Stages Of Intrusion Research Articles

Petrogenesis of volcanic and intrusive rocks of the Zhuanqiao stage, Luzong Basin, Yangtze metallogenic belt, east China: implications for ore deposition

The Mesozoic Luzong volcanic basin is located in the Lower Yangtze River fault-depression, along the northern margin of the Yangtze Block. Volcanic and plutonic rocks are widely distributed in the basin and are spatially related to Cu, Fe, Au, Pb, and Zn ore deposits. The magmatic rocks are dominated by an alkali-rich shoshonitic suite of volcanics and intrusives, including both a trachybasalt-basaltic trachyandesite-trachyte series and a diorite-monzonite-syenite-alkali feldspar granite series. Volcanic sequences within the Luzong Basin are subdivided into four stages, namely the Longmenyuan, Zhuanqiao, Shuangmiao, and Fushan stages with magmatism occurring between 136 and 124 Ma. Most mineral deposits were formed during the Zhuanqiao stage from about 134 to 131 Ma, during a longer (140–130 Ma) period of transition from compression to extension within the Luzong Basin. Major element concentrations in the Zhuanqiao volcanic rocks range from 53.97 to 62.59 wt.% SiO2, 0.57–0.94 wt.% TiO2, 3.52–6.07 wt.% Na2O, and 3.60–8.66 wt.% K2O. Combined K2O + Na2O totals lie between 7.87 and 12.49 wt.%, and K2O + Na2O/Al2O3 ranges between 0.47 and 0.71. In comparison, the Zhuanqiao intrusions have SiO2 concentrations between 52.19 and 67.70 wt.%, TiO2 between 0.26 and 1.13 wt.%, Na2O between 1.33 and 6.55 wt.%, and K2O between 2.15 and 8.25 wt.%, with K2O + Na2O values ranging from 5.92 to 12.39 wt.% and K2O + Na2O/Al2O3 ratios between 0.37 and 0.75. The Zhuanqiao volcanic rocks have an average ∑REE (rare earth element) content of 223.17 ppm, whereas the average ∑REE of the Zhuanqiao intrusives is 250.06 ppm. Weak negative Eu anomalies (Eu/Eu* between 0.69 and 1.00) characterize the volcanics, whereas a larger range with more significant negative Eu anomalies (Eu/Eu* values of 0.35–0.94) is present in the plutonics. The Zhuanqiao volcanic rocks and plutons have (Nb/Th)PM ratios of 0.05–0.14 and 0.02–0.14 and (La/Sm)PM of 3.33–4.95 and 3.36–7.29, respectively. Initial 87Sr/86Sr and 143Nd/144Nd ratios and ϵSr(t) and ϵNd(t) of the Zhuanqiao volcanic rocks are 0.7059–0.7067, 0.51194–0.51218, 22.0–33.3, and −10.2 to −5.5, respectively; those of the intrusives are 0.7060–0.7082 and 0.51203–0.51214 and 23.3–54.7 and −8.6 to −6.4, respectively. The geochemistry presented here suggests that both volcanic and intrusive Zhuanqiao stage magmatic rocks were cogenetic and were probably derived from an enriched mantle (EM) source, most probably metasomatized mantle relating to the EM type-I (EM-I). The Zhuanqiao stage magmatism apparently was controlled by differentiation and assimilation of crustal material in a high-level magma chamber. Formation of the Zhuanqiao stage magmatic rocks coincided with the formation of much of the Cu and Fe mineralization within the Luzong Basin. This coeval magmatism and mineralization during the Zhuanqiao stage can be subdivided into three differing mineral deposit affinities: magmatism associated with magmato-hydrothermal vein Cu (e.g. the Jingbian, Shimenan, and Chuanshandong deposits), porphyry-hosted Fe (e.g. the Luohe and Nihe deposits), and skarn Fe (e.g. the Longqiao deposit). Combining geological characteristics with variations in SiO2, K2O + Na2O, and MgO enabled the division of the Zhuanqiao stage magmatism in the Luzong Basin into geochemically distinct units associated with these differing styles of mineralization.

