Late Eocene To Middle Miocene Chemical Weathering And Climate Evolution In Leiwuqi Area,Eastern Tibetan Plateau

Silicate weathering processes play an important role in regulating atmospheric CO₂content and maintaining the balance of the geological carbon cycle.The hypothesis of“Plateau uplift-weathering erosion-climate change"linking the uplift of the Tibetan Plateau with the Cenozoic global climate change by silicate weathering has made the study of tectonic/climate interactions become a frontier in current geological research.However,this hypothesis is currently disputed due to the lack of records of long silicate chemical weathering sequences within the Tibetan Plateau during the Cenozoic.On the other hand,the formation and northward advance of the South Asian monsoon is closely related to the expansion and uplift of the Tibetan Plateau,but the formation and northward advance processes of the South Asian monsoon are also controversial.Therefore,obtaining reliable records of long sequence Cenozoic climate change and silicate chemical weathering in key regions of the Tibetan Plateau is an important way to gain insight into tackling these scientific questions.The eastern Tibetan Plateau is located at the turning belt of the east-west to the north-south tectonic zone of the plateau,and is situated at the intersection of the South Asian monsoon region and the alpine region of the Tibetan Plateau,which is an ideal area for studying the interaction of plateau tectonic uplift-weathering erosion-climate change.Nevertheless,previous studies on plateau tectonics associated with regional paleoclimate are limited to before 35 Ma due to the lack of the outcrops in the area.In order to solve the above scientific questions,this paper selects the continuous Cenozoic sedimentary sequence（38.3-15.9 Ma）in the Jiasangka area of the eastern Tibetan Plateau.Through studying clay mineral species,content and geochemical characteristics（major and trace elements）of sediment clay grain fraction（<2μm）,combined with the chromaticity,calcium carbonate content,the strontium isotope of acid insoluble fraction and sedimentary characteristics,this paper recovers the late Eocene to mid-Miocene paleoclimate and chemical weathering process in the study area,and detects the push timing of the South Asian monsoon to this region.In addition,on the basis of the previous study results of regional tectonic events and global climate change from global deep-sea oxygen isotopes,this research further discusses the driving factors of the chemical weathering strengthen changes as well as the northward advancing process of the South Asian monsoon from the late Eocene to mid-Miocene in the eastern Tibetan Plateau.This study provides fundamental geological evidences for the evolution of the South Asian monsoon and the interaction of plateau uplift-weathering erosion-climate change.The main insights are as follows:（1）This paper obtains the sequence of intensity changes of silicate chemical weathering during the late Eocene to mid-Miocene in the Leiwuqi area,and finds that chemical weathering was weak at 38.3-36.2 Ma,relatively enhanced at 36.2-34.0 Ma,continuously weakened at 34.0-26.4 Ma,and gradually enhanced at 26.4-15.9 Ma.（2）This paper reconstructs the climate change history of the Leiwuqi area in the eastern Tibetan Plateau during 38.3-15.9 Ma,which is characterized by a generally arid climate 38.3-26.4 Ma and generally humid climate 26.4-15.9 Ma with obvious dry-wet cyclical fluctuations.（3）The South Asian monsoon intensifies and advances northward to the Leiwuqi area（32°N）in the eastern Tibetan Plateau at～26.4 Ma and further strengthen at～20.7 Ma,which is mainly controlled by the uplift of the Tibetan Plateau and global warming.Before 26.4 Ma,the chemical weathering intensity in the Leiwuqi area was mainly affected by global and regional climate change.Since 26.4 Ma,the chemical weathering intensity had gradually increased,which is mainly controlled by the combination of global climate change,the uplift of the Tibetan Plateau and South Asian monsoon.