Search

Granite genesis is crucial to understanding the evolution of continental crust, yet many concerns about granite genesis remain not well answered, such as whether I-type granite contains metasedimentary components, what controls granite compositional diversity, and how granitic plutons are constructed. To explore these issues, we conducted a detailed study on the two-mica plagiogranite, tonalite, and biotite plagiogranite units of the Wujinxia composite pluton in the eastern Qilian orogen, NE Tibetan Plateau. These units comprise two-mica plagiogranite, tonalite (with diorite enclave), and biotite plagiogranite. Zircon U–Pb data reveal that three granitic units formed at ~ 487 Ma, ~ 464 Ma, and ~ 430 Ma, respectively. Magmatic and xenocrystic garnet were identified from the tonalite and biotite plagiogranite, respectively. The two-mica plagiogranite, tonalite, and biotite plagiogranite all belong to low-K series rocks (K2O/Na2O = 0.10–0.26), and were derived from deep crustal sources mainly consisting of juvenile mafic rocks, with involvement of minor metasedimentary rocks in the magma sources of the two-mica plagiogranite and tonalite. The diorite enclave within the tonalite was probably derived from an enriched mantle-derived basaltic magma. Mineral compositions, thermobarometric calculations, and whole-rock geochemical data indicate that the low-K intrusive units of the Wujinxia composite pluton resulted from multiple magmatic systems at different depths. The results suggest that I-type granites can contain metasedimentary components by partial melting of a mixed crustal source, and high-Mn content helps the preservation of high-Ca garnet within such rocks. For a composite pluton spanning a large compositional variation, its compositional diversity is jointly controlled by magma source composition, melting condition and thermal evolution of individual magma pulses, and the resulted assembly style during pluton construction. [ABSTRACT FROM AUTHOR]

Voluminous Early Paleozoic intrusive rocks occur in the Qilian orogenic belt, northeastern margin of the Tibetan Plateau. Their petrogenesis can provide insights into the tectonic evolution of Qilian and its adjacent areas. This paper carries out an integrated study of U–Pb zircon dating, geochemical and Sr–Nd–Hf isotopic compositions for the Bamishan and Heishishan plutons in the eastern Qilian orogen. Both the Bamishan and Heishishan plutons consist of mafic, intermediate and felsic intrusive rocks. U–Pb zircon dating yielded the magma crystallization ages of 459–449 Ma for the Bamishan pluton and 447–438 Ma for the Heishishan pluton. Their geochemical and Sr–Nd–Hf isotopic data show that the parental magmas of the Bamishan monzogranites and quartz diorites were generated by slab (MORB and overlying sediments) melting. The Bamishan hornblende gabbros have extremely high Cr (1159–1163 ppm), Ni (220–353 ppm) and Mg# (73–74), indicating a cumulate origin. The Heishishan granodiorite–granite has adakitic geochemical signatures and they were produced by partial melting of the mafic lower crust. The Heishishan hornblende gabbro and quartz diorites were derived from the enriched lithospheric mantle metasomatized by subduction-related fluid/melt. In light of the available data, we propose that there was an Early Paleozoic ocean basin between the Central-South Qilian and Qaidam–West Qiling belts. The northward closure of this basin and subsequent continental collision and post-collisional processes resulted in the generation of the Early Paleozoic magmatism in the eastern Central Qilian. The Late Ordovician to Early Silurian (~ 460–440 Ma) intrusive rocks in the eastern Central Qilian formed in a post-collisional setting. A slab break-off model may account for the magma generation. [ABSTRACT FROM AUTHOR]

The high-altitude hypoxic environment represents one of the most extreme challenges for mammals. Previous studies of humans on the Tibetan plateau and in the Andes Mountains have identified statistical signatures of selection in different sets of loci. Here, we first measured the hemoglobin levels in village dogs from Tibet and those from Chinese lowlands. We found that the hemoglobin levels are very similar between the two groups, suggesting that Tibetan dogs might share similar adaptive strategies as the Tibetan people. Through a whole-genome sequencing approach, we have identified EPAS1 and HBB as candidate genes for the hypoxic adaptation on the Tibetan plateau. The population genetic analysis shows a significant convergence between humans and dogs in Tibet. The similarities in the sets of loci that exhibit putative signatures of selection and the hemoglobin levels between humans and dogs of the same environment, but not between human populations in different regions, suggests an extraordinary landscape of convergent evolution between human beings and their best friend on the Tibetan plateau. [ABSTRACT FROM AUTHOR]

