Tectonostratigraphic properties and evolution of the Yeba volcanic arc in South Gangdese, Tibet

doi:10.13745/j.esf.sf.2021.7.33

Abstract

Abstract:

In the South Gangdese magmatic belt a set of exposed Early-Middle Jurassic volcanic-sedimentary formations underwent multi-stage structural deformation, which resulted in intense foliation displacing the volcanic-sedimentary sequence and forming the typical tectonic-rock strata. According to the stratigraphic division scheme for orogenic belt, the Early-Middle Jurassic volcanic arc is defined as Yeba rock group, which is further divided into the Bangdui, Yeba and Jiama rock formations based on its internal lithologic assemblages and structural deformation modes. The three-stage deformation is characterized as below. In D₁ stage, the brittle-ductile shear deformation is pure shear dominant general shear deformation, and beddings (S₀) are mostly replaced by penetrative foliations (S₁) (S₁∥S₀). The deformation is characterized as pure westward shearing, from the top, with a steep stretching lineation to 85-100° according to kinematic observations. EBSD results showed the deformation temperature is no more than 380 ℃, and quartz particles are clearly fine-grained, formed by sub-particle rotational recrystallization.⁴⁰Ar-³⁹Ar dating results suggests the D₁ tectonic deformation happened around 79 Ma, therefore it could represent an extrusion structure formed by the low angle (flatten) Neo-Tethys ocean plate subduction in the back-arc compression background. In D₂ stage, longitudinal folding of S₁ led to the axial-plane cleavage (S₂) that dips to N or S, with an inclination of 40-70°, and hinges toward W or NWW. Combining with the regional geological evolutionary history, we believe the Southern Gangdse back-arc basin was extruded upward under continuous N-S compressional stress during the Late Cretaceous (79-68 Ma), which resulted in upper crustal shortening and thickening, then led to folding. In D₃ stage, deformation is mainly kink-bands and near E-W normal faults. The maximum principal compressive stress is in the vertical direction, while the minimum (extension direction) is in near N-S direction. Combining with the regional tectonic evolutionary history, we suggest that the near N-S extensional event during the late Oligocene-early Miocene (23.74-21.1 Ma) may represent the uplift of the Gangdese batholith caused by the delamination of the Indian lithosphere and/or Tibetan plateau lithosphere (the main dynamic mechanism) and the Gangdese counter thrust activity.

Key words: Southern Gangdese belt in Tibet, Yeba volcanic arc, tectonostratigraphy, deformation age, tectonic evolution

CLC Number:

P542
P544.4

TANG Yu, WANG Genhou, FENG Yipeng, CI Dan, LI Dian, FAN Zhengzhe, GAO Xi, WEI Yufei, HU Jixin, ZHANG Peilie. Tectonostratigraphic properties and evolution of the Yeba volcanic arc in South Gangdese, Tibet[J]. Earth Science Frontiers, 2022, 29(1): 285-302.

