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吉林省下三叠统卢家屯组LA-ICP-MS锆石U-Pb定年及其地质意义
聂立军, 于宏斌, 张建泽, 王聪, 李栋, 李阳    
吉林省区域地质矿产调查所, 长春 130022
摘要:卢家屯组按岩性组合自下而上分为影背山砾岩段、漏斗山杂色岩段、杨树河子黑色岩段,前人采集到的Palaeanodonta-Palaeomutela动物群、Pleuroneia? sp.和叶肢介等生物化石组合指示时代为二叠纪。本次对九台市影背山双顶山卢家屯组建组剖面下、中、上段进行了系统的碎屑锆石U-Pb同位素年代学研究,证实卢家屯组由下至上存在3个最小锆石年龄峰值,分别为(283.4±7.9)、(262.4±3.9)、(255.5±5.8) Ma,确定了卢家屯组的上限为晚二叠世。根据卢家屯组中碎屑锆石存在1 800 Ma和2 500 Ma左右的典型华北板块基底年龄,认为华北板块北缘与其北侧地块群最终闭合时间应为P3-T1
关键词卢家屯组     下三叠统     碎屑锆石     LA-ICP-MS锆石U-Pb定年     吉林省    
Zircons LA-ICP-MS U-Pb Ages of the Lower Triassic Lujiatun Group and Its Geological Significance in Jilin Province
Nie Lijun, Yu Hongbin, Zhang Jianze, Wang Cong, Li Dong, Li Yang    
Survey of Regional Geological and Mineral Resource of Jilin Province, Changchun 130022, China
Abstract:According to the associated lithologic feature, the Lujiatun Formation is divided into Yingbeishan conglomerate section, Loudoushan variegated rock section, and Yangshuhezi black rock section. Based on the fossil assemblages, such as Palaeanodonta-Palaeomutela fauna, Pleuroneia? sp. and the conchostracan, it was formed in Permian. A systematic U-Pb isotopic chronology of the detrital zircon is studied for the Bottom, Middle, and Upper Section of the construction profiles of Lujiatun Formation in Yingbeishan-Shuangdingshan in Jiutai. The results show three minimum zircon age peaks at (283.4±7.9) Ma, (262.4±3.9) Ma, and (255.5±5.8) Ma from the bottom to the top. It can be confirmed that the top section of the formation belonged to the Late Permian. The detrital zircon ages of 1 800 Ma and 2 500 Ma in the Lujiantun Group are typical for the base plate age of North China Plate. In conclusion, the plate closure happened probably during P3-T1 between the northern margin of North China Plate and the group of plates to its north.
Key words: Lujiatun Formation     Lower Triassic     detrital zircon     zircon LA-ICP-MS U-Pb age     Jilin Province    

0 引言

卢家屯组作为吉林省目前唯一确认的下三叠统地层[1],其构造环境及构造意义在区域地质构造研究中占有重要的位置。而二叠纪——三叠纪这一时间段对于吉林省乃至整个东北亚地质构造演化意义重大。很多学者将其和华北板块北缘与其北侧地块的碰撞拼贴的演化过程及最终的闭合时间联系在一起,并有如下几种观点:吉黑复合造山带古亚洲洋构造体制结束的综合标志时间为250~230 Ma[2];古亚洲构造域一部分的古亚洲洋结束于中三叠世[3];华北北部晚古生代末——中生代初正处在2个构造域叠加的重要时期[4];兴蒙造山带东段的西拉木伦河——长春——延吉板块缝合带应于二叠纪末期最终闭合[5]

最新的年代学研究[6]表明,现划分的华北板块北缘以北地区出露的蛇绿岩的形成时代多集中在中二叠世:如温都尔庙蛇绿岩年龄为(260±12) Ma,半拉山蛇绿岩年龄为256 Ma。此外,西拉木伦河北部杏树洼蛇绿岩带硅质岩中放射虫的时代为二叠纪[7];古亚洲洋在华北板块以北地区的最晚闭合位置为索伦——延吉缝合带,自西向东闭合时间为260~250 Ma[8];西拉木伦河沿岸双井地区同碰撞花岗岩体侵位时间主要集中在晚二叠世——早三叠世[9];西拉木伦河缝合带东段吉中地区同碰撞花岗岩、碰撞相关的变质事件的年龄也主要集中在二叠纪末——早三叠世[10, 11]。可见,二叠纪——三叠纪是华北板块北缘与其北侧地块碰撞拼贴演化的关键时期。但对于二者之间的具体演化过程和模式,不同学者对它们的认识有所不同。针对这一问题,笔者从碎屑锆石年代学的角度,对卢家屯组碎屑岩进行碎屑锆石年代学研究,以进一步对古亚洲洋的最终闭合时间和华北板块与蒙古陆块的最终碰撞时间等问题进行探讨。

1 区域地质概况

研究区位于兴蒙显生宙造山带东段,大黑山条垒东北端。西侧为松辽地块,由四平——德惠断裂与条垒相隔;东侧有伊通——依兰伸展-走滑复合盆地,其内沉降了巨厚层的新生代陆相碎屑岩,并且基性火山活动强烈,该盆地与条垒由伊通——依兰断裂带的西支断裂相隔。

研究区内最老地层为上二叠统杨家沟组,分布于南侧鸡冠山一带,主要岩性组合为含砾砂岩、黑灰色粉砂岩、细砂岩、板岩等,其内产海相瓣鳃、苔藓虫和陆相瓣鳃及植物化石,具有海陆交互相特征,被上三叠统西土山组角度不整合覆盖和早侏罗世花岗岩侵入;其次为下三叠统卢家屯组(图 1),分布面积较大,被上三叠统西土山组或下白垩统营城组角度不整合覆盖,是本次研究的地质体。上三叠统西土山组分布于大孤家子南,主要为一套中——酸性火山岩夹少量碎屑岩,底部为砾岩,被下白垩统营城组角度不整合覆盖及早侏罗世花岗岩侵入。西土山组上部为下白垩统营城组火山岩和古近系碎屑岩及第四系沉积物。

侵入岩主要为一套中生代侵入岩,主要有早侏罗世石英闪长岩、花岗闪长岩、二长花岗岩和早白垩世碱长花岗岩。

图 1 九台市沐石河——卢家地质图

Fig. 1 Geological map of the Mushihe-Lujia in Jiutai

2 卢家屯组地质特征

卢家屯组分布于吉林省九台市卢家屯、李家屯、永安屯、大孤家子影背山等地,呈北东东方向展布,被早侏罗世二长花岗岩侵入,构造单元属大黑山地垒。1959年九台县工业局九台地质队曾将该套地层定为波泥河组。吉林地质局、长春地质学院合办队1975年将该地层下部杂色砂岩、砾岩归入一拉溪组,上部含化石的黑色粉砂岩、泥岩归入杨家沟组,时代为晚二叠世。1980年吉林省地质矿产局区域地质调查所开展1∶20万舒兰县幅区域地质调查期间,在九台市影背山、杨家沟、双顶山发现了大量的动、植物化石,其中瓣鳃类有Palaeanodonta tungussica (Ragozin)、P. opinata (Ragozin)、P. obrutschevi (Ragozin),叶肢介有Cornia subquadrata Zaspelove、C.lutkevichi Zasp、C .elata Zasp,植物有Neocalamites sp.、Cladophlebis sp.、Taeniopteris sp.等,首次提出在华北板块北缘有早三叠世地层存在,并建立了卢家屯组。卢家屯组可划分下、中、上三段:下段(影背山砾岩段)以粗碎屑岩为主,构成砾岩-含砾砂岩-砂岩基本层序,砾石成分复杂,沉积物以杂色为主,厚度上千米,从沉积物颗粒分析,反映为从山麓相向河流相发展阶段堆积的产物,明显具磨拉石建造特征;中段(漏斗山杂色岩段)以杂色石英长石粉砂岩、泥岩互层,底部为紫色砂、砾岩;上段(杨树河子黑色岩段)以细碎屑为主,由砾岩、砂岩、泥岩(夹泥质岩及石膏)构成两个韵律层,并产动、植物化石,沉积物以黑色为主夹紫色,厚度逾千米,反映湖相阶段形成。

