Electrical Structure of Narusongduo Ore Concentration District and Its Constraints on Mineralization
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摘要: 为了研究西藏纳如松多矿集区的电性结构特征和对成矿作用的约束，对覆盖矿集区的大地电磁测深数据进行全面的数据处理分析，得到了可靠的二维电性结构模型.研究结果表明，分别在深度为40~50 km，20~30 km和10 km处见高导体，推测这些高导体可能为部分熔融和水流体共同所致.由于纳如松多矿集区内矿床为岩浆-热液型，深部岩浆的上涌在成矿作用中起到关键作用，所以壳内高导体可能为与成矿有关岩浆房的电性痕迹，将这些高导体连起来可能代表着深部热液向上运移的古通道.电性结构主要体现了壳内高导体与区域成矿动力作用的关系，向上运移的富矿岩浆也可能通过局部的隐伏构造运移到Pb-Zn和Fe-Cu矿床的位置，再演化形成矿体.Abstract: To understand the electrical structure in Narusongduo ore concentration district in the Tibetan Plateau and its constraints on mineralization, the magnetotellurics data in the district were carefully processed and analyzed, obtaining a reliable 2-D electrical model. The study shows that there are some conductors at depths of about 40-50 km, 20-30 km and 10 km, which may be resulted from the partial melting and aqueous fluids. As the deposits in the district belong to the magmatic-hydrothermal type, and the upwelling deep-seated magma played an important role in the mineralization, the crustal conductors may offer constraints to the ore-related magma reservoirs, and connecting these conductors also may represent the ancient ascending channels. The electrical structure indicates the relationship between the crustal conductors and the regional metallogenic dynamics in our study. The ascending ore-bearing magma also may migrate to the Pb-Zn and Fe-Cu locations by the local hidden structures, and subsequently evolved into the ore body.
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图 1 (a) 研究区点位图; (b)青藏高原及邻区地形图
a图中包括主要大地构造和MT测点.黑色圆点表示宽频大地电磁测深点位, 红色圆点表示长周期大地电磁测深点位, 蓝色圆圈表示典型测点点位.b图中红色矩形为研究区.TH.特提斯-喜马拉雅地块; LS.拉萨地块; QT.羌塘地块; SPGZ.松潘-甘孜地块; QD.柴达木盆地; TB.塔里木盆地; IYS.印度-雅鲁藏布江缝合带; LMF.洛巴堆-米拉山断裂; BNS.班公湖-怒江缝合带; JRS.金沙江缝合带; AMS.阿尼玛卿缝合带.矿集区位置引自中国地质科学院地质研究所岩石圈中心——冈底斯成矿带深地震反射剖面探测
Fig. 1. (a) Topography map showing major tectonic structures and MT station locations in the survey area, (b) topography of the Tibetan Plateau and its adjacent areas
图 2 宽频(点号NR-06、NR-17和NR-24)及长周期(点号NR-15)数据曲线
Fig. 2. The combination of broad-band (station NR-06, NR-17, NR-24) and long-period (NR-15) MT data
图 4 阻抗张量分解图
a.0.1~1.0 s, b.1~10 s, c.10~100 s, d.100~1 000 s; 玫瑰花图显示相应频段的走向分析结果
Fig. 4. Impedance tensor maps
图 5 模型粗糙度、拟合误差随正则化因子变化的曲线
Fig. 5. L-curve of RMS values and roughness corresponding to different tau values
图 6 二维TE模式和TM模式联合反演模型
a.反演单点拟合差(RMS); b.二维反演电性模型, LMF.洛巴堆-米拉山断裂; NR1~NR3.地壳内高导体; 黑色虚线为上、中、下地壳分界面(源自Hou et al., 2015); c.基于电性结构的纳如松多矿集区成矿动力模型示意图
Fig. 6. 2-D electrical structure model using TE+TM data
图 7 30~50 km电导曲线
Fig. 7. The curve of the total longitudinal conductance at the depth of 30~50 km
图 8 (a) 8~15 km电导曲线; (b)20~30 km电导曲线
Fig. 8. (a) is the curve of the conductance at the depth of 8-15 km; (b) is the curve of the conductance at the depth of 20-30 km
图 9 印度-欧亚大陆主碰撞期间(65~50 Ma)南-中拉萨地块内矽卡岩型Fe(Fe-Cu)矿床和花岗岩有关的Pb-Zn矿床成矿示意
Fig. 9. Sketch topography of South-Central Lhasa terrane during the main-stage of India-Eurasia continental collision (65-50 Ma) and the mineralization of the skarn Fe (Fe-Cu) ore deposit and the granite-related Pb-Zn ore deposit
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