The Mechanism and Dynamics of N-S trends normal faults in Tibetan Plateau: Insight From Thermochronology, Magnetotellurics, Magmatism and GPS Measurements

2020 ◽  
Author(s):  
Han-Ao Li ◽  
in-Gen Dai ◽  
Le-Tian Zhang ◽  
Ya-Lin Li ◽  
Guang-Hao Ha ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Lower Crust ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Gps Measurements ◽  
Southern Tibet ◽  
Magnetotelluric Data ◽  
Deep Process ◽  
Lower Crustal Flow ◽  
Lower Crustal

<p>The N-S trends normal faults are widespread through the whole Tibetan Plateau. It records key information for the growth and uplift of the Tibetan Plateau. Numerous models are provided to explain the causes of rifting in the Tibetan Plateau based on the low-temperature thermochronology<sup>1</sup>. With the developments of the geophysical and magmatic geochemistry methods and its applications on the Tibetan Plateau, we could gain more profound understanding on the sphere structure of the Tibetan Plateau. This would give us more clues on how the deep process affect the formation and evolution of the shallow normal faults. However, few researchers pay attention on this and the relationship between the surface evolution and deep process of these faults. In order to solve these puzzles, we collected the published thermochronology data, magnetotelluric data, faults-related ultrapotassic, potassic and the adakitic rocks ages and present-day GPS measurements. We find that the distribution of the N-S trends normal faults are closely related to the weak zones in the middle to lower crust (15-50 km) revealed by the magmatism and magnetotelluric data<sup>2</sup>. Besides, the present-day GPS data show that the E-W extension rates match well with the eastward movements speeds interior Tibetan Plateau<sup>3</sup>. Combined with the thermochronology data (25-4 Ma), we concluded that 1.The weak zone in the middle to lower crust influence the developments and evolution of the N-S trends normal faults. 2. The material eastward flow enhance the N-S normal faults developments. 3. The timing of the middle to lower crustal flow may begin in the Miocene.</p><p><strong>Key words:</strong> N-S trends normal faults; Thermochronology; Magnetotellurics; Magmatism; GPS Measurements; middle to lower crustal flow</p><p><strong>References:</strong></p><p><sup>1</sup>Lee, J., Hager, C., Wallis, S.R., Stockli, D.F., Whitehouse, M.J., Aoya, M. and Wang, Y., 2011. Middle to Late Miocene Extremely Rapid Exhumation and Thermal Reequilibration in the Kung Co Rift, Southern Tibet. Tectonics, 30(2).</p><p><sup>2</sup>Pang, Y., Zhang, H., Gerya, T.V., Liao, J., Cheng, H. and Shi, Y., 2018. The Mechanism and Dynamics of N-S Rifting in Southern Tibet: Insight from 3-D Thermomechanical Modeling. Journal of Geophysical Research: Solid Earth.</p><p><sup>3</sup>Zhang, P.-Z., Shen, Z., Wang, M., Gan, W., Bürgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J., Hanrong, S. and Xinzhao, Y., 2004. Continuous Deformation of the Tibetan Plateau from Global Positioning System Data. Geology, 32(9).</p><p><strong>Acknowledgements:</strong></p><p>We thank Shi-Ying Xu, Xu Han, Bo-Rong Liu for collecting data. Special thanks are given to Dr. Guang-Hao Ha and Professors Jin-Gen Dai, Le-Tian Zhang，Ya-Lin Li and Cheng-Shan Wang for many critical and constructive comments.</p>

Geochemical and isotopic data of Zheduo-Gongga granitic intrusive complex, eastern margin of the Tibetan Plateau: no evidence for middle-lower crustal flow

2020 ◽  
Author(s):  
Fangyang Hu ◽  
Fuyuan Wu ◽  
Mihai Ducea ◽  
James Chapman
Keyword(s):  
Tibetan Plateau ◽  
Partial Melting ◽  
Lower Crust ◽  
Biotite Granite ◽  
The Tibetan Plateau ◽  
Eastern Margin ◽  
Granitoid Rocks ◽  
Lower Crustal Flow ◽  
Group 2 ◽  
Lower Crustal