卢家屯组还产有丰富的双壳类化石:Palaeanodonta tungussca(Ragozin)、P. opinata(Ragozin)、P.obrutchevi (Ragozin)等见于俄罗斯西伯利亚库兹巴斯的库兹涅茨克盆地三叠系下统马里采夫组和通古斯盆地三叠系下统卡尔文昌组,与Ferganoconcha伴生;Ferganoconcha见于俄罗斯远东地区、中国东北的中生代地层中,至今没有在二叠纪地层中发现;叶肢介Cornia subquadrata Zaspelove、C.lutkevichi Zasp、C.elata Zasp 等是前苏联乌拉尔西北部伯朝拉盆地中早三叠世地层中的重要分子。而从介形虫Langdaia?sp.、Sphenota sp.、Sphenobaiela sp. 等的组合面貌看,其时代区限是在早三叠世至早中侏罗世之间的组合特点,其中Langdaia?sp.见于贵州朗岱三叠系下统飞仙关组。植物Palacalamites sp.、Neocalamites sp.、Cladophlebis sp.、Taeniopteris sp.、Thinnfeldia sp.、Podozamites sp.等化石保存欠佳,无法鉴定到种,其组合除Palacalamites sp.外,常见于三叠纪——侏罗纪。而Paracalamites sp. 是晚期安加拉植物群的代表性分子,时代一般为晚二叠世,除卢家屯组外没有在吉林省其他中生代地层中发现过。

纵观卢家屯组生物化石特征,既有二叠纪标准生物分子(Paracalamites sp.),又有早三叠世——侏罗纪存在的生物化石,时代意义确定还有待商榷。笔者也尝试从碎屑锆石测年统计学研究对其形成时代进行探讨,力求从另一种思路对生物化石依据不充分或哑地层进行年代学研究。

3 同位素样品的采集

在对卢家屯组建组剖面修测(图 2)时,于影背山砾岩段2层(东经126°14′13″,北纬44°13′17″)、漏斗山杂色岩段17层(东经126°14′13″,北纬44°14′44″)及杨树河子黑色岩段24层(东经126°13′53″,北纬44°17′04″)分别采集3件样品:Pm003-2,野外岩石定名为紫灰色厚层复成分砾岩,其单层厚度为50~60 cm,砾石成分复杂,有花岗岩、石英脉、中细粒砂岩及紫色粉砂岩,砾石分选差,最大者8.0 cm,小者0.5 cm,砾石磨圆差,多为棱角状和次棱角状,硅质胶结;Pm003-17,野外定名为灰色中薄层细粒长石石英砂岩,单层厚度10~20 cm,细砂岩中的微层理比较发育,镜下为钙质细砂岩;Pm003-24,野外定名为灰色中薄层泥质细砂岩,单层厚度>20 cm,其内含泥质成分较多。露头处发育碳酸盐细脉,宽0.5~1.0 mm,同时见有原生黄铁矿立方体,单晶1.0 mm±,部分氧化形成褐铁矿,镜下定名为褐铁矿化泥质细砂岩。

图 2 九台市影背山——双顶山下三叠统卢家屯组剖面图(Pm003)

Fig. 2 Profile of the lower Triassic Lujiatun Formation at Yingbeishan-Shuangdingshan in Jiutai City,Jilin Province(Pm003)

卢家屯组层型剖面地层层序特征及样品采集位置如下:

未 见 顶

杨树河子黑色岩段

24.灰色褐铁矿化泥质细砂岩,采集碎屑锆石 163.5 m

23. 黑灰色凝灰质粉砂岩,单层厚度为10~20 cm,产动物化石 57.3 m

22.黄灰色粉砂岩夹粉砂质泥岩 64.1 m

21.灰白色粉砂质泥岩 94.8 m

漏斗山杂色岩段

20.紫色泥岩 143.5 m

19.青灰色含粉砂质泥岩 57.9 m

18.黑灰色粉砂岩,局部菱铁矿化 30.5 m

17. 灰色钙质细砂岩,见褐铁矿化,采集碎屑锆

石 127.9 m

16.褐铁矿化石英长石粉砂岩 127.9 m

15.褐铁矿化石英长石细砂岩 127.9 m

14.灰黑色钙质粉砂岩 39.5 m

13.黄灰色褐铁矿化石英长石粉砂岩 74.4 m

12.紫色泥岩 91.5 m

11.青灰色含粉砂质泥岩,含有褐铁矿斑点 59.8 m

10.黄灰色杂砂质石英长石粉砂岩 59.8 m

9.青灰色粉砂岩 59.8 m

8.紫色细粒杂砂岩 278.9 m

7.紫色砾岩 235.5 m

影背山砾岩段

6.紫色凝灰质粉砂岩 124.7 m

5.灰绿色轻微变质粉砂岩 720.7 m

4.青灰色钙质细粒杂砂岩 233.7 m

3.灰黑色泥质粉砂岩 157.2 m

2.紫灰色厚层复成分砾岩,采集碎屑锆石 169.4 m

1.青灰色中粒杂砂岩 1 073.0 m

早侏罗世二长花岗岩侵入 4 同位素样品分析方法及测试结果

4.1 样品制作及分析方法

将上述3件人工重砂样品,委托吉林省区域地质矿产调查所岩矿室加工分选。按常规方法分别进行破碎至80~100目,后经重力分选,利用矿物介电分选仪进行磁选,重液先选,于双目镜下挑选出晶形相对较好、无明显裂痕和包体的单颗粒锆石晶体,将其粘贴在双面胶上,灌入环氧树脂冷却凝固后,打磨抛光露出锆石表面,对其进行透射光、反射光和阴极发光(CL)图像的采集。锆石的制靶和显微图像的采集均在中国地质科学研究院国家重点开放实验室完成。

锆石LA-ICP-MS U-Pb同位素分析在国家地质实验测试中心完成。U-Pb同位素测定使用Agilent 7500Ce( New Wave UP213)和德国Lambdaphysik公司的Compex102 ArF准分子激光器以及Microlas 公司的Geolas 200M光学系统联机进行。锆石测定过程中激光束斑直径为30 μm,激光剥蚀样品的深度为20~40 μm。实验中采用He作为剥蚀物质载气;用人工合成硅酸盐玻璃标准参考物质NISTSRM610进行仪器最佳化。锆石年龄采用国际标准锆石91500作为外标标准物质;含量采用NISTSRM610作为外标,同时使用锆石中含量稳定的29Si作为内标。所测单点的同位素比值及元素含量采用Glitter (Var4.0 Macquarie University)程序进行计算。对所有数据进行普通铅校正,谐和图的绘制采用Isololt 3.0完成[12, 13]。单个分析点的同位素比值和同位素年龄的误差(标准偏差)为1σ206Pb/238U加权平均年龄按95%的置信度给出。详细的实验分析步骤和数据处理方法均按文献[14]所提出的精度和要求进行。

4.2 同位素测试结果

Pm003-2(影背山砾岩段),测定了120个单颗粒锆石,每个锆石1个点。从图 3中可见,所有锆石均显示清晰的振荡生长环带,个别具核幔结构;由表 1可知,Th/U为0.05~1.71,平均值为0.65,故所测锆石均具岩浆成因特点[15]。其表面年龄按分布频率明显可划分为7组(图 4):第一组,n=20,(1 738.7±16.3)~(2 579.6±19.9) Ma;第二组,n=5,(1 496.8±13.2)~(1 602.1±14.9) Ma;第三组,n=2,(1 177.8±11.1)~(1 214.7±11.0)Ma;第四组,n=7,(837.2±10.9)~(955.8±7.9)Ma;第五组,n=22,(411.9±3.7)~(542.1±5.2)Ma;第六组,n=53,(251.5±2.4)~(398.8±4.3)Ma;第七组,n=11,(179.6±1.6)~(243.8±2.3)Ma。从图 5a中可明显地看到第五组年龄数据点密集地分布在谐和线上,剔除远离谐和线的样品,获得206Pb/238U加权平均年龄为(283.4±7.9)Ma(n=41,MSWD=71)(图 5b),代表了样品沉积时限晚于早二叠世。特别指出,第一组加权年龄值((2 448.0±23.0)Ma,n=3,MSWD = 0.48)(图 5c)可能为捕获松嫩地块的残留(老)锆石年龄,也可能为来自华北板块的基底锆石年龄。

