摘要
基于鄂尔多斯地块及周缘地区稠密分布的地震台站所记录的远震波形资料,采用FMTOMO走时层析成像方法获得了深至400 km的高分辨率地壳上地幔P波速度结构,并分析和探讨了研究区的深部构造与火山、强震活动及克拉通破坏等相关的地球动力学问题.地壳上地幔速度结构横向变化和纵向差异的构造含义如下:鄂尔多斯地块下方正异常速度的巨厚岩石圈是鄂尔多斯地块缺乏克拉通大规模破坏的证据;大同火山群下方深至400km的柱状低速异常表明大同火山的岩浆作用起源于地幔过渡带,由太平洋板块俯冲作用引起熔融的玄武质岩浆上涌造成;鄂尔多斯地块与四川盆地之间呈东西向分布的上地幔低速异常带,可能是青藏高原东北缘软流圈流出的通道;鄂尔多斯周缘地区深至上地幔的低速异常分布表明,青藏高原北东向推挤和太平洋板块西向俯冲的共同作用,促使鄂尔多斯地块整体的抬升和周缘拉张断陷带的形成,为强震的孕育和发生提供了良好的应力环境,导致鄂尔多斯地块周缘地区地震频繁发生.
The Ordos Block in the western North China Craton(NCC) occupies an important position in the tectonic evolution and deep earthquake environment research in China continent. In previous seismic tomography studies, the sparse distribution of seismic stations resulted in a relatively low lateral resolution of 3 D structure of crust and upper mantle in the Ordos Block. In this paper, a dense broadband seismograph network was established, including the permanent seismic stations of the regional networks and the temporary seismic stations funded by the "Destruction of the North China Craton" project and the North China Scientific Seismic Array. Based on the waveform data recorded by 338 seismic stations in the Ordos Block and surrounding regions, we used FMTOMO traveltime tomography method to determine the high-resolution P-wave velocity structures of the crust and upper mantle down to 400 km depth, and analyzed the relationship between deep structure and a range of geodynamic issues, such as the volcanic and strong earthquake activities and the destruction of the NCC. The tectonic implications of the lateral and the vertical variations of P-wave velocity in the crust and upper mantle structures are described as follow. The transverse variation and vertical difference of velocity structure of crust and uppermost mantle indicate significant correlations between deep tectonics and surface geological setting. The thick lithosphere with positive velocity anomaly beneath the Ordos block suggests that the Ordos block did not suffer extensive destruction. The velocity anomaly distribution of the Taihang orogenic belt in the central NCC is characterized by discontinuous strip anomalies, which is significantly different from that of the North China Plain and Ordos block. The low-velocity anomalies deeper than 400 km might be related to the lithosphere destruction in the eastern NCC. A low-velocity columnar anomaly down to 400 km depth beneath the Datong volcanic groups indicates that the magmatism of the Datong volcanic group might originate from the mantle transitional zone, due to the upwelling and expulsion of basaltic magma caused by the subduction of the Pacific plate. The low-velocity zone in approximately EW direction in the upper mantle between the Ordos Block and the Sichuan basin suggests the possible existence of a narrow outflow channel of the asthenosphere. In summary, the low-velocity anomaly down to the upper mantle in the Ordos Block and surrounding regions indicates that the north-eastward compressive stress of the Tibetan Plateau and the westward subduction of the Pacific plate may induce the migration and upwelling of mantle materials, causing the overall uplift of the Ordos Block and the formation of extensional fault belt in surrounding regions. The vertical upwelling and lateral movement of the deep materials provide the stress conditions for the preparation and occurrence of strong earthquakes resulting in frequent occurrence of strong earthquakes in the regions around the Ordos Block.
