藏南洛扎地区洛扎断裂构造特征及其地质意义

doi:10.19657/j.geoscience.1000-8527.2019.01.01

摘要/Abstract

摘要：

藏南洛扎地区洛扎断裂属于区域上定日—洛扎断裂的东段部分,是喜马拉雅造山带中一条重要的断裂,但其总体研究程度较低。运用地质填图和构造解析的方法研究了洛扎断裂的几何形态、运动表现和活动历史等,讨论其在喜马拉雅造山带构造格局形成中的意义。主要认识如下:(1)洛扎断裂现今主要表现为一条规模大的脆性-脆韧性断层, SWW—NEE走向,高角度倾向NNW。断层带内发育劈理带、断层泥、构造角砾岩等。运动性质主体表现为正断层。(2)洛扎断裂的南北两侧地块具有显著不同的变形特征,南侧为平缓的大型背斜-向斜构造,北侧为近NWW—SEE走向的倒转褶皱-断层构造。(3)洛扎断裂经历了多期活动,中生代正断活动,古近纪逆冲活动,中新世韧性伸展,中新世晚期逆冲活动以及上新世—第四纪正断活动。现今断层展示的更多是最后一期活动的形迹。(4)依据其规模大、多期活动性、两盘构造变形与沉积的系统差异性等肯定了其作为构造分区断层而存在。(5)洛扎断裂和藏南拆离断层(STD)在研究区均有出露,局部二者出露线近于重合,但洛扎断裂以高角度断面切割了平缓的STD。洛扎断裂是比STD具有更悠久地质历史的区域性断层,只是后者中新世以来的活动性更多受到关注。

关键词: 洛扎断裂, 区域性断层, 多期活动, 藏南拆离断层, ESR测年

Abstract:

Lhozhag fault,the eastern segment of the famous Dingri-Lhozhag Fault,is a tectonically significant structure in the Himalayan orogen, but it remains poorly constrained so far. Geologic mapping and structural analysis of Lhozhag fault in Lhozhag area, southeastern Tibet, were carried out to reveal its geometry, kinematics, evolutional history and tectonic significance. The major structural features of Lhozhag fault are described as follows:(1)Lhozhag fault is now mainly characterized by a large brittle, brittle-ductile normal fault with a SWW-NEE strike and steep NNW dipping. The fault zone materials are comprised of cleavages, fault gouge, fault breccia,etc. (2)Two blocks in Tethys Himalaya unit separated by Lhozhag fault have significantly different deformation characteristics, the south with gentle deformation, and the north with strong deformation. (3)Lhozhag fault has experienced five deformation events,i.e.normally faulting during the Mesozoic, thrusting during the Paleogene, ductile extension during the Miocene, thrusting during the late Miocene, and normally faulting during the Pliocene and Quaternary. Present fault features show more of the last episode of the activities.(4)Lhozhag fault on its large scale, multi-phase activities, and controlling the deformational and sedimentary differences between the northern and southern blocks, reveals that it plays the role of separating tectonic units on Himalayan orogeny.(5)Both Lhozhag fault and the south Tibetan detachment fault (STD) outcrop in Lhozhag area, and in some places,they are close to each other. Field data show steep Lhozhag fault has cut gentle STD. Lhozhag fault is a regional fault with a longer geological history than STD, but the latter’s activities since Miocene have attracted more attention.

Key words: Lhozhag fault, regional fault, multi-phase activity, south Tibetan detachment fault, ESR dating

中图分类号:

P542
P548

刘顺, 夏特, 武梅千, 周俊, 王源, 魏明浩. 藏南洛扎地区洛扎断裂构造特征及其地质意义[J]. 现代地质, 2019, 33(01): 1-12.

LIU Shun, XIA Te, WU Meiqian, ZHOU Jun, WANG Yuan, WEI Minghao. Structural Features and Geological Significance of Lhozhag Fault in Lhozhag Area, Southeastern Tibet[J]. Geoscience, 2019, 33(01): 1-12.

