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1.
An array of sigmoidal tension gashes from the Idaho—Wyoming thrust belt changes laterally into a continuous vein. Detailed mechanical twin analysis was used to determine the strain variation in the optically and chemically homogeneous blocky calcite filling. In the continuous portion of the vein complex, the shortening axes are parallel to the vein boundary. However, the orientation of the shortening axes in the tip areas of the sigmoidal gashes are at an angle of approximately 35° to the vein boundary, and are parallel to the trend of the tips. Twinning patterns in the central portions of the gashes record two principal strain axes of shortening of nearly equal magnitude with the maximum perpendicular to the vein trend. Everywhere in the vein complex the orientation of the maximum extension axis is parallel to the twist axis of the gashes. The petrofabric strain results show that the vein filling has largely recorded local strains. The pattern of variation in orientation of the principal strains in the vein complex is in close agreement with the theoretically determined stress distribution in similar structures. Our results show that the sigmoidal gashes were formed at the leading edge of a propagating vein and that the sigmoidal shape reflects changes in the local strain field rather than a remote shear. The orientation of these local strains closely corresponds to the orientation of the local stresses.  相似文献   

2.
Fluid inclusions and clay mineralogy of the Permo-Triassic rocks from the Espina and Espadà Ranges (SE Iberian Chain, Spain) have been investigated to establish their relationship with hydrothermal fluid circulation during the Alpine Orogeny. Primary fluid inclusions in quartz-filled tension gashes in Permo-Triassic sandstones reveal maximum temperatures around 230 °C and very constant salinities of 8.5% wt. eq. NaCl. Secondary fluid inclusions found in quartz from the Santonian Ba–Cu–Hg deposits show similar compositional and thermodynamic characteristics, denoting an Alpine recrystallization. Clay mineral composition of Permo-Triassic mudrocks is characterized by pyrophyillite, indicating low-grade metamorphic conditions. Field observations and experimental data suggest that the crystallization of quartz in tension gashes, the formation of secondary fluid inclusions and the development of the metamorphism are contemporaneous and related to fluid circulation during the Alpine compression. Fluid flow took place along the Hercynian fault system that was reactivated during the Mesozoic rift stage and inverted during the Alpine deformation.  相似文献   

3.
Magnetovariational studies have been carried out in Singhbhum and surrounding regions during 1987 and 1989. Three deep-seated linear conductors have been identified. One of them is located to the north of Ranchi, Bokaro and Purulia extending in E-W direction coinciding with high heat flow region and Gondwana sediments. The trend of anomaly at Ranchi and Purulia at longer periods suggests a conductivity anomaly due to the mafic and ultramafic intrusions, considered to be responsible for the uplift of Chhotanagpur plateau. The second conductor is associated with the basin margin fault that separates the Singhbhum craton and Chhotanagpur plateau from the West Bengal basin. This conductive zone appears to extend further south and join the high heat flow region of Attri-Tarabalo. This conductor could be isolated only after eliminating the coast effect from the observed induction vectors. The third conductive zone follows the trend of Mahanadi valley located south of the Sukinda thrust. Conductive anomaly associated with the Sukinda and Singhbhum thrust zones could not be resolved due to the interference from neighbouring conductive structures. These two thrusts may not be very deep-seated structures. The Singhbhum granite batholith is found to be highly resistive and seems to extend to greater depths.  相似文献   

4.
Some peculiar ‘bone-shaped’ boudins are observed in two areas of progressive shearing. They are characterized by large quartz-filled gashes that separate thinner boudins. These gashes often have a consistent obliquity, suggesting a rotation synthetic to the shear sense. These may be formed by rigid material that crystallizes in tension gashes between the boudins; during further ongoing deformation these behaved as rigid inclusions in a more ductile matrix and show systematic rotations. The sense of rotation of the gashes constitutes a shear criterion.  相似文献   