图 3 Pm003-2典型锆石阴极发光图像

Fig. 3 A typical Cathodoluminescence image of Zircon of Pm003-2
图 4 Pm003-2碎屑锆石U-Pb年龄分布频率图

Fig. 4 Distribution frequence of the detrital zircon U-Pb ages of Pm003-2
表 1 卢家屯组下段Pm003-2碎屑锆石LA-ICP-MS U-Pb分析结果 Table 1 LA-ICP-MS U-Pb Results of the detrital zircon of Pm003-2 from the lower section of Lujiatun Formation
样品测点Th/
U
同位素比值t/Ma
207Pb/206Pb±1σ206Pb/238U±1σ207Pb/235U±1σ 206Pb/238U±1σ
Pm003-2-10.090.054 010.001 760.078 580.001 200.563 050.024 634887
Pm003-2-20.080.053 100.000 990.040 560.000 490.292 210.006 332563
Pm003-2-30.620.070 420.000 720.153 960.001 541.513 910.017 659239
Pm003-2-40.370.146 160.001 410.481 110.005 419.551 740.122 572 53224
Pm003-2-50.400.052 920.000 620.049 410.000 490.360 250.004 493113
Pm003-2-60.180.164 460.002 750.057 820.000 681.296 320.032 723624
Pm003-2-70.470.157 800.001 570.463 370.004 6410.216 950.122 442 45420
Pm003-2-80.660.157 410.001 550.464 450.004 8210.189 610.125 792 45921
Pm003-2-90.090.104 990.001 540.143 220.001 721.996 570.048 4286310
Pm003-2-100.050.065 890.001 010.087 290.000 900.769 630.015 685405
Pm003-2-110.660.053 230.000 600.043 770.000 440.316 540.003 832763
Pm003-2-120.310.052 610.000 770.039 970.000 400.290 710.004 712532
Pm003-2-130.950.055 030.000 770.069 860.000 660.518 210.008 464354
Pm003-2-141.040.052 740.000 660.046 570.000 430.338 060.004 462933
Pm003-2-150.930.052 620.000 720.044 540.000 450.326 140.004 992813
Pm003-2-161.000.051 010.000 630.044 550.000 450.317 770.004 272813
Pm003-2-170.890.108 280.001 190.318 960.003 064.804 850.082 671 78515
Pm003-2-180.760.056 190.000 980.050 430.000 520.378 800.007 843173
Pm003-2-190.660.053 880.000 980.045 910.000 480.345 170.007 342893
Pm003-2-200.890.052 750.000 820.044 950.000 500.328 020.005 922843
Pm003-2-210.830.150 790.001 640.404 640.004 008.535 650.162 872 19018
Pm003-2-220.930.162 270.001 630.436 120.004 769.726 080.141 132 33321
Pm003-2-230.810.111 190.001 150.282 140.002 974.213 390.058 261 60215
Pm003-2-240.760.152 480.001 540.403 050.004 228.322 920.116 322 18319
Pm003-2-250.720.061 720.000 970.048 380.000 460.412 140.007 503053
Pm003-2-260.830.059 450.000 730.074 900.000 660.600 580.008 014664
Pm003-2-270.780.058 990.000 930.045 940.000 460.381 250.006 912903
Pm003-2-281.000.114 870.001 190.332 110.003 315.373 130.073 191 84916
Pm003-2-290.880.117 970.001 210.350 980.003 375.777 770.072 701 93916
Pm003-2-301.030.053 990.001 000.049 690.000 600.364 890.008 103134
Pm003-2-310.590.066 490.001 250.044 830.000 460.421 540.009 572833
Pm003-2-320.630.055 020.000 860.044 890.000 420.346 910.006 092833
Pm003-2-330.170.120 530.001 300.159 830.001 422.689 820.035 679568
Pm003-2-340.870.056 380.000 780.036 570.000 340.291 480.004 282322
Pm003-2-350.480.052 300.000 640.028 240.000 250.207 420.002 481802
Pm003-2-360.610.055 850.000 990.039 780.000 390.300 870.006 052522
Pm003-2-370.410.051 310.000 650.030 660.000 270.214 970.002 711952
Pm003-2-380.950.080 650.001 260.152 000.001 501.737 150.045 919128
Pm003-2-390.390.057 020.000 810.068 390.000 630.548 120.009 214274
Pm003-2-400.530.057 350.001 090.058 990.000 600.475 580.011 293704
Pm003-2-410.650.051 370.001 390.041 420.000 480.301 680.009 782623
Pm003-2-421.650.620 470.010 490.138 680.001 9311.921 890.586 9883711
Pm003-2-430.580.057 340.000 730.079 920.000 720.617 490.009 034964
Pm003-2-440.770.053 890.000 780.049 500.000 450.369 760.005 943123
Pm003-2-450.540.055 000.000 960.084 720.000 830.642 240.014 875245
Pm003-2-460.330.158 780.001 650.429 140.003 749.330 650.135 702 30217
Pm003-2-470.500.058 910.000 810.083 460.000 760.656 730.010 955175
Pm003-2-480.980.114 020.001 300.336 310.003 025.234 250.103 831 86915
Pm003-2-490.790.059 140.001 100.045 610.000 460.363 430.007 992883
Pm003-2-500.370.056 790.000 820.054 970.000 510.427 460.007 063453
Pm003-2-510.440.057 190.001 100.033 360.000 340.262 350.005 632122
Pm003-2-520.510.054 060.000 890.038 550.000 370.290 340.005 292442
Pm003-2-530.950.056 250.001 130.034 850.000 360.264 950.006 012212
Pm003-2-540.730.056 700.000 860.065 970.000 610.523 590.009 514124
Pm003-2-550.620.051 840.001 170.035 620.000 380.252 680.006 492262
Pm003-2-561.040.053 700.000 890.055 190.000 520.400 530.007 813463
Pm003-2-570.680.056 620.000 880.047 800.000 450.370 210.006 543013
Pm003-2-580.730.051 910.001 010.038 330.000 380.271 420.006 012432
Pm003-2-590.930.111 360.001 150.147 380.001 262.287 270.023 608867
Pm003-2-600.700.059 700.000 920.068 190.000 640.557 630.010 534254
Pm003-2-610.090.118 520.001 240.384 450.004 106.432 870.105 392 09719
Pm003-2-620.390.115 000.001 390.309 580.003 305.154 030.119 101 73916
Pm003-2-630.460.112 610.001 220.323 120.003 325.109 360.084 721 80516
Pm003-2-640.820.063 490.001 570.046 400.000 590.407 910.012 452924
Pm003-2-650.470.052 730.000 770.042 290.000 420.301 810.004 872673
Pm003-2-660.490.145 790.001 550.388 080.004 178.025 750.144 312 11419
Pm003-2-670.590.111 200.001 220.269 290.002 814.010 550.065 741 53714
Pm003-2-680.700.064 800.001 640.058 540.000 730.489 550.015 913674
Pm003-2-690.490.057 540.001 040.046 660.000 540.383 980.008 272943
Pm003-2-700.430.076 440.000 910.200 450.002 072.075 450.035 341 17811
Pm003-2-710.680.054 080.001 250.041 220.000 450.304 280.008 242603
Pm003-2-720.740.113 760.001 200.261 360.002 584.174 790.057 501 49713
Pm003-2-730.370.053 130.000 720.040 850.000 430.300 610.004 482583
Pm003-2-740.610.060 400.000 920.079 620.000 860.659 500.012 704945
Pm003-2-750.660.055 340.000 930.071 330.000 760.552 950.011 714445
Pm003-2-761.190.051 730.001 110.043 310.000 530.315 890.007 962733
Pm003-2-770.300.067 620.000 790.143 350.001 511.334 090.020 408649
Pm003-2-780.730.059 370.000 960.070 060.000 810.572 140.011 684375
Pm003-2-790.670.050 380.000 770.033 620.000 340.239 000.003 962132
Pm003-2-801.470.053 390.001 000.049 690.000 550.367 180.008 193133
Pm003-2-810.560.061 640.000 890.038 430.000 380.326 550.005 192432
Pm003-2-820.390.138 860.001 480.378 050.003 697.388 460.114 252 06717
Pm003-2-830.520.056 560.001 630.036 920.000 480.309 220.010 472343
Pm003-2-840.320.118 310.001 300.362 100.003 636.023 400.104 201 99217
Pm003-2-850.780.054 310.000 980.042 610.000 490.331 950.007 082693
Pm003-2-860.380.057 720.001 050.077 660.000 920.617 310.014 664826
Pm003-2-871.070.058 260.000 850.086 990.000 940.697 690.012 895386
Pm003-2-881.710.057 510.001 130.052 680.000 650.422 300.010 203314
Pm003-2-891.150.058 430.002 300.050 160.000 850.387 380.018 863165
Pm003-2-900.590.052 810.000 810.042 750.000 440.317 470.005 502703
Pm003-2-910.560.057 700.000 790.080 730.000 810.645 540.010 755015
Pm003-2-920.180.168 970.001 760.492 070.004 6111.635 600.167 542 58020
Pm003-2-930.700.061 250.001 200.067 950.000 750.568 380.014 384245
Pm003-2-941.010.059 470.000 780.052 840.000 510.434 760.006 303323
Pm003-2-950.590.063 170.001 350.076 540.000 910.653 910.018 994755
Pm003-2-960.660.063 060.001 380.044 250.000 520.394 760.010 502793
Pm003-2-970.470.057 280.000 630.087 740.000 880.691 000.008 445425
Pm003-2-980.570.053 230.001 160.057 150.000 640.421 340.011 303584
Pm003-2-990.780.102 280.001 120.207 360.002 062.904 400.042 741 21511
Pm003-2-1000.540.055 550.001 680.062 820.000 810.499 270.020 133935
Pm003-2-1010.790.056 580.000 990.051 070.000 580.414 050.008 753214
Pm003-2-1020.550.057 380.000 970.051 310.000 570.409 530.008 313234
Pm003-2-1030.620.053 650.001 040.042 340.000 510.317 830.007 262673
Pm003-2-1040.770.055 250.001 030.052 570.000 570.407 180.009 193303
Pm003-2-1050.670.053 140.000 870.047 530.000 490.346 200.006 512993
Pm003-2-1060.640.156 870.001 800.458 440.004 5610.023 850.246 602 43320
Pm003-2-1070.160.124 600.001 280.265 270.002 664.534 490.057 581 51714
Pm003-2-1081.020.061 300.001 160.045 110.000 520.373 000.008 402843
Pm003-2-1090.600.072 900.001 880.060 760.000 780.602 260.020 993805
Pm003-2-1100.590.058 660.000 960.075 890.000 810.602 390.012 564725
Pm003-2-1110.590.052 570.001 250.051 750.000 600.373 860.010 863254
Pm003-2-1120.420.112 250.001 210.275 960.002 914.381 010.069 521 57115
Pm003-2-1130.350.112 930.001 230.317 400.003 035.013 830.080 301 77715
Pm003-2-1140.980.055 210.000 910.063 820.000 710.485 250.009 893994
Pm003-2-1150.580.055 610.000 950.079 700.000 930.611 000.013 654946
Pm003-2-1160.410.057 180.001 610.078 530.001 000.609 990.023 634876
Pm003-2-1170.930.052 690.001 080.044 790.000 530.328 650.008 002833
Pm003-2-1180.680.053 140.001 250.046 590.000 580.340 490.009 592944
Pm003-2-1190.500.049 060.000 800.043 430.000 480.299 810.005 682743
Pm003-2-1200.810.056 480.001 850.044 100.000 650.370 690.014 802784
图 5 Pm003-2碎屑锆石U-Pb年龄谐和图

