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1. Permian plume-strengthened Tarim lithosphere controls the Cenozoic deformation pattern of the Himalayan-Tibetan orogen

   https://doi.org/10.1130/G47961.1  

   Xu, Xi; Zuza, Andrew V.; Yin, An; Lin, Xiubin; Chen, Hanlin; Yang, Shufeng (September 2020, Geology)

   null (Ed.)

   Abstract The high strength of the Tarim Basin (northwestern China) lithosphere, widely regarded as a Precambrian craton, is evidenced by its resistance to Cenozoic deformation in the Himalayan-Tibetan orogen. However, Neoproterozoic suturing and early Paleozoic shortening within the Tarim Basin suggest that its rigidity is a relatively recent phenomenon with unknown cause. We reprocessed high-resolution magnetic data that show a 300–400-km-diameter radial pattern of linear anomalies emanating from a central region characterized by mixed positive-negative anomalies. We suggest that this pattern was generated by the previously hypothesized Permian (ca. 300–270 Ma) plume beneath the Tarim Basin. Constrained by published geochemical and geochronological data from plume-related igneous rocks, we propose that the ∼30 m.y. Permian plume activity resulted in a more viscous, depleted, thicker, dehydrated, and low-density mantle lithosphere. The resulting stronger lithosphere deflected strain from the Cenozoic India-Asia convergence around Tarim Basin, including Pamir overthrusting to the northwest and Altyn Tagh left-slip displacement to the northeast, thus shaping the geometry of the Himalayan-Tibetan orogen. 

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2. 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)

   Abstract 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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3. 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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4. Zircon geochemistry from early evolved terranes records coeval stagnant- and mobile-lid tectonic regimes

   https://doi.org/10.1073/pnas.2405378121  

   Mixon, Emily E; Bauer, Ann M; Blum, Tyler B; Valley, John W; Rizo, Hanika; O’Neil, Jonathan; Kitajima, Kouki (September 2024, Proceedings of the National Academy of Sciences)

   Determining the mechanisms by which the earliest continental crust was generated and reworked is important for constraining the evolution of Earth’s geodynamic, surface, and atmospheric conditions. However, the details of early plate tectonic settings often remain obscured by the intervening ~4 Ga of crustal recycling. Covariations of U, Nb, Sc, and Yb in zircon have been shown to faithfully reflect Phanerozoic whole-rock-based plate-tectonic discriminators and are therefore useful in distinguishing zircons crystallized in ridge, plume, and arc-like environments, both in the present and in deep time. However, application of these proxies to deciphering tectonic settings on the early Earth has thus far been limited to select portions of the detrital zircon record. Here, we present in situ trace-element and oxygen isotope compositions for magmatic zircons from crystalline crustal rocks of the Acasta Gneiss Complex and the Saglek-Hebron Complex, Canada. Integrated with information from whole-rock geochemistry and zircon U-Pb, Hf, and O isotopes, our zircon U-Nb-Sc-Yb results reveal that melting of hydrated basalt was not restricted to a single tectonomagmatic process during the Archean but was operative during the reworking of Hadean protocrust and the generation of juvenile crust within two cratons, as early as 3.9 Ga. We observe zircon trace-element compositions indicative of hydrous melting in settings that otherwise host seemingly differing whole-rock geochemistry, zircon Hf, and zircon O isotopes, suggesting contemporaneous operation of stagnant-lid (oceanic plateau) and mobile-lid (arc-like) regimes in the early Archean. 

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5. Evolution of tungsten isotope systematics in the Mauna Kea volcano provides new constraints on anomalous µ182W and high 3He/4He in the mantle

   https://doi.org/10.1016/j.epsl.2024.118795  

   Willhite, Lori N; Finlayson, Valerie A; Walker, Richard J (August 2024, Earth and Planetary Science Letters)

   Highly siderophile element abundances and 182W/184W and 187Os/188Os were determined for a suite of Mauna Kea lavas from the Hawaiian Scientific Drilling Project phase 2 drill core. The new analyses, combined with previous measurements, compose the largest database for μ182W (the parts-per-million deviation of 182W/184W from a terrestrial standard) for a single volcano (n = 16). Although most lavas analyzed are characterized by negative μ182W values, lavas with values similar to the modern bulk silicate Earth are found throughout the entire stratigraphic column. This suggests that components with normal μ182W are collocated with components that host μ182W deficits in the plume. Negative μ182W values are associated with elevated 3He/4He, as well as elevated Ti and Nb. These correlations may link μ182W anomalies to ancient deep mantle crystal-liquid fractionation processes. Consistent with previously measured 3He/4He (R/RA) in the drill core, the magnitude of negative μ182W values was greatest when Mauna Kea was close to the plume axis then generally decreased over the ~400 kyr captured by the stratigraphic section. The component with anomalous μ182W was either concentrated near the plume axis, or was more effectively sampled by melting near the plume axis where the temperature excess was greatest, suggesting it was less fusible than the dominant plume components. The process leading to the generation of a mantle component with a negative μ182W anomaly could either be related to some form of core-mantle isotopic equilibration, or early-Earth fractionation within the silicate Earth. At present each possibility remains viable. 

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