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通过资料收集和整理,对湖南深部地球物理场布格重力异常、航磁异常、莫霍面、地热场和地壳结构反映出来的特征进行了总结和分析,同时对湖南历史地震(Ms≥434级)和近代地震(ML≥3.0级)与这些深部地球物理场特征的关系进行了讨论。结果表明:湖南地震活动的空间分布与深部地球物理场特征有一定的内在关联,有较好的对应关系。 相似文献
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穿过波特兰市区西部图拉丁山脉(波特兰山)的高分辨率重力测量,展现出以前根据地表地质学和航磁测绘识别出的断层的证据。本次重力测量是在1996年沿着长4.5km的双孔隧道进行的,该隧道在当时的建设中及现在一直在波特兰市区与波特兰山以西的居民区之间通轻便火车。在隧道内的重力从西到东逐渐增加,这种情况反映了隧道位于西边的图拉丁盆地低密度沉积物与其东边高密度大部分隐蔽的始新世玄武岩之间。叠加在这一梯度之上的是几个阶梯状异常,我们将其解释为密度明显差异的岩石之间断续接触的证据。这些异常的最大值发生在西尔万克里克之下,这里存在一条以前测绘出的断层。另一异常发生在距西洞口1200m处,大约是隧道与航磁异常相交汇的部位,航磁异常与西尔万断层(原来称为奥特菲尔德断层)有关。以这些重力资料为依据的岩石学横剖面显示出阶梯状异常与陡倾逆断层相一致,虽然走滑位移也许同样重要。与上方地形洼地相对应的3个重力低异常可能反映存在着剪切带。几个中等地震(M≥3.5)1991年发生在隧道当前的位置,说明这些断层中的几条或波特兰山断层带的其他断层是地震活动断层。 相似文献
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重、磁勘探具有效率高、成本低、工作范围广等优点,已在地球物理勘探中得到了广泛应用.前人大多在不考虑重、磁勘探观测精度的条件下进行了垂向识别能力的研究,但在考虑重、磁观测精度条件下,重力(重力异常、重力张量)与磁力(磁力异常、磁力三分量、磁力张量)对孤立异常的垂向识别能力如何则需要进行深入的理论研究.本文从重、磁场正演理论出发,以球体(点源模型)和无限延伸水平圆柱体(线源模型)为例,考虑给定观测精度条件下,以重力和磁力幅值大小与观测精度的关系来研究垂向识别能力,从而消除了背景场的影响,提高了研究结果的可靠度.通过研究表明,对于孤立异常,重力张量在浅部一定深度内比重力异常的垂向识别能力强,该深度与重力异常和重力张量观测精度的比值成正比;垂直磁化磁力张量在浅部一定深度内比化极磁力异常的垂向识别能力强,该深度与磁力异常与磁力张量观测精度的比值成正比;磁力在浅部一定深度内比重力的垂向识别能力强,该深度与地质体的磁化强度和剩余密度比值、重力观测精度和磁力观测精度比值成正比.通过重力和磁力垂向识别能力的研究将为重、磁勘探的实际应用起到指导作用. 相似文献
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坦桑尼亚是东非第一产金大国,构造蚀变岩型金矿是该国的一个重要金矿床类型,该类型金矿床与断裂构造中的构造蚀变带密切相关,主要分布在坦桑尼亚环维多利亚湖东部、西南部及东南部绿岩带中;凯巴卡瑞地区内岩石磁性表现为强-中-弱-微或无的强度等级,岩石相互之间磁性差异明显,其航磁异常显示的地质信息比较详尽,反映的磁性地层、岩体界线清晰,线性构造特征明显.依据坦桑尼亚凯巴卡瑞地区尼亚斯罗利金矿床上的航磁异常表现形式,对凯巴卡瑞地区航磁异常强度、规模、形态及延伸等特征进行了认真分析和对比研判,认为该区域航磁异常客观地反映了与构造蚀变岩型金矿有关联的断裂构造和绿岩分布区,构造蚀变带、金矿脉以及所赋存的绿岩地层在航磁异常上表现为低强度磁异常,其他岩石(条带状铁建造、辉绿岩、花岗岩)在航磁异常上表现为高强度磁异常,据此选择的找矿靶区通过地面物探方法(高精度磁测、微磁测量)查证,取得了明显的找矿效果;凯巴卡瑞地区航磁异常解译厘定的地质信息,为进一步预测成矿区域、圈定找矿靶区及间接发现构造蚀变岩型金矿床奠定了基础,因而预判坦桑尼亚凯巴卡瑞地区分布的航磁异常具有寻找构造蚀变岩型金矿的较大潜力. 相似文献
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M. WAESELYNCK 《Geophysical Prospecting》1974,22(1):107-121
First, we review briefly the principle of the method, the computation of theoretical curves for a layered earth, and the recording technique in use in our surveys. The case history deals with an area covered with overthrust nappes (marls of Miocene age), which had slid on a Triassic sole, obscuring the geological picture. The magnetotelluric survey followed those of gravity and aeromagnetics and preceded the seismic one from North to South, it displayed a shallow and gently dipping basin, a major fault system, and a deep basin with a thick resistive layer, often underlying a conducting one. The seismics, and later the drilling of a well East of the profile, confirmed these features; in particular, the thick resistive layer was revealed to be Jurassic; only its thickness had been slightly overestimated. This fact lead the people in charge of the operations to ask for a reinterpretation synthesis of magnetotellurics, seismics and gravity, the results of which are also presented. 相似文献
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岩浆岩在青藏高原的大陆动力学研究中有着重要的作用,它既是构造演化的记录,又是重要构造-岩浆-成矿带的指示.本文主要基于冈底斯带及邻区的地面重力和航磁数据,首先进行地质-地球物理先验信息约束下的重磁2.5维交互式反演,再将2.5维反演结果作为参考模型加入到三维反演计算中,得到地下三维密度和磁化率结构.结合岩浆岩密度、磁化率统计资料和岩浆岩地球化学成果,推断研究区基性岩、I型花岗岩和S型花岗岩的三维分布图,得到如下结论:S型花岗岩主要分布在冈底斯东带和冈底斯弧背断隆带以北;北冈底斯的西部无明显的岩浆活动,而在其南侧和北侧,发现大量的隐伏基性岩和零散分布的I型花岗岩;中生代I型花岗岩在南冈底斯和冈底斯弧背断隆带广泛分布,且到新生代才出现大量的S型花岗岩.上述结果为中生代班公湖—怒江洋壳和新特提斯洋壳的双向剪刀式俯冲模式的观点提供了重要佐证,并认为班公湖—怒江洋壳在北冈底斯西部约84°E—88°E的范围内先后存在向北和向南俯冲的可能,北向羌塘地体下俯冲,南向冈底斯地体下俯冲. 相似文献
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David. B. Wenner 《Earth and Planetary Science Letters》1981,54(2):186-199
Data were acquired from 143 whole rock samples from 20 late orogenic, post-metamorphic, Hercynian-age granitic plutons from the Piedmont of the southern Appalachians, principally in Georgia and South Carolina. These plutons exhibit a regional gradient in oxygen isotopic compositions in which the granites confined to the Inner Piedmont to the northwest are18O-enriched (11.4 to 7.9) whereas those toward the southeast within the Charlotte-Slate and portions of the Kiokee belts have distinctly lower18O/16O compositions (8.2 to 5.5); one body that lies along the southeastern edge of the Piedmont in South Carolina, however, appears to be