5.
The potential of using sigmoidal tension gashes as strain markers for assessing strain localisation in shear zones is discussed. The appropriate analytical methods for this purpose depend on the assumed mechanism of tension gash formation. Two such models are considered. The first is one in which the curvature of the gash is produced by passive rotation of different segments of the gash in response shear strain gradients across the shear zone. The other model is one in which the curvature of the gashes is governed by the folding of the competent rock bridges between adjacent gashes. In the latter case, the tension gashes progressively grow within spaces created by the buckling bridges and therefore lead to a bulk dilatation of the shear zone. However, for the folded bridge mechanism to continue to operate beyond shear strains greater than unity requires a significant volume loss which in turn may signal the increase of the shear strength of the zone. The geometrical characteristics of gash arrays resulting from these two mechanisms are described and criteria given for the recognition of the two types of gash arrays. A new graphical method is proposed for the analysis of deformation in shear zones containing folded-bridge tension gashes. Tension gash arrays from Marloes, West Wales are used as examples of the procedures for shear zone analysis.  相似文献   

6.
江西省兴源冲地区深部找矿潜力评价   总被引：1，自引：0，他引：1       下载免费PDF全文
江西省兴源冲地区处于九岭南缘逆冲推覆构造系中,NEE向的慈化—宜丰板缘深断裂带及大型推（滑）覆构造西段向南呈弧型转弯并与湘赣边界的NNE向走滑推覆冲断带复合,形成了对铜多金属矿成矿有利的异常构造、岩浆岩、矿源层及赋矿层、矿化异常等控矿因素耦合区。该区具有明显的地、物、化、遥找矿信息：区域1∶20万和1∶5万水系沉积物测量显示Cu,Pb,Zn高异常区;1∶2.5万和1∶1万土壤地化测量已圈定出Cu,Pb,Zn,Au,Ag元素异常多处,综合异常4处;1∶1万激电异常明显;少量探槽、钻孔控制求得333＋3341资源量已具小型规模。根据成矿地质条件及物、化异常分析,该区深部找矿潜力较大,有望扩大为中型以上规模铜矿床。  相似文献   

7.
There are, in principle, direct relations between several important phenomena associated with subduction zones: the depth of oceanic trenches, the magnitude of the net force from trenches acting on subducting plates, the distribution and fault plane orientations of earthquakes, the magnitude of stresses on subduction faults, the bathymetry of back-arc regions, and the magnitudes of gravity and geoid anomalies. These phenomena are related through the stresses transmitted through surface and subducted lithosphere, and are associated with the mass anomaly of the subducted lithosphere. Quantitative estimates suggest that observed trench depths imply a trench pull force on subducting plates which is comparable to the ridge push force but much less than the excess weight of the subducted lithospheric slab. It is further suggested that either the mass anomaly of subducted lithosphere is much less than would be expected on the basis of conventional thermal and compositional models or that (a) a large resistance acts on the upper part of slabs due to high-stress corner flow, and (b) the mass anomaly of the slab is 70–90% compensated either by a broad 1 km-deep back-arc depression or a low density mantle wedge above the slab or both.  相似文献   

8.
Consistent arrangement of en-echelon gashes occurring within kink zones was observed and measured at several localities in the Lubec—Belleisle structural zone of southwestern New Brunswick.The special geometric relationship of both kinks and en-echelon fracture systems allow an interpretation of the regional and local stress orientations necessary to produce such combined features.Mohr-circle stress analysis of a modified direct shear model is used to postulate a mechanism whereby varying orientations of en-echelon tension gashes and boundary shears within kink zones can be explained. Using this analysis, the observed gash orientations can be generated by reduction in the local normal stress acting on original kink-zone boundaries, coupled with a corresponding increase in the normal stress acting transverse to such boundaries. These stress adjustments could be due to deflection of regional stress trajectories around local zones of yielding (by kinking) rock.  相似文献   

9.
The structural geometry, kinematics and density structure along the rear of the offshore Taiwan accretionary prism were studied using seismic reflection profiling and gravity modeling. Deformation between the offshore prism and forearc basin at the point of incipient collision, and southward into the region of subduction, has been interpreted as a tectonic wedge, similar to those observed along the front of mountain ranges. This tectonic wedge is bounded by an east-dipping roof thrust and a blind, west-dipping floor thrust. An east-dipping sequence of forearc-basin strata in the hanging wall of the roof thrust reaches a thickness in excess of 4 km near the tip of the interpreted tectonic wedge. Section restoration of the roof sequence yields an estimate of 4 km of shortening, which is small compared with that inferred in the collision area to the north, based on the variation in distance between the apex of the prism and the island arc.Previous studies propose that either high-angle normal faulting or backfolding has exhumed the metamorphic rocks along the eastern flank of the Central Range in the collision zone on land. To better constrain the initial crustal configuration, we tested 350 crustal models to fit the free-air gravity anomaly data in the offshore region to study the density structure along the rear of the accretionary prism in the subduction and initial collision zones before the structures become more complex in the collision zone on land. The gravity anomaly, observed in the region of subduction (20.2°N), can be modeled with the arc basement forming a trenchward-dipping backstop that is overlain by materials with densities in the range of sedimentary rocks. Near the point of incipient collision (20.9°N), however, the free-air gravity anomaly over the rear of the prism is approximately 40 mgal higher, compared with the region of subduction, and requires a significant component of high density crustal rocks within the tectonic wedge. These results suggest that the forearc basement may be deformed along the rear of the prism, associated with the onset of collision, but not in the subduction region further to the south.  相似文献   