引文
1 Zhu R X,Chen L,Wu F Y,et al.Timing,scale and mechanism of the destruction of the North China Craton.Sci China Earth Sci,2011,54:789-797[朱日祥,陈凌,吴福元,等.华北克拉通破坏的时间、范围与机制.中国科学:地球科学,2011,41:583-592]
2 Deng Q D,You H C.The tectonic activity and formation mechanism of the down-faulted basin around Ordos Block(in Chinese).In:Institute of Geology,State Seismological Bureau of China,ed.Research on Recent Crustal Movement.Beijing:Seismological Press,1985.58-78[邓起东,尤惠川.鄂尔多斯周缘断陷盆地的构造活动和形成机制.见:国家地震局地质研究所,编.现代地壳运动研究.北京:地震出版社,1985.58-78]
3 Molnar P,Tapponnier P.Cenozoic tectonics of Asia:Effects of a continental collision.Science,1975,189:419-426
4 Tapponnier P,Peltzer G,Dain A Y L,et al.Propagating extrusion tectonics in Asia:New insights from simple experiments with plasticine.Geology,1982,10:611-616
5 Northrup C J,Royden H,Burchfiel B C.Motion of the Pacific plate relative to Eurasia and its potential relation to Cenozoic extension along the eastern margin of Eurasia.Geology,1995,23:719-722
6 Deng Q D,Cheng S P,Min W,et al.Discussion on Cenozoic tectonics and dynamics of Ordos Block(in Chinese).J Geomech,1999,5:13-21[邓起东,程绍平,闵伟,等.鄂尔多斯块体新生代构造活动和动力学的讨论.地质力学学报,1999,5:13-21]
7 Gu G X.Catalog of Chinese Earthquakes(1831 B.C.-1969 A.D.)(in Chinese).Beijing:Science Press,1983.200-201[顾功叙.中国地震目录(公元前1831~公元1969).北京:科学出版社,1983.200-201]
8 Zhang S Q,Wu L J,Guo J M,et al.Interpretation of Menyuan-Pingliang-Weinan DSS profile in west China(in Chinese).Chin J Geophys,1985,28:460-472[张少泉,武利均,郭建明,等.中国西部地区门源-平凉-渭南地震测深剖面资料的分析解释.地球物理学报,1985,28:460-472]
9 Li Q H,Guo S,LüD H.Deep Structures in Western and Southwestern Edges of the Ordos Block and Their Tectonic Implications(in Chinese).Beijing:Seismological Press,1999.153-167[李清河,郭守年,吕德徽.鄂尔多斯西缘与西南缘深部结构与构造.北京:地震出版社,1999.153-167]
10 Li S L,Zhang X K,Zhang C,et al.A preliminary study on the crustal velocity structure of Maqên-Lanzhou-Jingbian by means of deep seismic sounding profile(in Chinese).Chin J Geophys,2002,45:210-217[李松林,张先康,张成科,等.玛沁-兰州-靖边地震测深剖面地壳速度结构初步研究.地球物理学报,2002,45:210-217]
11 Liu M J,Mooney W D,Li S L,et al.Crustal structure of the northeastern margin of the Tibetan Plateau from the Songpan-Ganzi terrane to the Ordos Basin.Tectonophysics,2006,420:253-266
12 Teng J W,Wang F Y,Zhao W Z,et al.Velocity structure of layered block and deep dynamic process in the lithosphere beneath the Yinshan orogenic belt and Ordos Basin(in Chinese).Chin J Geophys,2010,53:67-85[滕吉文,王夫运,赵文智,等.阴山造山带-鄂尔多斯盆地岩石圈层、块速度结构与深层动力过程.地球物理学报,2010,53:67-85]
13 Zhang X K,Li S L,Wang F Y,et al.Differences of crustal structures in northeastern edge of Tibet Plateau,Ordos and Tangshan earthquake region in north China-Results of deep seismic sounding(in Chinese).Seismol Geol,2003,25:52-60[张先康,李松林,王夫运,等.青藏高原东北缘、鄂尔多斯和华北唐山震区的地壳结构差异-深地震测深的结果.地震地质,2003,25:52-60]
14 Wang C Y,Lin Z Y,Chen X B.Comprehensive study of geophysical data on geoscience transect from Menyuan,Qinghai Province,to Ningde,Fujian Province,China(in Chinese).Chin J Geophys,1995,38:590-598[王椿镛,林中洋,陈学波.青海门源-福建宁德地学断面综合地球物理研究.地球物理学报,1995,38:590-598]
15 Chen L,Cheng C,Wei Z G.Seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western North China Craton.Earth Planet Sci Lett,2009,286:171-183
16 Wang C Y,Sandvol L E,Zhu L P,et al.Lateral variation of crustal structure in the Ordos Block and surrounding regions,North China,and its tectonic implications.Earth Planet Sci Lett,2014,387:198-211