Fig. 5 Concordan diagrams of the detrital zircon U-Pb ages of Pm003-2

Pm003-17(漏斗山杂色岩段),测定了80个单颗粒锆石,每个锆石1个点。从图 6中可见,所有锆石均显示清晰的振荡生长环带;从表 2可知,Th/U值为0.34~10.89,平均值为2.00,故所测锆石均具岩浆成因特点。其表面年龄明显可划分为10组(图 7):第一组,n=3,(2 093.6±19.1)~(2 562.4±20.8)Ma;第二组,n=2,(1 452.4±14.1)~(1 508.9±14.0)Ma;第三组,n=3,(1 144.7±12.6)~(1 261.8±13.0)Ma;第四组,n=3,(940.6±9.2)~(978.5±9.9)Ma;第五组,n=3,(659.9±7.7)~(752.8±7.9)Ma;第六组,n=8,(464.3±5.2)~(558.5±6.3)Ma;第七组,n=6,(367.8±4.5)~(423.5±4.7)Ma;第八组,n=8,(311.0±3.5)~(355.7±5.1)Ma;第九组,n=37,(201.5±3.0)~(298.2±3.7)Ma;第十组,n=7,(163.±1.7)~(199.6±2.3)Ma。从图 8a中可明显地看到第九组年龄数据点密集地分布在谐和线上,剔除远离谐和线的样品,获得206Pb/238U加权平均年龄为(262.4±3.9)Ma(n=23,MSWD=9)(图 8b),代表了样品沉积时限晚于晚二叠世。第十组加权年龄值((197.3±2.5)Ma,n=7,MSWD = 1.4)(图 8c)可能混有早侏罗世结晶锆石。