10.
The May 12, 2008, Mw 7.9 Wenchuan earthquake was induced by failure of two of the major faults of the Longmen Shan thrust fault zone along the eastern margin of Tibet Plateau. Our study focused on trenches across the Yingxiu–Bichuan fault, the central fault in the Longmen Shan belt that has a coseismic surface break of more than 200 km long. Trenching excavation across the 2008 earthquake rupture on three representative sites reveals the styles and amounts of the deformation and paleoseismicity along the Longmen Shan fault. Styles of coseismic deformation along the 2008 earthquake rupture at these three sites represent three models of deformation along a thrust fault. Two of the three trench exposures reveal one pre-2008 earthquake event, which is coincident with the pre-existing scarps. Based on the observation of exposed stratigraphy and structures in the trenches and the geomorphic expressions on ground surface, we interpret the 2008 earthquake as a characteristic earthquake along this fault. The interval of reoccurrence of large earthquake events on the Central Longmen Shan fault (the Yingxiu–Beichuan fault) can be inferred to be about 11,000 years according to 14C and OSL dating. The amounts of the vertical displacement and shortening across the surface rupture during the 2008 earthquake are determined to be 1.0–2.8 m and 0.15–1.32 m, respectively. The shortening rate and uplift rate are then estimated to be 0.09–0.12 mm/yr and 0.18–0.2 mm/yr, respectively. It is indicated that the deformation is absorbed mainly not by shortening, but by uplift along the rupture during the 2008 earthquake.  相似文献   

11.
王洋  冯君  谢先当  赖冰  杨涛 《岩土力学》2018,39(11):4226-4231
针对有顶板连接的“八”字形微型桩组合结构,依托广大（广通至大理）线扩能改造工程,现场监测微型桩工作状态下轴力变化,对微型桩组合支护体系应用于分级开挖边坡加固的受力机制进行研究分析。结果表明：在滑坡推力作用下,各排桩桩身轴向力的分布形式不尽相同,沿推力方向依次呈现出反“S”型、“双弓”型和“S”型的分布规律;各排桩峰值轴力均为拉力,比例关系为：靠山侧桩:中间桩:靠路侧桩=2.5:4.1:3.2,其中靠山侧桩最大轴力出现在桩体下部,中间桩出现在中上部,靠路侧桩最大轴力出现在桩体上部;顶部承台对有斜桩的微型桩群的制约协调作用比一般的竖直桩群显著,水平荷载作用下的桩群易发生较大的挠曲变形,在群桩效应、坡体滑裂面等的综合影响下,引发桩体拉-压等受力形式的转变;组合结构的受力机制表现为先承受滑坡主推力的前两排桩受拉,第3排桩底部嵌固段受压,且随着持续推力作用受压区存在向上发展趋势;各单桩桩身轴力以拉力为主,有利于内部钢筋受拉优势的发挥。  相似文献   

12.
Analysis of anisotropy of magnetic susceptibility (AMS) and brittle mesostructures (hydroplastic synsedimentary faults and tension gashes) is applied in this study in order to characterize the Mesozoic tectonic events in the Cameros basin (NW Iberian Range), formed between Tithonian and Albian times. Low-field AMS at room and low temperature (LF-AMS at RT and LF-AMS at LT, respectively) together with high-field AMS (HF-AMS) measurements allow separating ferro- and paramagnetic fabrics. The combination of LF-AMS at LT and HF-AMS torque measurements confirms the reliability of both procedures in terms of isolating the paramagnetic contribution to the AMS. Magnetic fabric results combined with the analyses of synsedimentary faults indicate a NW–SE extension direction during Aptian (and probably Barremian) times. This extension direction is perpendicular to the main extension direction (NE–SW) prevailing during early and late stages of basin evolution. It is also consistent with extension direction deduced from large-scale bending folds and tension gashes, developed after partial lithification. Cleavage development during Albian enhanced the orientation of the magnetic fabric in lithologies where the previous extensional magnetic lineation is coaxial with the expected one for compression.  相似文献   

