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1. Lower Crustal Rheology Controls Strain Partitioning and Mode of Intracontinental Deformation

   https://doi.org/10.1029/2023TC007748  

   Xu, Xi ; Zuza, Andrew V. ; Yin, An ; Yu, Peng ; Chen, Zhiyong ; Zhao, Chongjin ; Wang, Baodi ; Chen, Hanlin ; Lin, Xiubin ; Wu, Lei ; et al ( November 2023 , Tectonics)

   The factors that control strain partitioning along plate boundaries and within continental interiors remains poorly resolved. Plate convergence may be accommodated via distributed crustal shortening or discrete crustal‐scale strike‐slip faulting, but what controls these differing modes of deformation is debated. Here we address this question by examining the actively deforming regions that surround the Tarim Basin in central Asia, where deformation is uniquely partitioned into predominately strike‐slip faults in the east and distributed fold‐thrust belts in the west to accommodate Cenozoic India‐Asia plate convergence. We present integrated geological and geophysical observations to elucidate patterns in crustal deformation and compositional structure in and around the Tarim Basin. The thrust‐dominated western Tarim Basin correlates with a strongly‐magnetic lower crust, whereas strike‐slip faulting along the eastern margins of the Tarim Basin lack such magnetic signals. We suggest that the lower crust of the western Tarim is more mafic and stronger than in the east, which impacts intra‐plate strain partitioning. A stronger lower crust results in vertical decoupling to drive mid‐crust horizontal detachments and facilitate thrust faulting, whereas a more homogenized crust favored vertical transcrustal strike‐slip faulting. These rheological differences likely originated from the impingement of the Permian Tarim plume focused in the west. A comparison with the Longmen Shan of eastern Tibetan Plateau reveals remarkably similar strain partitioning that correlates with variations in foreland rheology. Our results highlight how variations in lower‐crust viscosity impact strain partitioning in an intra‐plate setting and how plume processes exert a strong control on later continental tectonic processes.

    

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2. Phanerozoic cratonization by plume welding

   https://doi.org/10.1130/G50615.1  

   Xu, Xi ; Chen, Hanlin ; Zuza, Andrew V. ; Yin, An ; Yu, Peng ; Lin, Xiubin ; Zhao, Chongjin ; Luo, Juncheng ; Yang, Shufeng ; Wang, Baodi ( January 2023 , Geology)

   Deformation-resistant cratons comprise >60% of the continental landmass on Earth. Because they were formed mostly in the Archean to Mesoproterozoic, it remains unclear if cratonization was a process unique to early Earth. We address this question by presenting an integrated geological-geophysical data set from the Tarim region of central Asia. This data set shows that the Tarim region was a deformable domain from the Proterozoic to early Paleozoic, but deformation ceased after the emplacement of a Permian plume despite the fact that deformation continued to the north and south due to the closure of the Paleo-Asian and Tethyan Oceans. We interpret this spatiotemporal correlation to indicate plume-driven welding of the earlier deformable continents and the formation of Tarim’s stable cratonic lithosphere. Our work highlights the Phanerozoic plume-driven cratonization process and implies that mantle plumes may have significantly contributed to the development of cratons on early Earth. 

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3. Constraints on the timing of the India‐Asia collision and unroofing history of the Himalayan orogen using detrital zircon U‐Pb‐Hf and whole‐rock Sr‐Nd isotopes in Cretaceous‐Miocene Lesser Himalayan sedimentary rocks

   https://doi.org/10.1111/bre.12742  

   Feng, Wei ; Meng, Qingquan ; Song, Chunhui ; Fang, Xiaomin ; Zhuang, Guangsheng ; He, Pengju ; Yang, Shufen ; Zhang, Jing ; Chen, Yongfa ; Zhang, Yihu ( December 2022 , Basin Research)

   Cretaceous‐Miocene sedimentary rocks in the Nepalese Lesser Himalaya provide an opportunity to decipher the timing of India‐Asia collision and unroofing history of the Himalayan orogen, which are significant for understanding the growth processes of the Himalayan‐Tibetan orogen. Our new data indicate that detrital zircon ages and whole‐rock Sr‐Nd isotopes in Cretaceous‐Miocene Lesser Himalayan sedimentary rocks underwent two significant changes. First, from the Upper Cretaceous‐Palaeocene Amile Formation to the Eocene Bhainskati Formation, the proportion of late Proterozoic‐early Palaeozoic zircons (quantified by an index of 500–1200 Ma/1600–2800 Ma) increased from nearly 0 to 0.7–1.4, and the percentage of Mesozoic zircons decreased from ca. 14% to 5–12%. The whole‐rock⁸⁷Sr/⁸⁶Sr and εNd(t = 0) values changed markedly from 0.732139 and −17.2 for the Amile Formation to 0.718106 and −11.4 for the Bhainskati Formation. Second, from the Bhainskati Formation to the lower‐middle Miocene Dumri Formation, the index of 500–1200 Ma/1600–2800 Ma increased to 2.2–3.7 and the percentage of Mesozoic zircons abruptly decreased to nearly 0. The whole‐rock⁸⁷Sr/⁸⁶Sr and εNd(t = 0) values changed significantly to 0.750124 and −15.8 for the Dumri Formation. The εHf(t) values of Early Cretaceous zircons in the Taltung Formation and Amile Formation plot in the U‐Pb‐εHf(t) field of Indian derivation, whereas εHf(t) values of Triassic‐Palaeocene zircons in the Bhainskati Formation demonstrate the arrival of Asian‐derived detritus in the Himalayan foreland basin in the Eocene based on available datasets. Our data indicate that (1) the timing of terminal India‐Asia collision was no later than the early‐middle Eocene in the central Himalaya, and (2) the Greater Himalaya served as a source for the Himalayan foreland basin by the early Miocene. When coupled with previous Palaeocene‐early Eocene provenance records of the Tethyan Himalaya, our new data challenge dual‐stage India‐Asia collision models, such as the Greater India Basin hypothesis and its variants and the arc–continent collision model.

