冀东地区冷口断裂重磁异常特征及其地质作用

利用冀东地区1∶2．5万高精度航空磁测资料及收集的地面重力资料,阐述了冷口断裂及其两侧航磁、重力异常特征,并结合物性特征,分析了航磁、重力异常的地质成因及其对地质构造和矿产的控制作用。冷口断裂两侧航磁、重力异常特征差别十分明显,反映了两侧结晶基底、盖层和侵入岩分布规律差异较大,认为该断裂不仅控制了地质构造分布,也间接控制了矿产分布,可为地学研究和矿产勘查提供必要的地球物理依据。     

东天山戈壁沙漠覆盖区重磁场特征与构造格架研究

依据重力和航磁异常数据及其处理结果（Tilt导数和欧拉反褶积）,对东天山戈壁沙漠覆盖区断裂构造和岩体重新进行了解译,结合岩石密度和磁性特征及前人研究成果,分析了东天山的构造格架。结果表明,东天山构造线主体方向为近EW向,构造格局具有南北分带的特点,重力和航磁异常图上密集梯级带对应研究区一级断裂,即康古尔塔格一黄山深断裂和阿奇克库都克一沙泉子断裂。重力和航磁原始异常经过Tilt导数和欧拉反褶积处理后,微弱信息得到明显增强,进而识别出一些新的断裂构造和岩体。     

西南地区航磁区域特征

通过对西南地区航磁数据进行化极、垂导和延拓等处理,研究西南地区航磁区域特征,确定采用航磁化极上延20 km等值线图作为西南地区航磁区域异常,对西南地区区域航磁异常划分了13个分区。结合地质、重力、天然地震和遥感等资料进行综合推断解释,将西南地区划分为3个一级构造单元,9个二级构造单元,22个三级构造单元,并重点对6个二级构造单元的地质、矿产和航磁异常特征进行了深入分析研究,认为班公湖—怒江异常带、雅鲁藏布江异常带、三江异常带等串珠状磁异常与该成矿带的矿产地位置吻合较好,证明航磁异常在找磁性矿产方面效果显著。通过航磁异常上延10 km与地震震中点位对比分析,证明航磁反映深部断裂构造特征明显,能明显反映出西南地区区域地质构造特征。     

基于重磁场特征的敦化盆地构造格架研究

依据重力、磁力异常数据及其处理结果( 水平梯度模和斜导数) ,对敦化盆地边界、基底起伏、断裂位置及以火成岩为代表的磁性体分布进行了研究。盆地重力异常的分析和水平梯度模及斜导数的计算结果表明,盆地基底具南部凹陷、中央凸起和北部凹陷的“两凹一凸”的起伏形态特征,盆地内断裂以SW--NE 向为主,盆地为单断半地堑式盆地。依据航磁异常,将盆地划分为4 个异常区: 东北部磁异常区、中部低磁异常区、西南高磁异常区和西南边部相对低磁异常区。结合磁异常水平梯度模和斜导数的计算结果显示,以火成岩为代表的磁性体受SW--NE 向构造控制。     

利用重磁资料对贵州西部玄武岩出露区火山口的初步圈定

根据火山口及岩浆喷溢后可能在重力和航磁上引起的重力异常和航磁异常的特性，该文利用重磁资料对该区火山口进行了初步圈定。为该区的地质、矿产研究及成矿预测提供一点深部信息。     

卡乌留克塔格地区地质及磁异常特征

卡乌留克塔格C-12磁异常位于兴地大断裂南侧,航磁为低缓异常,地磁异常则极值较大.通过地面高精度磁法工作,确定了航磁异常在地面的具体位置及形态、范围及变化特征.根据磁异常的推断解释,C-12异常为超基性岩体引起.由此可见,磁法测量对寻找基性、超基性含铁磷岩体具有重要的意义.     

成都市区域化探深层样品元素异常与物探重、磁异常及遥感解译构造的关系

通过深层样化探异常与物探重力、航磁和遥感解译关系的研究,认为深层样元素异常是由隐伏构造指示元素Au、Hg,与重力负异常有关的酸性岩元素Sn、Be、F、Y,与航磁正异常有关的基性岩元素Fe、Co、Ni、V、Cr和与地层有关元素Cd、C、Tl四部分组成;解释了深层样元素异常的原因,开拓出区域化探与区域物探、遥感解译相结合的新路。     