13.
Geometric and kinematic analysis was performed in an area located in the central part of the Seridó Belt (NE Brazil), where supracrustal rocks affected by polyphase deformation are well exposed. The first event recognized in this area (and regionally known as the D2 deformation) is characterized by top to the south thrust tectonics while a second one (D3 deformation) is marked by upright folds, strike-slip or transpressive shear zones and the development of flower structures. Major pegmatite swarms were emplaced during and late as regards the second event (dated ca. 580 Ma), being part of the Brasiliano orogeny; similar dyke swarms are known from the Nigerian Shield. These pegmatite swarms provide reliable kinematic markers of the late evolutionary stage of the Neoproterozoic Trans-Sahara-Borborema collisional belt. Mineralogical, geometric and kinematic features support two stages of pegmatite emplacement during the strike-slip event: (i) older, syn-D3 homogeneous pegmatites intruded mostly along lithological and structural discontinuities, such as foliation surfaces; (ii) late, D3 heterogeneous pegmatites were emplaced along tension gashes and other dilation structures. The heterogeneous pegmatites are economically more important, being exploited for precious metals and stones, as well as industrial minerals.  相似文献   

14.
About seven hundred gravity stations were established 2–3 miles apart over the Precambrian terrain of Singhbhum that lies between latitude 22° 15′ to 23°°15′N and longitude 85° to 87°E. Bouguer anomalies ranging from +4 to −62 mGal are found in the area. The observed Bouguer anomaly map was analyzed into regional and residual components. The residual anomaly map shows an excellent correlation with geology. The Singhbhum granite batholith is associated with several gravity lows. The residual anomaly map outlines nine plutonic granitic masses within the Singhbhum batholith. Negative residuals are also observed over some intrusive granites outside the batholith. Residual gravity highs are noted over the Dalma hill as well as over the Dhanjori lava complex on the eastern part of the Singhbhum batholith.Two-dimensional models suggestive of subsurface configuration of several major geologic units in the area are presented. These indicate that some of the plutonic granites within the Singhbhum batholith are of relatively large dimensions. The basin containing the Iron Ore Group of rocks to the west of the batholith, as well as the basin containing Singhbhum Group of rocks outside the Copper Belt thrust, may have sedimentary thicknesses of the order of 6–7 km. The Dalma lavas attain their maximum thickness of about 2.5 km in the form of a syncline, underneath which the Singhbhum Group of rocks is also found to be the thickest. The Copper Belt thrust, a major Precambrian fracture around the Singhbhum batholith, is moderately north-dipping near the surface but possibly attains a steeper slope at depth. The thrust appears to be quite deep seated. A threedimensional computer-based model for the Dhanjori lava—gabbro complex on the eastern part of the Singhbhum batholith has been deduced. Maximum thickness of these basic rocks is found to exist underneath a thin cap of granophyre. The geological implication of these results is discussed.Variation in the regional anomalies seems to be attributable to a mass deficiency under the Singhbhum batholith. The batholith may extend subsurfacially towards the north across the Copper Belt thrust. The northern tip of the batholith probably became dissected along the line of intersection of the two orogenic trends in the area and subsided. Over this subsided part, the Singhbhum Group of rocks was deposited at a later stage. Gravity data suggest a fairly large amount of subsidence in the area.  相似文献   

