祁连山中部地壳各向异性研究:来自远震接收函数的证据

doi:10.13745/j.esf.sf.2022.4.23

摘要/Abstract

摘要：

青藏高原的隆升由印度-欧亚板块的碰撞而驱动,其生长演化,特别是从内到外的扩展机制仍尚存争议。祁连山地处青藏高原向东北扩展的前缘位置,其地壳结构与各向异性对于理解青藏高原向北扩展的生长机制具有重要意义。祁连山中部是青藏高原东北缘地壳遭受挤压强烈变形的区域,已有的研究已经揭示出地壳内部非耦合不均匀变形的几何行为,揭露其对应机制是亟待探索的前沿科学问题。此前该区域的各向异性研究大多基于面状台网数据,台站间距大,无法反映横跨祁连山地壳各向异性的精细变化。为此,本研究选用一条密集线性地震台阵,使用H-κ-c叠加方法,得到了横过祁连山中部的地壳厚度,泊松比以及地壳各向异性的横向变化。结果显示,在中祁连以及南祁连北部地壳厚度最大,平均泊松比最低,反映了地壳加厚过程中铁镁质下地壳的丢失以及长英质中上地壳的水平缩短。此外,偏长英质成分的泊松比值也不支持地壳流在该区域存在。在祁连山内部,地壳各向异性快波的偏振方向与地壳向外扩展方向一致,而与地幔各向异性快波方向近垂直,揭示了壳幔变形可能是解耦的。而在地壳较薄的南祁连和北祁连南部区域,快波方向与古缝合线的走向一致,说明早古生代的构造格局仍对现今的祁连山缩短隆升产生影响。

关键词: 祁连山, 地壳各向异性, 接收函数, H-κ-c叠加

Abstract:

The Tibetan Plateau uplift is driven by the collision between the Indian and Eurasian plates. Its growth and evolution, especially the mechanism of its outward expansion, is still controversial. At the forefront of its northeastward expansion lies the Qilian Mountains, whose crustal structure and anisotropy are of great significance for understanding the northward growth of the Tibetan Plateau. The central Qilian Mountains on the northeastern margin of the Tibetan Plateau experienced strong crustal compressional deformation. Existing studies have described phenomenons of non-coupling non-uniform deformations of crust and upper mantle, while understanding the deformation mechanism has become a frontier scientific issue. Previous anisotropy researches in this region mostly relied on seismic network data using large station spacing, however, which could not reflect the fine changes in the crustal anisotropy across the mountain range. To solve this problem, this study used the stacking method based on a dense linear seismic array to obtain the lateral variation of the crustal thickness, Poisson’s ratio and crustal anisotropy. The crust was found to be at its thickest in the Central Qilian and northern South Qilian, while the average Poisson’s ratio was the lowest in these areas, indicating loss of mafic lower crust and shortening of felsic upper-middle crust during crustal thickening. In addition, the Poisson’s ratio of felsic component did not support the existence of crustal flow in this region. In the interior of the mountain range, the fast polarization directions (FPDs) of the crust followed the direction of crustal outward expansion and were nearly perpendicular to the FPDs of the upper mantle, suggesting the crust-mantle deformation might be decoupled. In southern South Qilian and southern North Qilian where the crust is thinner, FPDs were parallel to the strike of the ancient suture, indicating the Early Paleozoic tectonic frame still had an impact on the shortening and uplifting of the Qilian Mountains.

Key words: Qilian Mountain, crustal anisotropy, receiver function, stacking

中图分类号:

P631.4
P542

周鹏哲, 高锐, 叶卓. 祁连山中部地壳各向异性研究:来自远震接收函数的证据[J]. 地学前缘, 2022, 29(4): 265-277.

ZHOU Pengzhe, GAO Rui, YE Zhuo. Crustal anisotropy study in the central Qilian Mountains: Evidence from teleseismic P wave receiver functions[J]. Earth Science Frontiers, 2022, 29(4): 265-277.

