摘要
南岭地区处于欧亚板块的东南端,东与太平洋板块毗邻,西接印度洋板块,在地理上是指五岭和九连山脉地区;南岭成矿带是我国重点部署矿产勘查的16个重点金属成矿区带中的五个重中之重之一。研究区内以与酸性岩浆岩有关的有色、稀有矿产高度富集为特色,是世界“钨都”、“锑都”和“锡都”。上个世纪以来,南岭地区诞生了许多成矿理论和学说,如花岗岩的壳源改造和同熔型成因理论、成矿系列理论和地洼构造学说等,近十几年来,随着大陆成矿作用研究的兴起,南岭再次成为相关理论研究的热点地区。本文依托国土资源部十二五科研专项:南岭地区燕山期深部岩浆活动与大规模成矿复杂性研究(编号:1212011121101),以地球物理探测为主要研究手段,运用重磁小波多分辨率分析、位场边界识别方法和技术,提取南岭地区不同深源层的岩体和构造信息,识别区内隐伏花岗岩分布,并对花岗岩侵入体的延深、形态等空间侵位特征进行反演,揭示岩石圈结构特征,探讨和分析区内岩浆系统结构和花岗岩成因等问题,并对南岭地区多金属成矿预测进行研究。论文取得的主要研究成果如下:(1)利用小波分析对1:20万布格重力和1:50万航磁数据进行多级分解,提取了场源似深度分别约为lkm、3km、8km、15km、25km的1-5阶细节。研究结果表明:重力异常小波1阶细节主要反映浅部及出露的小岩体的分布,这些小岩体往往是成矿的有利地带;如千里山岩体,其地表出露的岩体面积并不大,但其周围却有东坡、红旗岭、柿竹园、瑶岗仙、野鸡尾等;重力异常小波2阶细节主要反映浅部半隐伏岩体的分布,矿田往往分布在此类较大的局部重力异常周围。本文将1-5d细节之和作为南岭地区花岗岩引起的局部异常,花岗岩剩余重力异常信息呈现明显分区特征,以茶陵-郴县断裂为界,研究区北西部位岩体局部重力异常较大,变化范围-14~-27mGa1不等,南东地区较小,变化范围-8-20mGa1不等,说明北西区岩体较厚或者密度较小;而且不同时期花岗岩剩余重力异常信息也存在一定差异,早期花岗岩比晚期花岗岩的重力负异常值要大,其中早期花岗岩主要分布在北西区。(2)利用不同方向水平导数以及多尺度小波断裂识别方法,划分了南岭地区的断裂体系,指出了隐伏断裂、深大断裂的分布特征,并结合以往大地电磁和地震测深结果,指出了研究区的岩石圈断裂2条:城步-桃江断裂、常德-安仁断裂,莫霍面断裂5条:茶陵-郴州断裂、赣州-韶关断裂、大义山-郴州-大宝山断裂等。古俯冲带地幔楔与莫霍面断裂部位是岩浆入侵的突破口和诞生地,花岗质岩浆主要沿深大断裂上涌至上地壳形成地表岩体,并在线性断裂交汇处岩浆侵入最为有利,以断层为界的花岗岩断块的厚度较大,如诸广山,九嶷山等岩体。(3)利用水平总梯度模、Tilt梯度、Theta map以及归一化标准差的方法对南岭重力异常进行边缘识别,研究南岭地区隐伏花岗岩体分布范围,绘制了预测结果图。研究结果表明:区内全隐伏岩体分布在三才界、香花岭、钟山珊瑚等地.这类岩体中有些地表仪见小岩株,而地下隐伏规模较大,往往是成矿的重点区域;半隐伏岩体如骑田岭、瓦屋塘、萌诸岭-海洋山、阳明山-大义山等,这类岩体深部和周围存在延伸和扩大:此外,区内部分岩体呈深部相连,如千里山-骑田岭-香花岭、海洋山-都庞岭、阳明山-大义山等。(4)利用3D密度成像技术,揭示了千里山-骑田岭矿集区和九嶷山岩体的3D密度结构,并根据二度半人机交互反演和大地电磁测深剖而进一步深化对密度成像结果的认识,研究结果表明:千里山-骑田岭-香花岭岩体深部相连,并沿着北东向郴州-茶陵断裂可能直延伸到北东部的万洋山-诸广山,形成千里山-骑田岭-香花岭隐伏岩浆侵位通道,而九嶷山岩体特征为西厚东薄:南岭花岗岩体厚度一般为6~15km,少数接近30km:薄岩体一般比厚岩体宽度大,如越城岭岩体宽度为45kmm,厚度仅6km,而大义山岩体宽度26km,厚度可达22kmm。(5)根据重磁资料揭示的结果,对南岭花岗岩岩成因问题进行探讨和分析.得到以下认识:南岭地区花岗岩大多数岩体起源深度不超过30km,属于无根花岗岩,为该区“花岗岩成因以陆壳重熔为主”地质推论提供了直接的地球物理证据。本文认为在燕山运动早期太平洋板块向华夏板块的俯冲过程中,岩石圈发生减薄.软流圈上涌和玄武岩浆底侵提供的热源导敛原岩的部分熔融而形成燕山早期的“南岭花岗带”;推测郴州地区深部的上地幔顶部存在软流圈上涌形成的残留岩浆房,这个残留岩浆房岩浆底侵为下地壳原岩部分熔融提供了热源,并形成以诸广山-万洋山为中心的陆壳重熔区,为周围中生代岩浆大爆发的发源地,也为该地区大规模区域成矿作用提供了矿源和热源,从而形成了以千里山-骑田岭为中心的南岭深部矿集区的最佳场所。此外,猫儿山-越城岭地区中下地壳位置可能也存在大规模陆壳重熔区,(6)根据南岭深部构造特征,如莫霍面起伏、隐伏断裂和隐伏岩体分布等,研究它们与已知矿矿床的对应关系,得到以下认识:幔隆区通常对应着浅层构造的中、新生代盆地,与内生金属矿产关系小大;幔凹区则往往与浅层构造的隆起带相对应,虽有矿床形成,但小是成矿最有利地段在幔隆与幔拗之间的变异区(带),处在地壳增厚、减薄的交替地带,浅层构造活动强烈,多金属矿床分布很多。区内拧制岩浆活动和矿床分布的主要为北东向和北西向构造,不同方向和不同深度层次大断裂的交汇部位是岩浆侵入的突破口,也是矿床聚集的最佳场所,尤其是燕山期北(北)东向构造与先期东西构造交汇部位。(7)总结和归纳了南岭主要矿床的地质成矿规律以及地球物理、地球球化学特征,总结了“三高两低”的地质异常找矿模式,三高是指有较明显的视极化率、磁异常及地球化学多元素异常,两低是指低重力和低视电阻率部位,
The Nanling region, located in the southeast end of the Eurasian plate, adjacent to the east of the Pacific plate and to the west of Indian Ocean plate, geographically refers to the Wuling and the Jiulianshan areas. Nanling metallogenic belt is one of the five most important of the16key metal mineralization belts which our country set off metal exploration. This study area, abundant in non-ferrous and rare metals related to acidic magmatic rocks, is called the capital of tungsten, antimony and tin mineral in the world. Since the last century, many metallogenic theories were emerged in Nanling region, such as the theory of transforming granite crust source, the theory of metallogenic series and construction of geodepression theory etc.. In recent ten years, with the development of continental mineralization research, Nanling become a hot spot again to research related theory. This paper, based on the12-five-years research special project of Land and Resources department "Research on deep magmatic activity in Yanshan period in Nanling region and its metallogenic complexity (N:1212011121101)", using geophysical exploration as the main research means, with the help of method and the technology used in wavelet multi-resolution analysis and boundary detection of potential field to extract the information about granites and structures from different layers of deep source in Nanling region, identify the distribution of buried granite in the areas, invert the spatial features including buried depth and spatial shape of granite intrusions, reveals