anomalously18O-enriched (8.9). Most plutons display18O/16O variations of <1‰ although two vary by as much as 3–4‰. The regional oxygen isotopic pattern among plutons appears to correlate directly with: (1) regional Bouguer gravity patterns, in which the18O-enriched plutons occupy areas characterized by negative anomalies, whereas low-18O bodies are invariably restricted to regions of positive anomalies; (2)87Sr/86Sr data, where granites with δ18O values <8‰ have low initial strontium ratios of ~0.703 to 0.705, while18O-enriched plutons (>9‰) have ratios >0.710; (3) contrasting chemical and accessory mineral compositions, in which many18O-depleted granites have a number of I-type characteristics, whereas several of the most18O-enriched plutons exhibit a number of S-type features. It can be inferred from these data that the18O-enriched granites were formed from continental crustal protoliths that underlie much of the Inner Piedmont and portions of the Kiokee belt, whereas the low-18O plutons were derived from more mafic sources beneath the Charlotte-Slate and portions of the Kiokee belt. The overall correspondence between the regional18O/16O patterns exhibited by the granites and gravity data implies that these grantes may be essentially rooted to their protoliths, in turn suggesting that the large-scale translational movement recently proposed for the Southern Piedmont may have occurred prior to intrusion of these granites ~320 m.y. ago. 相似文献
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Vratislav Blecha Miroslav Štemprok Tomáš Fischer 《Studia Geophysica et Geodaetica》2009,53(3):295-314
We examined the shape of the Late Variscan Karlovy Vary granite massif located south of the Ohre/Eger graben in Northern Bohemia
by reinterpretation of existing gravity data on two perpendicular profiles. The granite body of about 360 km2 total outcrop size has the elongation ratio 0.35 with the major axis trending NE-SW. The SW part of the body was crossed
in the nineties by the seismic profile 9HR which localized the bottom of granites in a depth of about 10 km. We used this
value as a reference datum in our gravity profiles. We positioned one of our profiles along the seismic profile 9HR and the
other one perpendicularly, i.e. parallel with the elongation of the outcrop surface. We interpret the shape of the main granite
body in the vicinity of Karlovy Vary as a continuous desk whose floor is horizontal (or subhorizontal) and varies along its
whole extension about a depth of 10 km. This thickness is approximately identical with that of the Saxothuringian nappes imaged
by seismic reflection. The near surface upper contact of the granite body is mildly inclined, and outward dipping. It changes
to steep sides or inward inclined contacts in deeper levels. The Lesny-Lysina (Kynžvart) massif is a separate granite body
about 324 km thick, not continuously connected with the main Karlovy Vary massif. The gravity curve suggests that granites
often enclose in their endocontact large blocks of country metasediments or metabasites the existence of which is partly evidenced
by their outcrops outside the line of the profile. The granite body is found density-homogenous. Minor density differences
between granite varieties are caused mainly by more intense hydrothermal alterations in younger suite granites. We interpret
vertical conduits for the ascent of granitic magmas to be parallel to the Jáchymov-Gera and Ohře (Eger) lineaments or the
Mariánské Lázně fault zone as indicated by the elongation of some outcrops. However, they are not clearly imaged from the
gravity data. The effect of the depression of the Sokolov basin along the faults parallel with the Ohře (Eger) lineament is
shallow and it is not indicated by any change in the floor depth of the granite body. Comparison of the seismicity distribution
suggests that the hypocenters occur mostly outside of the granite bodies or near their contact with the country rock. 相似文献
