the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Uplift and denudation history of the Ellsworth Mountains: insights from low temperature thermochronology
Joaquín Bastías-Silva
David Chew
Fernando Poblete
Paula Castillo
William Guenthner
Anne Grunow
Ian W. D. Dalziel
Airton Dias
Cristóbal Ramírez de Arellano
Rodrigo Fernanddez
Abstract. While thermochronological studies have constrained the landscape evolution of several of the crustal blocks of West and East Antarctica, the tectono-thermal evolution of the Ellsworth Mountains remains relatively poorly constrained. These mountains are among the crustal blocks that comprise West Antarctica and exhibit an exceptionally well-preserved Palaeozoic sedimentary sequence. Despite the seminal contribution of Fitzgerald and Stump (1991), who suggested an Early Cretaceous uplift event for the Ellsworth Mountains, further thermochronological studies are required to improve the current understanding of the landscape evolution of this mountain chain. We present new zircon (U-Th)/He (ZHe) ages, which provide insights into the landscape evolution of the Ellsworth Mountains. The ZHe ages collected from near the base and the top of the sequence suggest that these rocks underwent burial reheating after deposition. A cooling event is recorded during the Jurassic–Early Cretaceous, which we interpret as representing exhumation in response to rock uplift of the Ellsworth Mountains. Moreover, our results show that, while ZHe ages at the base of the sequence are fully reset, towards the top ZHe are partially reset. Uplift and exhumation of the Ellsworth Mountains during the Jurassic–Early Cretaceous was contemporaneous with the rotation and translation of this crustal block with respect to East Antarctica and possibly the Antarctic Peninsula. Furthermore, this period is characterised by widespread extension associated with the disassembly and breakup of Gondwana, with the Ellsworth Mountains playing a key role in the opening of the far South Atlantic. Based on these results, we suggest that uplift of the Ellsworth Mountains during the disassembly of Gondwana provides additional evidence for major rearrangement of the crustal blocks between the South American, African, Australian and Antarctic plates. Finally, uplift of the Ellsworth Mountains commenced during the Jurassic, which predates the Early Cretaceous uplift of the Transantarctic Mountains. This may indicate that continental scale, rift-related exhumation was diachronous, initiating in the Ellsworth Mountains in the Jurassic and then propagating southwards into the Transantarctic Mountains during the Early Cretaceous.
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Joaquín Bastías-Silva et al.
Status: open (until 21 Oct 2023)
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RC1: 'Comment on egusphere-2023-1769', Anonymous Referee #1, 02 Oct 2023
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Review of “Uplift and denudation history of the Ellsworth Mountains: insights from low temperature thermochronology”. This paper presents new evidence for when the elevated topography of the Ellsworth Mountains was first uplifted. The recovered cooling dates are generally late Jurassic to Early Cretaceous in age. Isolated older dates associated with stratigraphically shallower rocks are consistent with the temperature thermochronology not being fully reset by burial. The authors conclude that the main phase of uplift occurred during the Jurassic breakup of Gondwana which initiated in the Weddell Sea region.
Overall the paper seems well written and the conclusions are supported by the data given. I have a couple of suggestions for the authors to consider.
I hope the authors find these suggestions useful.
First: L184-186 the authors note that “This suggests that these rocks cooled through the ~200-130°C ZHe retention zone during the Jurassic and Early Cretaceous, which we interpret as exhumation related to a specific rock uplift event which supports the seminal work of Fitzgerald and Stump (1991)”. It is correct that the results do not contradict the work of Fitzgerald and Stump (1991), as no upper limit (prior to 141 Ma) was given in the 1991 paper. However, almost all the new results pre-date the 141 Ma given in the previous paper, and only two are Cretaceous, while 9 are Jurassic (excluding older outliers). I think the authors could reasonably argue that their results provide an older, but not inconsistent, age for the uplift of the Ellsworth Mountains compared to Fitzgerald and Stump (1991). I think this is worth saying, as the top line 140 Ma age provided in the 1991 paper suggests a more ‘Transantarctic’/Cretaceous origin for the uplift, while the provided data seems to point more to an older Jurassic/Weddell Sea breakup origin.
Second: The authors suggest the Ellsworth Mountains contain a distinct Jurassic uplift signal compared with the rest of the Transantarctic Mountains, and argue quite convincingly that this is associated with Weddell Sea rifting. However, on L217 they suggest and alternative model where by “the uplift of the Ellsworth Mountains and the Transantarctic Mountains may be part of a diachronous exhumation event whereby uplift commenced in the Ellsworth Mountains during the Jurassic and advanced progressively towards the south, propagating into the Transantarctic Mountains during the Early Cretaceous”. It is well understood that Gondwana breakup progressed clockwise splitting Africa, India, Australia and New Zealand away from Antarctica. A diachronous event moving in the opposite direction, although not possible to totally rule out, seems less likely, and maybe this sentence should be caveated. More likely two uplift events impacted the Ellsworth Mountains, one in the Jurassic associated with the Weddell Sea, and a secondary overprint in the Cretaceous associated with the Wider Transantarctic Mountain system.
Citation: https://doi.org/10.5194/egusphere-2023-1769-RC1
Joaquín Bastías-Silva et al.
Joaquín Bastías-Silva et al.
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