<p>Geophysical studies have shown that middle-lower crustal flow started from central Tibetan Plateau may exist in the eastern margin of the Tibetan Plateau, which controls the mountain building, crustal thickening and deformation (Schoenbohm et al., 2006; Bai et al., 2010; Bao et al., 2015; Zhu et al., 2017). However, no geological and petrological evidence have been presented. We carried out detailed studies on the geochemical and isotopic compositions of the Mesozoic-Cenozoic Zheduo-Gongga granitic intrusive complex on the eastern margin of the Tibet Plateau. Geochronology studies show that these granitoid rocks are formed during Mesozoic to Cenozoic, including ~220-200 Ma Gongga granodiorite to biotite granite with mafic enclaves, ~40 Ma Zheduo gneissic granite, ~28 Ma Zheduo monzogranite, and ~20-4 Ma Zheduo biotite granite and monzogranite. Two groups of geochemical features are obtained: Group 1 (gnessic granite, granodiorite, monzogranite, and leucogranite) has relatively low K2O, Th/La, La/Yb and Rb/Sr ratios, but high Sr/Y ratio with no Eu negative anomalies; Group 2 (biotite granite) has relatively high K2O, Th/La, La/Yb and Rb/Sr ratios, but low Sr/Y with strong negative Eu anomalies. The Sr-Nd-Hf-O isotopic studies on plagioclase, apatite and zircon show that their sources are primarily the basement of the western margin of Yangtze Craton and Songpan-Ganzi sediments. These features indicate that they have different petrogenesis processes. Group 1 is mainly derived from partial melting of mafic rocks in the lower crust, whereas the Group 2 is primarily derived from partial melting of metasedimentary rocks experiencing fractionation of plagioclase. Magma derived from different sources mixing with each other are observed as well. Therefore, from geochemical aspects, no exotic materials are involved in the formation of granitoid rocks during Mesozoic to present. The flow of crustal material in the middle-lower crust may be not existed. The low velocity and high conductivity layer in the middle-lower crust may represent a regional partial melting zone, which could be related to the upwelling of asthenosphere. Both crustal deformation and upwelling of asthenosphere may contribute to the crustal thicknening and uplift.</p>

scholarly journals Cenozoic shortening budget for the northeastern edge of the Tibetan Plateau: Is lower crustal flow necessary?

Tectonics ◽  
2012 ◽  
Vol 31 (3) ◽  
pp. n/a-n/a ◽  
Author(s):  
Richard O. Lease ◽  
Douglas W. Burbank ◽  
Huiping Zhang ◽  
Jianhui Liu ◽  
Daoyang Yuan
Keyword(s):  
Tibetan Plateau ◽  
The Tibetan Plateau ◽  
Lower Crustal Flow ◽  
Lower Crustal

scholarly journals The Role of Lower Crustal Rheology in Lithospheric Delamination During Orogeny

2021 ◽  
Vol 9 ◽  
Author(s):  
Lin Chen
Keyword(s):  
Lower Crust ◽  
Numerical Models ◽  
The Tibetan Plateau ◽  
Mantle Lithosphere ◽  
Laboratory Studies ◽  
Surface Uplift ◽  
Continental Lower Crust ◽  
Lower Crustal ◽  
Flow Laws

The continental lower crust is an important composition- and strength-jump layer in the lithosphere. Laboratory studies show its strength varies greatly due to a wide variety of composition. How the lower crust rheology influences the collisional orogeny remains poorly understood. Here I investigate the role of the lower crust rheology in the evolution of an orogen subject to horizontal shortening using 2D numerical models. A range of lower crustal flow laws from laboratory studies are tested to examine their effects on the styles of the accommodation of convergence. Three distinct styles are observed: 1) downwelling and subsequent delamination of orogen lithosphere mantle as a coherent slab; 2) localized thickening of orogen lithosphere; and 3) underthrusting of peripheral strong lithospheres below the orogen. Delamination occurs only if the orogen lower crust rheology is represented by the weak end-member of flow laws. The delamination is followed by partial melting of the lower crust and punctuated surface uplift confined to the orogen central region. For a moderately or extremely strong orogen lower crust, topography highs only develop on both sides of the orogen. In the Tibetan plateau, the crust has been doubly thickened but the underlying mantle lithosphere is highly heterogeneous. I suggest that the subvertical high-velocity mantle structures, as observed in southern and western Tibet, may exemplify localized delamination of the mantle lithosphere due to rheological weakening of the Tibetan lower crust.