图/表 12

图1 洛扎断裂构造位置图(据潘桂棠等[2]资料编绘)

Fig.1 Tectonic map showing the location of Lhozhag fault

图2 洛扎地区地质略图(综合“1:25万洛扎县幅地质图”和野外资料编绘) 1.拉康组;2.维美组;3.遮拉组;4.陆热组;5.日当组;6.涅如组;7.元古宇—下古生界; 8.中新世电气石二长花岗岩;9.中新世二长花岗岩;10.粗线带箭头,一级正断层;细线带箭头,次级正断层;细线,次级平移断层;11.藏南拆离断层;12.地层产状(°);13.剖面线

Fig.2 Geological map of Lhozhag area

图3 曲美村南洛扎断裂实景(a)及素描(b) ①涅如组板岩;②正断层;③早古生代片岩及中新世花岗岩;照片镜向,E

Fig.3 Photo(a) and sketch(b) of Lhozhag fault near the south of Qumei village

图4 鞋吉南沟洛扎断裂剖面(图2中剖面b) 1.J1r,日当组,黑灰色板岩; 2.Pz1,下古生界,黑色石榴二云片岩;3.断层带边界断层;4.内部分割断层及板劈理

Fig.4 Structural cross-section of Lhozhag fault in Xieji valley

图5 扎美村洛扎断裂剖面(图2中剖面c) 1.Pz1片岩;2.泥灰岩;3.辉长岩;4.断层带边界断层;5.断层带内部分割断层;6.劈理-构造透镜体带;7.构造透镜体带;8.从左至右分别为砂岩透镜体、石英脉透镜体和辉长岩透镜体;9.内部分割断层及板劈理牵引构造;10.破劈理带

Fig.5 Structural cross-section of Lhozhag fault in Zhamei village

图6 门当沟洛扎断裂剖面(图2中剖面d) 1.粉砂质板岩;2.结晶灰岩;3.变质砂岩;4.断层带边界断层;5.断层带内部分割断层;6.劈理带;7.劈理-构造透镜体带;8.石英脉透镜体;9.内部分割断层及板劈理

Fig.6 Structural cross-section of Lhozhag fault in Mendang valley

图7 贡祖沟得嘎洛扎断裂剖面(图2中剖面e) 1.变质砂岩;2.结晶灰岩;3.坡积物/崩积物;4.断层带边界断层;5.断层带内部分割断层;6.劈理带;7.劈理-构造角砾岩带;8.内部分割断层及板劈理牵引构造;9.小褶皱

Fig.7 Structural cross-section of Lhozhag fault in Dega of Gongzu valley

图8 否午普巴洛扎断裂剖面(图2中剖面f) 1.变质砂岩;2.泥灰岩;3.泥岩/粉砂岩;4.坡积物/残积物;5.断层带边界断层;6.断层带内部分割断层;7.劈理-构造透镜体带;8.S-C劈理带;9.断层角砾岩

Fig.8 Structural cross-section of Lhozhag fault in Fouwupuba

图9 洛扎地区地质剖面图(剖面线见图2) 1.拉康组;2.陆热组;3.日当组;4.元古宇—下古生界; 5.中新世电气石二长花岗岩;6.板岩;7.结晶灰岩;8.片岩、片麻岩、变粒岩;9.电气石二长花岗岩;10.洛扎断裂;11.韧性剪切带

Fig.9 Geological cross-section of Lhozhag area

图10 鞋吉南沟洛扎断裂南分支实景(a)及素描(b) ①片岩;②变粒岩;γ6.中新世花岗岩类;③主断层,下部牵引构造示逆冲运动,上部牵引构造示正断运动;④次级断层,正断运动;照片镜向,E

Fig.10 Photo (a) and sketch (b) of the south branch of Lhozhag fault in Xieji valley

图11 曲美村南洛扎断裂南盘地质剖面图 1.片麻岩;2.花岗岩;3.韧性流动标志;4.小断层、节理及分组号;5.劈理及分组号

Fig.11 Geological cross-section across the footwall of Lhozhag fault near the south of Qumei village

