Spatio-Temporal Heterogeneity of Climate Warming in the Chinese Tianshan Mountainous Region

The Chinese Tianshan mountainous region (CTMR) is a typical alpine region with high topographic heterogeneity, characterized by a large altitude span, complex topography, and diverse landscapes. A significant increase in air temperature had occurred in the CTMR during the last five decades. However, the detailed, comprehensive, and systematical characteristics of climate warming, such as its temporal and spatial heterogeneity, remain unclear. In this study, the temporal and spatial heterogeneity of climate warming across the CTMR had been comprehensively analyzed based on the 10-day air temperature data gathered during 1961–2020 from 26 meteorological stations. The results revealed local cooling in the context of general warming in the CTMR. The amplitude of variation (AV) varied from −0.57 to 3.64 °C, with the average value of 1.19 °C during the last six decades. The lapse rates of the elevation-dependent warming that existed annually, and in spring, summer, and autumn are −0.5 °C/100 m, −0.5 °C/100 m, −0.7 °C/100 m, and −0.4 °C/100 m, respectively. The warming in the CTMR is characteristic of high temporal heterogeneity, as represented by the amplified warming at 10-d scale for more than half a year, and the values of AV were higher than 1.09 °C of the global warming during 2011–2020 (GWV2011–2020). Meanwhile, the amplitudes of warming differed greatly on a seasonal scale, with the rates in spring, autumn, and winter higher than that in summer. The large spatial heterogeneity of climate warming also occurred across the CTMR. The warming pole existed in the warm part, the Turpan-Hami basin (below 1000 m asl) where the air temperature itself was high. That is, the warm places were warmer across the CTMR. The cooling pole was also found in the Kuqa region (about 1000 m asl). This study could greatly improve the understanding of the spatio-temporal dynamics, patterns, and regional heterogeneity of climate warming across the CTMR and even northwest China.

Role of Longitudinal Lithological Contrast On the Channel Evolution of Piedmont Rivers

<p>The cut-and-fill terrace sequence, resulted from aggradation and incision cycles of alluvial rivers on the piedmont of active orogens, is a common tectonic geomorphological feature observed across different continents under different climatic regimes. Such aggradation and incision cycles are identified on both the orbital and sub-orbital cycles, which poses a question about their origins. Efforts have been put into disentangling the contributions from tectonics, climate and other autogenic sources. In this study, we investigated it by exploring the cut-and-fill terrace sequences along the Jingou River on the northern piedmont of Chinese Tianshan, where numerous terraces are seen along tens of alluvial rivers flowing through the fold-and-thrust belt. More than ten terrace flights, are observed where Jingou River flows across the active Huoerguosi anticline. We collected sediment samples for OSL dating to decipher the building and abandonment processes of these terraces and made topographic measurements to evaluate the paleo-slope of this section of Jingou River. Detailed field survey of sedimentary structure and luminescence dates unambiguously unveil the aggradation and incision cycles on sub-orbital cycles since the last interglacial. Down-cutting of no less than 80 meters is identified during the last ten thousands of years. We tentatively evaluated the possible roles of regional climatic variation, anticline deformation and the autogenic processes. Of all these factors, we detailedly investigated the role of longitudinal contrast of lithologies along the river due to the deformation of the Huoerguosi anticline, which always promotes the channel incision.</p>

Retrograde carbon sequestration in orogenic complexes: a case study from the Chinese Southwestern Tianshan

