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Mio‐Pliocene sedimentary archives of the East Asian summer monsoon (EASM) in NE Tibet record a monotonic response to orbital forcing, dominated by eccentricity. By contrast, Pleistocene archives display a more stochastic response that varies regionally and temporally. When and why this response changed is poorly understood. Here, we present a new high‐resolution Rb/Sr ratio data set of EASM intensity from the Sanmenxia Basin, North China, that spans the Plio‐Pleistocene transition. Our results indicate decreased monsoonal rainfall in the late Pliocene, dated at 2.75–2.6 Ma, associated with an intensified response to obliquity and enhanced climate stochasticity. This transition is attributed to the increase of Northern Hemisphere ice volume. Quaternary monsoons display a sensitivity unique to the modern icehouse with large bipolar ice sheets, while pre‐Quaternary monsoons were solely impacted by Antarctic ice sheet dynamics on orbital time‐scales. Plain Language Summary: The late Pliocene‐early Pleistocene transition (LP/EP) is a period of global cooling and the intensification of Northern Hemisphere glaciation. Yet, the evolution of the East Asian summer monsoon (EASM) during this time remains a topic of ongoing discussion and debate. Here we present high‐resolution paleoclimate data from a record of lake sediments across the Pliocene‐Pleistocene transition period. We show that there was a reorganization of the East Asian monsoon system 2.75–2.6 million years ago, associated with an increase in climate forcing caused by cyclic changes in Earth's tilt and in climate stochasticity. This transition is attributed to the appearance of new high‐latitude forcing mechanisms on monsoon intensity caused by the growth of ice sheets in the Northern Hemisphere. Key Points: Cyclic patterns in East Asian summer monsoonal intensity during the Pliocene were mainly driven by Antarctic ice sheet variationsA major reorganization of the East Asian climate system occurred at 2.75–2.6 Ma in response to Northern Hemisphere glaciationQuaternary East Asian summer monsoon on orbital scales displays a sensitivity that is unique to the modern icehouse with bipolar ice sheets [ABSTRACT FROM AUTHOR]

The Lhasa terrane of the southern Tibetan Plateau participated in a Mesozoic Andean-type orogeny caused by the northward subduction of the Neo-Tethyan oceanic lithosphere. However, metamorphic rocks, which can unravel details of the geodynamic evolution, are rare and only exposed in the south-eastern part of the Lhasa terrane. Therefore, we conducted a detailed petrological, geochemical and U–Pb zircon geochronological study of the late Cretaceous metamorphic rocks and associated gabbros from the Nyemo inlier of the southern Lhasa terrane. The Nyemo metamorphic rocks including gneisses, schists, marbles and calc-silicate rocks, experienced peak amphibolite-facies contact metamorphism under P–T conditions of 3.5–4.0 kbar and 642–657 °C with a very high geothermal gradient of 45–50 °C/km, revealing a distinct deflection from the steady-state geotherm during low-pressure metamorphism. Inherited magmatic zircon cores from the metamorphic rocks yielded protolith ages of 197–194 Ma, while overgrowth zircon rims yielded metamorphic ages of ca. 86 Ma. Whole-rock chemistry and zircon Hf isotopes suggest that the protoliths of the gneisses and schists are andesites and tuffs of the early Jurassic Sangri Group, which were derived from a depleted mantle source of a continental arc affinity. The coeval intimately-associated gabbro (ca. 86 Ma) crystallized under P–T conditions of 3.5–5.3 kbar and 914–970 °C, supplying the heat flux high enough to cause the contact metamorphism of the Sangri Group rock types. We propose that the intrusion of the gabbro and a simultaneous pressure increase of up to 4.0 kbar, which is related to crustal thickening due to crustal overthrusting and the intrusion of mafic material, resulted in the late Cretaceous metamorphism of the early Jurassic Sangri Group during an Andean-type orogeny. Furthermore the Nyemo metamorphic rocks, which have previously been considered to represent slivers of the Precambrian metamorphic basement of the Lhasa terrane, are late Cretaceous metamorphic supracrustal rocks. [ABSTRACT FROM AUTHOR]