Polyphase thrusting and dyke emplacement in the central Southern Alps (Northern Italy)

The Triassic succession of the central Southern Alps (Italy) is stacked into several units bounded by south-verging low-angle thrust faults, which are related to two successive steps of crustal shortening. The thrust surfaces are cut by high-angle extensional and strike-slip faults, which controlled the emplacement of hypabissal magmatic intrusions that post-date thrusts motions. Intrusion ages based on SHRIMP U–Pb zircon dating span between 42 ± 1 and 39 ± 1 Ma, suggesting close time relationships with the earliest Adamello intrusion stages and, more in general, with the widespread calc-alkaline magmatism described in the Southern Alps. Fission-track ages of magmatic apatites are indistinguishable from U–Pb crystallization ages of zircons, suggesting that the intrusion occurred in country rocks already exhumed above the partial annealing zone of apatite (depth < 2–4 km). These data indicate that the central Southern Alps were already structured and largely exhumed in the Middle Eocene. Although we describe minor faults affecting magmatic bodies and local reactivations of older structures, no major internal deformations have occurred in the area after the Bartonian. Neogene deformations were instead concentrated farther south, along the frontal part of the belt.

Microstructures of different soil layers caused by the high-rise building group in Shanghai

The engineering characteristics of soils are controlled by the state of the microstructure of soils to a great extent. With the withdrawal of groundwater controlled reasonably, the engineering-environmental effect of the high-rise building group becomes the main cause of land subsidence in Shanghai. This paper studied the microstructure of each soil layer under the building loads in the centrifuge model by the scanning electron microscopy and the mercury intrusion porosimetry (MIP) for qualitative analysis and quantitative analysis, respectively. The shape, size and contact condition of the basic unit of the soil microstructure were analyzed. The pore structure of each soil layer was studied by MIP, and the pore distribution of each soil layer was studied by the fractal theory. The ink-bottle effect exists in the intrusion stage in the MIP test. There are four different fractal dimensions for silty clay of layer No. 4 and clayey soil of layer No. 8 and three different fractal dimensions for silty sand of layer No. 7 and layer No. 9. The micro and macro mechanisms of land subsidence caused by the high-rise building group were analyzed.

Land subsidence and pore structure of soils caused by the high-rise building group through centrifuge model test

In the urban area of Shanghai, the dewatering of groundwater was controlled strictly and the engineering–environment effect of the high-rise building group became to be the main cause of land subsidence in Shanghai. Based on the high-rise building group in the soft soil area in Shanghai, the mechanism of land subsidence was studied in this paper by the centrifuge model test. The central area of the building group has larger subsidence and the subsidence superimposition effect is obvious. It can exceed the allowance and cause land subsidence hazard. The land subsidence affected by the different building distances was also studied. For smaller building distances, the subsidence superimposition effect is more obvious. The engineering characteristics of soils are controlled by the state of pore structure of soils to a great extent. The parameter of specific subsidence was put forward as a tie to analyze the relationship between land subsidence and pore structure of soils. The pore structure of each soil layer was studied by the mercury intrusion porosimetry test (MIP) and the pore distribution of each soil layer was studied by the fractal theory. There are mainly macropores in silty clay of layer no. 4, clayey soil of layer no. 8, silty sand of layer no. 7 and layer no. 9 in Shanghai. The ink-bottle effect exists in the intrusion stage in the MIP test. There are four different fractal dimensions in silty clay of layer no. 4 and clayey soil of layer no. 8 and three different fractal dimensions in silty sand of layer no. 7 and layer no. 9.