图/表 7

图1 研究区地质构造及台站位置分布图(据文献[40-41]补充修改) 三角形代表宽频地震台站的位置。其中,灰色三角形代表不满足H-κ-c叠加方法所要求的地震事件反方位角覆盖台站的位置;蓝色三角形代表H-κ-c叠加结果异常台站的位置。断裂简称:YMSF—榆木山断裂;NQLF—祁连山北缘断裂;HYF—海原断裂;RYSF—日月山断裂;ELSF—鄂拉山断裂;KLF—昆仑断裂;ATF—阿尔金断裂。缝合带简称:SQS—南祁连缝合带;DNS—党河南山缝合带;NQS—北祁连缝合带。右上图显示本次研究用来提取接收函数的远震事件。左下图用黄色方框在青藏高原数字高程图上标出研究区所在位置。

Fig.1 Topographic map of the study area showing major tectonic feature and distribution of stations. Modified after [40-41].

图2 台站QL17的H-κ-c叠加结果针对PS转换波(a)、M1多次波(b)和M2多次波(c)的谐波拟合结果展现了拟合曲线、搜索谐波参数的能量叠加图和汇总的搜索结果。谐波校正前后的H-κ叠加结果如图(d),(e)所示。

Fig.2 H-κ-c stacking results on station QL17

图3 谐波校正前(灰)后(白)地壳厚度与波速比的误差分布直方图

Fig.3 Histograms of the errors (standard deviation) of crustal thickness and velocity ratio before (grey) and after (white) harmonic corrections

图4 地壳厚度沿纬度的变化黑色误差棒为H-κ-c叠加方法所得到的地壳厚度,灰色误差棒为H-κ叠加方法所得到的地壳厚度。其中,蓝色误差棒代表H-κ-c叠加方法所得结果存在异常的台站;红色和蓝色十字分别在台站叠加接收函数上标注着由H-κ-c叠加方法,H-κ叠加方法计算得到的地壳厚度和波速比代入公式(2)中得到的PS转换波到时。

Fig.4 The variation of crustal thickness with altitude

图5 地壳波速比沿纬度的变化黑色误差棒为H-κ-c叠加方法所得到的地壳波速比;灰色误差棒为H-κ叠加方法所得到的地壳波速比。其中,蓝色误差棒代表H-κ-c叠加方法所得结果存在异常的台站。

Fig.5 The variation of crustal velocity ratio with altitude

图6 PS转换波经过谐波拟合所得分裂参数分布图(据文献[18,36-37,57-58]补充修改) 红色短棒代表本研究所得到的分裂参数;紫色短棒代表前人所得结果[18,36-37,57]。由棕色箭头指示相对于欧亚大陆的GPS速度场[58]。黑色粗箭头代表来自MORVEL模型的板块绝对运动(APM)方向[59]。

Fig.6 Splitting parameters obtained by harmonic fitting of PS converted wave. Modified after [18,36-37,57-58].

图7 地壳厚度与波速比的相关性分析图自下到上颜色逐渐变深的4个区域分别代表泊松比值σ<0.26,0.26≤σ<0.28,0.28≤σ<0.30以及σ≤0.30。白色圆点为被排除在相关性分析之外的数据点。