庐枞地区重磁场特征及其地质认识

基于重力、航磁异常的地质解释,对庐枞盆地线性（断裂）构造、环形构造（火山机构）和隐伏岩体分布提出认识,并对深部构造（莫霍面、变质基底）特征进行探讨。     

皖南屯溪地区重磁异常特征及找矿方向

利用屯溪地区重磁、地质和矿产资料,阐述了屯溪地区航磁、重力异常特征,并结合物性特征,分析了航磁、重力异常的地质成因及其对地质构造和矿产的反映。屯溪地区重磁异常特征十分清晰,反映了屯溪盆地地基底、盖层和侵入岩分布规律,标明屯溪盆地是古生代基底,这一认识大大扩展了屯溪地区找矿空间,说明在红层盆地古生代基底中有寻找朱溪式超大型矽卡岩钨铜矿床的可能性。     

东北地区火成岩的航磁异常特征分析

为了解不同时代火成岩的航磁异常特征,对东北地区1∶20万的航磁资料进行了化极、向上延拓及垂向导数的处理。通过与地质图进行对比分析,总结出研究区火成岩的航磁特征:区内广泛分布的各时代花岗岩表现出了不同的磁异常特征,寒武纪、石炭纪、三叠纪等时代的花岗岩表现为高磁异常,而二叠纪及侏罗纪花岗岩表现为低磁异常,其中磁异常最高的岩性为石炭纪花岗岩,磁异常最低的是二叠纪花岗岩。测区内存在的喷出岩-古近纪玄武岩磁异常较高,而更新统玄武岩并未见明显的异常特征。     

藏东马牧普地区斑岩型铜金银多金属矿化带地球化学异常评价

藏东玉龙成矿带马牧普地区1:5万水系沉积物中的成矿元素Au、Ag、Cu、Pb、Zn的研究,采用分形方法确定异常下限,得出其异常下限值分别为10×10-9、0.48×10-6、75×10-6、120×10-6、130×10-6;用因子分析研究成矿元素的异常组合规律,指出测区西南异常区为Au、Cu、Pb、Zn、Ag组合异常,是矿致异常;中西部异常为Ag、Cu、Pb、Zn综合异常,为指示斑岩分散流的异常,是非矿致异常。     

河南桐柏刘山岩铜锌矿带深部找矿前景分析

刘山岩铜锌矿带位于东秦岭造山带之北秦岭褶皱带核部。矿体赋存于硅质—钠长石岩层中。自矿体中心向边缘存在黄铁矿—黄铜矿—方铅矿—重晶石—石英的相对矿物分带。经矿带物化探资料的综合研究认为,深部及外围有较大的找矿空间。文章从地质背景、成矿作用及地球物理、地球化学特征分析入手,对深部找矿前景作出了判断,以期为在刘山岩矿带及攻深找盲有所突破。     

塔里木盆地中部航磁异常带新解译

横亘于塔里木盆地中部的纬向航磁高ΔTa异常带,一直是探讨盆地及深部基底的物质组成及结构构造的焦点。根据钻井及地震资料综合分析,发现满加尔坳陷中南部上奥陶统内发育大型地震反射异常体,平面上主要由8个地震反射异常体近东西向呈带状展布,与盆地中部航磁高ΔTa异常带相关。从地层发育及地震相特征分析,这些地震反射异常体应为辉绿岩-玄武岩等基性火成岩体,且与航磁ΔTa异常带上的磁力高相对应。异常体具有垂直向下的通道,与断裂及岩浆活动通道有关。盆地中部高航磁异常带为多期构造易活动带,反映了满加尔坳陷震旦纪与中晚奥陶世处于拉张的构造背景。     

腾冲火山构造区马站岩浆囊地球物理特征的再探讨

云南腾冲火山盆地深部存在岩浆囊是人们关注的问题,多方面进行了大量的研究且存在不同意见。作者此前依据低电阻异常推断出位于小空山、大空山、黑空山等火山口的下部,深13~30 km范围内东西向25 km,南北向30km的低电阻率的岩浆囊,其东侧为大盈江断裂。文章利用反射地震、重力、航空磁测资料进一步探讨了岩浆囊的其他地球物理特征。由于火山喷发,不仅在火山口附近形成了局部物质亏损,而且,岩浆囊本身也亏损了岩浆物质,在重力上延图中滤去了表层的火山局部负重力异常后,呈现出大空山北侧的与低阻体相对应的负重力异常,这与岩浆囊高温熔融状态含水低密度物质有密切关系。整体的重力负异常印证了低阻岩浆囊的存在。腾冲马站岩浆囊的温度为397~651°C,平均温度为524°C,其主体中心部位不可能存在磁性体。对航磁资料的处理,消除表层火山岩影响后,仍然发现有较强磁异常,其平面投影范围与低阻体相近,推断磁异常是岩浆囊顶层,在15 km深度以上范围内,随着岩浆囊体温度逐步下降,当低于480°C以后会形成新的铁磁性矿物,因此,在囊体上层出现了范围与囊体相近的较强的磁性体。反射地震仅仅在浅部较清楚地观测到较连续的反射波界面,是浅部火山岩、含水层、以及花岗岩顶界面的反映。向深部反射界面很不连续推测是由于多次岩浆上涌,其喷发时间有先后,成分有差异,故岩浆囊物质的不均匀性,虽然由于含水、矿化、熔融体构成了低电阻的共性,可温度的不均匀,却又显示了不同期次岩浆成分有变化,由岩浆囊向地表的通道上,东部花岗岩下为高速,相对于较低温度的物质,在小空山、大空山和黑空山深部沿大盈江断裂带有东西两个大的隐伏花岗岩体之间是最新的火山喷发通道,具有相对低速的通道。     