15.
A eutrophication gradient was assembled from four spring-fed estuaries and four surface-fed estuaries to determine whether changes in zooplankton and hyperbenthos abundance along the gradient were gradual or abrupt. For 1 year in each estuary, monthly faunal surveys were conducted during nighttime flood tides using oblique plankton-net tows, producing abundance data for 316 taxa. Indicator taxa for the spring-fed and surface-fed groups were identified from a combination of abundance and encounter frequencies. Seventeen of the 20 strong indicator taxa for the spring-fed group (85 %) were benthic, whereas 10 of the 13 strong indicators for the surface-fed group (77 %) were plankton-oriented. The eight communities were ordinated by canonical analysis of principal coordinates (CAP); the estuarine faunas were found to be uniquely distributed along the principal CAP axis. Success of blind reclassification of plankton samples to their respective estuaries of origin ranged from 75 to 100 % (mean, 91 %). Given the assembled gradient was composed of distinctive communities that were distributed across a broad range of trophic states, the transition between benthic and plankton-oriented indicators was investigated and found to be abrupt, with strong shifts occurring nearer the oligotrophic end of the gradient. The CAP ordination agreed with trends in light attenuation, but not dissolved oxygen. We conclude that the abrupt faunal shifts were likely related to differences in basal resource (primary producer) availability brought about by differences in light environment. Abrupt loss of benthic basal resources will affect benthic consumers and those plankton-oriented consumers that intermittently depend on benthic biomass pathways whenever plankton-based pathways are unproductive.  相似文献   

16.
. The Glarus thrust is a prominent tectonic feature in the eastern Helvetic Alps. It has been recognized as a potential major pathway for syntectonic crustal scale fluid flow. The oxygen, carbon and strontium isotope patterns obtained from two vertical profiles across the thrust indicate fundamentally different flow regimes in the southern section of the thrust, where the footwall is represented by Mesozoic limestones, and in the northern section, where the footwall is represented by Tertiary flysch. At the Grauberg locality in the south, the observed isotope patterns give evidence of a net mass transport component from the hanging wall Verrucano to the footwall limestone with a maximum time-integrated volumetric fluid flux of 6.1 m3/m2 In the south, the hydration of the lowermost 10 to 20 m of the hanging wall Verrucano requires introduction of an aqueous fluid by subhorizontal flow along the thrust with a minimum time integrated flux of 240 m3/m2. At the Lochseite locality in the north, the isotope patterns indicate a vertical mass transport component from the footwall flysch to the hanging wall Verrucano with a time-integrated fluid flux of 2.6 m3/m2. In the north, the fluids were probably derived from compaction and dehydration of the footwall flysch during thrusting. The ascending fluids were ponded below the Verrucano and 'lubricated' the thrust. Short-term pressure drops associated with seismic motion along the thrust led to the precipitation of calcite in veins at the thrust surface contributing material to the Lochseiten calc-mylonite, a thin calc-mylonite layer at the thrust contact. Although cross thrust fluid flow may have been two to three orders of magnitude smaller than flow along the thrust, it had a major impact on the isotopic composition of the Lochseiten calc-mylonite. In particular, it buffered the oxygen isotope composition of the calc-mylonite towards the relatively 18O-depleted composition of the hanging wall Verrucano in the south and towards the relatively 18O-enriched compositions of the footwall flysch in the north. By this mechanism a regional south to north 18O-enrichment trend was simulated within the Lochseiten calc-mylonite.  相似文献   

17.
A simple mechanism of arcuate fold belt and back-arc basin formation is presented based on the opening of mega-continental tension gashes along pre-existing, deep, parallel and steep faults that separate lithospheric units with different properties. If plate convergence is parallel to these faults, the fault-bounded units open at right angles to the convergence vector, adopting an arcuate shape with thrusting in front of the bowed-out units and extensional basin opening between the separated units. This model is applied to the Cenozoic geodynamic evolution of the western Mediterranean. After the Iberian collision 35–30 Ma, several ellipsoidal basins (Valencia, Alboran, North Algerian and Liguro–Provençal) developed by 10 Ma along the eastern margin of the Iberian plate. The formation of these basins is attributed to an increase in NE–SW horizontal tectonic palaeostress during early–middle Miocene times resulting from the post-subduction collision of the Tethyan oceanic lithosphere.  相似文献   