Fig.7 The correlation analysis of the crustal thickness and Poisson’s ratio

参考文献 75

[1]	LEECH M L, SINGH S, JAIN A K, et al. The onset of India-Asia continental collision: early, steep subduction required by the timing of UHP metamorphism in the western Himalaya[J]. Earth and Planetary Science Letters, 2005, 234(1/2): 83-97.
[2]	ROWLEY D B. Age of initiation of collision between India and Asia: a review of stratigraphic data[J]. Earth and Planetary Science Letters, 1996, 145(1/2/3/4): 1-13.
[3]	KLOOTWIJK C T, GEE J S, PEIRCE J W, et al. An early India-Asia contact: paleomagnetic constraints from Ninetyeast ridge, ODP Leg 121[J]. Geology, 1992, 20(5): 395-398.
[4]	DING L, KAPP P, WAN X. Paleocene-Eocene record of ophiolite obduction and initial India-Asia collision, south central Tibet[J]. Tectonics, 2005, 24(3): TC3001.
[5]	PANG J, YU J, ZHENG D, et al. Neogene expansion of the Qilian Shan, North Tibet: implications for the dynamic evolution of the Tibetan Plateau[J]. Tectonics, 2019, 38(3): 1018-1032.
[6]	WANG W, ZHENG D, LI C, et al. Cenozoic Exhumation of the Qilian Shan in the northeastern Tibetan Plateau: evidence from low-temperature thermochronology[J]. Tectonics, 2020, 39(4): 1-16.
[7]	ZHENG W, ZHANG P, HE W, et al. Transformation of displacement between strike-slip and crustal shortening in the northern margin of the Tibetan Plateau: evidence from decadal GPS measurements and late Quaternary slip rates on faults[J]. Tectonophysics, 2013, 584: 267-280.
[8]	ZUZA A V, WU C, REITH R C, et al. Tectonic evolution of the Qilian Shan: an early Paleozoic orogen reactivated in the Cenozoic[J]. Bulletin of the Geological Society of America, 2018, 130(5/6): 881-925.
[9]	YANG H, YANG X, ZHANG H, et al. Active fold deformation and crustal shortening rates of the Qilian Shan Foreland Thrust Belt, NE Tibet, since the Late Pleistocene[J]. Tectonophysics, 2018, 742: 84-100.
[10]	HETZEL R, HAMPEL A, GEBBEKEN P, et al. A constant slip rate for the western Qilian Shan frontal thrust during the last 200 ka consistent with GPS-derived and geological shortening rates[J]. Earth and Planetary Science Letters, 2019, 509: 100-113.
[11]	HOUSEMAN G, ENGLAND P. Finite strain calculations of continental deformation - Comparison with the India-Asia collision zone[J]. Journal of Geophysical Research: Solid Earth, 1986, 91: 3664-3676.
[12]	TAPPONNIER P, ZHIQIN X, ROGER F, et al. Oblique stepwise rise and growth of the tibet plateau[J]. Science, 2001, 294(5547): 1671-1677.
[13]	CLARK M K, ROYDEN L H. Topographic ooze: building the eastern margin of Tibet by lower crustal flow[J]. Geology, 2000, 28(8): 703-706.
[14]	ROYDEN L H, BURCHFIEL B C, VAN DER HILST R D. The geological evolution of the Tibetan plateau[J]. Science, 2008, 321(5892): 1054-1058.
[15]	SUN Y, NIU F, LIU H, et al. Crustal structure and deformation of the SE Tibetan plateau revealed by receiver function data[J]. Earth and Planetary Science Letters, 2012, 349: 186-197.
[16]	HAO S, HUANG Z, HAN C, et al. Layered crustal azimuthal anisotropy beneath the northeastern Tibetan Plateau revealed by Rayleigh-wave Eikonal tomography[J]. Earth and Planetary Science Letters, 2021, 563: 116891.
[17]	SHERRINGTON H F, ZANDT G, FREDERIKSEN A. Crustal fabric in the Tibetan Plateau based on waveform inversions for seismic anisotropy parameters[J]. Journal of Geophysical Research: Solid Earth, 2004, 109(B2).