“赤水—涟源东西向构造带”厘定的地质-地球物理证据

中上扬子地块现今深部结构构造的研究,不仅具有科学意义,而且对于研究其与形成演化相关的油气生成、运移、聚集及构造保存和矿产资源的分布赋存规律等更具有重要的社会经济价值。通过地球物理场的详细处理、分离提取技术,结合地表地质的综合分析,发现并厘定了赤水—涟源东西向基底构造带,详述了相关的地质-地球物理证据。结果表明,该构造带是位于中上扬子地块与湘桂地区元古宙也许更早时期南北不同构造块体之间的重要界线,具有从基底到盖层多期次复活演化特点,在空间上有由南往北穿时推进的趋势,而形成演化时间上可主要归为两个时间段:前寒武纪晚期和白垩纪晚期之后。     

Geophysical prospecting of copper-nickel deposits in Beishan rift zone,Xinjiang

The Beishan rift zone in Xinjiang Uygur Autonomous Region was formed due to strong activities of faults on the basement of the Tarim continental crust. Despite the fact that many geological research results of the rift zone have been achieved, only a few studies have been conducted on its regional geophysical characteristics. In this paper, the gravity and magnetic anomalies of the rift zone were highlighted through specific data processing of 1:50000 high-precision aeromagnetic data and gravity data with a grid spacing of 2 km × 2 km. Based on this, the geophysical evidence for the scope and internal structures of the Beishan rift zone was obtained for the first time. The distinct characteristics of magnetic and gravity fields in the areas to the north and south of the Beishan rift zone reveal that deep faults exist between the Beishan rift zone and the geological units on the southern and northern sides. Furthermore, the faults on the two areas contain the bidirectional thrusts and have flower-shaped structures according to the characteristics of the magnetic and gravity fields. The Beishan rift zone can be divided into two tectonomagmatic zones, namely the Zhongposhan-Bijiashan-Cihai-Baishanliang zone (the northern zone) and the Bayiquan-Qixin-Baishan zone (the southern zone). The northern zone can be further subdivided into three comet-shaped anomaly groups (tectonomagmatic areas), while the southern zone can be further subdivided into two tectonomagmatic areas. According to the characteristics of aeromagnetic anomalies and gravity field, 19 mafic-ultramafic complexes were delineated. The known Pobei, Hongshishan, and Qixin complexes are all located within the inferred complexes, with estimates of total explored resources of Ni, Cu, and Au of 3×10⁶ t, 10×10³ t and 10 t, respectively. The prospecting of high-grade copper-nickel deposits should focus on the periphery and deep parts of the known and inferred mafic-ultramafic complexes. Among them, the peripheral strata of the complexes specifically have great prospecting potential of large-scale high-grade copper-nickel deposits of magma injection type. Finally, this paper analyzed the application effects of the rapid airborne-ground-drilling synergetic exploration method in the prospecting of copper-nickel deposits in Qixin, Beishan, Xinjiang, which will provide references for further exploration of copper-nickel deposits in Beishan area, Xinjiang.©2021 China Geology Editorial Office.     

勃利金山金矿化区土壤地球化学异常特征及矿体预测

根据金山金矿化区20 km2土壤地球化学测量结果,运用聚类分析和因子分析,显示Au与Ag、As、Sb相关性较好,可作为金矿找矿间接指示元素;并通过计算各元素背景值及异常下限,圈定出9处金异常和其他元素异常35处。区内主要发育含硫化物蚀变岩型和含硫化物石英脉型金矿体。其中北西向断裂控制矿体走向,为重要的控矿构造。综合地质条件及元素异常特征,预测并圈定出3个Ⅰ级靶区和2个Ⅱ级靶区,并在Ⅰ级靶区经地表槽探工程验证,发现并控制14条矿体。     