17 Li Y H,Wu Q J,An Z H,et al.The Poisson ratio and crustal structure across the NE Tibetan Plateau determined from receiver functions(in Chinese).Chin J Geophys,2006,49:1359-1368[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.地球物理学报,2006,49:1359-1368]
18 Tian Y,Zhao D P,Sun R M,et al.Seismic imaging of the crust and upper mantle beneath the North China Craton.Phys Earth Planet Inter,2009,172:169-182
19 Yu D X,Li Y H,Wu Q J,et al.S-wave velocity structure of the northeastern Tibetan Plateau from joint inversion of Rayleigh wave phase and group velocities(in Chinese).Chin J Geophys,2014,57:800-811[余大新,李永华,吴庆举,等.利用Rayleigh波相速度和群速度联合反演青藏高原东北缘S波速度结构.地球物理学报,2014,57:800-811]
20 Wei Z,Chen L,Jiang M,et al.Lithospheric structure beneath the central and western North China Craton and the adjacent Qilian orogenic belt from Rayleigh wave dispersion analysis.Tectonophysics,2015,646:130-140
21 Tang Y C,Chen Y S,Yang Y J,et al.Ambient noise tomography in North China Craton(in Chinese).Chin J Geophys,2011,54:2011-2022[唐有彩,陈永顺,杨英杰,等.华北克拉通中部地区背景噪声成像.地球物理学报,2011,54:2011-2022]
22 Fang L H,Wu J P,Wang W L,et al.Love wave tomography from ambient seismic noise in North China(in Chinese).Chin J Geophys,2013,56:2268-2279[房立华,吴建平,王未来,等.华北地区勒夫波噪声层析成像研究.地球物理学报,2013,56:2268-2279]
23 Chang L J,Wang C Y,Ding Z F.Upper mantle anisotropy in the Ordos Block and its margins.Sci China Earth Sci,2011,54:888-900[常利军,王椿镛,丁志峰.鄂尔多斯块体及周缘上地幔各向异性研究.中国科学:地球科学,2011,41:686-699]
24 Wang C Y,Chang L J,Ding Z F,et al.Upper mantle anisotropy and crust-mantle deformation pattern beneath the Chinese mainland(in Chinese).Sci China Earth Sci,2014,57:132-143[王椿镛,常利军,丁志峰,等.中国大陆上地幔各向异性和壳幔变形模式.中国科学:地球科学,2014,24:98-110]
25 LüZ Y,Wu J P.3D P wave velocity structure of crust and upper mantle beneath North China(in Chinese).Acta Seismol Sin,2010,32:1-11[吕作勇,吴建平.华北地区地壳上地幔三维P波速度结构.地震学报,2010,32:1-11]
26 Zheng X F,Ouyang B,Zhang D N,et al.Technical system construction of Data Backup Centre for China Seismograph Network and the data support to researches on the Wenchuan earthquake(in Chinese).Chin J Geophys,2009,52:1412-1417[郑秀芬,欧阳飚,张东宁,等.“国家数字测震台网数据备份中心”技术系统建设及其对汶川大地震研究的数据支撑.地球物理学报,2009,52:1412-1417]
27 Rawlinson N,Kennett B L N.Rapid estimate of relative and absolute delay times across a network by adaptive stacking.Geophys J Int,2004,157:332-340
28 Rawlinson N,Sambridge M.Multiple reflection and transmission phases in complex layered media using a multistage fast marching method.J Geophys,2004,69:1338-1350
29 Zhang F X,Li Y H,Wu Q J,et al.The P wave velocity structure of upper mantle beneath the North China and surrounding regions from FMTT(in Chinese).Chin J Geophys,2011,54:1233-1242[张风雪,李永华,吴庆举,等.FMTT方法研究华北及邻区上地幔P波速度结构.地球物理学报,2011,54:1233-1242]
30 Kennett B L N,Engdahl E R,Buland R.Constraints on seismic velocities in the earth from travel times.Geophys J Int,1995,122:108-124
31 Wang C Y,Chan W W,Mooney W D.3D velocity structure of crust and upper mantle in southwestern China and its tectonic implications.J Geophys Res,2003,108:2442,doi:10.1029/2002JB001973
32 Rawlinson N,Reading A M,Kennett B L N.Lithospheric structure of Tasmania from a novel form of teleseismic tomography.J Geophys Res-Solid Earth,2006,111:1-5
33 Mao H H,Lei J S,Teng J W.Teleseismic P-wave tomography of the upper mantle along the north-south profile under the northern Ordos basin(in Chinese).Chin J Geophys,2016,59:2056-2065[毛慧慧,雷建设,滕吉文.鄂尔多斯盆地北缘南北向剖面上地幔远震P波层析成像.地球物理学报,2016,59:2056-2065]