the structure characteristic of lithosphere, discusses and analysizes problems about the structure of magma system and granite formation and research the polymetallic metallogenic prediction in Nanling region. Paper's main research results are as follows:(1) We Multistaged1:200000bouguer gravity and1:50aeromagnetic data by Wavelet decompsition and wxtractd the1th~5th order details from the source in the depth of about1km,3km,8km,15km and25km respectively. The research results show that the the1th wavelet order details of gravity anomaly mainly reflects the distribution of small granite rocks in shallow and exposed areas and the small granites often are favorable belt for forming mineralization; Such as granites in Qianli shan whose exposed area is not large, but surrounded by Dongpo, Hongqiling, Yaogangxian, Shizuyuan, Yejinwei, etc.; The2th order details of Gravity anomaly mainly reflects the distribution of concealed granites in shallow layers, and orefields are often distributed in this area with larger negative gravity anomaly. This paper studies granite local anomalies caused by the sum of1th~5th order details in Nanling region, and information about the granites'residual gravity anomaly has assumed obvious zoning characteristics. Bounded by Chaling-Chenzhou fault, granites in the north west of the study area has a lager anomaly,ranged from14to27mgal, and south east area is smaller, ranged8to20mgal, which explain that rock in north west is thick or less density; And information in different periods about granites'residual gravity anomaly also has certain differences, the value of the early granites'negative of gravity anomaly is larger than that of late granites, and the early granite are mainly distributed in the north west.(2) By using the different direction of horizontal derivative and the multi-scale wavelet fault identification methods, we divided the fracture system in Nanling region, pointed out distribution characteristics of the concealed faults and deep faults; combined with the previous results of magnetotelluric and seismic prospecting, we pointed out2lithosphere faults in the study areas, including Chengbu-Taojiang fault, Changde-Anren fault; and5Moho fracture, such as Cha ling-Chenzhou fault, Ganzhou-Shaoguan fault, Dayi shan-chenzhou-Dabaoshan fault, etc. Ancient mantle wedge in subduction zones and Moho fault sites are an important controlling factor of granites instrusion. Magma mainly upwelled along the deep big faults to the earth's crust, then near the faults distribution, and corresponded to the gravity anomaly gradient belts, for which magma intrusion is most favorable place in the interchange of linear fracture, and a block of granite for fault is the biggest thickness, such as the granites in Zhuguang shan and Jiuyi shan,etc.(3) Using the method including the level total gradient modulus. Tilt gradient, Theta map and normalized standard deviation to conduct edge recognition to gravity anomaly in Nanling, we mapped the forecast result by studying the buried distribution of granite rock mass in Nanling region. The research results show that the concealed granite rocks distributed in the areas of Sancaijie. Xianghualing, Zhongshanshanhu and other places. Only small rock strain was found in some of this kind of rock mass surface, but the larger rock was underground concealed granite rocks where often is the key area of the metallogenic; Half concealed rock mass such as QitianLing, Wawutang, Mengzhuling and Mengzhu shans, Yangming shan and Dayi shan and so on. This kind of rock further expands into deep rock, and part of which is linked together in deep, such as Qianli shan-Qitianling-Xianghualing Haiyang shans-DouPangLing, Yangming shan-Dayi shan and so on.