (Glikson et al., 1995; Sun et al., 1996), along suggest that the Kuunga orogeny is an intracra- to unify the concepts of previous studies of with surfi cial volcanic rocks now exposed at the tonic response to the East African–Antarctic orogenic architecture at multiple scales. In margins of the Musgrave Province (Glikson et orogen, which is interpreted by several authors this paper, we combine interpretation of high- al., 1995). Although not well defi ned, the extent to record the major event in the amalgamation resolution aeromagnetic data with 3D gravity and orientation of this event may be defi ned of Gondwana (Jacobs and Thomas, 2004; Stern, inversions to produce a crustal-scale model of by east-to-east-southeast–trending shear zones 1994). A third hypothesis for Gondwana assem- the architecture and kinematics of the intra- that predate or are synchronous with the dike bly recognizes the dominance of transpressional plate Petermann orogeny in the eastern Mus- emplacement events (Aitken et al., 2008; Ait- orogenic belts, and proposes that oblique sub- grave Province. This model is constrained by ken and Betts, 2009b; Clarke et al., 1995); the duction along the Pacifi c margin of Gondwana geological observations at a number of scales, alignment of Giles Complex mafi c intrusions from ca. 560 Ma onwards led to continental including pressure-temperature-time (P-T-t) along the axis of the Musgrave Province with blocks becoming a “counter-rotating cog” in data, structural interpretations, petrophysical no geophysical evidence for buried Giles Com- Gondwana (Veevers, 2003). sampling, and macro-scale geological obser- plex plutons outside of this zone (Glikson et al., The localization of strain in the Musgrave vations, and constraint is also derived from 1995; Glikson et al., 1996); and the orientation Province during the Petermann orogeny has crustal-scale seismic refl ection lines and pas- and extent of the Warakurna large igneous prov- been the subject of some discussion. An early sive seismic models. From this architectural ince (LIP), of which the Giles Complex is a key model suggested thermal blanketing of an upper and kinematic model, we infer the most infl u- constituent, which extends from northern West- crust high in heat-producing elements by the ential lithospheric processes that have shaped, ern Australia to the Musgrave Province (Wing- thick sediments of the Centralian Superbasin as and been controlled by, the architecture and ate et al., 2004). a mechanism to create anomalously weak lith- kinematics of the Petermann orogeny. After a hiatus of ca. 200 million years, mafi c osphere beneath the deepest part of the basin, dikes were emplaced at ca. 800 Ma along east- which was interpreted to overlie the Musgrave THE GEOLOGIC SETTING OF THE southeast– and southeast-oriented structures Province (Hand and Sandiford, 1999; Sandiford PETERMANN OROGENY (Zhao et al., 1994). The inception of the Offi cer and Hand, 1998). This model has since been and Amadeus basins is broadly contemporane- disputed on the grounds of an emergent Mus- The Musgrave Province preserves a variety ous with these dikes, and probably formed as grave Province as the source for detrital zircons of Mesoproterozoic gneissic rocks of domi- part of the once contiguous Centralian Superba- in ca. 700 Ma to ca. 500 Ma Amadeus Basin nantly felsic lithology with precursors dated at sin (Walter et al., 1995). This ca. 800 Ma exten- sedimentary rocks (Camacho et al., 2002), and ca.