表 2 卢家屯组中段Pm003-17碎屑锆石LA-ICP-MS U-Pb分析结果 Table 2 LA-ICP-MS U-Pb Results of the detrital zircon of Pm003-17 from the middle section of Lujiatun Formation
样品测点Th/
U
同位素比值t/Ma
207Pb/206Pb±1σ206Pb/238U±1σ207Pb/235U±1σ 206Pb/238U±1σ
Pm003-17-13.770.046 790.001 250.030 780.000 370.211 460.006 391952
Pm003-17-20.340.050 400.000 880.039 300.000 410.273 870.005 432493
Pm003-17-31.940.049 860.000 890.030 460.000 310.212 410.004 151932
Pm003-17-41.150.052 520.001 490.039 750.000 520.280 060.009 312513
Pm003-17-51.200.060 480.000 790.046 710.000 570.364 930.005 872944
Pm003-17-62.960.059 440.000 950.089 690.000 980.721 770.015 315546
Pm003-17-72.190.052 260.000 940.044 150.000 460.315 720.006 552793
Pm003-17-81.140.070 220.001 720.041 920.000 600.417 990.012 752654
Pm003-17-92.680.056 840.001 000.083 070.000 890.666 480.015 655145
Pm003-17-101.740.090 610.001 010.252 710.002 743.189 400.051 151 45214
Pm003-17-110.900.053 700.001 160.052 950.000 650.390 520.010 273334
Pm003-17-121.070.059 610.001 240.065 030.000 820.522 490.013 894065
Pm003-17-131.520.050 790.001 100.040 580.000 470.287 350.007 292563
Pm003-17-141.210.071 140.000 810.163 910.001 781.548 460.022 7797910
Pm003-17-150.820.056 050.001 410.047 350.000 600.367 950.011 252984
Pm003-17-167.160.064 690.000 740.123 860.001 371.101 060.015 607538
Pm003-17-1710.890.060 490.001 060.090 500.001 060.748 790.017 615596
Pm003-17-185.020.072 500.000 760.159 690.001 711.594 850.019 3395510
Pm003-17-191.460.054 400.000 770.043 040.000 480.324 750.005 262723
Pm003-17-201.980.107 100.001 330.263 730.002 753.963 760.086 571 50914
Pm003-17-211.760.053 610.001 320.036 630.000 430.260 400.007 382323
Pm003-17-221.010.061 430.000 960.107 780.001 320.913 810.019 746608
Pm003-17-231.840.052 740.001 080.043 300.000 560.314 010.007 612733
Pm003-17-240.850.057 570.001 170.039 300.000 480.308 570.007 272493
Pm003-17-251.880.055 470.001 060.065 420.000 750.493 750.011 854095
Pm003-17-261.640.060 120.002 130.040 780.000 610.325 550.013 822584
Pm003-17-271.810.106 960.001 610.194 320.002 343.020 820.085 151 14513
Pm003-17-282.300.066 110.001 140.067 290.000 760.611 530.013 464205
Pm003-17-291.630.052 220.000 860.042 040.000 510.304 110.005 852663
Pm003-17-301.490.051 580.000 910.031 110.000 350.217 290.004 241982
Pm003-17-311.130.056 890.001 100.053 190.000 630.421 120.009 953344
Pm003-17-321.700.084 670.000 920.205 090.002 312.450 060.035 681 20312
Pm003-17-331.740.121 280.001 290.216 200.002 453.622 470.052 401 26213
Pm003-17-341.080.077 950.000 970.055 040.000 620.598 210.008 923454
Pm003-17-351.760.051 690.001 020.032 640.000 420.238 180.005 392073
Pm003-17-360.730.052 430.001 240.046 070.000 650.342 080.009 812904
Pm003-17-371.330.053 090.000 760.049 430.000 560.361 760.006 093113
Pm003-17-381.480.052 290.001 760.056 720.000 830.415 890.017 593565
Pm003-17-394.270.055 650.000 790.042 030.000 470.329 640.005 362653
Pm003-17-401.350.139 840.001 470.383 720.004 117.590 210.115 252 09419
Pm003-17-410.740.059 680.001 420.054 210.000 720.427 870.012 603404
Pm003-17-420.670.066 340.001 560.058 720.000 740.543 770.016 723684
Pm003-17-431.710.055 740.001 290.033 570.000 430.254 810.006 742133
Pm003-17-442.260.052 610.000 750.042 700.000 460.304 530.004 932703
Pm003-17-451.160.059 470.001 200.044 240.000 560.372 480.009 032793
Pm003-17-461.000.051 240.001 840.039 290.000 590.275 780.011 552484
Pm003-17-471.990.072 910.001 100.038 430.000 420.380 200.006 532433
Pm003-17-481.080.122 780.001 710.025 740.000 270.402 040.006 211642
Pm003-17-492.480.053 260.000 730.041 450.000 430.308 030.004 632623
Pm003-17-500.500.061 070.001 000.038 420.000 430.324 960.006 122433
Pm003-17-511.500.053 440.000 960.031 140.000 350.234 280.004 661982
Pm003-17-521.400.056 810.001 040.067 910.000 780.517 930.011 904245
Pm003-17-533.710.063 360.000 790.079 800.000 870.687 520.010 474955
Pm003-17-541.360.050 110.000 890.044 000.000 580.314 810.006 772784
Pm003-17-550.640.051 130.000 930.039 310.000 460.279 570.005 862493
Pm003-17-564.910.070 620.000 970.157 090.001 661.546 850.031 489419
Pm003-17-571.860.052 930.000 640.042 070.000 440.299 620.003 952663
Pm003-17-581.350.054 100.000 980.033 370.000 380.257 820.005 282122
Pm003-17-591.200.053 510.000 720.051 000.000 610.383 980.006 243214
Pm003-17-601.680.053690.000 840.031 440.000 370.233 960.004 142002
Pm003-17-611.900.053 880.000 660.031 360.000 370.225 300.003 191992
Pm003-17-621.380.050 390.000 940.040 940.000 490.289 250.006 282593
Pm003-17-631.310.056 520.001 320.042 740.000 600.337 820.009 462704
Pm003-17-641.850.056 590.000 810.079 690.000 980.626 350.011 664946
Pm003-17-650.790.160 660.001 880.454 540.005 1210.290 590.263 602 41523
Pm003-17-661.900.051 630.001 840.031 760.000 480.221 470.008 882023
Pm003-17-670.850.069 720.001 530.043 210.000 590.434 620.011 742734
Pm003-17-682.360.058 020.000 920.086 770.001 090.696 870.014 855366
Pm003-17-699.250.051 940.000 660.040 920.000 450.287 710.004 092593
Pm003-17-701.250.055 410.000 840.040 910.000 480.310 580.005 482593
Pm003-17-711.110.054 370.000 820.061 870.000 750.464 010.008 713875
Pm003-17-721.880.051 100.000 970.042 450.000 490.303 530.006 782683
Pm003-17-733.090.056 690.000 760.078 950.000 820.621 720.010 044905
Pm003-17-741.940.056 550.001 010.074 680.000 870.589 200.013 554645
Pm003-17-754.350.064 990.000 670.119 090.001 231.040 270.011 707257
Pm003-17-760.860.051 820.002 430.044 930.000 810.344 060.019 432835
Pm003-17-771.920.054 880.000 800.040 840.000 460.308 190.005 152583
Pm003-17-781.500.056 080.001 010.052 760.000 540.421 620.009 113323
Pm003-17-791.590.172 840.001 850.488 080.004 7911.521 470.195 942 56221
Pm003-17-802.120.057 600.000 800.041 440.000 420.328 950.005 082623
图 6 Pm003-17典型锆石阴极发光图像

Fig. 6 A typical cathodoluminescence image of zircon of Pm003-17
图 7 Pm003-17碎屑锆石U-Pb年龄分布频率图

Fig. 7 Distribution frequence of the detrital zircon U-Pb ages of Pm003-17

图 8 Pm003-17碎屑锆石U-Pb年龄谐和图

Fig. 8 Concordan diagrams of the detrital zircon U-Pb ages of Pm003-17

Pm003-24(杨树河子黑色岩段),测定了120个单颗粒锆石,每个锆石1个点。从图 9中可见,所有锆石均显示清晰的振荡生长环带;由表 3可知,Th/U值为0.09~3.13,平均值为0.84,故所测锆石均具岩浆成因特点。其表面年龄明显可划分为7组(图 10图 11):第一组,n=5,(2 267.4±21.6)~(2 506.4±20.9)Ma;第二组,n=3,(1 819.4±16.4)~(1 984.0±19.8)Ma;第三组,n=2,(1 503.8±15.3)~(1 542.3±16.4)Ma;第四组,n=3,(845.8±8.8)~(1 079.4±13.7)Ma;第五组,n=25,(403.1±5.3)~(507.6±7.2)Ma;第六组,n=47,(200.0±2.2)~(356.3±3.8)Ma;第七组,n=35,(131.6±1.3)~(198.5±2.4)Ma。由图 11可见:第五组剔除远离谐和线的样品,表面加权平均年龄为(439.3±7.9)Ma(n=23,MSWD=13);第六组表面加权平均年龄为(255.5±5.8)Ma(n=23,MSWD=14);第七组表面加权平均年龄为(158.7±8.3)Ma(n=34,MSWD=138)。采样点附近花岗斑岩脉发育,样品中可能混有微细脉岩中的锆石。第五组表面加权年龄((439.3±7.9)Ma)可能代表晚奥陶世——早志留世时期残留锆石年龄;第六组表面加权平均年龄((255.5±5.8)Ma)可能代表卢家屯组沉积时限晚于晚二叠世;第七组表面加权平均年龄((158.7±8.3)Ma)可能混有周围晚侏罗世——早白垩世花岗斑岩结晶锆石年龄。