表1 构造变形相关石英脉采样情况及ESR测年结果

Table 1 Tectonic deformation-associated quartz veins’ sampling situation and ESR dating results

采样位置及样品编号	石英脉产状	相对于洛扎断裂的位置	(顺磁中心浓度/ (10¹⁵自旋/g))/ (铀当量含量 /(μg/g))	铀含量/ (μg/g)	钍含量/ (μg/g)	钾含量/%	年龄/Ma	年龄解释
公主沟/D055-2	顺层脉,N∠(5°~10°)	南盘	0.405/1.02	0.30±0.03	0.90±0.08	0.20±0.02	80.65±8.00	白垩纪晚期,板块汇聚期层间滑动中充填
公主南/D011-1	北倾褶皱地层(345°∠15°)中充填脉	北盘	0.066/2.21	0.92±0.09	2.69±0.25	0.50±0.05	59.76±5.80	古近纪早期,板块汇聚-碰撞期,北盘褶皱带充填
门当沟/S1949-1	弱切层(18°∠24°)煌斑岩中脉,示向南逆冲	北盘	0.404/2	0.85±0.08	2.48±0.20	0.39±0.03	40.40±4.00	古近纪,板块碰撞期,北盘褶皱带中充填
乃西北/S420-1	劈理(290°∠76°)充填脉	北盘	0.103/0.874	0.35±0.03	1.05±0.10	0.04±0.01	23.62±2.30	古近纪晚期,板块碰撞期,北盘褶皱带中充填
仲觉北/S402-1	顺(切)层脉,SW 倾	北盘	0.064/3.577	1.49±0.14	4.77±0.45	0.38±0.03	17.67±1.50	中新世,与拆离相关的顺层滑动中充填
曲美北/S337-1	平缓地层,近顺层脉	北盘	0.069/2.6	1.10±0.10	3.66±0.30	0.04±0.01	14.87±1.40	中新世,与拆离相关的顺层滑动中充填
曲美北/S344-1	平缓地层,顺层脉	北盘	0.057/0.844	0.34±0.03	1.02±0.01	0.02±0.01	13.60±1.30	中新世,与拆离相关的顺层滑动中充填
台巴南/S467-2	顺层脉(45°∠40°),向倾向下倾方向运动	北盘	0.091/1.625	0.68±0.06	2.03±0.20	0.03±0.01	11.18±1.00	中新世,与拆离相关的顺层滑动中充填
扎美南/S1788-2	顺层(166°∠ 14°)脉	南盘	0.087/1.522	0.64±0.05	1.93±0.18	0.26±0.02	11.04±1.00	中新世,与拆离相关的顺层滑动中充填
得江果/S265-1	逆断层(6°∠71°) 充填脉	北盘	0.405/1.02	0.40±0.04	1.21±0.10	0.12±0.01	9.08±1.00	中新世晚期,挤压变形中充填
措美东/S432-1	断层 (70°∠70°) 充填脉,右旋逆冲	北盘	0.043/1.248	0.51±0.05	1.64±0.14	0.07±0.01	6.82±0.60	中新世晚期,挤压变形中充填

表1 构造变形相关石英脉采样情况及ESR测年结果

Table 1 Tectonic deformation-associated quartz veins’ sampling situation and ESR dating results

