Exhumation of the Indus-Yarlung Tsangpo Suture Zone (NW India): New constraints from low-temperature thermochronology

Zhou, Renjie1, Aitchison, Jonathan C.1

1School of Earth and Environmental Sciences, The University of Queensland, St Lucia, QLD 4072, Australia

The Indus-Yarlung Tsangpo Suture Zone (IYTS) is the zone of original contact between two colliding masses of continental lithosphere, the Indian subcontinent and Eurasia. It extends for several thousand kilometres and is well exposed in NW India, southern Tibetan Plateau, and near the border between India and Myanmar. The rock record in the IYTS contains information regarding evolution of the now vanished Tethyan Ocean, its closure, and the on-going growth of the Himalaya. In the NW Himalaya, the IYTS zone is well exposed in the Zanskar River valley, and incorporates an array of sedimentary rock units collectively referred as the Indus Basin. On its northern side, the Indus Basin is in depositional contact with the Ladakh Batholith, the exhumed ‘root’ of the Trans-Himalayan continental arc that developed along the southern margin of Eurasia in association with subduction of Tethyan oceanic lithosphere. To the south, the Indus Basin contains rock units that are in faulted contact with rocks that represent the former margin of the Indian continent.

We present new low-temperature thermochronologic data produced by apatite U-Th/He, apatite fission-track and zircon fission-track methods. Samples were taken from the southern edge of the Ladakh Batholith where the depositional contact between the batholith and the Indus Basin (the Indus Molasse) is observed. A series of samples was also taken from the Indus Basin along river gorges that traverse the IYTS. Previous apatite fission track (AFT) ages from across the Ladakh Batholith are generally young along its northern flank (as young as ~5-6 Ma) while AFT ages from the south are older, spanning from ~22 to 35 Ma. We further constrain exhumation of the northern Indus Basin and southern Ladakh Batholith by applying geologic constraints to our thermal models, yielding evidence for two episodes of rapid exhumation in the late Eocene and Miocene. Preliminary AFT ages from the Indus Basin indicate exhumation at around 15 Ma, consistent with the second cooling episode observed along the southern Ladakh Batholith.


Biography

Dr Renjie Zhou holds the position of Lecturer in Tectonics at School of Earth and Environmental Sciences (SEES) at UQ. His research focuses on reconstructing the evolution of modern and past tectonic plate boundaries using a combination of field and laboratory (mostly geochronology and thermochronology) approaches.

Detachment fault and metamorphic core complex at the distal continental margin of the northern South China Sea

Deng, Dr Hongdan1, Ren, Jianye1, Rey, Patrice2, McClay, Ken3

1China University Of Geosciences, Wuhan, China, 2Earthbyte Research Group, Basin Genesis Hub, School of Geosciences, The University of Sydney, Sydney, Australia, 3Australian School of Petroleum, Adelaide University, Adelaide, Australia

Detachment fault and metamorphic core complex (MCC) are widely documented structures in extensional environment where continental lithosphere has been thermally weakened. The North American Cordillera and Aegean Sea have a widespread deformation of extension (up to 1000 km) and are regions that exemplify detachment fault and MCC development in natural exposures. However, how these structures evolve from wide extended terrane to continental break-up remains enigmatic because there are a few exposed continental margins that preserved these type of deformation. In addition, thick package of sedimentary units on the passive margin could obscure the imaging of low-angle fault and dome structures at depth. Here we use high-resolution 2D and 3D seismic data together with International Ocean Drilling Program (IODP) result and industry wells to show that Eocene extension across the northern margin of the South China Sea records large detachment fault (displacement >100 km) and MCCs at the highly extended (<15 km), distal continental margin. The South China Sea has wide continental margins that span a width of up to 1000 km and 500 km in the north and in the south. On the basis of high-resolution seismic data, we document the presence of dome structures, a corrugated and grooved detachment fault, and subdetachment deformation involving crustal-scale nappe folds and magmatic intrusions, which are coeval with supradetachment basins. On the distal continental margin, we conclude that the thermal and mechanical weakening of this broad continental domain allowed for the formation of metamorphic core complexes, boudinage of the upper crust and exhumation of middle/lower crust through detachment faulting. The structural architecture of the northern South China Sea continental margin is strikingly similar to the broad continental rifts in the North American Cordillera and in the Aegean domain, and further indicates that detachment faulting and the development of metamorphic core complex play an important role in controlling continental break-up.


Biography

Hongdan Deng is a postdoc researcher at China University of Geosciences. His research has focused on fault-fold system evolution in orogenic belts and three-dimensional extensional structures and basins evolution on passive margins. This involves field and seismic studies integrated with analogue modelling of sedimentary basin structures.