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From our interpretation of the Bouguer gravity and aeromagnetic anomalies in south-east Scotland, we conclude that a massive granite batholith underlies the greater part of the eastern Southern Uplands. The granite model which we computed earlier from gravity anomalies in the Tweeddale area fits the observed magnetic anomalies closely, if a normal magnetization of 0.095 A m–1 is assigned, similar to values found for exposed local granites. Further gravity modelling shows that, apart from the Tweeddale boss, the granite shallows to less than 1 km near Lammer Law in East Lothian and extends north of the Lammermuir Fault. A model for the East Lothian volcanics was computed from their aeromagnetic anomalies, then their gravitational effect was combined with that estimated for the Devonian and Carboniferous sediments and the result stripped off the observed gravity field. The residual gravity anomalies were used to generate a two-dimensional model for the granite north of the Lammermuir Fault. The expected tectonic consequences of a massive granite batholith in the eastern Southern Uplands are compared with the known development of faults and sedimentary basins around its margins. 相似文献
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《Journal of Geodynamics》2003,35(1-2):209-220
The occurrence of swarm earthquakes in the Vogtland/NW-Bohemia area results probably from the physical interactions of fluids, the stress field and the geometry of the geological units. Therefore the present study aims at the development of a 3-D density model of the region with a vertical range of 35 km. A new Bouguer anomaly map is presented containing about 17 000 gravity data points. Prominent Bouguer anomalies are produced by the granites of Eibenstock and Karlovy Vary (low with −75 mGal), the metabasites near Mariánzké Lázně (high with 5 mGal) and the Münchberg Gneiss Massif (gravity high of Hof with 10 mGal). The geometry of the internal model structures correspond to geological units and, thus, the modelled gravity fits well the observed Bouguer anomaly. The 3-D gravimetric modellings indicate detailed geometries of the geological settings. With regard to the periodic occurrence of swarm earthquakes in the Vogtland region the existence of an upwelling mantle or a magmatic body is investigated. Precise information only can be given, if the vertical extension of the near surface bodies is known. 相似文献
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《中国科学:地球科学(英文版)》2017,(11)
The Nanling and adjacent regions of South China host a series of tin deposits related to Mesozoic granites with diverse petrological characteristics. The rocks are amphibole-bearing biotite granites, or(topaz-) albite-lepidolite(zinnwaldite) granites,and geochemically correspond to mealuminous and peraluminous types, respectively. Mineralogical studies demonstrate highly distinctive and critical patterns for each type of granites. In mealuminous tin granites amphibole, biotite and perthite are the typical rock-forming mineral association; titanite and magnetite are typical accessory minerals, indicating high fO2 magmatic conditions;cassiterite, biotite and titanite are the principal Sn-bearing minerals; and pure cassiterite has low trace-element contents. However,in peraluminous tin granites zinnwaldite-lepidolite, K-feldspar and albite are typical rock-forming minerals; topaz is a common accessory phase, indicative of high peraluminity of this type of granites; cassiterite is present as a uniquely important tin mineral,typically rich in Nb and Ta. Mineralogical distinction between the two types of tin granites is largely controlled by redox state,volatile content and differentiation of magmatic melts. In oxidized metaluminous granitic melts, Sn4+ is readily concentrated in Ti-bearing rock-forming and accessory minerals. Such Sn-bearing minerals are typical of oxidized tin granites, and are enriched in granites at the late fractionation stage. In relatively reduced peraluminous granitic melts, Sn2+ is not readily incorporated into rock-forming and accessory minerals, except for cassiterite at fractionation stage of granite magma, which serves as an indicator of tin mineralization associated with this type of granites. The nature of magma and the geochemical behavior of tin in the two types of granites thus result in the formation of different types of tin deposits. Metaluminous granites host disseminated tin mineralization,and are locally related to deposits of the chlorite quartz-vein, greisen, and skarn types. Greisen, skarn, and quartz-vein tin deposits can occur related to peraluminous granites, but disseminated mineralization of cassiterite is more typical. 相似文献