    

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4. Reversible subsidence on the North West Shelf of Australia

   https://doi.org/10.1016/j.epsl.2020.116070  

   Gurnis, M. ( March 2020 , Earth and planetary science letters)

   null (Ed.)

   The Northwest Shelf (NWS) of Australia is characterized by offshore basins associated with Permian and Jurassic rifting and was only slowly subsiding by the Neogene. International Ocean Discovery Program (IODP) Expedition 356 targeted this region by coring four sites in the Northern Carnarvon and Roebuck Basins and two sites in the Perth Basin to the south on the Australian western margin. We use detailed lithological, physical property and age data with paleobathymetric interpretations, to infer tectonic subsidence apparently confined to the NWS that reverses (uplifts) with about the same amplitude and rate as an earlier subsidence event. About 300 m of tectonic subsidence occurred over one million years from 6 to 5 million years ago and then reverses when 300 m of tectonic uplift occurred from 2 to 1 Ma. The along strike extent of this subsidence pattern is ∼ 400 km. The similarity of magnitude and duration of the subsidence and uplift phases suggest that the subsidence is reversible. The results cannot be explained by glacial eustatic variability nor can the uplift event be attributed to sediments filling the accommodation space generated earlier. Reversible subsidence is a key fingerprint of dynamic topography. Although the rates of subsidence and uplift are roughly ∼ 300 m/Myr, a substantial portion of the changes occur over less than 1 Myr and the rates inferred from a detailed least squares analysis can reach up to about 500 m/Myr. These rates are incompatible with dynamic topography associated with motion of Australia over large-scale convection (10 to 40 m/Myr) or that associated with instability of the base of the lithosphere (<15 m/Myr). The vertical motions are too large to be associated with simple flexure of a plate and plate buckling in that the required amplitudes would lead to permanent deformation of the plate. A new geodynamic mechanism is required to fit the observations. 

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5. Growth of the southern Tian Shan-Pamir and its impact on central Asian climate

   https://doi.org/10.1130/B36471.1  

   Richter, Fabiana ; Pearson, Jozi ; Vilkas, Marius ; Heermance, Richard V. ; Garzione, Carmala N. ; Cecil, M. Robinson ; Jepson, Gilby ; Moe, Annelisa ; Xu, Jianhong ; Liu, Langtao ; et al ( October 2022 , GSA Bulletin)

   Uplift and amalgamation of the high-elevation (>3000 m) Tian Shan and Pamir ranges in Central Asia restricts westerly atmospheric flow and thereby limits moisture delivery to the leeward Taklimakan Desert in the Tarim Basin (<1500 m), the second largest modern sand dune desert on Earth. Although some research suggests that the hyper-arid conditions observed today in the Tarim Basin developed by ca. 25 Ma, stratigraphic evidence suggests the first erg system did not appear until 12.2 Ma. To address this controversy and to understand the tectonic influences on climate in Central Asia, we studied a continuous, 3800-m-thick stratigraphic section deposited from 15.1 to 0.9 Ma now exposed within the western Kepintagh fold-and-thrust belt in the southern Tian Shan foreland. We present new detrital zircon data (n = 839), new carbonate oxygen (δ18Oc) and carbon (δ13Cc) stable isotope compositions (n = 368), structural modeling, and stratigraphic observations, and combine these data with recently published magnetostratigraphy and regional studies to reconstruct the history of deposition, deformation, and climate change in the northwestern Tarim Basin. We find that basins along the southern (this study) and northern (i.e., Ili Basin) margins of the Tian Shan were likely receiving similar westerly precipitation by 15 Ma (δ18Oc = ∼−8‰) and had similar lacustrine-playa environments at ca. 13.5 Ma, despite differences in sedimentary provenance. At ca. 12 Ma, an erg desert formed adjacent to the southern Tian Shan in the northwestern Tarim Basin, coincident with a mid- to late Miocene phase of deformation and exhumation within both the Pamir and southern Tian Shan. Desertification at ca. 12 Ma was marked by a negative δ18Oc excursion from −7.8 ± 0.4‰ to −8.7 ± 0.7‰ in the southern Tian Shan foreland (this study), coeval with a negative δ18Oc excursion (∼−11 to −13‰) in the Tajik Basin, west of the Pamir. These data suggest that only after ca. 12 Ma did the Pamir-Tian Shan create a high-elevation barrier that effectively blocked westerly moisture, forming a rain shadow in the northwestern Tarim Basin. After 7 Ma, the southern Tian Shan foreland migrated southward as this region experienced widespread deformation. In our study area, rapid shortening and deformation above two frontal foreland faults initiated between 6.0 and 3.5 Ma resulted in positive δ13Cc excursions to values close to 0‰, which is interpreted to reflect exhumation in the Tian Shan and recycling of Paleozoic carbonates. Shortening led to isolation of the study site as a piggy-back basin by 3.5 Ma, when the sediment provenance was limited to the exhumed Paleozoic basement rocks of the Kepintagh fold belt. The abrupt sedimentologic and isotopic changes observed in the southern Tian Shan foreland appear to be decoupled from late Cenozoic global climate change and can be explained entirely by local tectonics. This study highlights how tectonics may overprint the more regional and global climate signals in active tectonic settings. 

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