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柴北缘西段早石炭世构造—沉积格局——来自下石炭统怀头他拉组稀土元素的证据

施辉 王波 胡俊杰 吴志雄 马立成

施辉, 王波, 胡俊杰, 吴志雄, 马立成. 柴北缘西段早石炭世构造—沉积格局——来自下石炭统怀头他拉组稀土元素的证据[J]. 沉积学报, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040
引用本文: 施辉, 王波, 胡俊杰, 吴志雄, 马立成. 柴北缘西段早石炭世构造—沉积格局——来自下石炭统怀头他拉组稀土元素的证据[J]. 沉积学报, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040
SHI Hui, WANG Bo, HU JunJie, WU ZhiXiong, MA LiCheng. Early Carboniferous Tectono-sedimentary Pattern in the Western North Margin of Qaidam Basin: Evidence from the rare earth elements of the Lower Carboniferous Huaitoutala Formation[J]. Acta Sedimentologica Sinica, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040
Citation: SHI Hui, WANG Bo, HU JunJie, WU ZhiXiong, MA LiCheng. Early Carboniferous Tectono-sedimentary Pattern in the Western North Margin of Qaidam Basin: Evidence from the rare earth elements of the Lower Carboniferous Huaitoutala Formation[J]. Acta Sedimentologica Sinica, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040

柴北缘西段早石炭世构造—沉积格局——来自下石炭统怀头他拉组稀土元素的证据

doi: 10.14027/j.issn.1000-0550.2023.040
基金项目: 

中国地质调查局地质调查项目 DD20230260

中国地质调查局地质调查项目 DD20230313

详细信息

Early Carboniferous Tectono-sedimentary Pattern in the Western North Margin of Qaidam Basin: Evidence from the rare earth elements of the Lower Carboniferous Huaitoutala Formation

Funds: 

The Geological Survey Projects of China Geological Survey DD20230260

The Geological Survey Projects of China Geological Survey DD20230313

  • 摘要: 目的 柴北缘构造带石炭系沉积地层记录了原特提斯洋向古特提斯洋转换历史,但石炭系变质程度高,制约了对区域构造—沉积格局的认知。泥质岩稀土元素化学性质稳定,是重建构造背景、物质来源与沉积环境的有效途径。 方法 采用电感耦合等离子质谱法(ICP-MS)分析小赛什腾山下石炭统怀头他拉组(C1h)泥质岩的稀土元素地化特征。 结果 早石炭世小赛什腾山地区是受南昆仑洋壳向北俯冲弧陆体系影响的弧后盆地,处在柴达木地块及北缘俯冲碰撞带所组成局部高地和宗务隆大陆裂谷之间,呈“南高北低,由陆向海”的整体古地貌格局;东南方向的碰撞带是重要物源区,早期供给花岗岩—碱性玄武岩—沉积岩的风化碎屑,随区域构造活动变弱顶部碳酸盐岩段泥质岩夹层的碎屑可能来源于先存沉积物的再搬运。沉积古水体表现为由浅变深复变浅的趋势,碎屑岩段泥页岩形成于相对缺氧环境,而碳酸盐岩段泥岩夹层则为氧化环境,发育“台地边缘浅滩—台地前斜坡—陆棚边缘—台地前斜坡—台地边缘生物礁”的相序。 结论 以上研究结果及认识为理解区域性古地理格局和原特提斯洋—古特提斯洋时空演化及能源矿产效应提供了依据。
  • 图  1  柴达木及邻区构造分区图(据文献[2,16]修改)

    Figure  1.  Simplified tectonic map of Qaidam and the adjacent region showing tectonic divisions (modified from references [2,16])

    图  2  小赛什腾山地区地质图及下石炭统剖面位置图(花岗岩侵入体锆石测年数据来源于文献[2224])

    Figure  2.  Geologic map of the Xiaosaishenteng Shan and the location of the Lower Carboniferous section (Zircon dating data of granite intrusions are obtained from references [22⁃24])

    图  3  小赛什腾山C1h综合岩性柱状图及泥质岩样品分布

    Figure  3.  Comprehensive stratigraphic column showing the C1h lithology and distribution of argillaceous rock samples, Xiaosaishenteng Shan outcrop

    图  4  小赛什腾山C1h岩石样品镜下照片

    (a) metamorphic coarse medium⁃grained feldspar lithic complex sandstone with phyllotic structure, XSST⁃50; (b) silky argillaceous slate, XSST⁃41; (c) sericeous phyllite as the protolith in silty mudstone, XSST⁃26; (d) marbled limestone showed in Fig.3k

    Figure  4.  Photomicrographs showing the C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

    Fig.4

    图  5  小赛什腾山C1h泥质岩样品REE分布型式

    (a) chondrite standardization; (b) NASC standardization

    Figure  5.  REE patterns from C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

    Fig.5

    图  6  小赛什腾山C1h泥质岩REE地化剖面

    Figure  6.  REE geochemical profile of C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

    图  7  小赛什腾山C1h构造—沉积模式图

    (a) carbonate sedimentary period; (b) clastic sedimentary period

    Figure  7.  Schematic diagram showing the C1h tectonic setting and paleogeography, Xiaosaishenteng Shan outcrop

    Fig.7

    图  8  小赛什腾山C1h泥质岩样品∑REE⁃La/Yb图解

    Figure  8.  ∑REE⁃La/Yb diagram of C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

    图  9  柴北缘下石炭统怀头他拉组岩性与沉积相对比

    Figure  9.  Lithology and depositional correlation of C1h in north Qaidam

    表  1  小赛什腾山C1h泥页岩稀土元素测试结果(μg/g)

    Table  1.   REE data from C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop (μg/g)

