Rapid cooling and exhumation in the western part of the Mesoproterozoic Albany-Fraser Orogen, Western Australia
Introduction
Exhumation processes can be difficult to ascertain, especially in ancient orogenic belts. Thermochronology can be used to determine the distribution of cooling ages and rates across an orogen, providing an important tool in resolving orogenic exhumation histories. Orogenic cooling rates may be highly variable, and when taken in isolation are not diagnostic of a particular exhumation mechanism (Ring et al., 1999). However, when integrated with other datasets such as structural and metamorphic histories, cooling rates may be correlated with tectonic setting and with exhumation mechanism. For example, in collisional settings, large hot orogens (LHO), which are characterised by a plateau in the hinterland, typically experience slow exhumation driven by orogenic collapse. In contrast, small cold orogens (SCO) are rheologically stronger and do not undergo orogenic collapse, but are exhumed more quickly by erosion (Jamieson and Beaumont, 2013).
A compounding factor in comparing cooling histories from different orogens is the empirical correlation between decreasing cooling rate and increasing orogenic age. Dunlap (2000) showed that cooling rates in ancient Proterozoic collisional orogens are slower than those in Phanerozoic orogens (Dunlap, 2000). Empirical estimates of cooling rates in Proterozoic orogens are between 0.5 and 5 °C/Ma, whereas those for Phanerozoic orogens range from 5 to 50 °C/Ma (Dunlap, 2000, Willigers et al., 2002) and up to 150–350 °C/Ma in young, tectonically active orogens (e.g. Arnaud et al., 1993, Zeck et al., 1992). Dunlap (2000) suggested that the difference in cooling rates reflects the decreasing preservation potential of the thermochronological record with age, as Proterozoic orogens are more vulnerable to isotopic resetting than Phanerozoic orogens. Additionally, the present-day surface exposures of many Proterozoic orogens consist of the deeply eroded orogenic cores, which were at deep crustal levels during orogeny and were not exhumed until well after the orogenic cycle was complete (Willigers et al., 2002). Consequently, the Proterozoic thermochronological record is therefore biased towards slow, post-orogenic cooling, rather than the faster, syn-orogenic processes recorded in the upper-crustal rocks typically exposed in Phanerozoic orogens (Willigers et al., 2002).
The cooling records of global Mesoproterozoic orogens vary in their degree of preservation, as thermal histories are vulnerable to overprinting by later heating events. For example, both the Natal Metamorphic Province of South Africa and the Eastern Ghats Belt of India were active in the Mesoproterozoic assembly of Rodinia, but yield few data about post-orogenic cooling due to overprinting by ca 500 Ma Pan-African tectonism (Jacobs et al., 1997, Mezger and Cosca, 1999). In contrast, records of cooling and exhumation from the Grenville Orogen of North America, its inferred counterpart in the South American Amazon Craton and the Sveconorwegian Orogen of Scandinavia have not been overprinted, and are comparatively well understood due to several thermochronological studies (e.g. Bingen et al., 1998, Bingen et al., 2008, Busch et al., 1997, Cosca et al., 1998, Page et al., 1996, Rivers, 2008, Tohver et al., 2004). Although less extensively studied, cooling histories have also been determined for the intracontinental Reynolds Range, Mt. Isa Province and Mount Woods Inlier in central and northern Australia (Forbes et al., 2012, McLaren et al., 1999, Spikings et al., 2002, Vry and Baker, 2006).
In this article, we introduce the Albany-Fraser Orogen of Western Australia (Fig. 1) as an example of a Mesoproterozoic orogen that preserves a strikingly fast cooling history, that appears to defy the trend of decreasing cooling rate with increasing orogenic age. Although the tectonic setting of the Albany-Fraser Orogen is not well understood, it is thought to record the Mesoproterozoic suturing of the Yilgarn Craton to the combined Mawson and Gawler cratons during the assembly of Rodinia (Clark et al., 2000). The orogen curves around the margin of the Yilgarn Craton, such that it strikes east-west in the western region, and strikes northeast-southwest in the northeastern region (Fig. 1). The direction of convergence during orogeny is interpreted to be northwest-southeast, and consequently the western part of the orogen experienced a significant component of transpressive deformation, whereas the eastern part of the orogen was deformed in a more directly compressive stress regime (Bodorkos and Clark, 2004b).