Magnetic field effect on the cooling of a low-Pr fluid in a vertical cylinder

Results of direct numerical simulations are presented for the transient and turbulent natural convection cooling of an initially isothermal quiescent liquid metal placed in a vertical cylinder in the presence of a vertical magnetic field. The electrically conductive low-Prandtl number fluid is put to motion when the cylindrical wall is suddenly cooled to a uniform lower temperature. For this particular cooling process, the flow is characterized by three sequential almost discrete stages: (a) development of momentum and thermal boundary layers along the cylindrical cold wall, (b) intrusion of the cooled fluid into the main fluid body, and (c) flow and thermal stratification. The selected Rayleigh numbers in the present study are high enough so that turbulent convection is established. The numerical results show that the magnetic field has no observable effect at the initial stage of the vertical boundary layer development and conduction heat transfer is favored during the intrusion stage. An interesting effect of the magnetic field during the stratification stage is the deceleration of the cooling process for low Rayleigh numbers and its acceleration for high ones. This dependence of the magnetic field effect on the Rayleigh number was found to be related to the cold vortices emanating from the vertical boundary layer. In contrast with the hydrodynamic cooling, the magnetic field was also found to accelerate the cooling near the bottom of the cylinder.

Crystallization of REE minerals and redistribution of U, Th, and REE at contact boundary between granite and gabbro during hydrothermal alteration

In this study, redistribution behaviors of U, Th, and rare earth elements (REE) in association with igneous activity in the Unazuki region of southwest Japan were investigated. At the contact boundary between granite and gabbro, REE minerals such as monazite, xenotime, and REE oxides formed with Fe–Ti oxides in K-feldspar assimilated by gabbro. U was enriched in xenotime (UO 2 > 0.72 wt.%) and REE oxides (UO 2 > 0.10 wt.%), whereas Th was concentrated in REE oxides (ThO 2 > 1.32 wt.%). Considering the similarity between the ionic radii of U 4+ and Y 3+, U was incorporated into xenotime and REE oxides together with heavy REE. Th incorporation into xenotime (eightfold coordinated site) and monazite (ninefold coordinated site) was constrained by the lower contents of Gd and Dy, respectively. Saussuritization of plagioclase in gabbro and chloritization of biotite in granite at the contact boundary suggest low-temperature hydrothermal alteration at late stages of gabbro intrusion that occurred at 253 ± 1 Ma. In contrast, zircon in the chloritized granite contained altered domains characterized by a dark response between back-scattered electron and cathodoluminescence images; this was caused by a low average atomic number due to the release of Zr and Hf; the incorporation of non-formula elements such as Ca, Fe, and Al; and low crystallinity because of radiation damage. The altered domains showed enrichments of Th (ThO 2 > 1.50 wt.%) and light REE (LREE) to middle REE (MREE) as well as positive Eu anomalies; this suggests the preferential incorporation of Th and LREE–MREE (particularly Eu 2+) with Ca occurring during the hydrothermal alteration. The redistribution behaviors of U, Th, and REE during low-temperature hydrothermal alteration strongly depend on their ionic radii. Thorite in zircon was probably formed by the exsolution of high-Th altered domains.

Zircon U-Pb geochronological framework of Qitianling granite batholith, middle part of Nanling Range, South China

The Qitianling granite batholith (QGB) is located in the southern Hunan Province, middle part of the Nanling Range, South China. Its total exposure area is about 520 km2. Based on our 25 single grain zircon U-Pb age data and 7 published data as well as the geological, petrological, and space distribution characteristics, we conclude that QGB is an Early Yanshanian (Jurassic) multi-staged composite pluton. Its formation process can be subdivided into three major stages. The first stage, emplaced at 163-160 Ma with a peak at about 161 Ma, is mainly composed of hornblende-biotite monzonitic granites and locally biotite granites, and distributed in the eastern, northern, and western peripheral parts of the pluton. The second stage, emplaced at 157-153 Ma with a peak at 157-156 Ma, is mainly composed of biotite granites and locally containing hornblende, and distributed in the middle and southeastern parts of the pluton. The third stage, emplaced at 150-146 Ma with a peak at about 149 Ma, is mainly composed of fine-grained (locally porphyritic) biotite granites, and distributed in the middle-southern part of the pluton. Each stage can be further disintegrated into several granite bodies. The first two intrusive stages comprise the major phase of QGB, and the third intrusive stage comprises the additional phase. Many second stage fine-grained granite bosses and dykes intruded into the first stage host granites with clear chilling margin-baking phenomena at their intrusive contacts. They were emplaced in the open fracture space of the earlier stage consolidated rocks. Their isotopic ages are mostly 2–6 Ma younger than their hosts. Conceivably, the time interval from magma emplacement, through cooling, crystallization, solidification, up to fracturing of the earlier stage granites cannot exceed 2–6 Ma. During the Middle-Late Jurassic in the Qitianling area and neighboring Nanling Range, the coeval granitic and basic-intermediate magmatic activities were widely developed. It indicates that the Early Yanshanian period was the culmination time of magmatic activities in this region. The Nanling Range was under a post-orogenic, intracontinental geotectonic environment with an obvious lithospheric extension and thinning. The crust-mantle interaction played an important role in formation of granitic rocks in this region.