    样品编号位置/m岩性LaCePrNdSmEuGdTbDyHoErTmYbLu
    XSST-16.21泥岩24.10049.3006.73025.5004.6501.2503.9800.6213.2100.6041.8100.2621.9200.282
    XSST-254.67灰质泥岩39.30073.9009.18032.8005.5701.1405.3900.8605.1500.9282.9000.4713.3200.454
    XSST-395.25灰质泥岩38.50072.1008.86033.8006.0601.2005.6700.9405.1600.9422.9700.4363.2300.480
    XSST-4229.81粉砂质泥岩15.00014.8002.92010.5001.8900.3701.9700.3071.7800.3221.0300.1370.9780.112
    XSST-5252.47粉砂质泥岩14.00011.9002.5309.3601.5500.3661.6300.2701.6200.3551.0200.1490.9320.126
    XSST-6300.34页岩17.30032.8004.05014.4002.7200.5642.5400.4282.4900.4371.4400.2141.6800.227
    XSST-7308.74页岩20.40037.4004.54016.8002.9300.4182.4700.4602.5000.4961.5200.2281.6700.217
    XSST-8316.72泥岩20.50032.5004.50016.5003.1800.6763.0600.5072.9600.5441.7400.2421.7700.244
    XSST-9324.70页岩14.80024.4003.27012.8002.3700.6852.4600.4762.7100.5281.5100.2291.6000.210
    XSST-10344.04泥岩46.30083.90010.30036.4006.8201.0805.8100.9244.8000.7632.4500.3402.6200.335
    XSST-11360.95页岩39.60075.4008.62032.3005.5401.0405.0100.8104.2500.7842.5400.3792.8100.373
    XSST-12378.00页岩41.20075.2009.35034.6006.5001.2605.7501.0205.4801.0003.1500.4753.3000.447
    XSST-13388.33粉砂质页岩44.60080.90010.60036.7006.8101.2805.8900.9565.2800.9633.1000.4513.2800.446
    XSST-14407.00粉砂质页岩30.80056.0006.98025.7004.6000.9774.2400.6993.7800.6721.9700.3102.2600.323
    XSST-15438.00碳质页岩38.20072.0009.39032.7006.4601.1805.9200.9915.3500.9303.2000.4753.6000.479
    XSST-16450.00页岩42.90083.30010.40036.2006.7401.2606.4901.0106.2501.0103.3700.4883.9100.497
    XSST-17463.50泥岩41.20087.8009.39032.6006.6201.2205.6800.9675.0900.8962.8600.4273.3400.453
    XSST-18474.12碳质页岩40.90072.4009.02032.2005.8401.2205.5701.0205.8300.9483.1800.4553.6100.491
    XSST-19503.32页岩40.80077.8009.18033.1006.7301.1906.2201.0706.1001.0303.3700.4993.7900.504
    XSST-20530.33页岩37.20074.1008.83033.3006.0101.1805.6000.9935.5000.9723.1900.4883.3400.491
    XSST-21544.20页岩43.70080.80010.10038.2006.3901.3506.2201.1205.4800.9573.0600.4803.6900.488
    XSST-22561.40页岩39.20074.8009.03033.8005.9501.2205.5500.9335.2700.9152.9500.4233.1600.440
    XSST-23582.48页岩33.50068.6008.46030.3006.2601.1705.3500.9065.0300.8592.7700.3803.0200.405
    XSST-24593.02粉砂质泥岩36.20064.7008.11030.1005.2100.9604.8700.7554.2900.7092.3200.3672.3800.338
    XSST-25606.04页岩37.50069.0008.25028.3005.4200.9644.7300.7704.6800.7792.6200.4413.0000.415
    XSST-26628.64粉砂质泥岩26.50050.0006.18023.8004.0100.8393.9700.6663.3800.6191.9600.3082.0200.305
    XSST-27645.72页岩32.40059.8007.73029.1005.5201.0704.9600.9044.9700.9152.7100.4503.2800.389
    XSST-28659.16粉砂质泥岩33.00063.5007.61027.8005.3901.0504.4500.7454.0600.7042.2800.3482.4800.355
    XSST-29673.49页岩37.10072.8008.94032.2005.9501.1705.2300.8554.9100.8182.7700.4472.8700.404
    XSST-30699.22页岩34.70068.8008.14031.5006.2601.1305.3100.8944.8000.8862.7900.4263.0700.427
    XSST-31728.86页岩31.60058.2007.32028.5005.9101.0404.8100.8894.8700.8602.6600.3953.0900.416
    XSST-32754.00页岩29.60058.5007.12027.9006.3800.9745.2001.0205.6000.9052.7500.4503.0000.445
    XSST-33781.59页岩42.60077.7009.46035.4006.1401.0205.4700.8434.5500.9062.4300.3652.7800.399
    XSST-34806.84碳质页岩35.00065.6008.17030.7006.0201.0305.3200.9574.9300.8552.7000.4262.9400.427
    XSST-35845.52碳质页岩29.00050.7006.85025.1004.9800.8524.4300.8074.3700.8482.9100.4323.1000.452
    XSST-36871.34页岩25.20043.9005.66021.3004.5400.8214.1100.7024.4200.8092.5600.3992.7900.389
    XSST-37896.97页岩31.60061.0008.02029.3006.9400.9745.7300.9625.1300.8292.6800.3852.6400.384
    XSST-38928.48粉砂质页岩29.80055.9007.03024.8005.4101.0104.3200.7303.9400.6872.2500.3402.5000.351
    XSST-39966.76页岩31.40056.0007.14023.4004.7901.0104.2200.7213.8800.6762.1400.3382.2600.335
    XSST-40986.89粉砂质页岩29.40052.3006.59025.7004.9901.0704.6300.7954.1400.7172.2100.3332.4700.331
    XSST-411 022.00页岩30.30058.5007.15027.8005.8701.0504.8600.8704.5400.7692.4300.3472.4600.354
    XSST-421 057.72页岩27.10052.8006.75023.3004.6801.0204.0800.7294.1200.7052.4100.3812.4900.383
    XSST-431 073.97粉砂质泥岩27.30048.0005.92022.2004.4100.8623.8600.6863.3600.6691.8900.2961.9800.298
    XSST-441 104.56粉砂质泥岩35.40071.6008.59032.6005.7401.0805.7500.8584.8600.8492.8300.4413.0300.417
    XSST-451 126.40粉砂质泥岩33.40062.3007.38026.7004.9500.8464.1000.6513.5300.5791.9000.2912.0700.290
    XSST-461 157.46页岩35.00067.7008.47032.1005.9701.0805.3301.0005.2300.9853.0300.4933.4500.503
    XSST-471 173.48页岩43.70083.60010.40040.0007.6001.3506.2801.0705.6201.0503.3000.4763.4300.503
    XSST-481 223.56页岩35.80073.0008.28032.3005.6801.2904.9900.8914.8400.9252.8300.4532.8300.431
    XSST-491 235.63泥岩35.70064.0007.90030.0005.3401.0804.8400.8364.7000.8872.7800.4303.1300.455
    XSST-501 252.22泥岩36.20068.6008.60030.4005.5401.0205.1100.8505.0100.8682.8800.4673.2400.432
    最小值14.00011.9002.5309.3601.5500.3661.6300.2701.6200.3221.0200.1370.9320.112
    最大值46.30087.80010.60040.0007.6001.3506.4901.1206.2501.0503.3700.4993.9100.504
    平均值33.13061.8127.68028.2575.3571.0194.7890.8154.4760.7932.5220.3832.7520.383
    球粒陨石0.3670.9570.1370.7110.2310.0870.3060.0580.3810.0850.2490.0360.2480.038
    UCC30.00064.0007.10026.0004.5000.8803.8000.6403.5000.8002.3000.3302.2000.320
    NASC32.00070.0007.90031.0005.7001.2405.2100.8505.5401.0403.4000.5003.1000.480
    PAAS38.20079.6008.83033.9005.5501.0804.6600.7744.6800.9912.8500.4052.8200.433
    下载: 导出CSV

    表  2  小赛什腾山C1h泥页岩稀土元素地球化学参数表

    Table  2.   REE geochemical parameters of C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