In this article, we report the first 40Ar/39Ar thermochronology from the western part of the Albany-Fraser Orogen. We use these results in combination with previously published data relating to the inferred bulk stress regime of collisional orogeny to constrain the post-peak metamorphic cooling and exhumation history of the orogen. The cooling of the western Albany-Fraser Orogen is shown to be much faster than that in other Mesoproterozoic orogens, and is interpreted to represent fast cooling in a transpressional setting.
Section snippets
Tectonic setting of the Albany-Fraser Orogen
The Albany-Fraser Orogen extends ca 1200 km along the southern and southeastern margins of the Yilgarn Craton of Western Australia (Fig. 1). The orogen consists of mostly Paleo- to Mesoproterozoic rocks formed on or close to the margin of the Yilgarn Craton, which were subsequently deformed to high metamorphic grades during the late Mesoproterozoic Albany-Fraser Orogeny (Kirkland et al., 2011a, Spaggiari et al., 2011). The tectonic setting of the Albany-Fraser Orogeny is not well constrained;
Sample collection
The primary aim during sample collection was to ensure representative lithologies and geographical spread across the different domains of the western Albany-Fraser Orogen. Nineteen samples were collected from a 360 km transect across the Northern Foreland, Nornalup and Biranup Zones (Fig. 1). From these samples, 22 individual crystals (16 biotite, 4 muscovite and 2 hornblende) were analysed using 40Ar/39Ar thermochronology. Sample lithologies are summarised in Table 1, and sample locations and
Nornalup Zone
One hornblende and five biotite grains from the Nornalup Zone produced robust 40Ar/39Ar cooling ages (Table 1). The hornblende from orthogneiss AF02-1 produced a flat step-heating spectrum with a cooling age of 1169 ± 7 Ma (Fig. 2). Four biotite grains (orthogneisses AF02-1, AF02-2 and AF03, and metagranite AF06) produced weighted plateau ages ranging from 1168 ± 5 Ma to 1144 ± 5 Ma, with no apparent geographical trend in cooling ages (Fig. 1, Fig. 2). Biotite from metagranite AF01 records a much
Cooling and exhumation of the western Albany-Fraser Orogen
Two hornblende, eight biotite and four muscovite grains yielded statistically robust age plateaus (>70% of 39Ar released); plateaus are generally flat and low in complexity (Fig. 2). One biotite from the Northern Foreland yielded a mini-plateau (50–70% of 39Ar released), and seven biotite samples from the Nornalup Zone yielded no age plateaus (Fig. 2). Results are summarised in Table 1, with all ages reported at the 2σ uncertainty level.
One biotite grain from the Nornalup Zone (AF01) yielded a
Conclusion
This article reports the first 40Ar/39Ar thermochronology from the western part of the Albany-Fraser Orogen of Western Australia. The Nornalup and Biranup Zones share a similar cooling history, with hornblende cooling ages at ca 1169 Ma, and biotite cooling ages clustered around ca 1159 Ma. These ages correspond to cooling rates of ca in the Nornalup Zone and ca in the Biranup Zone, for cooling between ca 585–365 °C. The Northern Foreland records muscovite cooling ages
Acknowledgements
We thank Dr. Dave Moecher for assistance with fieldwork, and Dr. Tony Kemp, whose review of an earlier draft greatly improved this article. Thoughtful reviews by Toby Rivers and an anonymous reviewer helped to focus the writing. We also gratefully acknowledge Celia Mayers and Adam Frew for their help in the Western Australian Argon Isotope Facility at Curtin University, and the staff at the UWA Centre for Microscopy and Microanalysis for their assistance. This research was sponsored by the
References (103)
- et al.
Chronology of nappe assembly in the Pan-African Dahomeyide orogen, West Africa: evidence from 40Ar/39Ar mineral ages
Precambrian Res.