Petrology of mafic-ultramafic rocks along North Puruliya Shear zone,West Bengal

The North Puruliya Shear zone (NPSZ) is characterized by occurrence of mafic-ultramafic rocks aligned parallel to the shear zone, intruding the high grade Proterozoic rocks of Chhotanagpur Gneissic Complex. The ultramafic rocks occur as small lenses, pockets, veins, thin dykes and are intimately associated with mafic (gabbro, norite) rocks. Pyroxenites (viz. olivine websterite, websterite, plagioclase websterite) and hornblendite are the two important members of the ultramafic rocks containing clinopyroxene, orthopyroxene, olivine, plagioclase, amphibole, phlogopite and ilmenite. The mafic-ultramafic rocks show evidence of shearing and retrogressive metamorphism. Linear correlation of chemical attributes suggests fractionation-controlled magmatic differentiation. Enrichment of LILE and LREE in the mafic-ultramafic suite suggests an enriched mantle source and pronounced negative Eu-anomalies in all the rock types except hornblendite suggest fractionation of plagioclase under low f_O2 condition. Progressive iron enrichment trend in rocks of the mafic-ultramafic suite also indicate magmatic differentiation under low f_O2 condition. Early fractionation and accumulation of clinopyroxene and plagioclase from a basaltic magma may have given rise to the ultramafic rocks of the area. Little change in the Nb/Zr and Ce/Zr ratios of ultramafic and mafic rocks (except alkali norite) strongly support low crustal contamination. A few samples of norite and gabbro-norites appeared to be variably contaminated by a crustal component or affected by late granitic intrusion resulting in enrichment of alkali in the former.     

滇西高黎贡构造带东缘中侏罗世玄武岩岩石地球化学特征及其构造意义

高黎贡构造带东南缘的混杂岩带形成的构造背景复杂。产于混杂岩带以东的中侏罗世玄武岩地球化学特征可能为该岩石形成的构造背景提供依据。滇西中侏罗世玄武岩分布于高黎贡构造带东缘的凤平镇-畹町(南带)和怒江(北带)一带。其中怒江一带玄武岩具有块状构造,气孔杏仁发育,间粒结构,发生了绿片岩相变质。岩石属于亚碱性拉斑系列,具有中等的MgO(5.09%～6.20%)、较高的钛(Ti O_21.64%～2.14%)、铁(Fe O~T9.19%～12.80%),且Na_2OK_2O。岩石Mg~#值(Mg~#=Mg~(2+)/(Mg~(2+)+Fe~(2+)))为0.51～0.59,反映了源区岩浆经历了明显的辉石和橄榄石分离结晶,同时存在低氧逸度下分离结晶。岩石富含稀土元素(78.52×10~(-6)～99.41×10~(-6)),具明显的轻、重稀土分馏((La/Yb)_N=4.06～5.54),无明显Eu异常(δEu=0.91～1.00),斜长石分离结晶不明显。同时,富集大离子亲石元素(Rb、Ba、Th、U)和高场强元素(Nb、Zr、Ti),具有弱的Nb、Zr、Ti负异常。较高的Zr/Y(3.58～5.88)、Ta/Yb(0.29～0.51)、Th/Yb(1.15～1.45)和(La/Nb)_N(1.03～1.41)比值,说明怒江一带玄武岩具有裂谷特征。相对高Nb含量(8.83×10~(-6)～15.60×10~(-6))和富集稀土元素不同于岛弧,周边及下部缺少洋壳和Nb负异常有别于OIB。岩浆源自富集的石榴石地幔橄榄岩部分熔融,在上涌过程中受到了地壳污染,显示Nb负异常。有限的岩浆作用规模和较短的喷发时间反映了高黎贡构造带东缘怒江一带具有被动拉张的裂谷性质,可能与古特提斯洋闭合引起的拉张作用有关。     

Seismological evidence for compositional variations at the base of the mantle transition zone under Japan Islands

Temperature and water content anomalies just above the 660-km discontinuity under the Japan Islands are estimated from seismological observations. Two sets of seismological observations of P-wave velocity perturbations and depth variations of the 660-km discontinuity are used, which are (1) long-wavelength (~ 500 km) variations from seismic tomography based on a grid parameterization and waveform analysis of ScS reverberations and (2) moderate-wavelength (~ 150 km) variations from seismic tomography with a block parameterization and receiver-function analysis. To estimate temperature and water content anomalies, partial derivatives of velocity and depth variations with respect to temperature and water content determined by mineral physics studies are used. Under Southwest Japan, low temperature and high water-content anomalies are obtained from both sets of seismological observations, which have already been found by a previous study. Under Northeast Japan, however, there are discrepancies between the results estimated from the two data sets, possibly due to the different resolution scales. This discrepancy is dismissed when examining distributions of the temperature and water content anomalies. These anomalies can be grouped into two geographical locations, one group under Southwest Japan, the other under Northeast Japan. The two groups are clearly separated and exhibit common features in both sets of the seismological observations. The grouping is interpreted by a compositional difference between the subducting Pacific slab under Southwest Japan and a normal mantle under Northeast Japan.