    样品编号∑REELREEHREELREE/HREELaN/YbNLaN/SmNGdN/YbNδEuδCeCeanom
    (μg/g)无量纲
    XSST-1124.219111.53012.6898.7908.4823.2621.6800.8880.907-0.042
    XSST-2181.363161.89019.4738.3147.9994.4411.3160.6360.912-0.045
    XSST-3180.348160.52019.8288.0968.0553.9991.4230.6260.915-0.054
    XSST-452.11645.4806.6366.85410.3644.9951.6330.5860.524-0.304
    XSST-545.80839.7066.1026.50710.1515.6851.4170.7040.468-0.363
    XSST-681.29071.8349.4567.5976.9594.0031.2250.6560.918-0.041
    XSST-792.04982.4889.5618.6288.2554.3821.1990.4750.911-0.054
    XSST-888.92377.85611.0677.0357.8264.0581.4010.6620.793-0.115
    XSST-968.04858.3259.7235.9996.2513.9311.2460.8670.822-0.107
    XSST-10202.842184.80018.04210.24311.9424.2731.7970.5240.900-0.054
    XSST-11179.456162.50016.9569.5849.5234.4991.4450.6030.956-0.037
    XSST-12188.732168.11020.6228.1528.4373.9901.4120.6300.898-0.059
    XSST-13201.256180.89020.3668.8829.1894.1221.4550.6180.872-0.059
    XSST-14139.311125.05714.2548.7739.2094.2141.5210.6760.895-0.060
    XSST-15180.875159.93020.9457.6367.1703.7221.3330.5830.891-0.047
    XSST-16203.825180.80023.0257.8527.4144.0061.3450.5820.924-0.033
    XSST-17198.543178.83019.7139.0728.3363.9171.3780.6081.0460.016
    XSST-18182.684161.58021.1047.6567.6564.4081.2500.6540.883-0.064
    XSST-19191.383168.80022.5837.4757.2753.8161.3300.5620.942-0.035
    XSST-20181.194160.62020.5747.8077.5263.8961.3590.6220.958-0.030
    XSST-21202.035180.54021.4958.3998.0034.3051.3660.6540.901-0.059
    XSST-22183.641164.00019.6418.3508.3834.1471.4230.6490.932-0.043
    XSST-23167.010148.29018.7207.9217.4963.3681.4360.6180.955-0.019
    XSST-24161.309145.28016.0299.06410.2784.3731.6580.5820.885-0.067
    XSST-25166.869149.43417.4358.5718.4474.3551.2780.5820.919-0.042
    XSST-26124.557111.32913.2288.4168.8654.1601.5930.6430.915-0.054
    XSST-27154.198135.62018.5787.3006.6753.6941.2260.6250.885-0.063
    XSST-28153.772138.35015.4228.9718.9923.8541.4540.6550.939-0.036
    XSST-29176.464158.16018.3048.6418.7353.9251.4770.6410.937-0.032
    XSST-30169.133150.53018.6038.0927.6383.4891.4020.5990.959-0.033
    XSST-31150.560132.57017.9907.3696.9113.3651.2620.5960.897-0.065
    XSST-32149.844130.47419.3706.7366.6672.9201.4050.5170.944-0.040
    XSST-33190.063172.32017.7439.71210.3554.3671.5950.5380.907-0.058
    XSST-34165.075146.52018.5557.8978.0453.6591.4670.5560.909-0.053
    XSST-35134.831117.48217.3496.7726.3223.6651.1580.5540.843-0.082
    XSST-36117.600101.42116.1796.2696.1043.4941.1940.5810.861-0.080
    XSST-37156.574137.83418.7407.3558.0892.8661.7590.4720.898-0.048
    XSST-38139.068123.95015.1188.1998.0553.4671.4000.6380.905-0.046
    XSST-39138.310123.74014.5708.4939.3894.1261.5130.6870.876-0.054
    XSST-40135.676120.05015.6267.6838.0433.7081.5190.6800.880-0.075
    XSST-41147.300130.67016.6307.8578.3233.2491.6010.6010.931-0.047
    XSST-42130.948115.65015.2987.5607.3553.6451.3280.7130.915-0.034
    XSST-43121.731108.69213.0398.3369.3173.8961.5800.6380.885-0.071
    XSST-44174.045155.01019.0358.1437.8953.8821.5380.5740.962-0.027
    XSST-45148.987135.57613.41110.10910.9034.2471.6050.5740.930-0.043
    XSST-46170.341150.32020.0217.5086.8553.6901.2520.5850.921-0.046
    XSST-47208.379186.65021.7298.5908.6093.6191.4840.5970.919-0.050
    XSST-48174.540156.35018.1908.5958.5483.9671.4290.7400.993-0.020
    XSST-49162.078144.02018.0587.9757.7074.2081.2530.6490.893-0.067
    XSST-50169.217150.36018.8577.9747.5504.1131.2780.5860.911-0.043
    最小值45.80839.7066.1025.9996.1042.8661.1580.4720.468-0.363
    最大值208.379186.65023.02510.24311.9425.6851.7970.8881.0460.016
    平均值154.168137.25516.9148.0768.2513.9491.4220.6220.895-0.062
    球粒陨石3.8912.4901.4011.7781.0001.0001.0001.0001.000-0.049
    UCC146.370132.48013.8909.5389.2154.1961.4000.6501.0270.005
    NASC167.960147.84020.1207.3486.9753.5341.3620.6951.0320
    PAAS184.773167.16017.6139.4919.1544.3321.3390.6491.016-0.009
    下载: 导出CSV

    表  3  不同构造背景沉积物REE特征

    Table  3.   Geochemical parameters of REEs in sediments from different tectonic backgrounds

    构造背景La/(μg/g)Ce/(μg/g)∑REE/(μg/g)La/Yb(La/Yb)N∑LREE/∑HREEδEu
    大洋岛弧8±1.719±3.758±104.2±1.32.8±0.93.8±0.91.04±0.11
    大陆岛弧27±4.559±8.2146±2011.0±3.67.5±2.57.7±1.70.79±0.13
    活动大陆边缘377818612.58.59.10.60
    被动大陆边缘398521015.910.88.50.56
    研究区C1h336215412.28.38.10.62
    下载: 导出CSV
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    [18] 王伟涛.  黑龙江省绥滨坳陷下白垩统碎屑岩源区分析及其构造意义 . 沉积学报, 2007, 25(2): 201-206.
    [19] 李 萍.  冲绳海槽现代沉积物磁学性质分布特征与环境的关系 . 沉积学报, 2007, 25(5): 753-758.
    [20] 陶晓风, 刘登忠, 朱利东.  陆相盆地沉积作用与构造作用的关系 . 沉积学报, 2001, 19(3): 410-414.
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  • 收稿日期:  2022-09-30
  • 修回日期:  2023-05-18
  • 录用日期:  2023-06-07
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  • 刊出日期:  2025-04-10

目录

    柴北缘西段早石炭世构造—沉积格局——来自下石炭统怀头他拉组稀土元素的证据

    doi: 10.14027/j.issn.1000-0550.2023.040
      基金项目:

      中国地质调查局地质调查项目 DD20230260

      中国地质调查局地质调查项目 DD20230313

      作者简介:

      施辉,男,1983年出生,副研究员,石油地质学,E-mail: shui@mail.cgs.gov.cn

      通讯作者: 胡俊杰,男,副研究员,E-mail: howimet@foxmail.com

    摘要: 目的 柴北缘构造带石炭系沉积地层记录了原特提斯洋向古特提斯洋转换历史,但石炭系变质程度高,制约了对区域构造—沉积格局的认知。泥质岩稀土元素化学性质稳定,是重建构造背景、物质来源与沉积环境的有效途径。 方法 采用电感耦合等离子质谱法(ICP-MS)分析小赛什腾山下石炭统怀头他拉组(C1h)泥质岩的稀土元素地化特征。 结果 早石炭世小赛什腾山地区是受南昆仑洋壳向北俯冲弧陆体系影响的弧后盆地,处在柴达木地块及北缘俯冲碰撞带所组成局部高地和宗务隆大陆裂谷之间,呈“南高北低,由陆向海”的整体古地貌格局;东南方向的碰撞带是重要物源区,早期供给花岗岩—碱性玄武岩—沉积岩的风化碎屑,随区域构造活动变弱顶部碳酸盐岩段泥质岩夹层的碎屑可能来源于先存沉积物的再搬运。沉积古水体表现为由浅变深复变浅的趋势,碎屑岩段泥页岩形成于相对缺氧环境,而碳酸盐岩段泥岩夹层则为氧化环境,发育“台地边缘浅滩—台地前斜坡—陆棚边缘—台地前斜坡—台地边缘生物礁”的相序。 结论 以上研究结果及认识为理解区域性古地理格局和原特提斯洋—古特提斯洋时空演化及能源矿产效应提供了依据。

    English Abstract

    施辉, 王波, 胡俊杰, 吴志雄, 马立成. 柴北缘西段早石炭世构造—沉积格局——来自下石炭统怀头他拉组稀土元素的证据[J]. 沉积学报, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040
    引用本文: 施辉, 王波, 胡俊杰, 吴志雄, 马立成. 柴北缘西段早石炭世构造—沉积格局——来自下石炭统怀头他拉组稀土元素的证据[J]. 沉积学报, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040
    SHI Hui, WANG Bo, HU JunJie, WU ZhiXiong, MA LiCheng. Early Carboniferous Tectono-sedimentary Pattern in the Western North Margin of Qaidam Basin: Evidence from the rare earth elements of the Lower Carboniferous Huaitoutala Formation[J]. Acta Sedimentologica Sinica, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040
    Citation: SHI Hui, WANG Bo, HU JunJie, WU ZhiXiong, MA LiCheng. Early Carboniferous Tectono-sedimentary Pattern in the Western North Margin of Qaidam Basin: Evidence from the rare earth elements of the Lower Carboniferous Huaitoutala Formation[J]. Acta Sedimentologica Sinica, 2025, 43(2): 408-422. doi: 10.14027/j.issn.1000-0550.2023.040
      • 早古生代的原特提斯洋应与古亚洲洋相连,处在低纬度处的秦祁昆(秦岭—祁连—昆仑)洋可能是古亚洲洋—原特提斯洋的分支或次生洋盆,这些次生洋盆自志留纪末期开始陆续关闭,一直持续至晚古生代泥盆纪末[1]。古特提斯洋是古亚洲洋在晚古生代的发展和继承,泛华夏陆块群,包括塔里木、柴达木、祁连、阿拉善、华北、北秦岭等地块组成了古特提斯洋的北岸陆缘[2]。柴达木盆地北缘(柴北缘)构造带,作为祁连与柴达木地块之间的结合部,经历了早古生代时期柴北缘洋壳发育(540~500 Ma,Є1~2)、洋壳俯冲消亡(约460~445 Ma,O2~3)、大陆深俯冲碰撞超高压变质(约445~420 Ma,S)和碰撞后隆升造山(约420~360 Ma,D)的原特提斯洋演化历史[35],以及晚古生代时期宗务隆构造带陆内裂谷(D3~C1)、有限洋盆(C2~P1)、洋壳俯冲(P2~3)和陆—陆碰撞造山(T1~2)的古特提斯洋开合过程[68]。柴北缘构造带广泛发育石炭系沉积地层[9],而石炭纪又是原特提斯洋向古特提斯洋转换的重要时间窗口,可能存在柴北缘洋壳俯冲消减与宗务隆地幔柱共同作用的情况[1],研究柴北缘构造带石炭系的沉积纪录并重建祁连—柴达木地区晚古生代古地理格局成为深入认识原特提斯洋—古特提斯洋的时空演化关系的关键环节之一。