表 3 卢家屯组上段Pm003-24碎屑锆石LA-ICP-MS U-Pb分析结果 Table 3 LA-ICP-MS U-Pb Results of the detrital zircon of Pm003-24 from the upper section of Lujiatun Formation
样品测点Th/
U
同位素比值t/Ma
207Pb/206Pb±1σ206Pb/238U±1σ207Pb/235U±1σ 206Pb/238U±1σ
Pm003-24-10.750.047 150.001 250.024 020.000 340.159 890.004 641532
Pm003-24-20.550.061 430.001 220.031 580.000 420.262 090.005 962003
Pm003-24-30.340.048 620.001 150.031 870.000 450.210 010.005 622023
Pm003-24-40.710.050 670.000 780.025 900.000 290.179 850.003 041652
Pm003-24-50.620.051 890.000 860.031 510.000 350.225 680.004 142002
Pm003-24-60.370.053 340.000 660.031 280.000 380.216 310.003 081992
Pm003-24-70.650.049 940.000 890.028 500.000 380.180 070.003 651812
Pm003-24-80.250.050 970.000 590.031 650.000 330.217 690.002 682012
Pm003-24-91.250.049 850.000 960.029 190.000 360.195 060.004 201862
Pm003-24-100.800.062 970.001 310.022 950.000 310.191 320.004 401462
Pm003-24-110.880.057 250.003 660.021 300.000 490.170 690.011 921363
Pm003-24-120.770.049 700.001 700.021 150.000 310.145 820.005 371352
Pm003-24-131.500.064 460.001 720.021 930.000 320.193 050.005 651402
Pm003-24-140.440.053 650.001 420.043 730.000 630.308 100.009 612764
Pm003-24-150.940.048 660.001 180.024 840.000 330.163 350.004 341582
Pm003-24-160.720.051 070.001 600.042 190.000 630.277 790.010 152664
Pm003-24-170.300.054 100.001 020.071 980.000 930.518 030.012 544486
Pm003-24-181.290.054 120.000 870.073 930.000 910.532 630.010 794605
Pm003-24-190.880.054 970.000 760.074 520.000 850.560 550.009 604635
Pm003-24-201.030.051 620.002 080.042 730.000 690.306 110.014 642704
Pm003-24-210.850.154 480.001 890.360 380.004 197.419 800.200 401 98420
Pm003-24-220.620.058 400.001 120.070 460.000 870.561 870.013 984395
Pm003-24-231.260.086 900.003 540.027 220.000 510.331 250.015 701733
Pm003-24-240.640.060 280.000 820.067 190.000 770.525 210.008 624195
Pm003-24-251.100.082 030.001 730.037 480.000 500.409 030.010 412373
Pm003-24-261.210.049 560.000 910.021 440.000 250.142 570.002 811372
Pm003-24-270.240.054 260.000 680.028 940.000 340.203 620.002 921842
Pm003-24-280.510.163 940.002 140.033 230.000 360.730 940.011 342112
Pm003-24-290.640.077 290.002 970.042 460.000 720.478 920.023 772684
Pm003-24-300.460.063 350.001 760.038 730.000 550.327 510.010 822453
Pm003-24-310.540.056 240.000 920.066 520.000 690.511 230.010 244154
Pm003-24-320.950.058 090.000 900.036 730.000 430.286 280.005 102333
Pm003-24-331.140.051 030.000 830.040 110.000 470.282 610.005 332543
Pm003-24-340.440.116 030.001 270.326 080.003 375.184 970.088 371 81916
Pm003-24-350.720.056 440.000 970.074 350.000 900.579 560.012 854625
Pm003-24-361.130.154 720.001 730.421 540.004 778.967 100.203 162 26722
Pm003-24-370.500.059 270.001 120.069 230.000 810.571 730.013 924325
Pm003-24-380.750.056 360.000 970.039 600.000 440.297 840.005 842503
Pm003-24-390.420.050 270.000 770.032 630.000 360.220 140.003 752072
Pm003-24-403.130.595 370.015 090.331 030.007 5828.705 263.349 821 84337
Pm003-24-412.580.053 330.001 440.022 660.000 300.168 670.004 981442
Pm003-24-420.630.057 780.001 110.069 500.000 800.583 540.014 464335
Pm003-24-430.630.063 110.000 980.043 600.000 500.380 200.006 962753
Pm003-24-440.910.051 630.001 090.041 310.000 500.288 000.007 052613
Pm003-24-450.150.070 610.000 920.167 350.001 861.571 470.029 4199810
Pm003-24-460.760.047 890.000 770.024 030.000 240.159 760.002 671532
Pm003-24-470.390.063 010.001 670.067 300.000 870.575 920.020 584205
Pm003-24-480.860.053 730.002 060.025 540.000 400.194 760.008 271632
Pm003-24-490.990.052 620.000 930.030 180.000 320.215 310.004 141922
Pm003-24-502.170.131 670.002 110.036 030.000 410.662 860.013 142283
Pm003-24-510.640.053 440.001 650.038 660.000 560.274 930.009 852453
Pm003-24-520.640.075 970.001 480.042 670.000 540.435 810.010 282693
Pm003-24-531.110.052 520.001 920.021 160.000 320.147 360.005 801352
Pm003-24-541.170.056 210.002 500.041 160.000 750.288 630.014 982605
Pm003-24-550.820.049 360.001 090.027 240.000 340.187 100.004 571732
Pm003-24-560.800.070 230.001 680.023 650.000 320.220 350.005 831512
Pm003-24-570.830.080 770.002 220.026 830.000 380.290 250.009 101712
Pm003-24-580.930.053 100.001 730.023 170.000 330.172 600.006 151482
Pm003-24-590.590.058 640.001 360.071 970.000 910.557 990.016 834485
Pm003-24-600.740.049 330.001 430.024 630.000 330.176 260.005 641572
Pm003-24-611.110.053 120.001 000.021 910.000 270.151 100.003 101402
Pm003-24-620.720.056 190.001 610.027 840.000 380.221 830.007 131772
Pm003-24-630.570.162 590.001 710.475 210.004 7810.744 710.184 462 50621
Pm003-24-640.700.083 880.002 980.049 880.000 830.546 430.025 583145
Pm003-24-650.750.057 240.000 810.071 170.000 710.557 610.009 464434
Pm003-24-660.920.087 840.002 270.081 930.001 210.980 370.037 595087
Pm003-24-670.830.076 840.002 210.044 390.000 660.493 650.017 952804
Pm003-24-680.880.067 000.002 710.047 160.000 820.435 960.022 142975
Pm003-24-691.050.057 190.001 240.041 730.000 530.328 180.008 422643
Pm003-24-700.860.053 460.000 900.045 080.000 530.329 190.006 452843
Pm003-24-711.190.053 310.002 310.021 580.000 360.150 230.007 021382
Pm003-24-721.450.055 160.002 140.021 190.000 350.162 350.006 831352
Pm003-24-730.850.055 990.000 750.066 900.000 720.515 140.008 174174
Pm003-24-740.850.059 770.001 830.040 320.000 560.332 450.012 172553
Pm003-24-750.860.062 610.002 120.042 830.000 690.372 130.015 292704
Pm003-24-760.830.053 210.002 660.027 650.000 520.192 530.010 651763
Pm003-24-771.250.049 210.000 940.025 770.000 310.177 360.003 731642
Pm003-24-781.060.050 820.000 870.020 620.000 210.145 700.002 591321
Pm003-24-791.300.085 350.001 360.040 110.000 490.463 550.008 952543
Pm003-24-800.770.055 740.001 470.043 000.000 580.309 540.009 582714
Pm003-24-810.930.050 870.002 080.038 660.000 660.274 390.013 052454
Pm003-24-821.010.060 260.001 020.056 830.000 630.471 110.009 693564
Pm003-24-830.990.058 990.003 720.038 900.000 930.282 850.020 762466
Pm003-24-840.690.057 240.000 870.070 810.000 820.544 850.010 404415
Pm003-24-850.990.050 060.001 340.041 740.000 570.290 880.009 182644
Pm003-24-860.930.053 740.000 870.072 110.000 840.522 110.010 634495
Pm003-24-870.860.056 670.000 990.070 050.000 840.552 490.012 334365
Pm003-24-880.710.057 100.001 320.075 620.001 010.564 840.017 254706
Pm003-24-890.490.100 390.001 300.262 730.003 003.503 860.083 951 50415
Pm003-24-900.360.066 930.001 370.182 280.002 511.608 250.058 001 07914
Pm003-24-911.110.054 130.003 110.021 290.000 440.159 840.009 941363
Pm003-24-920.960.162 000.001 720.431 950.004 659.516 720.177 522 31521
Pm003-24-931.060.152 720.001 780.270 100.003 235.244 080.115 771 54116
Pm003-24-940.800.058 440.001 660.031 170.000 440.251 590.008 151983
Pm003-24-950.850.054 170.001 000.030 630.000 340.226 310.004 601952
Pm003-24-960.590.056 000.000 860.069 750.000 800.529 000.010 154355
Pm003-24-971.240.067 900.001 510.055 990.000 750.500 420.014 193515
Pm003-24-980.860.162 020.001 860.421 710.004 839.416 580.235 312 26822
Pm003-24-990.730.066 460.001 650.039 920.000 530.355 920.010 562523
Pm003-24-1000.840.073 140.002 540.046 050.000 770.459 230.020 072905
Pm003-24-1010.780.055 910.001 430.064 520.000 870.505 030.016 664035
Pm003-24-1020.100.070 040.000 860.140 210.001 551.285 870.021 048469
Pm003-24-1030.790.049 370.001 110.041 550.000 520.276 800.007 192633
Pm003-24-1040.720.078 890.003 090.052 970.000 970.576 430.029 923336
Pm003-24-1051.610.049 800.001 190.027 430.000 330.188 900.004 971742
Pm003-24-1060.460.057 040.000 830.074 730.000 810.573 050.010 184655
Pm003-24-1070.770.056 330.001 220.048 470.000 630.365 200.009 563054
Pm003-24-1080.090.068 360.000 940.077 470.000 920.692 440.012 174815
Pm003-24-1090.650.057 410.001 740.047 640.000 690.347 750.012 713004
Pm003-24-1100.700.053 940.001 310.075 550.001 010.537 670.017 114706
Pm003-24-1111.030.057 330.002 780.037 780.000 720.284 770.016 152395
Pm003-24-1120.480.060 780.003 630.039 480.000 890.304 360.021 512506
Pm003-24-1131.250.050 390.001 380.038 110.000 530.270 190.008 592413
Pm003-24-1140.810.053 700.001 460.047 520.000 630.343 400.011 172994
Pm003-24-1150.800.057 340.001 010.071 720.000 830.539 040.011 944475
Pm003-24-1160.660.056 680.001 090.069 270.000 860.523 300.012 894325
Pm003-24-1170.160.100 880.002 050.040 920.000 520.563 600.014 352593
Pm003-24-1180.470.168 130.001 870.473 640.005 3710.387 460.230 082 50023
Pm003-24-1190.690.050 610.001 300.021 700.000 270.150 210.004 161382
Pm003-24-1201.110.064 640.003 890.039 720.000 940.329 140.023 562516
图 9 Pm003-24典型碎屑锆石阴极发光图像

