Thrust structures and uplift periods of the Nyainrong metamorphic complex and its neighboring areas
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摘要:
通过详细的野外观测结合地质填图资料，在聂荣变质杂岩及邻区厘定大规模逆冲推覆构造，不同时代的逆冲岩席自北-北东向南-南西逆冲推覆于上白垩统红层及下伏岩石地层之上，形成大量逆冲断层、滑脱构造、飞来峰、构造窗和褶皱构造。逆冲推覆构造运动导致侏罗纪蛇绿混杂岩、石炭系-二叠系构造层、古生界浅变质岩、变质基底之间发生拆离滑脱，在聂荣变质杂岩内部形成韧性剪切带和高角度斜冲断层。在唐古拉山口南侧形成北西-南东向土门-托纠-杂色右旋走滑断裂，走滑断裂末端转换为近东西向逆冲推覆构造。聂荣变质杂岩顶部逆冲推覆叠加滑覆，导致侏罗系混杂堆积和古生界沉积盖层向南西-西向运移86～110km，在那曲-巴尔达-班戈北形成近东西向长透镜状懂错蛇绿混杂岩逆冲岩席，沿缓倾斜断层发育向西倾斜的构造片理、摩擦镜面和近东西走向的矿物线理。裂变径迹测年表明，聂荣变质杂岩及邻区逆冲推覆及构造隆升时代主要为早白垩世晚期-晚白垩世早期（111±5～91±5Ma）、晚白垩世晚期（89±6～69±5Ma）、古新世晚期-始新世早期（55±4～44±2Ma），估算构造隆升视速率为0.10～0.69mm/a，部分断层逆冲推覆及构造隆升延续至古近纪晚期。综合各类观测资料，建立不同时期构造模式，探讨聂荣变质杂岩及邻区逆冲推覆构造演化过程及形成机理。
Abstract:Regional thrust systems consisting of thrust faults, tectonic slices and sheets, nappes, structural windows and accompanied folds were discovered in the Nyainrong metamorphic complex and its neighboring areas on the basis of field studies and geological mapping. Tectonic slices and thrust sheets surrounding the Nyainrong metamorphic complex were thrust southwest-westward over the Upper Cretaceous red beds and the Jurassic-Lower Cretaceous marine sedimentary rocks. Regional intensive thrust led to detach-ments among the ophiolite and Jurasssic mélanges, the Carboniferous-Permian clastic-carbonate, the Paleozoic low-grade metamor-phic rocks and the high-grade metamorphic basement, accompanied by ductile shear zones and oblique thrust faults in the Nyainrong metamorphic complex. Dextral-slip fault trending in northwest-southeast direction along the Tumen-Tuojiu-Zase zone trans-formed to regional thrust systems trending in east-west direction in southern Tanggula Range. Regional thrust and gravitational slide resulted in 86~120km southwest-westward movement of the Jurassic mélange and the Paleozoic covering layers, forming the Dong Co tectonic sheets of ophiolite mélanges along the Naqu-Baerda-North Baingoin in the west-southwest of the Nyainrong meta-morphic complex. Tectonic schist, slikensides and linear minerals trending in east-west direction were formed along the detachment faults beneath the Dong Co thrust slices of ophiolite mélanges. Fission-track dating indicates that thrust uplift mainly occurred at the late stage of the Early Cretaceous-the early stage of the Late Cretaceous (111±5~91±5Ma), late stage of the Late Cretaceous (89±6~69±5Ma) and Late Paleocene-Early Eocene (55±4~44±2Ma), and the corresponding rates of thrust uplift range from 0.10mm/a to 0.69mm/a in the Nyainrong metamorphic complex and its neighboring areas. Thrust uplift also occurred in Late Eocene and Oligo-cene in some areas. The process and mechanism of regional thrust in the Nyainrong metamorphic complex and its neighboring areas are discussed on the basis of the data available.
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致谢: 单矿物分选和裂变径迹测年分别由廊坊宇能岩石矿物分选实验室、中国地质大学（北京）裂变径迹实验室协助完成，野外工作得到拉萨野外工作站和米玛、加措、边巴等提供的支持和帮助，在此一并致谢。
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图 1 聂荣变质杂岩及邻区构造纲要图（据参考文献[①-⑥]结合野外观测资料编绘）
1—逆冲断层；2—走滑断层；3—正断层；4—背斜、向斜；5—混杂堆积；6—蛇绿岩；7—早白垩世火山岩；8—古近纪花岗岩；9—晚白垩世花岗岩；10—早白垩世花岗岩；11—侏罗纪花岗岩；12—现代湖泊；13—地质构造剖面及野外观测点。Q—第四系河湖相沉积；N—新近系（中新统）湖相沉积；E—古近系河湖相碎屑岩；K2—上白垩统陆相红层；K1—下白垩统；J2-3—中上侏罗统；J—侏罗系；Jmg—侏罗系混杂堆积；T—三叠系；P—二叠系；D—泥盆系；Pz—古生界（嘉玉桥群）中浅变质岩；Gn—中深变质岩（片麻岩）；EG—古近纪中酸性侵入岩；K2G—晚白垩世中酸性侵入岩；K1G—早白垩世中酸性侵入岩；KG—白垩纪中酸性侵入岩；B54—磷灰石裂变径迹样品编号及取样位置；165.5Ma/U5267—锆石U-Pb同位素年龄（详细测试资料另文发表）。引自参考文献[①-⑥]的同位素年龄：116.6Ma/U-Pb—铀-铅年龄；71.4Ma/K-Ar—钾-氩年龄