        近些年,针对柴北缘石炭系沉积地层的研究聚焦在北缘东段地区,确定其处在大陆边缘构造背景,北缘俯冲碰撞带(超高压变质带)向南供给陆源碎屑物质,宗务隆裂陷海槽的枕状玄武岩发生蚀变向北提供溶解硅,总体呈现“南山—北海”的盆山格局[1011]。然而,北缘西段地区石炭系出露情况较东部差,且沉积层遭受变质作用的破坏程度较高,导致对石炭纪沉积物的构造背景、物质来源、沉积环境等方面认识相对薄弱,制约了对柴北缘区域晚古生代构造—沉积演化和能源矿产响应的理解。泥质岩(泥岩、页岩或泥质粉砂岩等)中稀土元素(Rare Earth Element, REE)含量在沉积岩中最高,而REE是最不易溶解且化学性质非常稳定的微量元素,受变质、风化和热液蚀变等地质作用的影响较小,故REE分析广泛用于泥质岩沉积环境、构造背景、物质来源及成矿条件的判识研究[1214]。本文选取柴北缘西段小赛什腾山野外露头下石炭统怀头他拉组剖面,通过泥质岩REE地球化学特征探讨了北缘西段早石炭世的构造、物源与环境条件,为反演区域性古地理格局提供依据。

      • 柴北缘处于祁连地块与柴达木地块的拼合部位,是一个时间跨度大、物质组成多样的多单元复合构造带[15],由南向北依次划分为柴北缘俯冲碰撞带、欧龙布鲁克地块、宗务隆构造带和赛什腾构造带共4个次级构造单元(图1)。柴北缘俯冲碰撞带(超高压变质杂岩带)是祁连地块与柴达木地块在加里东期形成的造山带[16],自西向东沿鱼卡、绿梁山、锡铁山和都兰一线分布,与北祁连加里东期缝合带(北祁连俯冲增生带)呈大致平行关系。欧龙布鲁克地块(又称全吉地块)是具有古元古代变质结晶基底和新元古代以来沉积盖层的类克拉通性质大陆残片[17]。宗务隆构造带是在早—中三叠世祁连和欧龙布鲁克地块发生碰撞造山而形成的延伸约300 km的韧性剪切带[8]。赛什腾构造带主体由小赛什腾山、赛什腾山和绿梁山所构成,又被称为达肯大坂弧后盆地[1820],是目前古生代构造演化研究程度偏低的构造单元,本次研究的小赛什腾山地区属于该构造单元(图1)。

        图  1  柴达木及邻区构造分区图(据文献[2,16]修改)

        Figure 1.  Simplified tectonic map of Qaidam and the adjacent region showing tectonic divisions (modified from references [2,16])

        柴北缘西段小赛什腾山位于青海省海西州冷湖镇东北约20 km,向西和向东方向分别紧邻阿尔金山和赛什腾山,呈近东西向展布(图1)。山体自西向东出露二叠系(P)、下石炭统怀头他拉组(C1h)和元古界达肯大坂群(Pt1D)等地层[2024]图2)。山体东部出露的Pt1D从下至上可分成Pt1D1和Pt1D2共两个岩性段,Pt1D1以灰黑色黑云斜长变粒岩为主,夹灰白色浅粒岩、黑云斜长片岩、二云片岩、石英岩等,Pt1D2底部出现大理岩薄层以区别于Pt1D1,主体岩性为绿灰—浅灰色浅粒岩、含石榴矽线二长浅粒岩夹灰黑色黑云斜长变粒岩、灰白色大理岩等[20]

        图  2  小赛什腾山地区地质图及下石炭统剖面位置图(花岗岩侵入体锆石测年数据来源于文献[2224])

        Figure 2.  Geologic map of the Xiaosaishenteng Shan and the location of the Lower Carboniferous section (Zircon dating data of granite intrusions are obtained from references [22⁃24])

        小赛什腾山中部出露C1h厚度大于1 200 m,可划分为碎屑岩和碳酸盐岩两个岩性段(图3),与北缘东段地区C1h的“两段式”岩性组合相类似[21]。C1h下部(未见底)主要是一套肉红色或灰色细砾岩(粗砂岩)—灰色泥质粉砂岩—深灰或黑色页岩的韵律层;中部为灰—灰黑色(粉砂质)页岩与灰色—深灰色(泥质)粉砂—细砂岩互层,总体上呈“泥包砂”的岩性组合特征;上部以碳酸盐岩(大理岩化)为主要特征,岩性包括生物碎屑(颗粒)灰岩、泥晶灰岩、大理岩夹薄层(粉砂质/硅质)页岩或粉—细砂岩。C1h碎屑岩发生千枚岩化和板岩化的浅变质作用(图4a~c),碳酸盐岩亦经历一定程度大理岩化(图4d),可能与中—晚二叠世花岗岩侵入事件有关[2224]图2)。

        图  3  小赛什腾山C1h综合岩性柱状图及泥质岩样品分布

        Figure 3.  Comprehensive stratigraphic column showing the C1h lithology and distribution of argillaceous rock samples, Xiaosaishenteng Shan outcrop

        图  4  小赛什腾山C1h岩石样品镜下照片

        Figure 4.  Photomicrographs showing the C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

        根据前人地质调查研究[25],该套地层产Schuchertella sp.(舒克贝)、Cancrinella? sp.(蟹形贝)、Dictyoclostus? sp.(网格长身贝)、Rhipidomell sp.、Spirifer sp.和Dibunophyllum cf. Yui chi等化石,均为早石炭世常见分子,尤其是Dibunophyllum cf. Yui chi为怀头他拉组(C1h)的重要分子,可与国际年代地层的密西西比亚系维宪阶(346.7~330.9 Ma)相对比[26]

        山体西部以二叠系为主,由一套中—基性火山岩、火山碎屑岩和碎屑岩所组成,下部灰绿色安山质火山角砾岩、安山质凝灰岩夹安山岩,中部灰绿色、灰黑色安山岩,局部夹玄武岩,上部为暗紫色玄武岩、安山岩夹少量碎屑岩[23]。该套地层因遭受强烈的构造破坏且缺少有效生物化石,时代归属问题一直存在争议。20世纪50年代,柴达木石油地质普查大队曾在塞什腾山西段海合沟发现珊瑚化石,据西北区域地层表命名为志留系赛什腾群(Sss);20世纪70年代青海第一区调队在海合沟中采到较多珊瑚及腕足类,将该套地层划归至上奥陶统滩间山群(O3t[25]。中国地质科学院地质研究所曾在此地层中发现Belowea crassitesta Won、Astroentactinia multispinosa、Entactino⁃spharapalimbola等放射虫属种,经鉴定属于晚泥盆世晚期—早石炭世早期[27]。河北省区域地质矿产调查研究所发布了争议地层中玄武安山岩的锆石LA- ICP-MS(U-Pb)测年结果(256±0.7 Ma),据此判断其为晚二叠世岛弧型火山岩[20,23]。本文采纳了河北省区域地质矿产调查研究所的地层划分方案,认为C1h之上发育上二叠统的碎屑岩—火山(碎屑)岩系。