18.
《Geodinamica Acta》2013,26(3-4):165-184
Models consisting of a thick overburden resting on a buoyant layer were sheared and centrifruged in order to study the relationship between strike-slip shear zones and intrusions of buoyant material. Three experiments were carried out: In model 1, where the overburden consisted of a viscous material, no diapirs formed even after shearing for 40 mm (? = -1.07) and 27 min centrifuging. In models 2 and 3, where the overburden was semi-brittle, prescribed cuts at two different orientations (model 2: parallel to s1; model 3: perpendicular to s1) were initiated in the overburden in order to see whether such cuts acted as pathways for intrusion. In model 2 the prescribed cuts were used by the buoyant material as pathways when the cuts opened during shearing. Continued shearing widened the cuts and allowed the buoyant material to extrude on the surface of the model forming a coalesced elliptical sheet. In model 3. the cuts were closed during shearing and prevented the intrusion of the buoyant material. During further shearing, the cuts rotated and activated as strike-slip faults bounding pull-apart basins. Such pull-apart basins were not deep enough to tap the buoyant material. Nevertheless, the results of the experiments suggest that magma ascends in shear zones not as diapirs, but rises along preexisting pathways as dykes. Model results were used to evaluate emplacement of the Fürstenstein Intrusive Complex (FIC) in the Bavarian Forest, whose magnetic and structural inventory have been investigated in detail. The pluton consists of 5 magma batches, each with distinct magnetic fabrics. which are interpreted as the result of magma intrusion along opening and rotating tension gashes within the BPSZ stress field. Shear failure of the crust in the FIC area due to thermomechanical weakening provided the space for the emplacement of the last and biggest granite magma batch. Overall, the emplacement history of the FIC fits perfectly with the observations made during experiment 2 and indicates that magma ascent in shear zones is bound to tension gashes.  相似文献   

19.
The recent completion of a high-resolution aeromagnetic survey over the Pie de Palo uplift of the western Sierras Pampeanas has revealed an area of large magnetic anomalies associated with the Pie de Palo Complex. The Las Pirquitas thrust, which has transported and uplifted the Pie de Palo Complex, is recognized for at least 30 km in a roughly NE direction along the western boundary of the Pie de Palo Complex, beyond its limited outcrop. The type of sediments of the Caucete Group in the footwall of the Las Pirquitas thrust, which are regarded as the leading edge of the Precordillera terrane, are associated with much less pronounced magnetic anomalies.In addition, a conspicuous, NNE trending, broad magnetic high stands out in the survey, several kilometers to the east of the main outcrops of the Pie de Palo Complex; this broad magnetic anomaly bisects the Pie de Palo basement block, and continues further south at least as far as 32°S, the southern boundary of the latest aeromagnetic survey. This magnetic anomaly is interpreted to represent a structure corresponding to the Grenvillian Precordillera–Pie de Palo tectonic boundary zone, and would comprise the buried largest part of the mafic–ultramafic belt.The geophysical model of the magnetic data indicates that the boundary zone dips to the east, possibly suggesting the existence of a set of synthetic east dipping, west-verging thrusts, of which only one major structure (Las Pirquitas thrust) is exposed; the possibility of other slivers of upthrust boundary zone material cannot be excluded. It is considered that the Pie de Palo Complex represents a small sliver upthrust from the unexposed boundary zone material (containing highly magnetic mafic–ultramafic rocks).The east-dipping, west verging structures associated with the Pie de Palo Complex are suggested to represent an Ordovician reactivation of a Grenvillian suture zone developed when the Precordillera basement and Pie de Palo terrane docked; this reactivation probably resulted from the collision of the Cuyania terrane onto the western margin of Gondwana.  相似文献   

20.
Abstract Regional metamorphism in the external Variscides of southwest England varied from diagenetic level to greenschist facies. There is a fundamental difference in the metamorphic character between the northern and southern regions of the area. In the north, M1 metamorphism is of a sedimentary burial character associated with high heat flow, whilst to the south it is related to tectonic burial during thrust thickening processes, with lower geothermal gradients. This pattern appears to be related to the character of basin development and its subsequent tectonic evolution. The northern region has features that accord with a diastathermal (extensional) origin for the very low-grade metamorphism whilst in the southern region the very low-grade metamorphism is linked to thrusting as a consequence of Variscan compression. The Tintagel High-Strain Zone presents an anomaly in this regional pattern where an M2 metamorphic phase is attributed to localized D2 thrust stacking along the southern margin of the Culm Basin.
There is no extensive overprint of the regional metamorphic pattern by the contact aureoles surrounding the granite plutons of the region. However, there is a noticeable coincidence between the areas of regional epizone grade and the extent of the geophysically defined subsurface limit of the granite batholith (excluding the North Devon area). This link is attributed largely to the late-stage structural up-doming of the higher grade areas over the roof of the batholith.  相似文献   

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