(1997) - et al.
A structural and metamorphic traverse across the Albany Mobile Belt, Western Australia
Precambrian Res.
(1988) - et al.
Hornblende 40Ar/39Ar geochronology across terrane boundaries in the Sveconorwegian Province of S. Norway
Precambrian Res.
(1998) - et al.
Reworking of Archaean and Early Proterozoic components during a progressive, Middle Proterozoic tectonothermal event in the Albany Mobile Belt, Western Australia
Precambrian Res.
(1992) - et al.
Evolution of deep-crustal normal faults: constraints from thermobarometry in the Grenville Orogen, Ontario, Canada
Tectonophysics
(1996) - et al.
Flow of ultra-hot orogens: a view from the Precambrian, clues for the Phanerozoic
Tectonophysics
(2009) - et al.
Geochronological constraints for a two-stage history of the Albany-Fraser Orogen, Western Australia
Precambrian Res.
(2000) - et al.
Structure and kinematics of oblique continental convergence in northern Fiordland, New Zealand
Tectonophysics
(2002) - et al.
40Ar–39Ar chronology of Variscan tectono-metamorphic events in an exhumed crustal nappe: the Monts du Lyonnais complex (Massif Central, France)
Chem. Geol. (Isotope Geoscience Section)
(1993) - et al.
40Ar/39Ar geochronology and Neoproterozoic tectonics along the northern margin of the Eastern Ghats Belt in north Orissa, India
Precambrian Res.
(2001)
Regional correlation of Mesoproterozoic structures and deformational events in the Albany-Fraser orogen, Western Australia
Precambrian Res.
Isotopic evidence on the age and origin of the Fraser Complex, Western Australia: a sample of Mid-Proterozoic lower crust
Chem. Geol. (Isotope Geoscience Section)
Cooling and exhumation history of the northeastern Gawler Craton, South Australia
Precambrian Res.
Diffusion of 40Ar in muscovite
Geochim. Cosmochim. Acta
Diffusion of 40Ar in biotite: temperature, pressure and compositional effects
Geochim. Cosmochim. Acta
40Ar/39Ar thermochronological constraints on the structural evolution of the Mesoproterozoic Natal Metamorphic Province, SE Africa
Precambrian Res.
A titanite fission track profile across the southeastern Archaean Kaapvaal Craton and the Mesoproterozoic Natal Metamorphic Province, South Africa: evidence for differential cryptic Meso- to Neoproterozoic tectonism
J. Afr. Earth Sci.
On the edge: U–Pb, Lu–Hf, and Sm–Nd data suggests reworking of the Yilgarn craton margin during formation of the Albany-Fraser Orogen
Precambrian Res.
High closure temperatures of the U–Pb system in large apatites from the Tin Mountain pegmatite, Black Hills, South Dakota, USA
Geochim. Cosmochim. Acta
A redetermination of the isotopic abundance of atmospheric Ar
Geochim. Cosmochim. Acta
Rates of cooling and denudation of the Early Penglai Orogeny, Taiwan, as assessed by fission-track constraints
Tectonophysics
The thermal history of the Eastern Ghats Belt (India) as revealed by U–Pb and 40Ar/39Ar dating of metamorphic and magmatic minerals: implications for the SWEAT correlation
Precambrian Res.
U–Pb dating of metamorphic minerals: Pan-African metamorphism and prolonged slow cooling of high pressure granulites in Tanzania, East Africa
Precambrian Res.
The Neoproterozoic Brasiliano orogeny in northeast Brazil: 40Ar/39Ar and petrostructural data from Ceara
Precambrian Res.
40Ar/39Ar geochronology across the Mylonite Zone and the Southwestern Granulite Province in the Sveconorwegian Orogen of S Sweden
Precambrian Res.
Conflicting structural and geochronological data from the Ibituruna quartz-syenite (SE Brazil): effect of protracted hot orogeny and slow cooling rate?
Tectonophysics
Timing of plutonism in the Proterozoic Albany Mobile Belt, southwestern Australia
Precambrian Res.