        岩浆岩年代学数据显示,小赛什腾山地区显生宙以来存在至少两期花岗岩侵入活动[20,2224],早古生代(测年数据为490~400 Ma)花岗岩侵入体反映了柴北缘洋壳俯冲(O1,约480~470 Ma)、造山陆—陆碰撞(O3,450~440 Ma)和俯冲—碰撞晚期岩石圈拆沉(D3,400~390 Ma)的大地构造演化过程,晚古生代(P2,270~260 Ma)侵入活动代表宗务隆小洋盆向西可能延伸至小赛什腾山地区,在中二叠世发生洋壳俯冲,进入晚古生代—中生代的构造演化阶段。研究区在早石炭世处于持续拉伸的古特提斯演化阶段,形成陆相—浅海相沉积物,而从晚石炭世—早二叠世起,随着古特提斯洋的关闭构造应力由拉张变为收缩,逐步进入陆内俯冲阶段,发生深部幔源物质上侵导致的中下地壳物质重熔[15,28]

      • 本文稀土元素研究基于小赛什腾山剖面共计50块泥质岩样品,其中47块来源于C1h,其余3块来自二叠系底部,样品分布位置见图3。泥质岩主要包括泥岩、页岩、粉砂(灰)质(泥)页岩及厚层碳酸盐岩(或大理岩)中的夹层(页)泥岩。REE测试均在核工业北京地质研究院分析测试中心完成,采用电感耦合等离子质谱法(ICP-MS)检测REE含量(单位为μg/g),实验过程执行国家标准[29]

        为消除稀土元素的奇偶效应[30],本文主要利用球粒陨石[31]和北美页岩(North American Shale Composite,NASC)[32]标准样品REE丰度数据对岩石样品数据进行标准化处理,即样品的REE丰度除以球粒陨石相应REE丰度数据(下标为N),或除以北美页岩相应REE丰度数据(下标为n),同时采用后太古代澳大利亚页岩(post-Archean Australian Shale,PAAS)[33]和上部地壳(Upper Continental Crust,UCC)[34]的REE数据提高可对比性。REE分布型式采用Masuda-Coryell图解的构建方式,即利用球粒陨石或NASC的REE含量进行标准化处理以消除偶数规则的影响[35]

        其次,稀土元素总量∑REE=La+Ce+Pr+Nd+Sm+Eu+Gd+Tb+Dy+Ho+Er+Tm+Yb+Lu,轻稀土元素含量∑LREE=La+Ce+Pr+Nd+Sm+Eu,重稀土元素含量∑HREE=Gd+Tb+Dy+Ho+Er+Tm+Yb+Lu,∑LREE/∑HREE为轻稀土含量与重稀土含量之比,Eu和Ce异常值计算公式分别为δEu=EuN/SmN×GdNδCe=CeN/LaN×PrN,铈异常指数的计算公式为Ceanom=lg(3CeN/(2LaN+NdN)

      • 根据小赛什腾山C1h泥质岩稀土元素含量统计结果(表1),REE总量(∑REE)介于45.808~208.379 μg/g(平均为154.168 μg/g),略低于NASC的∑REE值(167.960 μg/g)[32];轻稀土元素(LREE)总量介于39.706~186.650 μg/g(平均为137.255 μg/g)、重稀土元素(HREE)总量介于6.102~23.025 μg/g(平均为16.914 μg/g),∑LREE/∑HREE比值介于5.999~10.243(平均为8.076),稍高于NASC的相对应比值(7.348),反应小赛什腾山C1h泥质岩总体上LREE相对富集、HREE相对亏损。

        表 1  小赛什腾山C1h泥页岩稀土元素测试结果(μg/g)

        Table 1.  REE data from C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop (μg/g)

        样品编号位置/m岩性LaCePrNdSmEuGdTbDyHoErTmYbLu
        XSST-16.21泥岩24.10049.3006.73025.5004.6501.2503.9800.6213.2100.6041.8100.2621.9200.282
        XSST-254.67灰质泥岩39.30073.9009.18032.8005.5701.1405.3900.8605.1500.9282.9000.4713.3200.454
        XSST-395.25灰质泥岩38.50072.1008.86033.8006.0601.2005.6700.9405.1600.9422.9700.4363.2300.480
        XSST-4229.81粉砂质泥岩15.00014.8002.92010.5001.8900.3701.9700.3071.7800.3221.0300.1370.9780.112
        XSST-5252.47粉砂质泥岩14.00011.9002.5309.3601.5500.3661.6300.2701.6200.3551.0200.1490.9320.126
        XSST-6300.34页岩17.30032.8004.05014.4002.7200.5642.5400.4282.4900.4371.4400.2141.6800.227
        XSST-7308.74页岩20.40037.4004.54016.8002.9300.4182.4700.4602.5000.4961.5200.2281.6700.217
        XSST-8316.72泥岩20.50032.5004.50016.5003.1800.6763.0600.5072.9600.5441.7400.2421.7700.244
        XSST-9324.70页岩14.80024.4003.27012.8002.3700.6852.4600.4762.7100.5281.5100.2291.6000.210
        XSST-10344.04泥岩46.30083.90010.30036.4006.8201.0805.8100.9244.8000.7632.4500.3402.6200.335
        XSST-11360.95页岩39.60075.4008.62032.3005.5401.0405.0100.8104.2500.7842.5400.3792.8100.373
        XSST-12378.00页岩41.20075.2009.35034.6006.5001.2605.7501.0205.4801.0003.1500.4753.3000.447
        XSST-13388.33粉砂质页岩44.60080.90010.60036.7006.8101.2805.8900.9565.2800.9633.1000.4513.2800.446
        XSST-14407.00粉砂质页岩30.80056.0006.98025.7004.6000.9774.2400.6993.7800.6721.9700.3102.2600.323
        XSST-15438.00碳质页岩38.20072.0009.39032.7006.4601.1805.9200.9915.3500.9303.2000.4753.6000.479
        XSST-16450.00页岩42.90083.30010.40036.2006.7401.2606.4901.0106.2501.0103.3700.4883.9100.497
        XSST-17463.50泥岩41.20087.8009.39032.6006.6201.2205.6800.9675.0900.8962.8600.4273.3400.453
        XSST-18474.12碳质页岩40.90072.4009.02032.2005.8401.2205.5701.0205.8300.9483.1800.4553.6100.491
        XSST-19503.32页岩40.80077.8009.18033.1006.7301.1906.2201.0706.1001.0303.3700.4993.7900.504
        XSST-20530.33页岩37.20074.1008.83033.3006.0101.1805.6000.9935.5000.9723.1900.4883.3400.491
        XSST-21544.20页岩43.70080.80010.10038.2006.3901.3506.2201.1205.4800.9573.0600.4803.6900.488
        XSST-22561.40页岩39.20074.8009.03033.8005.9501.2205.5500.9335.2700.9152.9500.4233.1600.440
        XSST-23582.48页岩33.50068.6008.46030.3006.2601.1705.3500.9065.0300.8592.7700.3803.0200.405
        XSST-24593.02粉砂质泥岩36.20064.7008.11030.1005.2100.9604.8700.7554.2900.7092.3200.3672.3800.338
        XSST-25606.04页岩37.50069.0008.25028.3005.4200.9644.7300.7704.6800.7792.6200.4413.0000.415
        XSST-26628.64粉砂质泥岩26.50050.0006.18023.8004.0100.8393.9700.6663.3800.6191.9600.3082.0200.305
        XSST-27645.72页岩32.40059.8007.73029.1005.5201.0704.9600.9044.9700.9152.7100.4503.2800.389
        XSST-28659.16粉砂质泥岩33.00063.5007.61027.8005.3901.0504.4500.7454.0600.7042.2800.3482.4800.355
        XSST-29673.49页岩37.10072.8008.94032.2005.9501.1705.2300.8554.9100.8182.7700.4472.8700.404
        XSST-30699.22页岩34.70068.8008.14031.5006.2601.1305.3100.8944.8000.8862.7900.4263.0700.427
        XSST-31728.86页岩31.60058.2007.32028.5005.9101.0404.8100.8894.8700.8602.6600.3953.0900.416
        XSST-32754.00页岩29.60058.5007.12027.9006.3800.9745.2001.0205.6000.9052.7500.4503.0000.445
        XSST-33781.59页岩42.60077.7009.46035.4006.1401.0205.4700.8434.5500.9062.4300.3652.7800.399
        XSST-34806.84碳质页岩35.00065.6008.17030.7006.0201.0305.3200.9574.9300.8552.7000.4262.9400.427
        XSST-35845.52碳质页岩29.00050.7006.85025.1004.9800.8524.4300.8074.3700.8482.9100.4323.1000.452
        XSST-36871.34页岩25.20043.9005.66021.3004.5400.8214.1100.7024.4200.8092.5600.3992.7900.389
        XSST-37896.97页岩31.60061.0008.02029.3006.9400.9745.7300.9625.1300.8292.6800.3852.6400.384
        XSST-38928.48粉砂质页岩29.80055.9007.03024.8005.4101.0104.3200.7303.9400.6872.2500.3402.5000.351
        XSST-39966.76页岩31.40056.0007.14023.4004.7901.0104.2200.7213.8800.6762.1400.3382.2600.335
        XSST-40986.89粉砂质页岩29.40052.3006.59025.7004.9901.0704.6300.7954.1400.7172.2100.3332.4700.331
        XSST-411 022.00页岩30.30058.5007.15027.8005.8701.0504.8600.8704.5400.7692.4300.3472.4600.354
        XSST-421 057.72页岩27.10052.8006.75023.3004.6801.0204.0800.7294.1200.7052.4100.3812.4900.383
        XSST-431 073.97粉砂质泥岩27.30048.0005.92022.2004.4100.8623.8600.6863.3600.6691.8900.2961.9800.298
        XSST-441 104.56粉砂质泥岩35.40071.6008.59032.6005.7401.0805.7500.8584.8600.8492.8300.4413.0300.417
        XSST-451 126.40粉砂质泥岩33.40062.3007.38026.7004.9500.8464.1000.6513.5300.5791.9000.2912.0700.290
        XSST-461 157.46页岩35.00067.7008.47032.1005.9701.0805.3301.0005.2300.9853.0300.4933.4500.503
        XSST-471 173.48页岩43.70083.60010.40040.0007.6001.3506.2801.0705.6201.0503.3000.4763.4300.503
        XSST-481 223.56页岩35.80073.0008.28032.3005.6801.2904.9900.8914.8400.9252.8300.4532.8300.431
        XSST-491 235.63泥岩35.70064.0007.90030.0005.3401.0804.8400.8364.7000.8872.7800.4303.1300.455
        XSST-501 252.22泥岩36.20068.6008.60030.4005.5401.0205.1100.8505.0100.8682.8800.4673.2400.432
        最小值14.00011.9002.5309.3601.5500.3661.6300.2701.6200.3221.0200.1370.9320.112
        最大值46.30087.80010.60040.0007.6001.3506.4901.1206.2501.0503.3700.4993.9100.504
        平均值33.13061.8127.68028.2575.3571.0194.7890.8154.4760.7932.5220.3832.7520.383
        球粒陨石0.3670.9570.1370.7110.2310.0870.3060.0580.3810.0850.2490.0360.2480.038
        UCC30.00064.0007.10026.0004.5000.8803.8000.6403.5000.8002.3000.3302.2000.320
        NASC32.00070.0007.90031.0005.7001.2405.2100.8505.5401.0403.4000.5003.1000.480
        PAAS38.20079.6008.83033.9005.5501.0804.6600.7744.6800.9912.8500.4052.8200.433