<p>The interaction between ascending carbonic fluids and rocks at shallow depths in orogenic systems plays an important role in carbon flux regulation. In subduction zones, most works have focused on processes related to carbon release from the subducting slab or sequestration via high-pressure (HP) carbonation of mafic or ultramafic lithologies. A significant fraction of the carbonic fluids released by deep metamorphic reactions can also reach orogenic complexes and react with crustal and exhumed metamorphic rocks. However, the amount of fluid-mediated carbonation that may take place at crustal depths in orogenic complexes is still poorly constrained.</p><p>We report the occurrence of retrograde mafic eclogites and metasomatic marbles in UHP units in the Chinese Tianshan orogenic belt. The mafic eclogites recorded two successive, superimposed metamorphic–metasomatic stages: graphite precipitation along fractures and veins at eclogite facies (Stage#1) and pervasive rock carbonation (i.e., Stage#2: silicate dissolution and carbonate precipitation) at retrograde amphibolite to greenschist facies. This work focuses on Stage#2 carbonation, which consists of the transformation of Stage#1 graphite-bearing eclogites into carbonate + paragonite (± zoisite) + quartz. We present field, microstructural, petrological, and geochemical results of carbonic fluid–rock interactions affecting exhumed mafic eclogites. These results are supported by thermodynamic modeling for low-pressure carbonation of mafic eclogite obtained by means of EQ3/6 and the Deep Earth Water model. Carbon and oxygen isotopic data and thermodynamic modeling suggest an external metasedimentary source for the Stage#2 carbonation. This deep carbon sequestration event can be referred to retrograde, greenschist-facies conditions at about 10 kbar and 450 °C, and redox conditions similar or more oxidized than the quartz–fayalite–magnetite (QFM) buffer. Our findings provide new insights into the reactivity of metastable, exhumed metamafic rocks with ascending carbonic fluids in orogenic systems. We conclude that retrograde, fluid-mediated rock carbonation can significantly impact on carbon fluxes from active collisional belts. </p>

Exhumation and Preservation of Paleozoic Porphyry Cu Deposits: Insights from the Yandong Deposit, Southern Central Asian Orogenic Belt

Paleozoic porphyry copper deposits are generally much less common than their Mesozoic or Cenozoic counterparts, as they can be completely eroded in rapidly uplifting arcs. There are, however, some large Paleozoic porphyry copper deposits preserved worldwide, especially in the Central Asian orogenic belt, although the processes by which these ancient porphyry deposits were preserved are poorly constrained. The Carboniferous Yandong porphyry copper deposit was selected as a case study to resolve this issue using a combination of thermal history models derived from low-temperature thermochronology data and regional geologic records. Our results show that Yandong preserves a record of at least two episodes of cooling separated by a phase of mild Middle Jurassic reheating. These two cooling events included one major event, linked to the Qiangtang collision or northward motion of Tarim plate during the late Permian to Triassic, and one minor event, possibly related to the Lhasa collision or closure of Mongol-Okhotsk Ocean from the Middle Jurassic to Early Cretaceous, respectively. Tectonic quiescence and limited exhumation prevailed from the Late Cretaceous to Cenozoic in the Yandong area. Combining our results with regional geologic records, we propose that extensional tectonic subsidence, postmineralization burial, dry paleoclimatic conditions, and Cenozoic tectonic quiescence were key factors for the preservation of Yandong. This study demonstrates that anomalously old apatite fission track ages, integrated with age-elevation relationships, can have implications for mineral exploration strategies in the Chinese Tianshan orogens.

Evidence for elevation-dependent warming from the Chinese Tianshan Mountains

The phenomenon that the warming rate of air temperature is amplified with elevation is termed elevation-dependent warming (EDW). It has been clarified that EDW can accelerate the retreat of glaciers and the melting of snow, which would have significant impacts on regional ecological environment. Owing to the lack of high-density ground observations in the high mountains, there is a widespread controversy on the existence of the EDW. Current evidences are mainly derived from some typical high mountains such as the Swiss Alps, the Colorado Rocky Mountains, the Tropical Andes and the Tibetan Plateau/Himalayas. Rare evidences in other mountains have been reported, especially in arid regions. In this study, EDW features in the Chinese Tianshan Mountains (CTM) are detected using a unique high-resolution (1 km, 6-hourly) air temperature data set (CTMD). The results showed that there are significant EDW signals at different altitudes on different time scales. The warming rate of the minimum temperature in winter shows significant elevation dependence, especially above 4000 m. The greatest altitudinal gradient in the warming rate of maximum temperature is found above 2500 m in April. For the mean temperature, the warming rates in January, February and March show prominent EDW features but with different significances. Within the CTM, the Tolm Mountains, the eastern part of the Borokoonu Mountains, the Bogda Mountains and the Balikun Mountains are the representative regions that show significant EDW features on different time scales. This new evidence partly explains the accelerated melting of glaciers in spring in the CTM.