Ore-forming event and geodynamic setting of molybdenum deposit at Wenquan in Gansu Province, Western Qinling

The Wenquan molybdenum deposit is associated with a Triassic granite in this area. The Wenquan granite is enriched in LILE and LREE, poor in HFSE, and has significantly higher contents of alkali (K2O+Na2O) and Sr, Ba than those of the island arc volcanic rocks. These geochemical characteristics are similar to post-collisional granites in high K calc-alkaline series. Studies of major elements, trace elements, REEs and chronology of the Wenquan pluton show that, in the geodynamic transition stage of continent-continent convergence to extension, the partial melting of the enriched lithospheric mantle generated the basaltic magma and triggered the partial melting of the thickened lower crust which produceded the acidic magma, and the Wenquan pluton was formed by mixing of the two magmas. Molybdenite Re-Os isotopic dating gave Os model ages of 212.7±2.6 Ma to 215.1±2.6 Ma with a weighted mean of 214.1±1.1 Ma, and an Re-Os isochron age of 214.4±7.1 Ma. These ages are close to K-Ar ages (223 to 226 Ma) and a SHRIMP zircon U-Pb age (223±7 Ma) for the Wenquan granite within the error range, but relatively younger. This implies that the Mo mineralization occurred in a late stage of the magmatic intrusion, and the metallogenesis took place in the transition stage from syn-collision to post-collision in the tectonic setting of the Qinling Orogenic Belt (QOB) after continental collision between the North China Block (NCB) and the South China Block (SCB). This process is also corresponding to the geological events of metamorphism and deformation in South Qinling, closure of the Mian-Lue oceanic basin, and exhumation of the Dabie-Sulu ultrahigh-pressure metamorphic rocks. The large-scale continent-continent collision between NCB and SCB in the middle Triassic triggered significant crustal thickening and exhumation of subducted slab. In the late Triassic, the tectonic setting was transformed to the transition stage from collision to extension. Materials from the asthenospheric mantle would ascend into the root of the lower crust, which could induce partial melting of the lower crust and generate Mo-enriched granitic magma. The ore-forming elements enriched in the fluid derived from the condensation and fraction of the magma resulted in the Mo mineralization. The Mo deposits in the QOB are mainly formed in two episodes, namely 220± Ma and 140± Ma. The two episodes of metallogenesis were developed in the tectonic transition settings from compression to extension, but they were in the different stages of the tectonic evolution. The occurrence of the Wenquan Mo-bearing pluton indicates that the Triassic tectonic-magmatic belt of Western Qinling is another favorable region for Mo mineralization in the QOB. Therefore, it is significant to pay more attention to evaluation of the ore-forming potentiality in the Triassic granites in Western Qinling.

Petrology and isotope geochemistry of the Mesoproterozoic anorthosite and related rocks of the Kunene Intrusive Complex, NW Namibia