The uplift history of the Nyika Plateau, Malawi: A long lived paleo-surface or a contemporary feature of the East African Rift?

McMillan, Malcolm1, Boone, Sam1, Kohn, Barry1, Gleadow, Andy1, Chindandali, Patrick2

1The University of Melbourne, Melbourne, Australia, 2Geological Survey of Malawi, Zomba, Malawi

The Malawi Rift is the southern-most expression of the magma-poor western branch of the East African Rift. A noticeable feature belonging to Malawi is the Neogene Lake Malawi (Nyasa), occurring directly above the main locus of the Malawi Rift. Lake Malawi hosts a series of half-grabens of alternating polarity with elevated shoulders. In the northern region of Lake Malawi, just ~10km west of the largest border fault system, the Nyika Plateau rises ~2100m above the surrounding landscape. Nyika is a Paleoproterozoic (Ubendian) granitic intrusion, surrounded by Neoproterozoic Pan-African metamorphic complexes with sparse Permian Karoo sediments outcropping to the north and east of the plateau. Similar elevations to Nyika occur in the area, on the Mozambiquan side of Lake Malawi above the Livingstone border fault and to the north of Lake Malawi, in the Oligocene Rungwe Volcanic Province (RVP).

Since King1 it has been contentiously hypothesized that such high-relief plateaux, like Nyika and the Livingstone mountains, are long-lived “Gondwana surfaces” and are largely unrelated to the modern-day Malawi Rift. However, recent seismic evidence2 suggests a zone of thinned lithosphere beneath the RVP persists broadly beneath the Nyika Plateau and the Livingstone Mountains, and may indicate that higher elevations in the surrounding region are actively supported by rising asthenospheric mantle, resulting in relatively rapid, recent, tectonic uplift.

Low-temperature thermochronology typically provides thermal history constraints on the upper ~3-7km of the crust, using radiometric dating techniques sensitive to changes in the thermal regime, from events such as rapid uplift causing denudation or changes in the geothermal gradient. Here, we use apatite fission track (AFT), apatite (U-Th-Sm)/He (AHe), and zircon (U-Th)/He (ZHe) thermochronology to further investigate the uplift history of the Nyika Plateau and the surrounding region from 25 samples collected with help from the Geological Mapping and Mineral Assessment Project (GEMMAP) and Malawi’s Geologic Survey Department.

We found consistently Permo-Triassic AFT apparent ages with moderate mean track lengths ranging from ~11.2-12µm. AHe ages are largely dispersed in all but two samples, which show consistent mid-Cretaceous apparent ages. ZHe ages are consistently Devonian. AFT and AHe ages are consistent with ages previously reported along the Livingstone Mountains3, 4. Thermal history models suggest that the Nyika Plateau is not a direct feature of modern-day rifting and has largely cooled slowly through the partial annealing zone since at least the late Mesozoic. The youngest AFT age (~70Ma) occurs off the plateau to the north, directly adjacent to a Permian Karoo sequence. Using this Karoo deposition as a thermal history constraint indicates the area may have been completely covered by Karoo deposition, up to ~2km (considering moderate geothermal gradients), that may have blanketed Nyika and the surrounding region in the Permo-Triassic.

References

1King, 1962. The Morphology of the Earth, Oliver and Boyd, Edinburg and London, 29.

2Njinju et al, 2019. Lithospheric Structure of the Malawi Rift: Implications for Magma-Poor Rifting Processes. Tectonics 38, 3835-3853.

3van der Beek et al, 1998. Denudation history of the Malawi and Rukwa Rift flanks (East African Rift         system) from apatite fission track thermochronology. J. African Earth Sciences 26, 363-385.

4Mortimer et al, 2016. Spatio-temporal trends in normal-fault segmentation recorded by low-temperature thermochronology: Livingstone fault scarp, Malawi Rift, East African Rift System. Earth and Planetary Science Letters 45, 65-72.


Biography

Malcolm is a PhD student at the University of Melbourne. His research focuses on investigating dynamic topography related to active rifting in Malawi using low temperature thermochronology.