Highlights: [•] The protoliths of the Basongco metamorphic rocks consist mainly of early Paleozoic sedimentary rocks. [•] These rocks experienced the early Mesozoic metamorphism, and associated with the coeval magmatism. [•] The metamorphic conditions are T =640–705°C and P =6.0–8.0kbar. [ABSTRACT FROM AUTHOR]

Orbital-scale East Asian summer monsoon (EASM) variability has been extensively investigated in Pliocene-Quaternary loess and marine sediments. In recent years, middle-late Miocene orbital-scale EASM variability has been depicted in lacustrine deposits from NE Tibetan basins, showing a dominant cyclicity of ∼100 kyr eccentricity. However, EASM variability during the early Miocene time remains poorly understood. Here, we investigate the sedimentary record of the early Miocene Xianshuihe Formation, Lanzhou Basin, in order to further constrain the NE Tibetan hydrological evolution and link it to orbital-scale monsoonal variability. By analyzing the lithology, magnetostratigraphy and cyclostratigraphic records of a 270-m section, we show that Lanzhou lake expansion cycles were consistently dominated by ∼100 kyr eccentricity forcing in early Miocene, except for the ∼20.8-19.8 Ma interval showing dominant obliquity control. These records are in agreement with deep-sea oxygen isotopic records, and are potentially linked to Antarctic ice sheet modulations related the precession amplitude modulation by eccentricity. A weakening of weathering intensity in Lanzhou Basin after 20.8 Ma may be attributed to orogenic barriers for westerly moisture and weakened surface temperature resulted from the rapid uplift of NE Tibet and surrounding mountains in the time interval of late Oligocene-early Miocene. • Eccentricity forcing Lanzhou lake evolution of ∼21.6-20.8 Ma and ∼17.2-19.8 Ma. • Obliquity forcing Lanzhou lake evolution between ∼19.8 and 20.8 Ma. • Weakening of the weathering intensity in Lanzhou Basin after 20.8 Ma. [ABSTRACT FROM AUTHOR]