The intrusion of the large (c. 18.000 km 2) anorthosite body of the Kunene Intrusive Complex, Angola/Namibia, which is associated with minor marginal granite bodies and syenite/syenodiorite dykes, marked the beginning of Mesoproterozoic igneous activity in NW Namibia. Anorthosites display an igneous mineral assemblage of dominating plagioclase, together with minor olivine, orthopyroxene or clinopyroxene, Fe–Ti oxides, whereas biotite and pargasite are late-magmatic phases. Apatite is a common accessory phase. In regionally associated felsic rocks K-feldspar, plagioclase, clinopyroxene and/or hastingsite crystallized first, followed by interstitial quartz, hastingsite, Fe–Ti oxides, and titanite. The general geochemical characteristics for the anorthositic rocks of the Kunene Intrusive Complex (i.e. high Al 2O 3, CaO, Sr and Eu, intermediate to high Mg numbers of 0.37–0.74, positive ɛNd (T) values of +3.0 to +1.0, and initial Sr ratios of 0.7028–0.7041) are in excellent agreement with their derivation from fractionated basaltic liquids. The δ 18O values obtained for plagioclase (5.88 ± 0.19‰ δ 18O) support their development from mantle-derived magmas. Relic crustal xenoliths of calc-silicate rocks and Sr and Nd isotope data, however, suggest that the anorthosite magma underwent minor crustal contamination, which was most prominent during the early intrusion stage. A U–Pb–zircon age of 1376 ± 2 Ma was obtained for a felsic rock associated with the 1385 ± 25 Ma anorthosites, which suggests that the two suites were emplaced during the same igneous event. The geochemical and isotope signatures of the granites, syenites, and syenodiorites provide convincing evidence against consanguinity of the anorthositic and the felsic rock suites, i.e.: (1) a compositional gap exists between the major and trace element contents of the two suites, (2) trace element and Sr, and Nd isotopic data of the felsic rocks point to a crustal source ( ɛNd: +2.0 to −0.4, initial Sr ratio: 0.7024–0.7063), (3) the REE patterns of the felsic rocks do not exhibit ubiquitous negative Eu anomalies, which would be expected from fractionation products of melts that previously formed extensive plagioclase cumulates, and (4) δ 18O values of magmatic feldspar from the felsic rock suite fall in a restricted range (7.20–7.92‰) that is about 1.6‰ higher than the average igneous plagioclase δ 18O of the anorthosites and suggests a formation of the felsic melts by anatexis of the lower crust.

Complex volcanic facies architecture of the Forest Reefs Volcanics near Cadia, New South Wales, associated with prolonged arc-related volcanism

The Ordovician to Lower Silurian Forest Reefs Volcanics in the Cadia – Neville region, northeastern Lachlan Orogen, represent the product of at least two shoshonitic volcanic centres intercalated with a volcaniclastic apron. The two episodes of shoshonitic volcanism in the Forest Reefs Volcanics are separated by between 15 and 20 million years. The Forest Reefs Volcanics are informally divided into lower and upper parts, separated by an inferred unconformity that broadly coincides in age with a limestone-forming hiatus in volcanism (449 – 447 Ma) and emplacement nearby of medium-K calc-alkaline dacitic intrusions (448 – 445 Ma). The lower part includes shoshonitic basaltic andesite, feldspar-rich sandstone, volcanic lithic breccia and lesser black mudstone; polymictic volcanic conglomerate with sandstone matrix and calcareous sandstone are important near the top. The basaltic facies association occurs near the base of the lower Forest Reefs Volcanics and could represent a submarine basaltic volcano at least 12 km in diameter. A major change in provenance for the upper Forest Reefs Volcanics is reflected in the increased abundance of ferromagnesian crystals and coarse mafic volcanic fragments, particularly in the mafic volcanic sandstone, polymictic volcanic conglomerate with coarse volcanic matrix and polymictic hornblende andesite breccia. The trachyandesite facies association records another episode of shoshonitic volcanism that probably occurred late in the accumulation of the upper Forest Reefs Volcanics and could represent an intrusive complex or the initial, largely shallow intrusive stages of a cone volcano. Highly porphyritic basalt to basaltic andesite intrusions were emplaced as sills before the volcaniclastic succession was lithified. The final magmatic activity generated coarsely equigranular, mafic to intermediate intrusions. The trachyandesite facies association, the highly porphyritic basalt to basaltic andesite intrusions and the coarsely equigranular intrusions were emplaced successively in a relatively short time (about 443 – 439 Ma). The complex facies architecture of the Forest Reefs Volcanics thus represents the product of prolonged broadly arc-related shoshonitic volcanism, separated by limestone deposition and the subsequent emplacement of medium-K calc-alkaline dacitic intrusions.

