0 引言
1 地质背景
图2 四川盆地北部须家河组剖面的野外照片(a)广元剖面须家河组厚层砂岩;(b)广元须家河组底部石英砂岩与碎屑砂岩界面;(c)旺苍剖面须家河组下部泥岩粉砂岩互层;(d)旺苍剖面须家河组具楔状交错层理的透镜状砂岩;(e)南江剖面须家河组巨厚砾岩;(f)南江剖面须家河组厚层砂岩,顶部侵蚀面之上充填了撕裂屑砾石;(g)土黄剖面须家河组厚层块状砂岩与下伏雷口坡组白云岩的分界;(h)土黄剖面须家河组厚层砂岩与砾岩夹层 Fig.2 Outcrop photographs from the sections of the Xujiahe Formation located along the northern Sichuan Basin |
2 砂岩薄片成分特征
2.1 砂岩薄片成分统计方法
图3 须家河组砂岩偏光显微镜下薄片照片(a)、(b)为石英岩屑砂岩,岩屑为定向排列的多晶石英碎片、千枚岩和片岩、火山岩岩屑和燧石;(c)、(d)为岩屑石英砂岩,含定向排列的多晶石英碎片、千枚岩和火山岩,可见白云母;(e)、(f)为岩屑石英砂岩,主要为定向排列的多晶石英碎片以及火成岩岩屑。注:Qm:石英;Qpt:定向排列的多晶石英;Chert:燧石;Lvm:微晶火山岩;Lvv:隐晶质火山岩;Sch:片岩;Phyll:千枚岩;Musc:白云母 Fig.3 Photographs of sandstone thin-sections of the Xujiahe Formation under polarizing microscope |
表1 砂岩薄片统计的矿物岩屑类型Table 1 Grain types recorded for the point-counting of sandstone thin-sections |
| 颗粒类型 | 代号 | 描述特征 | |
|---|---|---|---|
| 矿物 | Qm | 单晶石英 | |
| K | 钾长石 | ||
| P | 斜长石 | ||
| 岩屑 | 沉积岩 | Chert | 燧石 |
| Mud/Shale | 泥岩/页岩 | ||
| Silt | 粉砂岩 | ||
| Lc | 碳酸盐岩 | ||
| 变质岩 | Phyll | 千枚岩 | |
| Sch | 片岩 | ||
| Qpt | 定向排列的多晶石英 | ||
| 火成岩 | Qp | 没有定向排列特征的多晶石英 | |
| Lvl | 含长条状矿物的(基性)火山岩 | ||
| Lvm | 含微晶的(中性)火山岩 | ||
| Lvf | 酸性火山岩 | ||
| Lvv | 隐晶质火山岩 | ||
| 三角图参数 | Qm | 单晶石英 | |
| F | 总长石=K+P | ||
| Lt | 岩屑总量=Lv+Lm+Ls | ||
| Qt | 石英和石英质岩屑总量=Qm+Qp+Qpt+Chert | ||
| F | 总长石=K+P | ||
| L | 非石英质岩屑总量=Lv+Phy+Sch+Mud/shale+Silt+Lc | ||
| Lv | 火山岩岩屑总量=Lvl+Lvm+Lvf+Lvv | ||
| Lm | 变质岩岩屑总量=Qpt+Phy+Sch | ||
| Ls | 沉积岩岩屑总量=Chert+Mud/Shale+Silt+Lc | ||
表2 砂岩薄片碎屑颗粒统计结果(颗粒类型缩写含义见表1)Table 2 Results of sandstone thin-section point-counting(calculation of fragment types is shown in Table 1) |
| 样品 编号 | Qm/% | F/% | Lt/% | Qt/% | F/% | L/% | Lm/% | Lv/% | Ls/% |
|---|---|---|---|---|---|---|---|---|---|
| GY5 | 48 | 1 | 50 | 72 | 1 | 26 | 68 | 27 | 6 |
| GY7 | 52 | 8 | 39 | 76 | 8 | 16 | 57 | 18 | 25 |
| GY9 | 69 | 8 | 23 | 85 | 8 | 7 | 49 | 25 | 26 |
| GY11 | 59 | 14 | 28 | 73 | 14 | 13 | 56 | 23 | 21 |
| GY13 | 52 | 20 | 28 | 70 | 20 | 11 | 60 | 15 | 25 |
| GY20 | 58 | 13 | 29 | 76 | 13 | 11 | 57 | 16 | 27 |
| GY22 | 64 | 8 | 28 | 80 | 8 | 13 | 40 | 30 | 30 |
| GY23 | 63 | 14 | 23 | 76 | 14 | 10 | 51 | 31 | 18 |
| GY25 | 49 | 8 | 43 | 73 | 8 | 20 | 65 | 21 | 14 |
| 平均值 | 57 | 6 | 36 | 76 | 6 | 19 | 56 | 17 | 26 |
| WC2 | 56 | 12 | 31 | 71 | 12 | 17 | 56 | 28 | 16 |
| WC3 | 56 | 11 | 33 | 70 | 11 | 19 | 51 | 33 | 17 |
| WC4 | 66 | 7 | 27 | 79 | 7 | 15 | 45 | 26 | 29 |
| WC5 | 69 | 7 | 24 | 80 | 7 | 13 | 50 | 26 | 24 |