采样位置及样品编号	石英脉产状	相对于洛扎断裂的位置	(顺磁中心浓度/ (10¹⁵自旋/g))/ (铀当量含量 /(μg/g))	铀含量/ (μg/g)	钍含量/ (μg/g)	钾含量/%	年龄/Ma	年龄解释
公主沟/D055-2	顺层脉,N∠(5°~10°)	南盘	0.405/1.02	0.30±0.03	0.90±0.08	0.20±0.02	80.65±8.00	白垩纪晚期,板块汇聚期层间滑动中充填
公主南/D011-1	北倾褶皱地层(345°∠15°)中充填脉	北盘	0.066/2.21	0.92±0.09	2.69±0.25	0.50±0.05	59.76±5.80	古近纪早期,板块汇聚-碰撞期,北盘褶皱带充填
门当沟/S1949-1	弱切层(18°∠24°)煌斑岩中脉,示向南逆冲	北盘	0.404/2	0.85±0.08	2.48±0.20	0.39±0.03	40.40±4.00	古近纪,板块碰撞期,北盘褶皱带中充填
乃西北/S420-1	劈理(290°∠76°)充填脉	北盘	0.103/0.874	0.35±0.03	1.05±0.10	0.04±0.01	23.62±2.30	古近纪晚期,板块碰撞期,北盘褶皱带中充填
仲觉北/S402-1	顺(切)层脉,SW 倾	北盘	0.064/3.577	1.49±0.14	4.77±0.45	0.38±0.03	17.67±1.50	中新世,与拆离相关的顺层滑动中充填
曲美北/S337-1	平缓地层,近顺层脉	北盘	0.069/2.6	1.10±0.10	3.66±0.30	0.04±0.01	14.87±1.40	中新世,与拆离相关的顺层滑动中充填
曲美北/S344-1	平缓地层,顺层脉	北盘	0.057/0.844	0.34±0.03	1.02±0.01	0.02±0.01	13.60±1.30	中新世,与拆离相关的顺层滑动中充填
台巴南/S467-2	顺层脉(45°∠40°),向倾向下倾方向运动	北盘	0.091/1.625	0.68±0.06	2.03±0.20	0.03±0.01	11.18±1.00	中新世,与拆离相关的顺层滑动中充填
扎美南/S1788-2	顺层(166°∠ 14°)脉	南盘	0.087/1.522	0.64±0.05	1.93±0.18	0.26±0.02	11.04±1.00	中新世,与拆离相关的顺层滑动中充填
得江果/S265-1	逆断层(6°∠71°) 充填脉	北盘	0.405/1.02	0.40±0.04	1.21±0.10	0.12±0.01	9.08±1.00	中新世晚期,挤压变形中充填
措美东/S432-1	断层 (70°∠70°) 充填脉,右旋逆冲	北盘	0.043/1.248	0.51±0.05	1.64±0.14	0.07±0.01	6.82±0.60	中新世晚期,挤压变形中充填