[18]	LI Y, WU Q, ZHANG F, et al. Seismic anisotropy of the Northeastern Tibetan Plateau from shear wave splitting analysis[J]. Earth and Planetary Science Letters, 2011, 304(1/2): 147-157.
[19]	YE Z, LI Q, GAO R, et al. Anisotropic regime across northeastern Tibet and its geodynamic implications[J]. Tectonophysics, 2016, 671: 1-8.
[20]	ZHAO P, CHEN J, LIU Q, et al. Growth of Northern Tibet: insights from the crustal shear wave velocity structure of the Qilian Shan Orogenic Belt[J]. Geochemistry, Geophysics, Geosystems, 2021, 22(9): 1-16.
[21]	LI H, SHEN Y, HUANG Z, et al. The distribution of the mid-to-lower crustal low-velocity zone beneath the northeastern Tibetan Plateau revealed from ambient noise tomography[J]. Journal of Geophysical Research: Solid Earth, 2014, 119(3): 1954-1970.
[22]	LI X, LI H, SHEN Y, et al. Crustal velocity structure of the northeastern Tibetan plateau from ambient noise surface-wave tomography and its tectonic implications[J]. Bulletin of the Seismological Society of America, 2014, 104(3): 1045-1055.
[23]	SUN Q, PEI S, CUI Z, et al. A new growth model of the northeastern Tibetan Plateau from high-resolution seismic imaging by improved double-difference tomography[J]. Tectonophysics, 2021, 798: 228699.
[24]	JIANG C, YANG Y, ZHENG Y. Penetration of mid-crustal low velocity zone across the Kunlun Fault in the NE Tibetan Plateau revealed by ambient noise tomography[J]. Earth and Planetary Science Letters, 2014, 406: 81-92.
[25]	LI Y, PAN J, WU Q, et al. Lithospheric structure beneath the northeastern Tibetan Plateau and the western Sino-Korea Craton revealed by Rayleigh wave tomography[J]. Geophysical Journal International, 2017, 210(2): 570-584.
[26]	XIAO Q, ZHANG J, ZHAO G, et al. Electrical resistivity structures northeast of the Eastern Kunlun Fault in the Northeastern Tibet: tectonic implications[J]. Tectonophysics, 2013, 601: 125-138.
[27]	XIAO Q, SHAO G, YU G, et al. Electrical resistivity structures of the Kunlun-Qaidam-Qilian system at the northern Tibet and their tectonic implications[J]. Physics of the Earth and Planetary Interiors, 2016, 255: 1-17.
[28]	LIANG H, GAO R, XUE S, et al. Electrical structure of the middle Qilian Shan revealed by 3-D inversion of magnetotelluric data: new insights into the growth and deformation in the Northeastern Tibetan Plateau[J]. Tectonophysics, 2020, 789: 228523.
[29]	GAO R, WANG H, YIN A, et al. Tectonic development of the northeastern tibetan plateau as constrained by high-resolution deep seismicreflection data[J]. Lithosphere, 2013, 5(6): 555-574.
[30]	YE Z, GAO R, LI Q, et al. Seismic evidence for the North China plate underthrusting beneath northeastern Tibet and its implications for plateau growth[J]. Earth and Planetary Science Letters, 2015, 426: 109-117.
[31]	HUANG X, XU X, GAO R, et al. Shortening of lower crust beneath the NE Tibetan Plateau[J]. Journal of Asian Earth Sciences, 2020, 198(135).
[32]	张洪双, 高锐, 田小波, 等. 青藏高原东北缘地壳 S 波速度结构及其动力学含义: 远震接收函数提供的证据[J]. 地球物理学报, 2015, 58(11): 3982-3992.
[33]	YE Z, GAO R, LU Z, et al. A lithospheric-scale thrust-wedge model for the formation of the northern Tibetan plateau margin: evidence from high-resolution seismic imaging[J]. Earth and Planetary Science Letters, 2021, 574: 117170.
[34]	WANG Q, NIU F, GAO Y, et al. Crustal structure and deformation beneath the NE margin of the Tibetan plateau constrained by teleseismic receiver function data[J]. Geophysical Journal International, 2016, 204(1): 167-179.
[35]	王琼, 高原, 石玉涛, 等. 青藏高原东北缘上地幔地震各向异性: 来自 SKS, PKS 和 SKKS 震相分裂的证据[J]. 地球物理学报, 2013, 56(3): 892-905.