Figures/Tables 12

References 61

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T/℃	⁴⁰Ar/³⁹Ar	1σ	³⁷Ar/³⁹Ar	1σ	³⁶Ar/³⁹Ar	1σ	⁴⁰Ar^*/³⁹Ar_K±2σ	(Age± 2σ)/Ma
QY0807-1
650	47.875 9	0.098 9	0.000 0	0.036 5	0.133 2	0.001 4	8.525 9±0.82	56.98±5.38
720	32.631 2	0.052 4	0.037 7	0.005 2	0.080 1	0.000 6	8.953 6±0.33	59.79±2.16
760	12.105 4	0.019 6	0.026 2	0.004 0	0.006 3	0.000 1	10.253 2±0.07	68.31±0.48
800	12.077 8	0.019 7	0.005 6	0.003 5	0.003 8	0.000 1	10.962 2±0.08	72.94±0.55
840	12.462 5	0.020 1	0.004 8	0.002 1	0.002 9	0.000 1	11.600 4±0.07	77.09±0.44
880	12.908 0	0.021 1	0.014 5	0.001 9	0.003 0	0.000 1	12.025 4±0.06	79.86±0.36
920	12.985 2	0.021 0	0.007 7	0.002 8	0.003 4	0.000 1	11.971 5±0.07	79.51±0.49
960	13.082 5	0.021 6	0.000 0	0.005 7	0.004 2	0.000 2	11.837 2±0.13	78.63±0.81
1 010	13.285 7	0.021 7	0.000 0	0.004 4	0.005 1	0.000 2	11.783 6±0.13	78.28±0.86
1 060	13.529 4	0.022 9	0.000 0	0.005 7	0.006 8	0.000 2	11.532 0±0.14	76.65±0.91
1 120	13.416 2	0.022 0	0.000 0	0.005 5	0.007 3	0.000 2	11.249 4±0.14	74.81±0.92
1 180	15.543 8	0.026 7	0.000 0	0.005 1	0.014 2	0.000 5	11.340 5±0.28	75.40±1.80
1 400	74.011 0	0.161 5	0.082 7	0.028 8	0.191 8	0.001 8	17.328 8±1.05	113.98±6.70
T/℃	⁴⁰Ar/³⁹Ar	1σ	³⁷Ar/³⁹Ar	1σ	³⁶Ar/³⁹Ar	1σ	⁴⁰Ar^*/³⁹Ar_K±2σ	(Age± 2σ)/Ma
QY0807-4
600	102.673 1	0.303 8	0.000 0	0.035 7	0.337 2	0.002 9	3.028 8±1.61	20.24±10.70
680	21.169 5	0.035 1	0.006 9	0.007 4	0.045 1	0.000 5	7.856 0±0.32	52.03±2.07
720	32.079 7	0.054 3	0.000 0	0.012 3	0.076 1	0.000 7	9.599 6±0.38	63.37±2.46
760	15.509 9	0.025 1	0.000 0	0.004 0	0.015 4	0.000 2	10.956 8±0.13	72.16±0.81
800	13.057 1	0.021 0	0.019 7	0.004 2	0.005 7	0.000 2	11.362 4±0.12	74.77±0.75
840	13.417 1	0.021 6	0.000 0	0.002 0	0.004 6	0.000 1	12.043 0±0.08	79.16±0.52
880	13.375 6	0.022 0	0.000 0	0.004 4	0.004 5	0.000 2	12.044 9±0.10	79.17±0.65
920	13.717 8	0.022 0	0.000 9	0.001 5	0.004 7	0.000 1	12.318 1±0.07	80.92±0.45
960	13.928 1	0.022 5	0.000 0	0.005 3	0.006 6	0.000 2	11.990 6±0.13	78.82±0.81
1 020	14.341 9	0.024 5	0.000 0	0.012 4	0.007 2	0.000 3	12.217 3±0.21	80.28±1.35
1 100	15.310 1	0.025 1	0.000 3	0.003 1	0.010 8	0.000 1	12.110 3±0.09	79.59±0.59
1 180	16.814 2	0.027 3	0.008 0	0.003 5	0.014 5	0.000 2	12.520 3±0.11	82.22±0.68
1 260	29.340 9	0.061 4	0.000 0	0.032 9	0.043 3	0.001 2	16.539 7±0.72	107.84±4.57
1 400	57.797 3	0.181 3	0.000 0	0.058 4	0.125 3	0.001 9	20.763 2±1.10	134.38±6.84