参考文献 46

[1]	PAN G T, WANG L Q, LI R S, et al. Tectonic evolution of the Qinghai-Tibet Plateau[J]. Journal of Asian Earth Sciences, 2012,53:3-14. DOI URL
[2]	潘桂棠, 王立全, 张万平, 等. 青藏高原及邻区大地构造图及说明书(1∶1500000)[M]. 北京: 地质出版社, 2013: 1.
[3]	黄汲清, 任纪舜. 中国大地构造及其演化 1∶400万中国大地构造图简要说明[M]. 北京: 科学出版社, 1980: 59.
[4]	成都地质矿产研究所. 青藏高原及邻区地质图(1∶1500000)[M]. 北京: 地质出版社, 1988: 1.
[5]	刘增乾, 徐宪, 潘桂棠, 等. 青藏高原大地构造与形成演化[M]. 北京: 地质出版社, 1990: 56.
[6]	潘桂棠, 王培生, 徐耀荣, 等. 青藏高原新生代构造演化[M]. 北京: 地质出版社, 1990: 90-91.
[7]	朱同兴, 周明魁, 冯心涛, 等. 西藏喜马拉雅北坡显生宙多重地层及盆地演化[M]. 北京: 地质出版社, 2005: 11-12.
[8]	赵文津, INDEPTH项目组. 喜马拉雅山及雅鲁藏布江缝合带深部结构与构造研究[M]. 北京: 地质出版社, 2001: 326.
[9]	中国地质大学(北京). 中华人民共和国区域地质调查报告:江孜县幅、亚东县幅(1∶250000)[R]. 北京:中国地质大学(北京), 2005: 384-385.
[10]	LELOUP P H, MAHEO G, ARNAUD N, et al. The South Tibet detachment shear zone in the Dinggye area:time constraints on extrusion models of the Himalayas[J]. Earth and Planetary Science Letters, 2010,292(1/2):1-16. DOI URL
[11]	LI D, YIN A. Orogen-parallel, active left-slip faults in the Eastern Himalaya: Implications for the growth mechanism of the Himalayan Arc[J]. Earth and Planetary Science Letters, 2008,274:258-267. DOI URL
[12]	BURCHFIEL B C, CHEN Z, HODGES K V, et al. The South Tibetan detachment system, Himalayan orogen: extension contemporaneous with and parallel to shortening in a collisional mountain belt[J]. Geological Society of America Special Paper, 1992,269:1-41.
[13]	陈智梁, 刘宇平. 藏南拆离系[J]. 特提斯地质, 1996,20(1):31-51.
[14]	EDWARDS M A, KIDD W S F, LI J, et al. Multi-stage deve-lopment of the southern Tibet detachment system near Khula Kangri-New data from Gonto La[J]. Tectonophysics, 1996,260:1-19. DOI URL
[15]	EDWARDS M A, PECHER A, KIDD W S F, et al. Southern Tibet detachment system at Khula Kangri, Eastern Himalaya: A large-area,shallow detachment stretching into Bhutan?[J]. The Journal of Geology, 1999,107(5):623-631. DOI URL
[16]	HURTADO J M, HODGES K V, WHIPPLE K X. Neotectonics of the Thakkhola graben and implications for recent activity on the South Tibetan fault system in the central Nepal Himalaya[J]. GSA Bulletin, 2001,113(2):222-240. DOI URL
[17]	COOPER F J, HODGES K V, ADAMS B A. Metamorphic constraints on the character and displacement of the South Tibetan fault system, central Bhutanese Himalaya[J]. Lithosphere, 2012,5(1):67-81. DOI URL
[18]	HODGES K V. Tectonics of the Himalaya and southern Tibet from two perspectives[J]. GSA Bulletin, 2000,112(3):324-350. DOI URL
[19]	YIN An. Cenozoic tectonic evolution of the Himalayan orogen as constrained by along-strike variation of structural geometry, exhumation history, and foreland sedimentation[J]. Earth-Science Reviews, 2006,76:1-131. DOI URL
[20]	GREENWOOD L V, ARGLES T W, PARRISH R R, et al. The geology and tectonics of central Bhutan[J]. Journal of the Geological Society, 2016,173:352-369. DOI URL
[21]	安徽省地质调查院. 中华人民共和国区域地质调查报告:洛扎县幅(1∶250000)[R]. 合肥:安徽省地质调查院, 2002: 45-46, 185-189.
[22]	鲁如魁, 钟华明, 童劲松, 等. 西藏洛扎地区拆离断层构造变形特征[J]. 大地构造与成矿学, 2005,29(1):189-197.
[23]	任纪舜, 王作勋, 陈炳蔚, 等. 中国及邻区大地构造图[M]. 北京: 地质出版社, 1999: 1.
[24]	西藏自治区地矿局. 西藏自治区岩石地层[M]. 武汉: 中国地质大学出版社, 1997: 3.