[36]	CHANG L, DING Z, WANG C, et al. Vertical coherence of deformation in lithosphere in the NE margin of the Tibetan plateau using GPS and shear-wave splitting data[J]. Tectonophysics, 2017, 699: 93-101.
[37]	LEÓN SOTO G, SANDVOL E, NI J F, et al. Significant and vertically coherent seismic anisotropy beneath eastern Tibet[J]. Journal of Geophysical Research: Solid Earth, 2012, 117(5).
[38]	XU X, NIU F, DING Z, et al. Complicated crustal deformation beneath the NE margin of the Tibetan plateau and its adjacent areas revealed by multi-station receiver-function gathering[J]. Earth and Planetary Science Letters, 2018, 497: 204-216.
[39]	LI J, SONG X, WANG P, et al. A Generalized H-κ method with harmonic corrections on P_S and its crustal multiples in receiver functions[J]. Journal of Geophysical Research: Solid Earth, 2019, 124(4): 3782-3801.
[40]	YUAN D, GE W, CHEN Z, et al. The growth of northeastern Tibet and its relevance to large-scale continental geodynamics: a review of recent studies[J]. Tectonics, 2013, 32(5): 1358-1370.
[41]	YIN A, HARRISON T M. Geologic evolution of the Himalayan-Tibetan orogen[J]. Annual Reviews of Earth and Planetary Sciences, 2000, 28: 211-280.
[42]	MAINPRICE D, NICOLAS A. Development of shape and lattice preferred orientations: application to the seismic anisotropy of the lower crust[J]. Journal of Structural Geology, 1989, 11(1/2): 175-189.
[43]	ALMQVIST B S G, MAINPRICE D. Seismic properties and anisotropy of the continental crust: predictions based on mineral texture and rock microstructure[J]. Reviews of Geophysics, 2017, 55(2): 367-433.
[44]	RABBEL W, MOONEY W D. Seismic anisotropy of the crystalline crust: what does it tell us?[J]. Terra Nova, 1996, 8(1): 16-21.
[45]	CRAMPIN S. Effective anisotropic elastic constants for wave propagation through cracked solids[J]. Geophysical Journal of the Royal Astronomical Society, 1984, 76(1): 135-145.
[46]	CRAMPIN S. The fracture criticality of crustal rocks[J]. Geophysical Journal International, 1994, 118(2): 428-438.
[47]	TAN P, NIE S. Crustal deformation in eastern margin of Tibetan Plateau from a dense linear seismic array[J]. Physics of the Earth and Planetary Interiors, 2021, 321: 106801.
[48]	ZHU L. Crustal structure across the San Andreas Fault, southern California from teleseismic converted waves[J]. Earth and Planetary Science Letters, 2000, 179(1): 183-190.
[49]	WANG W, WU J, FANG L, et al. Sedimentary and crustal thicknesses and Poisson’s ratios for the NE Tibetan Plateau and its adjacent regions based on dense seismic arrays[J]. Earth and Planetary Science Letters, 2017, 462: 76-85.
[50]	PAN S, NIU F. Large contrasts in crustal structure and composition between the Ordos plateau and the NE Tibetan plateau from receiver function analysis[J]. Earth and Planetary Science Letters, 2011, 303(3/4): 291-298.
[51]	YUAN X, NI J, KIND R, et al. Lithospheric and upper mantle structure of southern Tibet from a seismological passive source experiment[J]. Journal of Geophysical Research B: Solid Earth, 1997, 102(12): 27491-27500.
[52]	YU Y, SONG J, LIU K H, et al. Determining crustal structure beneath seismic stations overlying a low-velocity sedimentary layer using receiver functions[J]. Journal of Geophysical Research: Solid Earth, 2015, 120(5): 3208-3218.
[53]	DING Z, CHENG B, DONG Y, et al. Seismic imaging of the crust and uppermost mantle beneath the Qilian Orogenic Belt and its geodynamic implications[J]. Tectonophysics, 2017, 705: 63-79.