T/℃	⁴⁰Ar/³⁹Ar	1σ	³⁷Ar/³⁹Ar	1σ	³⁶Ar/³⁹Ar	1σ	⁴⁰Ar^*/³⁹Ar_K±2σ	(Age± 2σ)/Ma
QY0807-1
650	47.875 9	0.098 9	0.000 0	0.036 5	0.133 2	0.001 4	8.525 9±0.82	56.98±5.38
720	32.631 2	0.052 4	0.037 7	0.005 2	0.080 1	0.000 6	8.953 6±0.33	59.79±2.16
760	12.105 4	0.019 6	0.026 2	0.004 0	0.006 3	0.000 1	10.253 2±0.07	68.31±0.48
800	12.077 8	0.019 7	0.005 6	0.003 5	0.003 8	0.000 1	10.962 2±0.08	72.94±0.55
840	12.462 5	0.020 1	0.004 8	0.002 1	0.002 9	0.000 1	11.600 4±0.07	77.09±0.44
880	12.908 0	0.021 1	0.014 5	0.001 9	0.003 0	0.000 1	12.025 4±0.06	79.86±0.36
920	12.985 2	0.021 0	0.007 7	0.002 8	0.003 4	0.000 1	11.971 5±0.07	79.51±0.49
960	13.082 5	0.021 6	0.000 0	0.005 7	0.004 2	0.000 2	11.837 2±0.13	78.63±0.81
1 010	13.285 7	0.021 7	0.000 0	0.004 4	0.005 1	0.000 2	11.783 6±0.13	78.28±0.86
1 060	13.529 4	0.022 9	0.000 0	0.005 7	0.006 8	0.000 2	11.532 0±0.14	76.65±0.91
1 120	13.416 2	0.022 0	0.000 0	0.005 5	0.007 3	0.000 2	11.249 4±0.14	74.81±0.92
1 180	15.543 8	0.026 7	0.000 0	0.005 1	0.014 2	0.000 5	11.340 5±0.28	75.40±1.80
1 400	74.011 0	0.161 5	0.082 7	0.028 8	0.191 8	0.001 8	17.328 8±1.05	113.98±6.70
T/℃	⁴⁰Ar/³⁹Ar	1σ	³⁷Ar/³⁹Ar	1σ	³⁶Ar/³⁹Ar	1σ	⁴⁰Ar^*/³⁹Ar_K±2σ	(Age± 2σ)/Ma
QY0807-4
600	102.673 1	0.303 8	0.000 0	0.035 7	0.337 2	0.002 9	3.028 8±1.61	20.24±10.70
680	21.169 5	0.035 1	0.006 9	0.007 4	0.045 1	0.000 5	7.856 0±0.32	52.03±2.07
720	32.079 7	0.054 3	0.000 0	0.012 3	0.076 1	0.000 7	9.599 6±0.38	63.37±2.46
760	15.509 9	0.025 1	0.000 0	0.004 0	0.015 4	0.000 2	10.956 8±0.13	72.16±0.81
800	13.057 1	0.021 0	0.019 7	0.004 2	0.005 7	0.000 2	11.362 4±0.12	74.77±0.75
840	13.417 1	0.021 6	0.000 0	0.002 0	0.004 6	0.000 1	12.043 0±0.08	79.16±0.52
880	13.375 6	0.022 0	0.000 0	0.004 4	0.004 5	0.000 2	12.044 9±0.10	79.17±0.65
920	13.717 8	0.022 0	0.000 9	0.001 5	0.004 7	0.000 1	12.318 1±0.07	80.92±0.45
960	13.928 1	0.022 5	0.000 0	0.005 3	0.006 6	0.000 2	11.990 6±0.13	78.82±0.81
1 020	14.341 9	0.024 5	0.000 0	0.012 4	0.007 2	0.000 3	12.217 3±0.21	80.28±1.35
1 100	15.310 1	0.025 1	0.000 3	0.003 1	0.010 8	0.000 1	12.110 3±0.09	79.59±0.59
1 180	16.814 2	0.027 3	0.008 0	0.003 5	0.014 5	0.000 2	12.520 3±0.11	82.22±0.68
1 260	29.340 9	0.061 4	0.000 0	0.032 9	0.043 3	0.001 2	16.539 7±0.72	107.84±4.57
1 400	57.797 3	0.181 3	0.000 0	0.058 4	0.125 3	0.001 9	20.763 2±1.10	134.38±6.84