A Compilation of New and Existing Thermochronology Data Concerning the Lhasa Terrane Combined with a Geological Synthesis of the Area

The Jitang metamorphic complex is key for studying the tectonic evolution of the Northern Lancangjiang zone. Through structural–lithological mapping, structural analysis and laboratory testing, the composition of the Jitang metamorphic complex was determined. The macro‐ and microstructural analyses of the ductile detachment shear zone (Guoxuepu ductile shear zone 2–4 km wide) between the metamorphic complex and the overlying sedimentary cap show that the shear sense of the ductile shear zones is top–to–the–southeast. The presence of various deformation features and quartz C–axis electron backscatter diffraction (EBSD) fabric analysis suggests multiple deformation events occurring at different temperatures. The average stress is 25.68 MPa, and the strain rates (έ) range from 9.77×10–14 s–1 to 6.52×10–16 s–1. The finite strain of the Guoxuepu ductile shear zone indicates an elongated strain pattern. The average kinematic vorticity of the Guoxuepu ductile shear zone is 0.88, implying that the shear zone is dominated by simple shear. The muscovite selected from the protomylonite samples in the Guoxuepu ductile shear zone yields a 40Ar–39Ar age of 60.09±0.38 Ma. It is suggested that coeval with the initial Indo–Eurasian collision, the development of strike‐slip faults led to weak and unstable crust. Then, upwelling of lower crust magma induced the detachment of the Jitang metamorphic complex in the Eocene.

Section: Regional and Tectonic Implicationsmentioning

confidence: 99%

Structural, ⁴⁰Ar/³⁹Ar Geochronological and Rheological Feature Analysis of the Guoxuepu Shear Zone: Indications for the Jitang Metamorphic Complex in the Northern Lancangjiang Zone

FENG,

WANG,

WANG

et al. 2024

“…The Cenozoic tectonic evolution of the Tibetan Plateau is thought to have exerted a strong influence on regional and even global geodynamics, as well as climate systems (An et al, 2001). During the last several decades, many studies have been conducted to provide insights into the mechanisms and dynamics of the outward growth of the Tibetan Plateau or the southeastward expansion of the plateau lithosphere (e.g., Wilson et al, 2011;Cao et al, 2019;Wang et al, 2020a, b;Xiong et al, 2022;Zhao et al, 2022). Different models have been proposed, including (1) the outward flow of the lower-middle crust beneath Tibet, and (2) intracontinental deformation.…”

Section: Introductionmentioning

confidence: 99%

Multiple Uplift and Exhumation of the Southeastern Tibetan Plateau: Evidence from Low‐Temperature Thermochronology

WU,

PENG,

FAN

et al. 2024

Since the Cenozoic, the Tibetan Plateau has experienced large‐scale uplift and outgrowth due to the India‐Asia collision. However, the mechanism and timing of these tectonic processes still remain debated. Here, using apatite fission track dating and inverse thermal modeling, we explore the mechanism of different phases of rapid cooling for different batholiths and intrusions in the southeastern Tibetan Plateau. In contrast to previous views, we find that the coeval granitic batholith exposed in the same tectonic zone experienced differential fast uplift in different sites, indicating that the present Tibetan Plateau was the result of differential uplift rather than the entire lithosphere uplift related to lithospheric collapse during Cenozoic times. In addition, we also suggest that the 5‐2 Ma mantle‐related magmatism should be regarded as the critical trigger for the widely coeval cooling event in the southeastern Tibetan Plateau, because it led to the increase in atmospheric CO2 level and a hotter upper crust than before, which are efficient for suddenly fast rock weathering and erosion. Finally, we propose that the current landform of the southeastern Tibetan Plateau was the combined influences of tectonic and climate.

Petrogenesis of Oligocene Granitoids and its Implications on Beryllium Mineralization at Pagele, Nianqingtanggula Mountain (Central Tibet)

ZHANG,

YANG,

HOU

et al. 2024

The newly discovered Oligocene granitoids (33.1–28.7 Ma) at Pagele are magmatic rocks related to beryllium mineralization during the India‐Asia late‐collisional stage. This discovery provides an ideal example to study the late‐collisional orogeny and beryllium prospecting in the Lhasa terrane. The Oligocene granitoids include porphyritic granodiorite, Stage I, II and III granites, and granitic pegmatite. Geochemical analysis shows that the porphyritic granodiorite is characterized by high SiO2, K2O, total ΣREE contents, and (La/Yb)N ratios; while the latter two by higher SiO2, lower ΣREE and (La/Yb)N ratios. Notably, the granitic pegmatite has extremely high Y/Ho, low K/Rb and Zr/Hf, and distinct REE tetrad effect (1.14–1.21). This study suggests that the porphyritic granodiorite may be derived from partial melting of beryllium‐rich materials composed of Lhasa ancient crust (70–80%) and enriched Lhasa lithospheric mantle (20–30%) under the tearing subduction of Indian slab. The three‐stage granites and granitic pegmatite, which contain higher beryllium contents or beryls, were likely generated by highly fractionation of the porphyritic granodioritic magma or other homologous magma. Considering the possible genetic and spatial link between Indian slab tear and rifts, we suggest that highly‐fractionated granites in rifting systems represent important Be prospecting targets in the Lhasa terrane.