[25]	张祥信, 刘文灿, 周志广, 等. 藏南亚东地区前寒武纪亚东岩群的建立及其特征[J]. 现代地质, 2005,19(3):341-347.
[26]	ALI J R, AITCHISON J C. Gondwana to Asia: Plate tectonics, paleogeography and the biological connectivity of the Indian sub-continent from the Middle Jurassic through latest Eocene (166-35 Ma)[J]. Earth-Science Reviews, 2008,88:145-166. DOI URL
[27]	PATRIAT P, ACHACHE J. India Eurasia collision chronology has implications for crustal shortening and driving mechanism of plates[J]. Nature, 1984,311:615-621. DOI URL
[28]	王根厚, 梁定益, 刘文灿, 等. 藏南海西期以来伸展运动及伸展作用[J]. 现代地质, 2000,14(2):133-139.
[29]	余光明, 王成善. 西藏特提斯沉积地质[M]. 北京: 地质出版社, 1990: 10-39.
[30]	BROOKFIELD M E. The Himalayan passive margin from Precambrian to Cretaceous times[J]. Sedimentary Geology, 1993,84:1-35. DOI URL
[31]	JADOUL F, BERRA F, GARZANTI E. The Tethys Himalayan passive margin from Late Triassic to Early Cretaceous (South Tibet)[J]. Journal of Asian Earth Sciences, 1998,16(2/3):173-194. DOI URL
[32]	RATSCHBACHER L, FRISCH W, LIU G, et al. Distributed deformation in southern and western Tibet during and after India-Asia collision[J]. Journal of Geophysical Research, 1994,99:19917-19945. DOI URL
[33]	YIN A, HARRISON T M. Geologic evolution of the Himalayan-Tibetan orogen[J]. Annual Review of Earth and Planetary Sciences, 2000,28:211-280. DOI URL
[34]	AIKMAN A B, HARRISON T M, DING L. Evidence for early (>44 Ma) Himalayan crustal thickening, Tethyan Himalaya, southeastern Tibet[J]. Earth and Planetary Science Letters, 2008,274:14-23. DOI URL
[35]	EDWARDS M A, HARRISON T M. When did the roof collapse? Late Miocene N-S extension in the High Himalaya revealed by Th-Pb monazite dating of the Khula Kangri granite[J]. Geology, 1997,25:543-546. DOI URL
[36]	HUANG C M, ZHAO Z D, LI G M, et al. Leucogranites in Lhozhag, southern Tibet: Implications for the tectonic evolution of the eastern Himalaya[J]. Lithos, 2017,294/295:246-262. DOI URL
[37]	钟华明, 夏军, 童劲松, 等. 洛扎县幅地质调查新成果及主要进展[J]. 地质通报, 2004,23(5):451-457.
[38]	魏文博, 陈乐寿, 谭捍东, 等. 关于印度板块俯冲的探讨——据INDEPTH-MT研究结果[J]. 现代地质, 1997,11(3):379-386.
[39]	崔作舟, 尹周勋, 高恩元, 等. 青藏高原速度结构与深部构造[M]. 北京: 地质出版社, 1992: 70.
[40]	孟令顺, 高锐. 青藏高原重力测量与岩石圈构造[M]. 北京: 地质出版社, 1992: 33.
[41]	STYRON R H, TAYLOR M H, MURPHY M A. Oblique convergence,arc-parallel extension,and the role of strike-slip faulting in the High Himalaya[J]. Geosphere, 2011,7(2):1-15. DOI URL
[42]	王世锋, 江万, 王超. 喀喇昆仑断裂沿雅鲁藏布江缝合带活动的构造地貌特征[J]. 地球科学与环境学报, 2016,38(4):483-493.
[43]	HAPROGGA P J, ZUZAA A V, YIN A. West-directed thrusting south of the eastern Himalayan syntaxis indicates clockwise crustal flow at the indenter corner during the India-Asia collision[J]. Tectonophysics, 2018,722:277-285. DOI URL
[44]	KELLETT D A, GRUJIC D, ERDMANN S. Miocene structural reorganization of the South Tibetan detachment, eastern Himalaya: Implications for continental collision[J]. Lithosphere, 2009,1(5):259-281. DOI URL
[45]	中国人民武装警察部队黄金第十一支队. 中华人民共和国区域地质调查报告:哲古幅、卡珠幅、邛多江幅、松多幅、让宗幅、卡果幅(1∶50000)[R]. 长沙:中国人民武装警察部队黄金第十一支队, 2015: 221-233.
[46]	张宏飞, HARRIS N, PARRISH R, 等. 北喜马拉雅淡色花岗岩地球化学:区域对比、岩石成因及其构造意义[J]. 地球科学, 2005,30(3):275-288.