Software fault tree and coloured Petri net based specification, design and implementation of agent-based intrusion detection systems

The integration of Software Fault Tree (SFT), which describes intrusions and Coloured Petri Nets (CPNs) that specifies design, is examined for an Intrusion Detection System (IDS). The IDS under development is a collection of mobile agents that detect, classify, and correlate the system and network activities. SFTs, augmented with nodes that describe trust, temporal and contextual relationships, are used to describe intrusions. CPNs for intrusion detection are built using CPN templates created from the augmented SFTs. Hierarchical CPNs are created to detect critical stages of intrusions. The agentbased implementation of the IDS is then constructed from the CPNs. Examples of intrusions and descriptions of the prototype implementation are used to demonstrate how the CPN approach has been used in the development of the IDS. The main contribution of this paper is an approach to systematic specification, design and implementation of an IDS; Innovations include (1) using stages of intrusions to structure the specification and design of the IDS; (2) augmentation of SFT with trust, temporal and contextual nodes to model intrusions; (3) algorithmic construction of CPNs from augmented SFT; and (4) generation of mobile agents from CPNs.

Origin of the Lyme Dome and implications for the timing of multiple Alleghanian deformational and intrusive events in southern Connecticut

Geologic mapping, structural analysis, and geochronology in the area of the Lyme dome, southern Connecticut provides constraints on the origin of the rocks in the core of the dome, the absolute timing of the principal deformational and thermal events attributed to Alleghanian orogenesis, and the processes that generated the dome. Detrital zircon geochronology in combination with ages on intrusive rocks brackets the deposition of quartzite in the core of the dome sometime between ca. 925 and 620 Ma. Granite and granodiorite intruded the Neoproteorozic metasedimentary rocks in the core of the dome at ca. 620 to 610 Ma. Four major early Permian events associated with the Alleghanian orogeny affected the rocks in the Lyme dome area. Syn-tectonic migmatization and widespread penetrative deformation (D1, ca. 300 –290 Ma) included emplacement of alaskite at 290 ± 4 Ma during regional foliation development and aluminosilicate-orthoclase metamorphic conditions. Rocks of the Avalon terrane may have wedged between Gander cover rocks and Gander basement in the core of the Lyme during D1. Limited structural evidence for diapiric uplift of the Lyme dome indicates that diapirism started late in D1 and was completed by D2 (ca. 290 –280 Ma) when horizontal WNW contractional stresses dominated over vertical stresses. Second sillimanite metamorphism continued and syn-tectonic D2 granite pegmatite (288 ± 4 Ma) and the Joshua Rock Granite Gniess (284 ± 3 Ma) intruded at this time. North-northwest extension during D3 (ca. 280 –275 Ma) led to granitic pegmatite intrusion along S3 cleavage planes and in extensional zones in boudin necks during hydraulic failure and decompression melting. Intrusion of a Westerly Granite dike at 275 ± 4 Ma suggests that D3 extension was active, and perhaps concluding, by ca. 275 Ma. Late randomly oriented but gently dipping pegmatite dikes record a final stage of intrusion during D4 (ca. 275 –260 Ma), and a switch from NNW extension to vertical unloading and exhumation. Monazite and metamorphic zircon rim ages record this event at ca. 259 Ma. The evolution of the Lyme dome involved D1 mylonitization, intrusion, and migmatization during north-directed contraction, limited late D1 diapirism, D2 migmatization during WNW contraction with associated flexural flow and fold interference, D3 NNW horizontal extension and decompression melting, and final D4 vertical extension and rapid exhumation. Late regional uplift, extension, and normal faulting at higher crustal levels may have been caused by diapiric rise of the lower crust, below the structural level of the Lyme dome. The rocks record no evidence of Acadian metamorphism or deformation, suggesting that the Gander zone here was not tectonically juxtaposed with Avalon until the Alleghanian orogeny.

