The Earth's Surface Chemical Weathering Intensity And Its Controlling Factors Of Northern Qinghai-Tibet Plateau

Chemical weathering is a crucial process of interaction between the surface system and the earth's spheres.It plays an important role in shaping the earth's surface morphology and controlling the cycling of geochemical elements.Particularly,the chemical weathering of silicates on geological time scale,which results in net consumption of atmospheric carbon dioxide,is considered as the "thermostat" of the earth.For the earth's surface chemical weathering is m ainly controlled by tectonics and climatic,the study of paleochemical weathering in geological history is often used to reconstruct paleoclimate evolution or tectonic history.The northern part of the Qinghai-Tibet Plateau is an important area to study the relationship between the uplift of the Qinghai-Tibet Plateau and chemical weathering.The northern part of the Qinghai-Tibet Plateau is in an active tectonic setting and is in an area where westerlies,Asian winter monsoon and summer monsoon interact.As the most important sedimentary basin in the northern part of the Qinghai-Tibet Plateau,Qaidam Basin has preserved a huge thickness of Mesozoic-Cenozoic strata and recorded the tectonic movement and climate change information of the area.Based on the study of Huaitoutala section strata in eastern Qaidam Basin,this paper will discuss the climate change and its driving mechanism in eastern Qaidam Basin since Miocene,and the relationship between chemical weathering and global climate and uplift of the Qinghai-Tibet Plateau,providing a reference for paleoclimate change in Qaidam Basin.In addition,this paper will also explore the dominant factors which affect the earth's surface chemical weathering intensity in the northeastern Qinghai-Tibet Plateau by study the sediment of typical modern rivers in northern Qinghai Province.The sediments in Huaitoutala section show low compositional and structural maturity,indicating the near-source deposition and not affected by sedimentary cycles.Heavy mineral analysis shows that the lithology of source rocks were mainly epimetamorphic rocks and medium-basic igneous rocks.Combining paleocurrent data,it is inferred that the source area of sediments is the Qilian Mountains in the northwest direction and the source area has not changed.The composition of clay minerals indicates the climate change since the Miocene.Between 15.3-12.6 Ma,the climate in the source area was relatively warm and humid.Between 12.6-6.6 Ma,the climate became cold,semi-humid and semi-arid.Between 6.6-1.8 Ma,the climate became cold and dry.Chemical weathering and climate cooling did not show the same continuous downward trend.At 15.3-12.2 Ma,chemical weathering intensity showed an increasing trend.At this time,the deposition rate was at a higher level,while the climate was relatively warm and humid,indicating that climate was the dominant factor controlling chemical weathering,followed by structure.At 12.2-9.55 Ma,the chemical weathering intensity gradually weakened,the climate gradually became cold and dry,and the tectonic activity gradually weakened.At this time,the controlling factors of chemical weathering intensity were mainly climate,followed by structure.At 9.55-6.8 Ma,the chemical weathering intensity gradually increased,while the climate continued to dry and the tectonic activity was at a low level,indicating that the main controlling factors of chemical weathering intensity in this period were climate,followed by structure.At 6.8-1.8 Ma,the intensity of chemical weathering became weaker and the tectonic activity became stronger,indicating that the main controlling factor of chemical weathering in this period was tectonics,followed by climate.Through the study of petrology,heavy minerals,geochemistry and clay minerals of Huaitoutala section sediments,the main factors affecting the chemical weathering intensity in the source area were climate and tectonic activity.Typical modern river sediments in northern Qinghai also show low compositional and structural maturity.More metamorphic debris and heavy mineral assemblages dominated by amphibole and garnet also reflect that the source rocks were dominated by metamorphic rocks and intermediate-basic magmatic rocks.The parent rocks of sediments had similar geochemical characteristics.The chemical weathering degree of silicates was low to medium,and they were in the stage of plagioclase weathering with Na and Ca leaching out.Chemical weathering intensity has no correlation with temperature,but has some correlation with precipitation.By analysing the petrology,heavy minerals,geochemistry and clay minerals of the typical modern river sediments in northern Qinghai Province,climate will affect the chemical weathering of source areas,and tectonic activities will also affect the chemical weathering of sediments.Based on the study of chemical weathering of sediments/rocks in different time and space in northern Qinghai-Tibet Plateau,the main controlling factors of surface chemical weathering in northern Qinghai-Tibet Plateau are climate and structure.