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Emplacement P-T condition estimations using granites are important for understanding metamorphic and erosional processes of orogenic belt.Granites are widespread in South China and a majority of them are peraluminous.Particularly,over 91%of the Indosinian granites exposed in the region are peraluminous in composition.It is extremely hard to determine the pressure of intrusion of these peraluminous granites due to the absence of amphibole,a good mineral barometer commonly identified in metaluminous granites.Muscovite is a common mineral in peraluminous granites,certain kind of it could be used as a mineral barometer to constrain the emplacement pressure of peraluminous granites.In this paper,results of petrographic and geochemical studies of muscovites from the Indosinian and early Yanshanian two-mica granites at the Longyuanba in the eastern Nanling Range are reported.Based on petrographic studies,the primary muscovite can be discriminated from the secondary muscovites.Muscovites from the Indosinian two-mica granites are enriched in Ti,Al,Mg,and Na,and depleted in Fe and Mn.Geochemically,these muscovites were considered as primary,whereas those from the Yanshanian two-mica granites fall into the area of secondary muscovite on discrimination diagrams.Barometer estimations show that pressures calculated for primary muscovites are accurate,but those calculated for secondary muscovites are overestimated.The average pressure of emplacement of the Longyuanba Indosinian two-mica granites is 5.9 kbar,corresponding to~19 km in depth,suggesting that the Indosinian granitic magmas were probably generated by partial melting of a thickened crust root in a compressional tectonic setting. 相似文献
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Multiple-aged granitoids and related tungsten-tin mineralization in the Nanling Range, South China 总被引:11,自引:0,他引:11
The Nanling metallogenic belt in South China is characterized by well-developed tungsten-tin mineralization related to multiple-aged granitoids. This belt is one of the 5 key prospecting and exploration areas among the 19 important metallogenic targets in China. Important progress has been made in recent years in understanding the Nanling granitoids and associated mineralization, and this paper introduces the latest major findings as follows: (1) there exists a series of Caledonian, Indosinian, and Yanshanian W-Sn-bearing granites; (2) the Sn-bearing Yanshanian granites in the Nanling Range form an NE-SW trending aluminous A-type granite belt that stretches over 350 km. The granites typically belong to the magnetite series, and dioritic micro-granular enclaves with mingling features are very common; (3) the Early Yanshanian Sn- and W-bearing granites possess different petrological and geochemical features to each other: most Sn-bearing granites are metaluminous to weakly peraluminous biotite (hornblende) granites, with zircon ?Hf(t) values of ca. ?2 to ?8, whereas most W-bearing granites are peraluminous two-mica granites or muscovite granites with ?Hf(t) values of ca. ?8 to ?12; (4) based on the petrology and geochemistry of the W-Sn-bearing granites, mineralogical studies have shown that common minerals such as titanite, magnetite, and biotite may be used as indicators for discriminating the mineralizing potential of the Sn-bearing granites. Similarly, W-bearing minerals such as wolframite may indicate the mineralizing potential of the W-bearing granites. Future studies should be focused on examining the internal relationships between the multiple-aged granites in composite bodies, the metallogenic peculiarities of multiple-aged W-Sn-bearing granites, the links between melt evolution and highly evolved ore-bearing felsic dykes, and the connections between granite domes and mineralization. 相似文献