SPATIAL VARIATIONS OF GRAIN SIZE OF LOOSE SEDIMENTS IN DAOCHENG HAIZI MOUNTAIN
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摘要: 稻城古冰帽中心海子山广布粒度成分不同的由冰碛物和冲洪积物等组成的松散堆积物,给高海拔宇宙线观测站(LHAASO)规划建设带来挑战。对高坡垄岗部位5处冰碛花岗岩砾石、堰塞盆地中2处阶地冲洪积物进行现场观测和取样分析。对106块砾石采用线面集中统计,得到冰碛物砾石数量占百分比较高的砾径为0.5~2.5 m,面积2.5~7.5 m2,体积5 m3。块石形状多为长方体-厚板状,部分面接触为主。采用音频大地电磁法(AMT)等进行探测,解释得到场地冰碛体厚约30 m。对冲洪积物的含砾土和细碎屑土的2个砂砾样品用筛分法和激光粒度法进行粒度成分测定,得中值粒径d50=2 mm、0.7mm,不均匀系数Cu=5.40、2.42,曲率系数Cc=0.60、0.95。这两种冲洪积物均为不良级配的土,即均粒土。这些成因和结构不同的冰碛物和冲洪积物对工程布设有不同影响,在工程实践中给予了区分利用。Abstract: Haizi Mountain in the center of Daocheng's Quaternary ice cap is widely distributed with glacial moraine of different grain magnitudes. The site, covered with various loosed sediments underlying by granite as medium coarse grained biotite granodiorite,is to be used according to the planning and construction of China's Large High Altitude Air Shower Observatory(LHAASO). This paper describes and analyses five locations with granite gravels of moraine ridge and two locations with alluvial proluvial materials of terrace at the site. The statistical results of 106 huge gravels show that the moraine gravels of major percentages are 0.5~2.5 m in diameter,and have 2.5~7.5 m2 in area and 5 m3 in volume to a certain extent. Two gravel samples of gravelly soil and fine debris soil of alluvial proluvium have the median particle size D50=2 mm and 0.7mm,the non-uniform coefficient Cu=5.40 and 2.42,the curvature coefficient Cc=0.60 and 0.95, respectively. Both are poorly graded soil,i.e. homogeneous soil. These moraines and alluvial proluvial deposits with different genetic structures and magnitudes have different important values for site planning and utilization,and have certain influence on the stability of excavation pit wall. Afterwards,the results in this paper were adopted for planning and designing of LHAASO.
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Key words:
- Daocheng /
- Moraine /
- Grain size /
- Moraine dam moraine /
- Sediments thickness
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图 1 研究区地理位置及区域构造概略图
资料来源:交通线路和水系:中国地图出版社(2010);山峰和高程:国家测绘局(1975);主要活动断裂及盆地:黄金忠等(1989);①. 邓柯-乡城断裂,②. 甘孜-理塘断裂,③. 理塘-德巫断裂,双齿线为上盘逆冲;Ⅶ. 理塘盆地
Figure 1. Site location and framework of regional faults
图 3 现场采集的5块花岗闪长岩标本(左列)及光学显微镜下单偏光(中间)和正交偏光图像(右列)
显微图像中矿物名称:Ap-磷灰石,Bt-黑云母,Hbl-普通角闪石,Kfs-钾长石,Pl-斜长石,Qtz-石英,Zrn-锆石. 样品采集位置见图 2
Figure 3. Five samples of granodiorite(left column) and single polarized(middle) and orthogonal polarized images(right column) of optical microscope
图 7 现场冰碛垄砾石测量照片(砾石统计点分布见图 2)
Figure 7. Distribution of debris in moraine ridge
表 1 现场5处冰碛砾石几何特征表
Table 1. Geometric characteristics of gravels in five moraine ridges on the site
点号 砾石数/块 统计面积/m2 测区边走向/(°)/测线长/m/倾角/(°) 砾石优势体积/m3 地貌单元 野外岩性/砾石一般尺寸/m 砾石面积占测窗面积(线密度)/% 推测冰川运动方向/(°) 16 35 30×30 30//
112//2.5 终碛垄 浅白色粗粒花岗岩,石英含量高。含细晶花岗岩突起团块 15.1 112 36 11 200 140//30~45 25 半弧形终碛垄巨型块石分布 长:5.5~7.0
宽:3.5~5.0
高2.0~3.5140 51 40 95/5/
183/5/砂砾堆积缓坡区,冰盆边缘 (71)(57.4) 87 10 130/21/
220/25/25 终碛垄巨型砾石分布区 (77.1)(41.2) 91 10 15 侧碛垄大块石分布区 长3.5~5.5
宽2.0~3.0
高1.5~2.5表 2 砂砾土样3种粒组百分含量(%)及定名
Table 2. Percentage and designation of three grain components in gravel and soil samples
编号 卵砾组(>2 mm) 砂粒组(2~0.05 mm) 粉黏粒组(<0.05 mm) 定名 DC9-1 49.91 48.61 1.48 含砾土 DC9-2 45.22 53.37 1.41 含砾土 DC14-1 3.68 94.11 2.21 细碎屑土 DC14-2 3.65 93.65 2.70 细碎屑土 -
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