Joint determination of 40K decay constants and 40Ar*/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology
Geochim. Cosmochim. Acta
Assembly and preservation of lower, mid, and upper orogenic crust in the Grenville Province – implications for the evolution of large hot long-duration orogens
Precambrian Res.
Post-orogenic (<1500 Ma) thermal history of the Palaeo-Mesoproterozoic, Mt. Isa province, NE Australia
Tectonophysics
Climatic control on rapid exhumation along the Southern Himalayan Front
Earth Planet. Sci. Lett.
LA-MC-ICPMS Pb–Pb dating of rutile from slowly cooled granulites: confirmation of the high closure temperature for Pb diffusion in rutile
Geochim. Cosmochim. Acta
Exhumation overrated at Nanga Parbat, northern Pakistan
Tectonophysics
Structural and geochronological evolution of the Malcolm Gneiss, Nornalup Zone, Albany-Fraser Orogen, Western Australia
Geological Survey of Western Australia Record 2012/4
Subduction and eduction of continental crust: major mechanisms during continent–continent collision and orogen extensional collapse, a model based on the south Norwegian Caledonides
Terra Nova
High cooling and denudation rates at Kongur Shan, Eastern Pamir (Xinjiang, China) revealed by 40Ar/39Ar alkali feldspar thermochronology
Tectonics
The timing of and nature of greenschist facies deformation and metamorphism in the upper Pennine Alps
Tectonics
Kinematics of bidirectional extension and coeval NW-directed contraction in orthogneisses of the Biranup Complex, Albany Fraser Orogen, Southwestern Australia
Geological Survey of Western Australia Report 109
Cenozoic plate boundary evolution in the South Island of New Zealand: new thermochronological constraints
Tectonics
Thermochronological analysis of the dynamics of the Southern Alps, New Zealand
GSA Bull.
Crustal flow modes in large hot orogens
A four-phase model for the Sveconorwegian orogeny, SW Scandinavia
Norw. J. Geol.
Evolution of a crustal-scale transpressive shear zone in the Albany-Fraser Orogen, SW Australia: 1. P–T conditions of Mesoproterozoic metamorphism in the Coramup Gneiss
J. Metamorph. Geol.
Evolution of a crustal-scale transpressive shear zone in the Albany-Fraser Orogen, SW, Australia: 2. Tectonic history of the Coramup Gneiss and a kinematic framework for Mesoproterozoic collision of the West Australian and Mawson cratons
J. Metamorph. Geol.
Proterozoic cooling and exhumation of the northern central Halls Creek Orogen, Western Australia: constraints from a reconnaissance 40Ar/39Ar study
Aust. J. Earth Sci.
Metamorphic conditions in orogenic belts: a record of secular change
Int. Geol. Rev.
Suturing and extensional reactivation in the Grenville orogen, Canada
Geology
Crustal thickening and lateral flow during compression of hot lithospheres, with particular reference to Precambrian times
Terra Nova
Intracratonic, strike-slip partitioned transpression and the formation and exhumation of eclogite facies rocks: an example from the Musgrave Block, central Australia
Tectonics
Proterozoic granulite formation driven by mafic magmatism: an example from the Fraser Range Metamorphics, Western Australia
Precambrian Res.
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2022, Precambrian ResearchCitation Excerpt :Rapid initial cooling may have resulted from a period of uplift; a slowed cooling regime may signify the transition to a more tectonically inactive period. Alternatively, the tectonic regime of the AFO may be underrepresented in the global Proterozoic orogen record (Scibiorski et al., 2015), and the reason for protracted cooling below the closure temperatures of the leuconorite apatite after initial fast cooling may be provided by prolonged thermal activity at a greater depth, which possibly resulted in the intrusion of the PQF-dyke. If cryptic excess argon in biotite throughout the AFO has resulted in older reported biotite cooling ages (Scibiorski, 2017), then the upper closure temperature for these apatite grains will be lower, due to a slower initial cooling rate (Scibiorski et al., 2016; Scibiorski, 2017).