Figure 1. Structural outline map of the Nyainrong metamorphic complex and its neighboring areas
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图 2 逆冲断层及褶皱构造照片
a—土门东侧侏罗系灰岩（J）逆冲推覆于上白垩统红层（K2）之上（镜向北西）；b—安多西侧侏罗系灰岩（J）逆冲推覆于上白垩统红层（K2）之上（镜向北东）；c—安多东北侏罗系灰岩（J）下伏下白垩统碎屑岩（K1）褶皱变形（镜向西南）
Figure 2. Photos of thrust faults and folds
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图 3 聂荣变质杂岩及邻区构造迹线（细点线表示最大主压应力迹线；黑色粗虚线及箭头表示逆冲推覆构造运动迹线及方向）
BNS—班公-怒江缝合线；Jmg—侏罗系混杂堆积；Oph—蛇绿岩；Pz—古生界中浅变质岩
Figure 3. Maximum stress and motion trajectories in the Nyainrong metamorphic complex and its neighboring areas
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图 4 磷灰石裂变径迹测年统计分布
Figure 4. Statistic diagrams of the fission-track dating of apatites
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表 1 聂荣变质杂岩磷灰石裂变径迹测年数据
Table 1 Fission track dating of apatites from granulite and granite of the Nyainrong metamorphic complex
样品编号 岩石类型 颗粒数
(n)ρs/{105·cm-2)
(Ns)ρi/(105·cm-2)
(Ni)ρd/(105·cm-2)
(N)P/% 中心年龄/Ma
(±1σ)池年龄/Ma
(±1σ)径迹长度/μm
(N)锆石裂变径迹年龄
/Ma (n)*B10 绿泥石
片岩29 2.146
(331)16.747
(2583)20.308
(9117)62.6 47±4 46士4 12.6士2.0
(106)B13 变粗砂岩 27 4.804
(841)12.481
(2185)9.412
(7463)0 57士5 64士4 12.5士2
(105)B15 片麻岩 28 5.823
(1225)13.700
(2882)11.543
(7463)55.9 86士5 86士5 13.1士2
(104)94士4
(n=22)B20 片麻岩 21 5.136
(977)10.509
(1999)10.406
(7463)9.5 89士6 89士6 13.5士1.8
(94)106士8
(n=7)B31 黑云母
花岗岩22 8.459
(2773)37.59
(12323)19.063
(9117)0.0 74士5 75士4 12.8士1.6
(103)117士5
(n=21)B32 斜长角
闪岩25 8.714
(2251)34.761
(8980)19.241
(9117)0.0 81士6 85士5 13.0士1.8
(100)B34 花岗片
麻岩27 9.273
(2257)49.961
(12160)19.507
(9117)0.0 63士4 64士4 12.6士1.7
(102)B38 花岗岩
黑云母28 3.515
(1431)25.453
(10361)19.85
(9117)0.0 47士3 48士3 13.5士1.8
(102)B39 花岗岩
片麻状28 2.483
(679)15.983
(4371)20.13
(9117)72.8 55士4 55士4 12.2士2.1
(102)B51 二云母花
岗片岩23 6.023
(1856)27.43
(8453)9.837
(6788)0 45
士344
士213士1.8
(101)B53 闪长岩
(包体）35 5.176
(1412)19.789
(5398)10.046
(6788)24.8 54
士354
士313.6士1.7
(107)B54 花岗片
麻岩35 9.08
(3382)35.846
(13351)10.255
(6788)0 53
士353
士313.4士1.8(119) 花岗片 5.156 20.851 10.464 53 53 12.9士1.8 B56 麻岩 35 (1082) (4376) (6788) 58.7 士3 士3 (102) B62 花岗片
麻岩28 3.338
(776)8.870
(2062)10.406
(7463)19.7 69士5 69士5 14士1.9
(93)99士4
(n=26)B65 花岗片
麻岩27 7.407
(2035)16.692
(4586)8.985
(7463)10.0 70士4 70士4 13.2士2
(102)107士7
(n=9)B71 变粗砂岩 28 0.536
(138)2.587
(666)9.696
(7463)47.2 36士4 35士4 13.8士2.1
(69)B77 变粗砂岩 25 5.039
(1229)9.172
(2237)8.985
(7463)95.9 87士6 87士6 13.1士2
(100)105士5
(n=16)B86 中粗粒
花岗岩28 5.838
(1188)15.068
(3066)10.549
(7463)42.9 72士5 72士5 13.7士2.1
(99)78士3
(n=22)B87 中粗粒
花岗岩25 6.730
(1677)15.370
(3830)9.98
(7463)73.2 77士5 77士5 13.2士2.1
(109)94士4
(n=25)B88 黑云母二
长花岗岩25 6.730
(1677)15.370
(3830)9.98
(7463)73.2 77士5 77士5 13.2士2.1
(109)91士5
(n=12)B93 黑云母二
长花岗岩28 9.486
(1851)20.725
(4044)9.269
(7463)18.2 75士5 74士4 13.9士2.1
(110)93士4
(n=26)B96 黑云母二
长花岗岩28 5.012
(1180)8.389
(1975)8.843
(7463)88.7 93士6 93士6 13.4士2.2
(110)111士5
(n=25)注：ρs、ρi、ρd分别为自发径迹密度、诱发径迹密度和标准径迹密度；Ns、Ni、Nd分别为自发径迹数、诱发径迹数和标准径迹数；P（χ2）为χ2检验的概率；*锆石裂变径迹年龄据参考文献[2, 17]；n=26表示裂变径迹测年锆石颗粒数量 
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