scholarly journals Diachronous Tibetan Plateau landscape evolution derived from lava field geomorphology

2020 ◽  
Author(s):  
Mark Allen ◽  
Robert Law
Keyword(s):  
Tibetan Plateau ◽  
Landscape Evolution ◽  
Tectonic Geomorphology ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Lava Field ◽  
Northern Tibetan Plateau ◽  
Tectonic Processes ◽  
Stepwise Evolution

<p><strong>Evolution of the Tibetan Plateau is important for understanding continental tectonics because of its exceptional elevation (~5 km above sea level) and crustal thickness (~70 km). Patterns of long-term landscape evolution can constrain tectonic processes, but have been hard to quantify, in contrast to established datasets for strain, exhumation and paleo-elevation. This study analyses the relief of the bases and tops of 17 Cenozoic lava fields on the central and northern Tibetan Plateau. Analyzed fields have typical lateral dimensions of 10s of km, and so have an appropriate scale for interpreting tectonic geomorphology. Fourteen of the fields have not been deformed since eruption. One field is cut by normal faults; two others are gently folded with limb dips <6<sup>o</sup></strong><strong>. </strong><strong>Relief of the bases and tops of the fields is comparable to modern, internally-drained, parts of the plateau, and distinctly lower than externally-drained regions. The lavas preserve a record of underlying low relief bedrock landscapes at the time they were erupted, which have undergone little change since. There is an overlap in each area between younger published low-temperature thermochronology ages and the oldest eruption in each area, here interpreted as the transition </strong><strong>between the end of significant (>3 km) exhumation and plateau landscape development. </strong><strong>This diachronous process took place between ~32.5<sup>o</sup> - ~36.5<sup>o</sup> N between ~40 and ~10 Ma, advancing northwards at a long-term rate of ~15 km/Myr. Results are consistent with incremental northwards growth of the plateau, rather than a stepwise evolution or synchronous uplift.</strong></p>

A lake-level chronology based on feldspar luminescence dating of beach ridges at Tangra Yum Co (Southern Tibet)

2015 ◽  
Vol 83 (3) ◽  
pp. 469-478 ◽  
Author(s):  
Eike F. Rades ◽  
Sumiko Tsukamoto ◽  
Manfred Frechen ◽  
Qiang Xu ◽  
Lin Ding
Keyword(s):  
Tibetan Plateau ◽  
Lake Level ◽  
Environmental Changes ◽  
Luminescence Dating ◽  
Rapid Decline ◽  
The Tibetan Plateau ◽  
Southern Tibet ◽  
Beach Ridges ◽  
Slow Decline ◽  
Fast Decline

Many lakes on the Tibetan Plateau exhibit strandplains with a series of beach ridges extending high above the current lake levels. These beach ridges mark former lake highstands and therefore dating their formation allows the reconstruction of lake-level histories and environmental changes. In this study, we establish a lake-level chronology of Tangra Yum Co (fifth largest lake on the Tibetan Plateau) based on luminescence dating of feldspar from 17 beach-ridge samples. The samples were collected from two strandplains southeast and north of the lake and range in elevation from the current shore to 140 m above the present lake. Using a modified post-infrared IRSL protocol at 170°C we successfully minimised the anomalous fading in the feldspar IRSL signal, and obtained reliable dating results. The luminescence ages indicate three different stages of lake-level decline during the Holocene: (1) a phase of rapid decline (~ 50 m) from ~ 6.4 to ~ 4.5 ka, (2) a period of slow decline between ~ 4.5 and ~ 2.0 ka (~ 20 m), and (3) a fast decline by 70 m between ~ 2 ka and today. Our findings suggest a link between a decrease in monsoonal activity and lake-level decline since the early Holocene.

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