        反映轻、重REE的分异程度的LaN/YbN、LaN/SmN和GdN/YbN值分别介于6.104~11.942(平均为8.251)、2.866~5.685(平均为3.949)和1.158~1.797(平均为1.422)(表2),说明泥质岩样品整体表现出轻REE分异程度高于重REE的特点。

        表 2  小赛什腾山C1h泥页岩稀土元素地球化学参数表

        Table 2.  REE geochemical parameters of C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

        样品编号∑REELREEHREELREE/HREELaN/YbNLaN/SmNGdN/YbNδEuδCeCeanom
        (μg/g)无量纲
        XSST-1124.219111.53012.6898.7908.4823.2621.6800.8880.907-0.042
        XSST-2181.363161.89019.4738.3147.9994.4411.3160.6360.912-0.045
        XSST-3180.348160.52019.8288.0968.0553.9991.4230.6260.915-0.054
        XSST-452.11645.4806.6366.85410.3644.9951.6330.5860.524-0.304
        XSST-545.80839.7066.1026.50710.1515.6851.4170.7040.468-0.363
        XSST-681.29071.8349.4567.5976.9594.0031.2250.6560.918-0.041
        XSST-792.04982.4889.5618.6288.2554.3821.1990.4750.911-0.054
        XSST-888.92377.85611.0677.0357.8264.0581.4010.6620.793-0.115
        XSST-968.04858.3259.7235.9996.2513.9311.2460.8670.822-0.107
        XSST-10202.842184.80018.04210.24311.9424.2731.7970.5240.900-0.054
        XSST-11179.456162.50016.9569.5849.5234.4991.4450.6030.956-0.037
        XSST-12188.732168.11020.6228.1528.4373.9901.4120.6300.898-0.059
        XSST-13201.256180.89020.3668.8829.1894.1221.4550.6180.872-0.059
        XSST-14139.311125.05714.2548.7739.2094.2141.5210.6760.895-0.060
        XSST-15180.875159.93020.9457.6367.1703.7221.3330.5830.891-0.047
        XSST-16203.825180.80023.0257.8527.4144.0061.3450.5820.924-0.033
        XSST-17198.543178.83019.7139.0728.3363.9171.3780.6081.0460.016
        XSST-18182.684161.58021.1047.6567.6564.4081.2500.6540.883-0.064
        XSST-19191.383168.80022.5837.4757.2753.8161.3300.5620.942-0.035
        XSST-20181.194160.62020.5747.8077.5263.8961.3590.6220.958-0.030
        XSST-21202.035180.54021.4958.3998.0034.3051.3660.6540.901-0.059
        XSST-22183.641164.00019.6418.3508.3834.1471.4230.6490.932-0.043
        XSST-23167.010148.29018.7207.9217.4963.3681.4360.6180.955-0.019
        XSST-24161.309145.28016.0299.06410.2784.3731.6580.5820.885-0.067
        XSST-25166.869149.43417.4358.5718.4474.3551.2780.5820.919-0.042
        XSST-26124.557111.32913.2288.4168.8654.1601.5930.6430.915-0.054
        XSST-27154.198135.62018.5787.3006.6753.6941.2260.6250.885-0.063
        XSST-28153.772138.35015.4228.9718.9923.8541.4540.6550.939-0.036
        XSST-29176.464158.16018.3048.6418.7353.9251.4770.6410.937-0.032
        XSST-30169.133150.53018.6038.0927.6383.4891.4020.5990.959-0.033
        XSST-31150.560132.57017.9907.3696.9113.3651.2620.5960.897-0.065
        XSST-32149.844130.47419.3706.7366.6672.9201.4050.5170.944-0.040
        XSST-33190.063172.32017.7439.71210.3554.3671.5950.5380.907-0.058
        XSST-34165.075146.52018.5557.8978.0453.6591.4670.5560.909-0.053
        XSST-35134.831117.48217.3496.7726.3223.6651.1580.5540.843-0.082
        XSST-36117.600101.42116.1796.2696.1043.4941.1940.5810.861-0.080
        XSST-37156.574137.83418.7407.3558.0892.8661.7590.4720.898-0.048
        XSST-38139.068123.95015.1188.1998.0553.4671.4000.6380.905-0.046
        XSST-39138.310123.74014.5708.4939.3894.1261.5130.6870.876-0.054
        XSST-40135.676120.05015.6267.6838.0433.7081.5190.6800.880-0.075
        XSST-41147.300130.67016.6307.8578.3233.2491.6010.6010.931-0.047
        XSST-42130.948115.65015.2987.5607.3553.6451.3280.7130.915-0.034
        XSST-43121.731108.69213.0398.3369.3173.8961.5800.6380.885-0.071
        XSST-44174.045155.01019.0358.1437.8953.8821.5380.5740.962-0.027
        XSST-45148.987135.57613.41110.10910.9034.2471.6050.5740.930-0.043
        XSST-46170.341150.32020.0217.5086.8553.6901.2520.5850.921-0.046
        XSST-47208.379186.65021.7298.5908.6093.6191.4840.5970.919-0.050
        XSST-48174.540156.35018.1908.5958.5483.9671.4290.7400.993-0.020
        XSST-49162.078144.02018.0587.9757.7074.2081.2530.6490.893-0.067
        XSST-50169.217150.36018.8577.9747.5504.1131.2780.5860.911-0.043
        最小值45.80839.7066.1025.9996.1042.8661.1580.4720.468-0.363
        最大值208.379186.65023.02510.24311.9425.6851.7970.8881.0460.016
        平均值154.168137.25516.9148.0768.2513.9491.4220.6220.895-0.062
        球粒陨石3.8912.4901.4011.7781.0001.0001.0001.0001.000-0.049
        UCC146.370132.48013.8909.5389.2154.1961.4000.6501.0270.005
        NASC167.960147.84020.1207.3486.9753.5341.3620.6951.0320
        PAAS184.773167.16017.6139.4919.1544.3321.3390.6491.016-0.009