(4) By technique of3D density imaging, we revealed3D density and structure of granites in Qianlishan-Qitianling and Jiuyishan, further understood the findings of magnetotelluric according to the results of MT prospecting and2.5D interactive inversion of gravity anomaly profile. The results show that the Qianlishan-Qitianling-Xianghualing ore concentration area links together in deep, and may extend to the north east of Wanyangshan-Zhuguangshan along the north east of Chenzhou-Chaling fault, which forms a passageway of concealed magmatic emplacement to Qianlishan-Qitianling-Xianghualing, while the Jiuyishan granites is characterized for thickness in west and thinness in east. The thickness of Granite rocks in Nanling is about6-15km, commonly a few close to30km. Thin rock mass is generally larger than thick roc k in the width, such as rock mass in YueChengLing, the width is45km, and thickness is only6km; The granites of Dayishan, the width is26km, and thickness can be up to22km.(5) According to the result of gravity, magnetic, MT and seismic data, and discussing the causes of formation of Nanling granite, we got the following understanding:most of granite rock mass in Nanling region originated in depth less than30km, which are belong to no root granites, and provide direct geophysical evidence reasoning for geological inference of the topic that granites is resulted from continental crustal remelting. This paper believes that in the early movement of Yanshanian, in the process of subduction of the Pacific plate to the Cathaysian plate, lithosphere became thin, and the heat provided by the upwelling of the asthenosphere and the basaltic magma invasion led to partially melt the original rock which formed the early Yanshanian Nanling granite belts. We speculate that there is a residual magma chamber in the top of the upper mantle in Chenzhou area due to the asthenosphere upwelling. This residual magma chamber provides heat source for the partial melting of lower crust protolith, and help form the continental crust remelting area as the center of Zhuguangshan-Wanyangshan, is the birthplace of Mesozoic magmatic explosion, also offers mine source and heat source for mineralization in large areas of this region, where is the best Nanling mineralization zone centered Qianlishan-Qitianling. In addition, the middle and lower crust in Miaoershan-Yuechengling area may be in large continental crust remelting zone.(6) According to deep tectonic features in Nanling, such as Moho rolling, concealed fault and concealed granites distribution, etc., researching their corresponding relation with the known deposits, we got the following understanding:the mantle uplift area has few relationships with endogenous metal mineral, but usually corresponds to the shallow structure in the Mesozoic and Cenozoic basin; Mantle concave area tends to correspond to shallow tectonic uplift, although there is miberal deposits, not the most favourable metallogenic location. Between the variation area (belt) of mantle uplift and Mantle concave area, in alternating belt of crustal thickening and thinning, shallow tectonic activity is strong, and there are many mineral deposits distribution.The in N-W trend structures have the function of constructing ore and mine, and is the main structure factors about the distribution of orefields. the N-E trend structures control both the granites and ore, and it is the center of the magmatic activity where the different depth and different direction faults intersect, and it is also the best metallogenic place, especially the intersection between NNE trend structures and previous.(7) We summarized the geological metallogenic regularity, the characteristics of geophysics and geochemical about the famous mineral deposits in Nanling region, summed up the model of geophysical and geochemical mineral prospecting-two lows and three highs, two lows refer to negative gravity and lower resistivity, three highs refer to high AT anomalies and high ηS resistivity, and high geochemical anomalies such as Pb, Zn, Ag, As.