| WC6 | 63 | 9 | 28 | 78 | 9 | 14 | 53 | 29 | 18 |
| WC7 | 74 | 6 | 20 | 86 | 6 | 8 | 55 | 15 | 31 |
| 平均值 | 64 | 9 | 27 | 77 | 9 | 14 | 52 | 26 | 22 |
| NJ1 | 64 | 0 | 36 | 74 | 0 | 25 | 59 | 20 | 21 |
| NJ3 | 57 | 2 | 41 | 74 | 2 | 24 | 47 | 33 | 19 |
| NJ4 | 64 | 3 | 33 | 75 | 3 | 22 | 61 | 22 | 17 |
| NJ5 | 57 | 6 | 36 | 70 | 6 | 24 | 59 | 24 | 17 |
| NJ6 | 53 | 11 | 36 | 65 | 11 | 24 | 72 | 9 | 20 |
| NJ7 | 53 | 11 | 36 | 82 | 11 | 7 | 48 | 8 | 45 |
| NJ8 | 56 | 11 | 33 | 80 | 11 | 9 | 47 | 11 | 42 |
| NJ9 | 57 | 6 | 37 | 80 | 6 | 14 | 66 | 14 | 20 |
| NJ10 | 81 | 0 | 19 | 97 | 0 | 3 | 53 | 17 | 29 |
| NJ12 | 46 | 5 | 49 | 62 | 5 | 33 | 51 | 16 | 33 |
| 平均值 | 59 | 6 | 36 | 76 | 6 | 19 | 56 | 17 | 26 |
| TH2 | 71 | 15 | 15 | 80 | 15 | 5 | 22 | 18 | 60 |
| TH5 | 69 | 18 | 13 | 75 | 18 | 7 | 27 | 35 | 38 |
| TH6 | 72 | 13 | 15 | 78 | 13 | 9 | 45 | 27 | 27 |
| TH8 | 77 | 12 | 11 | 83 | 12 | 5 | 35 | 30 | 35 |
| TH9 | 46 | 11 | 44 | 63 | 11 | 27 | 39 | 30 | 31 |
| TH10 | 52 | 5 | 43 | 64 | 5 | 30 | 30 | 38 | 32 |
| TH13 | 71 | 16 | 13 | 77 | 16 | 7 | 55 | 17 | 28 |
| TH15 | 76 | 3 | 21 | 85 | 3 | 12 | 57 | 10 | 33 |
| TH17 | 65 | 16 | 19 | 79 | 16 | 5 | 46 | 12 | 42 |
| 平均值 | 66 | 12 | 22 | 76 | 12 | 12 | 40 | 24 | 36 |
2.2 砂岩薄片成分统计结果
图4 四川盆地北部须家河组砂岩成分三角图(大地构造属性分区据文献[18]) Fig.4 Ternary diagrams of sandstone composition for the Xujiahe Formation in northern Sichuan Basin (the zoning of tectonic attributes in the earth is cited from Ref.[18]) |
3 重矿物组分与石榴子石、辉石成分特征
3.1 重矿物组分与石榴子石、辉石成分分析方法
3.2 重矿物组分
3.3 石榴子石、辉石成分
图6 广元、旺苍、南江和土黄剖面所含石榴子石源岩岩性判别图 Fig.6 Garnet source rock discrimination diagram for samples from Guangyuan, Wangcang, Nanjiang and Tuhuang sections |
图7 土黄剖面样品TH8所含辉石类型与来源岩浆类型(a)辉石类型判别图版,坐标为三端元成分百分比,底图据文献[26];(b)辉石来源岩浆类型判别图版,底图据文献[24];(c)辉石来源岩浆的大地构造环境判别图版,底图据文献[25]。注:F1、F2由氧化物的质量百分比计算得到(其中所有铁的氧化物换算成FeO),F1=-0.012×SiO2-0.080 7×TiO2+0.002 6×Al2O3-0.001 2×FeO-0.002 6×MnO+0.008 7×MgO-0.012 8×CaO-0.041 9×Na2O;F2=-0.046 9×SiO2-0.081 8×TiO2-0.021 2×A12O3-0.004 1×FeO-0.143 5×MnO-0.002 9×MgO+0.008 5×Ca+0.016 0×Na2O。S:Subalkaline,亚碱性;A: Alkaline,碱性;P: Peralkaline:过碱性; WPA: Within Plate Alkalic Basalt, 板内碱性玄武岩;VAB: Valcanic Arc Basalt,火山弧玄武岩;OFB: Ocean-floor Basalt,洋底玄武岩;WPT: Within Plate Tholeiitic Basalt,板内拉斑玄武岩 Fig.7 Pyroxene type and source magma type for sample TH8 from Tuhuang section |

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