        δEu和δCe是指示稀土元素Eu和Ce异常程度的重要参数。小赛什腾山C1h泥质岩δEu和δCe值介于0.472~0.888(平均为0.622)和0.468~1046(平均为0.895)(表2)。以“δEu或δCe值大于1.05为正异常,小于0.95为负异常”的判别标准[36],研究层段泥质岩的Eu和Ce均为负异常。相比较而言,样品δEu均值与UCC(0.650)、NASC(0.695)和PAAS(0.649)的对应值相当,而δCe值相对小于UCC(1.027)、NASC(1.032)和PAAS(1.016)的δCe值(表2),显示C1h泥质岩Eu为中等负异常、Ce则为弱负异常。Ceanom值介于-0.363~0.016,平均值约为-0.062,小于UCC(0.005)和PAAS(-0.009)的Ceanom值(表2)。

      • 小赛什腾山C1h泥质岩样品球粒陨石标准化REE分布型式曲线主要表现出明显的向右倾斜和Eu负异常特征,是典型Eu亏损—轻稀土富集型分布曲

        线(图5a)。LaN/YbN是REE经过球粒陨石标准化后图解中分布曲线的斜率,反映了曲线的倾斜程度,该值大于1时反映REE分布曲线为右倾分布,富集轻稀土元素,若小于1时则为左倾分布,富集重稀土元素[30]。小赛什腾山C1h泥质岩样品LaN/YbN值介于6.104~11.942(平均为8.251),代表REE分布曲线右倾程度相对较高,轻稀土元素相对富集。

        图  5  小赛什腾山C1h泥质岩样品REE分布型式

        Figure 5.  REE patterns from C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

        泥质岩样品经NASC标准化后的REE分布型式曲线整体近于平缓且无明显峰、谷异常(图5b),说明C1h泥质岩相对NASC并无明显分异。两种标准化REE分布曲线都展现出两种REE配分结构端元的类型,一种以Ce正常型曲线为代表,占泥质岩样品的多数且∑REE值较大,如球粒陨石(图5a)和NASC标准化(图5b)REE分布曲线稠密区;另一种类型所占比例较小,呈现显著Ce负异常,∑REE值较低,如球粒陨石(图5a)和NASC标准化(图5b)REE分布曲线范围底部区域。

      • 垂向上,REE地化参数根据碎屑岩段和碳酸盐岩段的岩性变化呈两段式变化(图6)。碳酸盐岩段中泥质岩夹层与碎屑岩段泥质岩相比,两者的∑LREE/∑HREE、LaN/YbN、GdN /YbNδEu值大致相当,但前者的∑REE、∑LREE、∑HREE、δCe和Ceanom值整体显著低于后者,LaN/SmN值略高于碎屑岩段泥质岩,表明两个岩性段内泥质岩稀土元素分馏条件与方式有所差异。

        图  6  小赛什腾山C1h泥质岩REE地化剖面

        Figure 6.  REE geochemical profile of C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

      • 小赛什腾山地区C1h沉积期总体处于活动大陆边缘的大地构造背景。不同构造背景形成的沉积物呈现不同的REE特征值和分布型式,Bhatia[37]总结了大洋岛弧、大陆岛弧、活动大陆边缘和被动大陆边缘共4种大地构造背景沉积物REE组成结构(图5表3)。通过与大洋岛弧、大陆岛弧、主动大陆边缘和被动大陆边缘REE(平均值)分布型式的对比,小赛什腾山地区C1h泥质岩样品REE分布型式与活动大陆边缘构造背景沉积物的分布型式相似度较高(图5)。

        表 3  不同构造背景沉积物REE特征

        Table 3.  Geochemical parameters of REEs in sediments from different tectonic backgrounds

        构造背景La/(μg/g)Ce/(μg/g)∑REE/(μg/g)La/Yb(La/Yb)N∑LREE/∑HREEδEu
        大洋岛弧8±1.719±3.758±104.2±1.32.8±0.93.8±0.91.04±0.11
        大陆岛弧27±4.559±8.2146±2011.0±3.67.5±2.57.7±1.70.79±0.13
        活动大陆边缘377818612.58.59.10.60
        被动大陆边缘398521015.910.88.50.56
        研究区C1h336215412.28.38.10.62

        早石炭世C1h沉积期,小赛什腾山的柴北缘西段地区与北缘东段同处在南昆仑洋壳向北俯冲的构造动力环境中[38],可能是受东昆仑—柴达木弧陆体系影响的弧后盆地。随着古特提斯洋的开启,裂陷作用起始于D1~2的宗务隆构造带在早石炭世已然形成大陆裂谷,并且向西延伸影响至北缘西段小赛什腾山以北地区[22]。由此可见,柴北缘西段小赛什腾山地区在早石炭世的构造背景为活动大陆边缘,处在柴达木地块及北缘俯冲碰撞带所组成局部高地和宗务隆大陆裂谷延伸区之间,呈“南高北低,由陆向海”的整体古地貌格局(图7)。

        图  7  小赛什腾山C1h构造—沉积模式图

        Figure 7.  Schematic diagram showing the C1h tectonic setting and paleogeography, Xiaosaishenteng Shan outcrop

      • REE在海水和河水等沉积物载体中的含量极低,因此泥质岩的REE含量主要受控于物源区岩石成分[39]。小赛什腾山C1h碳酸盐岩段中泥质岩夹层REE总含量(包括∑REE、∑LREE和∑HREE)明显低于碎屑岩段泥质岩(图7),说明两个岩性段碎屑物质来源可能有所不同。∑LREE/∑HREE值在一定程度上反映了REE的分异程度,该值越大表明重稀土越亏损;LaN/YbN是稀土元素球粒陨石标准化图解中分布曲线的斜率;GdN /YbN反映重稀土元素之间的分馏程度,比值越小说明重稀土富集程度越高[30]。以上3个REE组成结构参数值在碎屑岩段和碳酸盐岩段均无明显差别,仅反映轻稀土元素之间分馏程度的LaN/SmN值在碳酸盐岩段表现出增大的趋势,说明两个岩性段内泥质岩轻、重REE含量结构大致类似,均呈轻稀土富集型配分型式,碳酸盐岩泥质岩夹层中轻稀土组分分馏程度相对偏高。

        利用反映沉积物物源区母岩特征和∑REE-La/Yb图解[13]发现(图8),C1h泥质岩样品与UCC、NASC和PAAS一样处在∑REE-La/Yb图解中位于沉积岩、花岗岩和碱性玄武岩的混合区域,但∑REE值相对偏低的几块样品完全落在沉积岩区域,说明碳酸盐岩段内泥质岩(∑REE值相对偏低)的碎屑来源于相对单一的沉积岩母岩(偏向钙质泥岩),而碎屑岩段内泥质岩样品(∑REE值相对偏大)则混合了花岗岩、碱性玄武岩和少量沉积岩母岩。