The increased frequency of flooding on the Tibetan Plateau as a result of global warming has affected the lives of millions of people along the river valleys. The relationship between human settlement, climate change, and the frequency of flooding at long time scales is still unclear primarily due to the lack of a robust chronology for flooding deposits. In this study, AMS 14C dating, single-grain quartz OSL dating, and single-grain K-feldspar pIRIR dating using pIR 50 IR 170 and pIR 200 IR 290 signals were applied to the fluvial-paleosol sequence at the archaeology site Shalongka (SLK20) in the upper Yellow River valley on the northeastern Tibetan Plateau, where Paleolithic, Neolithic, and Bronze Age cultural layers were found. Utilizing luminescence characteristics analysis and a comparison of quartz OSL ages, K-feldspar pIRIR ages, and charcoal 14C ages, the reliability of single-grain quartz OSL and K-feldspar pIRIR ages was tested. Our results indicate that single-grain K-feldspar pIRIR 170 dating with the minimum age model (MAM) can be used to date Holocene fluvial deposit that have been poorly bleached. Based on the age-depth model, proxy data of the SLK20 grain size and magnetic susceptibility demonstrate that Yellow River overbank flooding increased during the periods 9.9–9.1, ∼8.0, 7.6–6.3 and 5.0-3.4 kyr BP; during the intervals between these periods, Yellow River overbank decreased and paleosols developed. Human occupations, as indicated by the appearance of cultural layers at the SLK20 site during the ∼8.1, ∼7.8, 6.3–5.0 and 3.4–2.0 kyr BP periods, occurred when paleosol developed. The variation in East Asian summer monsoon (EASM) intensities caused a moist and warm mid-Holocene climate at the SLK20 site, which was conducive to human settlement. Flood events caused by EASM precipitation changes during the mid-Holocene significantly influenced human settlement at the SLK20 site. During the middle to late Holocene, as EASM decreased in the region, the improvement of subsistence strategies likely dominated human settlement on the northeastern Tibetan Plateau. • Poorly bleached fluvial sediment can be dated using single-grain pIR 50 IR 170 dating. • Upper Yellow River floods occurred at 9.9–9.1, ∼8.0, 7.6–6.3 and 5.0–3.4 kyr BP. • Human settlement was established at ∼8.1, ∼7.8, 6.3–5.0 and 3.4–2.0 kyr BP. • Climate change, flood and subsistence strategy effect human settlement on the NE Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• Single grain K-feldspar pIR 50 IR 170 dating effectively dates samples over past 1 kyr. • Highest lake levels in Qaidam Basin over past 1 kyr during Little Ice Age. • Out-of-phase Central and East Asian precipitation drive asynchronous lake change. • EASM did not penetrate as far inland as Qaidam Basin during past 1 kyr. The moisture and precipitation evolution of mid-latitude Asia are dominated by the East Asian summer monsoon (EASM) and mid-latitude Westerlies atmospheric systems. How these two systems interacted along their transition zone in the northern Tibetan Plateau remains unclear, especially over centennially to millennial timescales. This study investigates moisture evolution along the EASM-Westerlies transition zone using 10 Late Holocene paleolake shorelines from Toson Lake in the northern Tibetan Plateau. Shorelines are dated using a newly developed single-grain post infrared-infrared stimulated luminescence (pIR 50 IR 170) dating protocol for 14,500 K-feldspar grains and used to reconstruct the evolution of Toson Lake over the past millennium. Results show that Toson Lake was stable during the Medieval Warm Period (MWP), expanded during the Little Ice Age (LIA) with a distinct highstand from AD1600–1700 punctuated by short-duration low period at ∼ CE 1650. After which, Toson Lake dramatically contracted into the Current Warm period (CWP). Lake level changes are consistent with Westerlies precipitation variability across Central Asia, in contrast to records from the EASM dominated northeastern Tibetan Plateau and northern China documenting an arid LIA and wet MWP. Reanalysis of modern climatic data are combined with our lake chronology to reveal that although EASM strength influences precipitation variability across northeastern Tibetan Plateau (NETP) and northern China, EASM precipitation has not directly penetrated deep inland over the past millennium. Instead, Westerlies moisture, modulated by the see-saw of the North Atlantic Oscillation, together with the moisture controlled by the anticyclonic circulation over Mongolia and negatively related to the EASM strength, dominated water vapour transport to the mid-latitudes of Central Asia. Out-of-phase moisture transport and interaction between the Westerlies and EASM drives asynchronous lake evolution between Central and East Asia over centennial-millennial timescales. [ABSTRACT FROM AUTHOR]