Fig. 9 A typical Cathodoluminescence image of Zircon of Pm003-24
图 10 Pm003-24碎屑锆石U-Pb年龄分布频率图

Fig. 10 Distribution frequence of the detrital zircon U-Pb ages of Pm003-24

图 11 Pm003-24碎屑锆石U-Pb年龄谐和图

Fig. 11 Concordan diagram of the detrital zircon U-Pb ages of Pm003-24

5 讨论

岩石地层的碎屑岩浆成因锆石高精度测年,当其有足够数量样品和测点时,特别是年谱结构,不仅可以确定岩石地层时代属性,而且可用以揭示盆地形成的构造环境,乃至作为反演区域构造演化的有效手段之一[16, 17, 18, 19]。由此,依据本文所提供卢家屯组自下而上3件样品320个测点所作的分析可获得如下有重要地质意义的认识。

卢家屯组建组之时,不同古生物门类的研究者曾对其地层时代有过晚二叠世说提出过不同认识。碎屑岩浆成因锆石所获年谱特征,为早三叠世说提供了有力的科学证明。这为对生物地层定年有争议的岩石地层单位,通过碎屑锆石的裁定提供了范例,亦为长期将Palaeanodonta-Palaeomutela动物群作为晚二叠世陆相地层有效的生物组合标志之一提供了新的解释,即其一些重要分子可以繁衍到早三叠世。

卢家屯组碎屑锆石年谱结构特征,与松嫩地块[20]、张广才岭构造带[21]所总结出的地质演化的年谱结构基本一致。区内卢家屯组系陆相沉积,沉积厚度巨大,达4 316.2 m,这表明自晚二叠世地槽回返以后,地壳的沉降幅度仍然很大。岩性生物特征表明了典型湖相沉积的特点,沉积物质来源较杂,有火山碎屑物质、铁质、钙质、泥质、砂、砾等,虽有沉积韵律,但不十分清晰,有粗细混杂的现象。这暗示了卢家屯组沉积盆地形成的构造背景为松嫩地块东南缘(现代方位)山弧带上所发育的磨拉石盆地。

比较3件测试样品年龄分布频率图,反映沉积盆地的演化、物源区裸露的地质体及其出露面积发生过显著的变化,表明其周边山地出现了快速隆升、快速剥蚀,并快速搬运至盆地形成快速堆积的磨拉石相地层。删除微细脉岩中的锆石,绝大多数年龄集中在晚古生代——早中生代:Pm003-2有86点集中在(179.6~243.8) ~(411.9~542.0)Ma;Pm003-17有59点集中在(201.5~298.2)~(464.3~558.5)Ma;Pm003-24有72点集中在(200.0~356.3)~(403.1~507.6)Ma,占测点总数68%以上。并且所取3件样品均捕获有较老碎屑锆石:Pm003-2有20点集中在(1 738.7~2 579.6)Ma;Pm003-17有3点集中在(2 093.6~2 562.4)Ma;Pm003-24有8点集中在(2 267.4~2 506.4)~(1 819.4~1 984.0) Ma。上述年龄峰值与1 800~2 500 Ma华北基底陆壳形成华北板块的时间吻合。白山镇、夹皮沟地区变质二长花岗岩-钾长花岗岩锆石U-Pb等时线年龄为(2 505±14)Ma[22]、紫苏花岗岩Sm-Nd全岩等时线年龄为(2 440±159)Ma[23]、柳河地区之麻粒岩锆石U-Pb不一致线年龄为(2 511.89±0.75)Ma[24]。可见华北板块北缘活动带与佳木斯——兴凯地块南缘活动带形成时代从晚古生代一直持续到早中生代。由此基本可以判断:古亚洲洋的封闭是通过晚古生代的“幕式”碰撞作用,于早三叠世磨拉石发育完成后,最终闭合,确定认为华北板块北缘与其北侧地块群最终闭合时间应为P3-T1