        图  8  小赛什腾山C1h泥质岩样品∑REE⁃La/Yb图解

        Figure 8.  ∑REE⁃La/Yb diagram of C1h argillaceous rock samples, Xiaosaishenteng Shan outcrop

        沉积岩REE中Eu异常能较灵敏地反映物源区信息[30]。碎屑岩Eu负异常主要与物源区母岩性质和化学风化程度有关,太古代以后的沉积岩均出现不同程度的Eu负异常,一方面是继承了上地壳(中—酸性火成岩为主)母岩的Eu负异常,另一方面则是因为化学风化作用通常也能优先移除Eu而造成留下的沉积物贫Eu2+[36]。小赛什腾山C1h泥质岩样品的Eu和Ce均表现为负异常,两个岩性段Eu负异常程度基本一致,表明C1h泥质岩样品仍主要来自上地壳物质,且经历过一定程度的化学风化学作用。

        早石炭世,研究区以南的东昆仑弧与研究区间隔柴达木地块及柴北缘俯冲碰撞带,北部北祁连俯冲增生带离研究区较远,两者对小赛什腾山地区的影响较弱(图7);宗务隆构造带陆—陆碰撞造山活动起始于T1,据此推测研究区东南方向柴北缘俯冲碰撞带西延造山带为重要物源供给区。柴北缘俯冲碰撞带及其西延与柴达木地块接触地带在C1h沉积早期处在碰撞隆升造山活动后的剥蚀期,超高压变质带以花岗质片麻岩、副片麻岩、蛇绿混杂岩、变质沉积岩为主要岩性组合[1,3,6,1516],经强烈风化削蚀作用向北部负地形小赛什腾山及周边地区供给陆源碎屑物质(图7b)。C1h碳酸盐岩段沉积期,柴北缘俯冲碰撞带进入一个构造活动相对沉寂时期,风化削蚀作用强度也随之减弱,向北供给的陆源碎屑物质大幅减少,基本未波及小赛什腾山附近(图7a);研究区在该时期处在相对“清水”的环境,以灰岩夹薄泥层的沉积物为典型特征,泥质岩夹层的碎屑物质主要来源于先存沉积物的再搬运。

      • 沉积岩中REE具有从泥质岩、砂岩到碳酸盐岩,∑REE逐渐降低的趋势,碳酸盐岩常出现Ce亏损和相对富集重稀土的特征,这主要因为海水对稀土元素的抽提作用所致[14,40]。陆源碎屑物质供给速率和沉积速率降低的情况下,沉积物碎屑组分比例降低、悬浮组分增大,在相对“清水”环境中与海水发生充分的交换反应,沉积物稀土总量会随之降低且出现Ce负异常[4142]。小赛什腾山C1h碳酸盐岩段内泥质岩样品δCe和Ceanom值显著低于碎屑岩段泥质岩,且伴随∑REE、∑LREE和∑HREE的减小,与物源供给强度变弱和海水抽提作用增强这两个因素有着密不可分的联系。

        REE的Ce异常是研究古海水氧化还原条件的常用指标[43]。Ce具有Ce3+和Ce4+两种价态,海水中Ce3+常被氧化成Ce4+,而Ce4+的络合能力较低,容易被Fe、Mn氢氧化物所吸附从海水中析出而形成Ce亏损(负异常)[44]。小赛什腾山C1h碳酸盐岩段泥质岩样品的δCe和Ceanom值低于碎屑岩段泥质岩样品,固然与物源供给强度变弱和海水抽提作用增强有关,也反映碳酸盐岩沉积的古水体介质氧化性增强。Ceanom值小于-0.10为Ce亏损,大于-0.1为Ce富集,分别指示了氧化条件和缺氧条件[43,45]。C1h碳酸盐岩段泥质岩Ceanom值约为-0.30,指示氧化条件,而碎屑岩段泥质Ceanom值均大于-0.10,指示缺氧条件(表2图7)。C1h从碎屑岩段泥质岩至碳酸盐岩段泥质岩,总体表现为沉积古水深变浅的趋势,从缺氧环境过渡至弱氧化的水介质条件。

        小赛什腾山C1h岩性组合和沉积构造显示(图3),底部肉红色细砂岩—粗砂岩发育交错层理和斜层理,反映水动力条件偏强的氧化环境;向上岩性逐渐变细,以平行和水平层理构造为主,颜色也从灰黄色过渡至深灰—黑色,表现为沉积古水体变深。毗邻碳酸盐岩段的碎屑岩开始出现植物碎片和含砾粗砂岩,且灰岩层段可见较丰富的生物碎屑,说明从深灰—黑色泥页段向碳酸盐岩段呈现出沉积水体复变浅的趋势。结合REE和岩性组合变化特征,认为C1h自下而上应为水体变深复变浅的演化序列(图9),深灰—黑色泥页岩段的沉积水体最深且缺氧程度最高(海泛面,FS),是柴北缘下石炭统优质烃源岩发育的潜在层段。

        图  9  柴北缘下石炭统怀头他拉组岩性与沉积相对比

        Figure 9.  Lithology and depositional correlation of C1h in north Qaidam

      • 柴北缘东段地区QDD1井和旺尕秀露头C1h岩性组合从下往上依次是砂泥互层(局部煤线)、泥晶灰岩(含燧石条带)和生物碎屑灰岩[19,25],与北缘西段小赛什腾山地区C1h的砂泥韵律层、页岩段(夹粉砂岩)和碳酸盐岩段的“两段式”岩性变化特征基本可对比(图9)。

        首先,柴北缘自西向东地层厚度减薄现象表明西段小赛什腾山地区在C1h时期更靠近沉积中心,古水深整体大于东段。其次,QDD1井—旺尕秀一带C1h的生物碎屑灰岩和泥晶灰岩较发育,而小赛什腾山细粒沉积物比碳酸盐岩丰富,推测前者邻近台地相带,而后者偏向于台地前斜坡—浅海陆棚相带。根据前人对柴北缘东段晚古生代沉积相研究结果[21],C1h自下而上呈现出“扇三角洲—台地边缘—开阔台地”的相变关系;结合REE和岩相组合的变化特征,判断柴北缘西段小赛什腾山地区C1h为“浅海陆棚—台地边缘”沉积体系,自下而上依次发育“台地边缘浅滩—台地前斜坡—陆棚边缘—台地前斜坡—台地边缘生物礁”的相序(图9)。

      • (1) 小赛什腾山C1h泥质岩REE总量介于45.808~208.379 μg/g,平均值约为154.168 μg/g,轻REE富集且分异程度高于重REE,Eu为中等程度负异常、Ce则为弱负异常;C1h自下而上划分为碎屑岩和碳酸盐岩两个岩性段,前者泥质岩样品的∑REE值较大、Ce负异常弱,后者∑REE值相对偏小、呈现较明显Ce负异常。

        (2) 小赛什腾山C1h泥质岩REE与主动大陆边缘构造背景沉积物相似度较高,推测其所在的柴北缘西段地区在早石炭世C1h沉积期受南昆仑洋壳向北俯冲的影响,处在柴达木地块及北缘俯冲碰撞带西延造山带所组成局部高地和宗务隆大陆裂谷延伸区之间,呈“南高北低,由陆向海”的整体古地貌格局。

        (3) 小赛什腾山C1h沉积物主要来源于上地壳的风化产物,研究区东南方向的柴北缘俯冲碰撞带西延造山带是重要的物源区,C1h碎屑岩段泥质岩的物源区母岩是花岗岩、碱性玄武岩和少量沉积岩的岩性组合,顶部碳酸盐岩段内泥质岩夹层则来源于相对单一的沉积岩母岩,两个岩性段泥质岩物质来源的变化与俯冲碰撞带造山活动由强变弱有关。

        (4) 研究区C1h沉积古水体为变深复变浅的演化趋势,碎屑岩段泥页岩形成于相对缺氧环境,碳酸盐岩段泥岩夹层则为氧化环境;C1h自下而上依次发育“台地边缘浅滩—台地前斜坡—陆棚边缘—台地前斜坡—台地边缘生物礁”的相序,中部深灰—黑色泥页岩段是下石炭统优质烃源岩发育的潜在层段。

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