[54]	郑文俊, 袁道阳, 张培震, 等. 青藏高原东北缘活动构造几何图像, 运动转换与高原扩展[J]. 第四纪研究, 2016, 36(4): 775-788.
[55]	袁道阳, 张培震, 刘百篪, 等. 青藏高原东北缘晚第四纪活动构造的几何图像与构造转换[J]. 地质学报, 2004, 78(2): 270-278.
[56]	ZHENG D, LI H, SHEN Y, et al. Crustal and upper mantle structure beneath the northeastern Tibetan Plateau from joint analysis of receiver functions and Rayleigh wave dispersions[J]. Geophysical Journal International, 2016, 204(1): 583-590.
[57]	ZHANG H, TENG J, TIAN X, et al. Lithospheric thickness and upper-mantle deformation beneath the NE Tibetan Plateau inferred from S receiver functions and SKS splitting measurements[J]. Geophysical Journal International, 2012, 191(3): 1285-1294.
[58]	WANG M, SHEN Z K. Present-day crustal deformation of continental China derived from GPS and its tectonic implications[J]. Journal of Geophysical Research: Solid Earth, 2020, 125(2): e2019JB018774.
[59]	DEMETS C, GORDON R G, ARGUS D F. Geologically current plate motions[J]. Geophysical Journal International, 2010, 181(1): 1-80.
[60]	张洪双, 滕吉文, 田小波, 等. 青藏高原东北缘岩石圈厚度与上地幔各向异性[J]. 地球物理学报, 2013, 56(2): 450-471.
[61]	KIND R, YUAN X, SAUL J, et al. Seismic images of crust and upper mantle beneath Tibet: evidence for Eurasian plate subduction[J]. Science, 2002, 298(5596): 1219-1221.
[62]	NÁBĚLEK J, HETÉNYI G, VERGNE J, et al. Underplating in the himalaya-tibet collision zone revealed by the Hi-CLIMB experiment[J]. Science, 2009, 325(5946): 1371-1374.
[63]	SHI D, WU Z, KLEMPERER S L, et al. Receiver function imaging of crustal suture, steep subduction, and mantle wedge in the eastern India-Tibet continental collision zone[J]. Earth and Planetary Science Letters, 2015, 414: 6-15.
[64]	FENG M, KUMAR P, MECHIE J, et al. Structure of the crust and mantle down to 700 km depth beneath the East Qaidam basin and Qilian Shan from P and S receiver functions[J]. Geophysical Journal International, 2014, 199(3): 1416-1429.
[65]	SHI J, SHI D, SHEN Y, et al. Growth of the northeastern margin of the Tibetan Plateau by squeezing up of the crust at the boundaries[J]. Scientific Reports, 2017, 7(1): 1-7.
[66]	WANG Y. Heat flow pattern and lateral variations of lithosphere strength in China mainland: constraints on active deformation[J]. Physics of the Earth and Planetary Interiors, 2001, 126(3/4): 121-146.
[67]	高锐, 齐蕊, 黄兴富, 等. 青藏高原东北缘祁连山中部精细地壳结构研究[J]. 地球物理学报, 2022(已接收).
[68]	WANG X, LI Y, DING Z, et al. Three-dimensional lithospheric S wave velocity model of the NE Tibetan Plateau and western North China Craton[J]. Journal of Geophysical Research: Solid Earth, 2017, 122(8): 6703-6720.
[69]	CRAMPIN S, BOOTH D C. Shear-wave polarizations near the North Anatolian Fault: II.Interpretation in terms of crack-induced anisotropy[J]. Geophysical Journal of the Royal Astronomical Society, 1985, 83(1): 75-92.
[70]	张辉, 高原, 石玉涛, 等. 基于地壳介质各向异性分析青藏高原东北缘构造应力特征[J]. 地球物理学报, 2012, 55(1): 95-104.
[71]	李永华, 吴庆举, 安张辉, 等. 青藏高原东北缘地壳 S 波速度结构与泊松比及其意义[J]. 地球物理学报, 2006, 49(5): 1359-1368.
[72]	杨晓松, 马瑾, 张先进. 大陆壳内低速层成因综述[J]. 地质科技情报, 2003, 22(2): 35-41.
[73]	周永胜, 何昌荣, 杨晓松. 中地壳韧性剪切带中的水与变形机制[J]. 中国科学: D 辑, 2008, 38(7): 819-832.
[74]	JI S, WANG Q, SALISBURY M H. Composition and tectonic evolution of the Chinese continental crust constrained by Poisson’s ratio[J]. Tectonophysics, 2009, 463(1/2/3/4): 15-30.
[75]	XIAO W, WINDLEY B F, YONG Y, et al. Early Paleozoic to Devonian multiple-accretionary model for the Qilian Shan, NW China[J]. Journal of Asian Earth Sciences, 2009, 35(3/4): 323-333.