6 结论

1)卢家屯组三组碎屑岩浆成因锆石数据有力地证明该组的沉积上限为晚二叠世,为早三叠世说提供了年代学证据。

2)当碎屑岩浆成因锆石有足够数量的样品和测点,特别是年谱结构时,不仅可以确定岩石地层时代属性,还可作为反演区域构造演化的有效手段之一。

3) 通过对卢家屯组大量碎屑锆石定年数据分析及区域对比可以认定:华北板块北缘与其北侧地块群最终闭合时间应为P3-T1

参考文献
[1] 李东津.吉林省岩石地层[M].北京:中国地质大学出版社, 1997:21-31. Li Dongjin. Jilin Rock Formations[M].Beijing: China University of Geosciences Press, 1997:21-31.
[2] 彭玉鲸, 齐成栋, 周晓东, 等.吉黑复合造山带古亚洲洋向滨太平洋构造域转换:时间标志与全球构造的联系[J].地质与资源, 2012, 21(3):261-265. Peng Yujing, Qi Chengdong, Zhou Xiaodong, et al. Ransition from Paleo-Asian Ocean Domain to Circum-Pacific Ocean Domain for the Ji-Hei Composite Orogenic Belt: Time Mark and Relationship to Global Tectonics[J].Geology and Resources, 2012, 21(3): 261-265.
[3] 王五力, 郭胜哲.中国东北古亚洲与古太平洋构造域演化与转换[J].地质与资源, 2012, 21(1):27-34. Wang Wuli, Guo Shengzhe. The Evolution and Transformation of Paleo-Asia and Paleo-Pacifictectonic Domain of Northeast China[J].Geology and Resources, 2012, 21(1): 27-34.
[4] 邵济安, 牟保磊, 何国琦, 等.华北北部在古亚洲域与古太平洋域构造叠加过程中的地质作用[J].中国科学:D辑, 1997, 27(5):390-394. Shao Ji'an, Mu Baolei, He Guoqi, et al. Geological Processes of the Process of Structural Overlapping Between Paleo-Asian Domain and Paleo-Pacific Domain in Northern Part of North China[J].Science in China:Series D, 1997, 27(5):390-394.
[5] 孙德有, 吴福元, 张艳斌, 等.西拉木伦河长春延吉板块缝合带的最后闭合时间:来自吉林大玉山花岗岩体的证据[J].吉林大学学报:地球科学版, 2004, 34(2):174-181. Sun Deyou, Wu Fuyuan, Zhang Yanbin, et al. The Final Closing Time of the West Lamulun River-Changchun-Yanji Plate Suture Zone:Evidence from the Dayushan Granitic Pluton, Jilin Province[J].Journal of Jilin University: Earth Science Edition, 2004, 34(2): 174-181.
[6] Miao L C, Fan W M, Liu D Y, et al. Geochronology and Geochemistry of the Hegenshan Ophiolitic Complex: Implications for Late-Stage Tectonic Evolution of the Inner Mongolia-Daxinganling Orogemc Belt, China[J]. Journal of Asian Earth Sciences, 2008, 32:348-370.
[7] 王玉净, 樊志勇.内蒙古西拉木伦河北部蛇绿岩带中二叠纪放射虫的发现及其地质意义[J].古生物学报, 1997, 36(1):58-69. Wang Yujing, Fan Zhiyong. Discovery of Permian Radiolarians in Ophiolite Belt on Northern Side of Xar Moron River, Nei Monggol and Its Geological Significance[J].Acta Palaeontologica Sinica, 1997, 36(1): 58-69.
[8] 陈衍景, 翟明国, 蒋少涌.华北大陆边缘造山过程与成矿研究的重要进展和问题[J].岩石学报, 2009, 25(11):2695-2726. Chen Yanjing, Zhai Mingguo, Jiang Shaoyong. Significant Achievements and Open Issues in Study of Orogenesis and Metallogenesis Surrounding the North China Continent[J].Acta Petrologica Sinica, 2009, 25(11):2695-2726.
[9] 李锦轶, 高立明, 孙桂华, 等.内蒙古东部双井子中三叠世同碰撞壳源花岗岩的确定及其对西伯利亚与中朝古板块碰撞时限的约束[J].岩石学报, 2007, 23(3):565-582. Li Jinyi, Gao Liming, Sun Guihua, et al. Shuangjingzi Middle Triassic Sys-Clooisional Crust-Derived Granite in the East Inner Mongolia and Its Constraint on the Timing of Collision Between Siberian and Sino-Korean Paleo-Plates[J].Acta Petrologica Sinica, 2007, 23(3):565-582.
[10] 张艳斌, 吴福元, 李惠民, 等.吉林黄泥岭花岗岩体的单颗粒锆石U-Pb年龄[J].岩石学报, 2002, 18(4):475-481. Zhang Yanbin, Wu Fuyuan, Li Huimin, et al. Single Grain Zircon U-Pb Ages of the Huangniling Granite in Jilin Province[J].Acta Petrologica Sinica, 2002, 18(4):475-481.
[11] 郗爱华, 任洪茂, 张宝福, 等.吉林中部呼兰群同位素年代学及其地质意义[J].吉林大学学报:地球科学版, 2003, 33(1):15-18. Xi Aihua, Ren Hongmao, Zhang Baofu, et al.Isotopic Chronology of the Hulan Group and Its Geological Significance in the Central Jilin Province[J].Journal of Jilin University: Earth Science Edition, 2003, 33(1):15-18.
[12] Andersen T. Correction of Common Lead in U-Pb Analyses that Do not Report 204Pb[J]. Chemical Geology, 2002, 192(1/2):59-79.
[13] Ludwing K R. Using Isoplot/Ex, Version 2.49: A Geochronological Toolkit for Microsoft Excel[M].Berkeley: Berkeley Geochronological Center Special Publiction, 2001:1-55.
[14] Yuan H L, Gao S, Liu X M, et al. Accurate U-Pb Age and Trace Element Determinations of Zircon by Laser Ablation Inductivey Coupled Plasma Mass Spectrometry[J].Geastandard Newsletter, 2004, 28(3):353-370.
[15] Koschek G. Origin and Significance of the SEM Cathodoluminescence from Zircon[J].Journal of Microscopy, 1993, 171(3):223-232.
[16] Leiss O. Orogenically Controlled Sedimentation in the Lechtaler Kreideschiefer(Lechtal Shale: Cretaceous) and Geodynamics of Inner Western CA(Northern Calearous Alps: Leehatl Alps)[J]. Geological Rundschau, 1992, 81(3):603-634.
[17] 肖庆辉, 李晓波, 贾跃明, 等.当代造山带研究中值得重视的若干前沿问题[J].地学前缘, 1995, 2(1/2):43-50. Xiao Qinghui, Li Xiaobo, Jia Yueming, et al. Frontiers on Orogenic Belt Researches[J].Earth Science Frontiers, 1995, 2(1/2):43-50.
[18] 闫义, 林舸, 李自安.利用锆石形态、成分组成及年龄分析进行沉积物源区示踪的综合研究[J].大地构造与成矿学, 2003, 27(2):184-190. Yan Yi, Lin Ge, Li Zian. Provenance Tracing of Sediments by Means of Synthetic Study of Shape, Composition and Chronology of Zircon[J].Geotectonica et Metallogenia, 2003, 27(2):184-190.
[19] 韩国卿, 刘永江, 温泉波, 等.西拉木伦河缝合带北侧二叠纪砂岩碎屑锆石LA-ICP-MS U-Pb年代学及其构造意义[J].地球科学:中国地质大学学报, 2011, 36(4):687-702. Han Guoqing, Liu Yongjiang, Wen Quanbo, et al. LA-ICP-MS U-Pb Dating of Detrital Zircons from the Permian Sandstones in North Side of Xar Moron River Suture Belt and Its Tectonic Implications[J].Earth Science:Journal of China University of Geosciences, 2011, 36(4):687-702.
[20] 梁爽, 彭玉鲸, 姜正龙.松辽盆地基底"多层结构"的探讨及其构造意义[J].世界地质, 2009, 28(4):430-437. Liang Shuang, Peng Yujing, Jiang Zhenglong. Discussion on "Multi-Laminate Structure" of Basement in Songliao Basin and Its Significance[J].Global Geology, 2009, 28(4):430-437.
[21] 许文良, 王枫, 孟恩, 等.黑龙江省东部古生代早中生代的构造演化:火成岩组合与碎屑锆石U-Pb年代学证据[J].吉林大学学报:地球科学版, 2012, 42(5):1378-1389. Xu Wenliang, Wang Feng, Meng En, et al. Paleozoic-Early Mesozoic Tectonic Evolution in the Eastern Heilongjiang Province, NE China:Evidence from Igneous Rock Association and U-Pb Geochronology of Detrital Zircons[J].Journal of Jilin University: Earth Science Edition, 2012, 42(5):1378-1389.
[22] 李俊建, 沈保丰, 李双保, 等.辽北吉南早前寒武纪大陆壳的地质特征和演化[J].中国区域地质, 1998, 17(1):30-38. Li Junjian, Shen Baofeng, Li Shuangbao, et al. Geological Feature and Evolution of the Early Precambrian Continental Crust in Northern Liaoning Province and Southern Jilin Province[J].Regional Geology of China, 1998, 17(1):30-38.
[23] 吴福元, 葛文春, 孙德有, 等.吉林南部太古代花岗岩Sm-Nd, Rb-Sr同位素年龄测定[J].岩石学报, 1997, 13(4):499-506. Wu Fuyuan, Ge Wenchun, Sun Deyou, et al. The Sm-Nd, Rb-Sr Isotopic Ages of the Archean Granites in Southern Jilin Province[J].Acta Petrologica Sinica, 1997, 13(4):499-506.
[24] 毕守业, 张殿发, 杨豹.吉林省南部太古宙花岗质岩石及其成因探讨[J].吉林地质, 1991(3):12-24. Bi Shouye, Zhang Dianfa, Yang Bao. A Prelininary Study Archaean Granitic Rocks and Its Origin in the Southern Part of Jilin Province[J].Jilin Geology, 1991(3):12-24.
http://dx.doi.org/10.13278/j.cnki.jjuese.201502110
吉林大学主办、教育部主管的以地学为特色的综合性学术期刊
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文章信息

聂立军, 于宏斌, 张建泽, 王聪, 李栋, 李阳
Nie Lijun, Yu Hongbin, Zhang Jianze, Wang Cong, Li Dong, Li Yang
吉林省下三叠统卢家屯组LA-ICP-MS锆石U-Pb定年及其地质意义
Zircons LA-ICP-MS U-Pb Ages of the Lower Triassic Lujiatun Group and Its Geological Significance in Jilin Province
吉林大学学报(地球科学版), 2015, 45(2): 453-470
Journal of Jilin University(Earth Science Edition), 2015, 45(2): 453-470.
http://dx.doi.org/10.13278/j.cnki.jjuese.201502110

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收稿: 2014-06-24

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