34 Guo H L,Ding Z F,Xu X M.Upper mantle structure beneath the northern South-Nouth Seismic Zone from teleseismic traveltime data(in Chinese).Chin J Geophys,2017,60:86-97[郭慧丽,丁志峰,徐小明.南北地震带北段的远震P波层析成像研究.地球物理学报,2017,60:86-97]
35 Zhang Y B.Characteristics of petrology of the Datong basalts(in Chinese).Seismol Geol,1986,(1):59-67,102[张彦波.大同地区玄武岩的岩石学特征.地震地质,1986,(1):59-67,102]
36 Liu M,Cui X J,Liu F T.Cenozoic rifting and volcanism in eastern China:A mantle dynamic link to the Indo-Asian collision?Tectonophysics,2004,393:29-42
37 Lei J.Upper-mantle tomography and dynamics beneath the North China Craton.J Geophys Res,2012,117:B06313,doi:10.1029/2012JB009212
38 Shen X,Zhou H,Kawakatsu H.Mapping the upper mantle discontinuities beneath China with teleseismic receiver functions.Earth Planet Space,2008,60:713-719
39 Huang J L,Zhao D.High-resolution mantle tomography of China and surrounding regions.J Geophys Res,2006,111:B09305,doi:10.1029/2005JB004066
40 Huang F,He L J,Wu Q J.Lithospheric thermal structure of the Ordos Basin and its implications to destruction of the North China Craton(in Chinese).Chin J Geophys,2015,58:3671-3686[黄方,何丽娟,吴庆举.鄂尔多斯盆地深部热结构特征及其对华北克拉通破坏的启示.地球物理学报,2015,58:3671-3686]
41 Kearey P,Klepeis K A,Vine F J.Global Tectonics.New Jersey:John Wiley&Sons,2009.152-208
42 Yang W C.Continental extension and rifting reveled by worldwide comparison of crust and upper mantle structures(in Chinese).Geol Rev,2014,60:945-961[杨文采.从地壳上地幔构造看大陆岩石圈伸展与裂解.地质论评,2014,60:945-961]
43 Cen M,Dong S W,Shi W,et al.Structural analysis on the formation mechanism of Datong Basin(in Chinese).Geol Rev,2015,(6):1235-1247[岑敏,董树文,施炜,等.大同盆地形成机制的构造研究.地质论评,2015,(6):1235-1247]
44 Shen X,Zhou Y,Zhang Y S,et al.Receiver function structures beneath the deep large faults in the northeastern margin of the Tibetan Plateau.Tectonophysics,2014,610:63-73
45 Shen X,Liu M,Gao Y,et al.Lithospheric structure across the northeastern margin of the Tibetan Plateau:Implications for the plateau’s lateral growth.Earth Planet Sci Lett,2017,459:80-92
46 Zhang Y Q,Mercier J L,Vergely P.Extension in the graben systems around the Ordos(China),and its contribution to the extrusion tectonics of south China with respect to Gobi-Mongolia.Tectonophysics,1998,285:41-75
47 Tian X B,Teng J W,Zhang H S,et al.Structure of crust and upper mantle beneath the Ordos Block and the Yinshan mountains revealed by receiver function analysis.Phys Earth Planet Inter,2010,184:186-193
48 Chang L J,Wang C Y,Ding Z F,et al.Study on upper mantle anisotropy in the northeastern margin of Tibetan Plateau(in Chinese).Chin J Geophys,2008,51:431-438[常利军,王椿镛,丁志峰,等.青藏高原东北缘上地幔各向异性研究.地球物理学报,2008,51:431-438]
49 Lei J,Li Y,Xie F,et al.Pn anisotropic tomography and dynamics under eastern Tibetan Plateau.J Geophys Res-Solid Earth,2014,119:2174-2198
50 Yin A,Harrison T W.Geologic evolution of the Himalayan-Tibetan orogen.Ann Rev Earth Planet Sci,2000,28:211-280
51 Lei J,Zhao D.Teleseismic P-wave tomography and mantle dynamics beneath Eastern Tibet.Geochem Geophys Geosyst,2016,17:1861-1884
52 Huang Z C,Xu M J,Wang L S,et al.Shear wave splitting in the southern margin of the Ordos Block,North China.Geophys Res Lett,2008,35:L19301,doi:10.1029/2008GL03518
53 Wessel P,Smith W H F.New improved version of generic mapping tools released.Eos Trans AGU,1998,79:579,doi:10.1029/98EO00426