The production of new crustal material at magmatic arcs is dominated by juvenile continental crust growth through the emplacement of voluminous mantle-derived magmatic rocks. There is evidence, however, that such settings can also accommodate the burial of supracrustal material to mid/lower crustal depths resulting in the production of the new crust through metamorphism and anatexis. Investigation of migmatitic garnet- and sillimanite-bearing schists and paragneisses demonstrate that rocks exposed within the exhumed, former middle to lower crust of eastern Gangdese arc, southern Tibet, underwent sillimanite-grade metamorphism and partial melting. Monazite in the studies rocks yield 208Pb/232Th ages of ca. 72–57 Ma, which overlaps with 206Pb/238U dates from zircon rim overgrowths of ca. 73–61 Ma. Inherited zircon cores in paragneisses and adjacent low-metamorphic grade Carboniferous sedimentary rocks of the Lhasa terrane yield similar U Pb dates, with main populations at 1220–1070 Ma, 570–470 Ma, and 370–320 Ma. When combined with previously published studies, these new data demonstrate that meta-sedimentary rocks are common in the middle/lower crust of the eastern Gangdese arc and were mainly derived from Carboniferous strata of the Lhasa terrane. The Carboniferous protolith rocks were buried to deep crustal levels via thrusting during crustal shortening during Late Cretaceous (ca. 90–70 Ma) flat subduction of the Neo-Tethyan slab. Subsequent (ca. 70–60 Ma) mantle-derived magmatism induced by slab rollback, likely facilitated metamorphism and anatexis of the sedimentary rocks in the arc. This study provides important new information on the origin of the meta-sedimentary rocks and on how they affected the evolution of the eastern Gangdese arc during the Late Cretaceous to Early Cenozoic. • 73–57 Ma sillimanite-grade meta-sedimentary rocks occur in the eastern Gangdese arc. • The meta-sedimentary rocks derived from the Carboniferous strata of the Lhasa terrane. • Crustal shortening and thrusting delivered the sedimentary rocks to the deep arc crust. • Melting of sedimentary rocks contribute to contemporaneous magmatism. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ca. 258 Ma high-magnesian andesites are identified in Northern Qiangtang. • The high-magnesian andesites were derived from MORB-like mantle wedge. • The magmatism was triggered by rollback of the Paleo-Tethyan oceanic slab. At convergent margins, high-magnesian andesitic rocks (HMAs) can offer vital information about the formation of the continental crust and the interactions between the deep crust and mantle. This study focuses on new identified HMAs from the Rongzharinian area, northern Qiangtang Terrane (NQT). We report the major, trace elemental, Sr-Nd-Hf isotopic data, and zircon U-Pb age of volcanic rocks with the aim of understanding their petrogenesis and tectonic setting. A concordant age of 257.7 ± 1.5 Ma for the Rongzharinian high-Mg andesites is determined by zircon U-Pb dating using LA-ICP-MS techniques. The Rongzharinian HMAs have high MgO contents (5.88–7.39 wt%), Mg# values (63–68), and Cr (143–185 ppm) and Ni (48–66 ppm) concentrations, close to primitive HMAs. They underwent variable degrees of fractionation of amphibole and minor clinopyroxene and negligible crustal contamination during magma evolution. REE modeling results show that the Rongzharinian HMAs can be generated by 4 %–7% melting of hydrous spinel lherzolite at relatively shallow depths. Geochemical data indicate that the Rongzharinian HMAs were dominantly derived from the mixed mantle wedge source composed of N-MORB-like and E-MORB-like components. Based on the regional tectonic evolution, we propose that the Late Permian rollback of the Paleo-Tethyan slab may induce upwelling of the asthenosphere mantle, resulting in melting of the mantle source and the generation of the Rongzharinian high-Mg andesites. [ABSTRACT FROM AUTHOR]

Across the Qinghai–Tibet Plateau (QTP) there is a narrow engineering corridor with widely distributed slopes called the Qinghai–Tibet Engineering Corridor (QTEC), where a variety of important infrastructures are concentrated. These facilities are transportation routes for people, materials, energy, etc. from inland China to the Tibet Autonomous Region. From Golmud to Lhasa, the engineering corridor covers 632 km of permafrost containing the densely developed Qinghai–Tibet Railway and Qinghai–Tibet Highway, as well as power and communication towers. Slope failure in permafrost regions, caused by permafrost degradation, ground ice melting, etc., affects the engineering construction and permafrost environments in the QTEC. We implement a variety of sensors to monitor the hydrological and thermal deformation between permafrost slopes and permafrost engineering projects in the corridor. In addition to soil temperature and moisture sensors, the global navigation satellite system (GNSS), terrestrial laser scanning (TLS), and unmanned aerial vehicles (UAVs) were adopted to monitor the spatial distribution and changes in thermal deformation. An integrated dataset of hydrological and thermal deformation in permafrost engineering and slopes in the QTEC from the 1950s to 2020, including meteorological and ground observations, TLS point cloud data, and RGB and thermal infrared (TIR) images, can be of great value for estimating the hydrological and thermal impact and stability between engineering and slopes under the influence of climate change and engineering disturbance. The dataset and code were uploaded to the Zenodo repository and can be accessed through https://zenodo.org/communities/qtec (last access: 23 June 2021), including meteorological and ground observations at 10.5281/zenodo.5009871 (Luo et al., 2020d), TLS measurements at 10.5281/zenodo.5009558 (Luo et al., 2020a), UAV RGB and TIR images at 10.5281/zenodo.5016192 (Luo et al., 2020b), and R code for permafrost indices and visualisation at 10.5281/zenodo.5002981 (Luo et al., 2020c). [ABSTRACT FROM AUTHOR]