Pangea Rifting Shaped the East Antarctic Landscape

Maritati, Alessandro1, Danišík, Dr Martin2, Halpin, Dr Jacqueline1, Whittaker, Dr Joanne1, Aitken, Dr Alan3

1Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, TAS 7001, Australia, 2John de Laeter Centre/The Institute for Geoscience Research, Curtin University, Perth, WA 6845, Australia, 3School of Earth Sciences, University of Western Australia, Perth, WA 6009, Australia

East Antarctica remains one of the few continental regions on Earth where an understanding of the origin and causal processes responsible for topographic relief is largely missing. Low‐temperature thermochronology studies of exposed Precambrian basement revealed discrete episodes of cooling and denudation during the Paleozoic–Mesozoic; however, the significance of these thermal events and their relationship to topography across the continental interior remains unclear. In this contribution, we present a model for the origin of topography of interior East Antarctica which seeks to establish a link between Paleozoic–Mesozoic AFT and AHe cooling ages and continent‐scale geodynamic processes. We use new zircon and apatite (U‐Th)/He thermochronology from Precambrian basement outcrops to determine the timing, magnitude, and style of Phanerozoic cooling of the Bunger Hills region, a poorly exposed section of East Antarctic basement across the large-scale domain of Indo-Antarctica and Australo-Antarctica. Thermal history modelling results indicate that Precambrian basement in the Bunger Hills region experienced a distinct cooling episode during the Late Paleozoic–Triassic, which we relate to ~2–4 km of regional exhumation associated with intracontinental rifting, followed by a second episode of localized cooling and ≤1 km exhumation during the Late Jurassic–Cretaceous separation of India from East Gondwana. Late Paleozoic–Triassic cooling and exhumation in the Bunger Hills region is consistent with the timing and magnitude of rift‐related cooling and exhumation reported in the Lambert Rift and George V Land, suggesting a single denudational system driven by Pangea‐wide extension. We propose that this event had a profound impact on the formation of topographic relief of East Antarctica via the exhumation of large sections of basement and the formation of vast intracontinental sedimentary deposits across the East Antarctic interior. By contrast, extension associated with the Jurassic–Cretaceous breakup of East Gondwana did not provide an equally widespread denudational response across the East Antarctic interior. The topographic framework formed during the Paleozoic–Mesozoic had a significant impact on the long‐term landscape evolution of East Antarctica and provided a template for Cenozoic erosion on the continent.


Biography

I am a PhD candidate at the University of Tasmania with a strong focus on petrology, geochronology and geochemistry. My current research activity focuses on integrating multiple geoscientific datasets at different scales to gain insights into the crustal architecture and tectonic evolution of East Antarctica.

Distal footprints of the Alice Springs Orogeny: An application of multi-kinetic thermochronology in the Pine Creek Orogen and Arnhem Province

Nixon, Angus L1, Glorie, Stijn1, Collins, Alan S1, Whelan, Jo A2, Reno, Barry L2, Danišík, Martin3, Wade, Benjamin P4 & Fraser, Geoff5

1Mineral Exploration Cooperative Research Centre, Department of Earth & Environmental Sciences, School of Physical Sciences, The University of Adelaide, SA 5005 Australia, 2Northern Territory Geological Survey, Department Industry Tourism and Trade, Darwin, NT 0801, Australia, 3John de Laeter Centre, Curtin University of Technology, Perth, WA 6845, Australia, 4Adelaide Microscopy, The University of Adelaide, Adelaide, SA 5005, Australia, 5Minerals Energy and Groundwater Division, Geoscience Australia, GPO Box 378, Canberra, ACT2601, Australia

The Precambrian Pine Creek Orogen and Arnhem Province represent two of the oldest basement terrains in northern Australia and are often considered to be devoid of major tectonic or deformational activity since the cessation of regional metamorphism in the Paleoproterozoic. A major caveat in the current hypothesis of long lived structural inactivity is the absence of published low-temperature thermochronological data and thermal history models for this area. This study presents the first apatite U–Pb, fission track and (U–Th–Sm)/He data for igneous samples from both the Pine Creek Orogen and Arnhem Province, complemented with apatite geochemistry data acquired by electron microprobe and laser ablation mass spectrometry methods, and presents detailed multi-kinetic low-temperature thermal history models. Low-temperature thermal history models for the Pine Creek Orogen and Arnhem Province reveal a distinct phase of denudation coeval with the Paleozoic Alice Springs Orogeny in central Australia, suggesting that this orogenic event impacted a larger area of the Australian crust than previously perceived. Low-temperature perturbations observed in northernmost Australia are consistent with widespread mid-Paleozoic denudation is preserved across both the North Australian Craton and South Australian Craton, indicative of a cratonic scale thermal event during north-south shortening via the Alice Springs Orogeny. Additionally, minor localised Mesozoic thermal perturbations proximal to the Pine Creek Shear-Zone record evidence for Mesozoic reactivation contemporaneous with modelled mantle-driven subsidence and the onset of sedimentation in the Money Shoal Basin, while the Arnhem Province samples demonstrate no evidence of Mesozoic thermal perturbations.


Biography

Angus Nixon is a PhD student at the University of Adelaide with research focused on unraveling the low-temperature evolution of the North Australia Craton throughout the Phanerozoic , aiming to identify and explain both local and craton scale thermo-tectonic events and their implications for terrain development.

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