Evolution of migmatitic granulite complexes: Implications from Lapland Granulite Belt, Part II: Isotopic dating

The migmatitic metapelites of the Lapland granulite belt (LGB) in the NE part of the Fennoscandian Shield represent an arc-related greywacke basin metamorphosed in the granulite facies. Detrital zircons from migmatitic metapelites are derived from 1.94 etrital zircons from migmatitic metapelites are derived from 1.94 zircons from migmatitic metapelites are derived from 1.94 derived from 1.94 − 2.9 Ga old acid source rocks (U-Pb SIMS ages). The clustering of detrital zircon ages between 1.97 and 2.2 Ga is problematic, because abundant felsic crust of this age is absent in the shield. The metasediments are characterized by Sm-Nd model ages of ca. 2.3 Ga. A younger, 1905 − 1880 Ma population of homogeneous zircons was formed during regional metamorphism. The peak high-grade metamorphism took place at ~1900 Ma and the latest chronological record from subsequent decompression and cooling phase is from ca. 1870 Ma. The norite-enderbite series of the LGB represents arc-magmas, which were intruded into the metasediments at ~1920 − 1905 Ma ago according to zircon U-Pb ages and were probably an important heat source for metamorphism. Older, zoned zircon grains in a quartz norite vein, initial e Nd values of 0 to +1 and the continuous spectrum of LILE enrichment in the enderbite-series probably reflect assimilation of metasediments by magmas. Monazite U-Pb ages of migmatitic metasediments in the range 1906 − 1910 ± 3 Ma overlap the late stage of enderbite intrusion and growth of early metamorphic zircons. Garnetwhole rock Sm-Nd ages from leucosomes in the range 1880 − 1886 ± 7 Ma are concurrent with the growth of the youngest metamorphic zircons and probably indicate the crystallization of leucosomes or the influence of a fluid liberated from them. Isotopic and pet rologic data reveal that the evolution of Lapland Granulite belt from the erosion of source rocks to the generation of a sedimentary basin, its burial, metamorphism and exhumation took place within ca. 60 Ma.

Progressive adjustments of ascent and emplacement controls during incremental construction of the 3.1 Ga Heerenveen batholith, South Africa

The Heerenveen batholith is part of a suite of areally extensive, shallow-crustal granitoid plutons intruded during the last regional phase of tectonism and NW-SE subhorizontal shortening recorded in the Mesoarchean Barberton granitoid-greenstone terrain of South Africa at 3.1 Ga. Intrusive relationships allow at least four main successively emplaced intrusive stages to be distinguished. Each of these shows distinct geometries and intrusive styles that provide evidence for the progressive change of emplacement controls during the incremental construction of the Heerenveen batholith. The earliest sheet-like granitoids intruded as foliation-parallel sills along the shallowly dipping basement gneissosity, emphasizing the role of favourably inclined pre-existing wall-rock anisotropies for granite emplacement during the early stages of pluton assembly. Continued sheeting and coalescence of sheets provided the thermal ground preparation that led to the formation of larger, coherent magma bodies and the main phase of homogeneous, commonly megacrystic granites. These megacrystic granites form the central parts of the Heerenveen batholith, and are interpreted to represent steady-state magma chambers. The introduction of the rheologically weaker melt bodies into the shallow crust resulted in the nucleation of conjugate synmagmatic transpressive shear zones around the central granites. The shear zones correspond to several km-wide zones of shear zone-parallel granite sheeting. This stage marks a dramatic switch in emplacement styles. While the initial stages of magma emplacement were largely determined by factors external to the magma, most importantly the pre-existing wall-rock anisotropies, subsequent stages are dominated by factors intrinsic to the magma, namely strain localization and partitioning along melt-bearing zones during syntectonic plutonism. The associated melt transfer along these zones is independent of pre-existing structures and mainly related to buoyancy- and strain-induced melt ascent. The last granites of the Heerenveen batholith are post-tectonic. They intrude as either plugs or stocks of seemingly random orientation, but display a clear control by wall-rock anisotropies where they are in contact with the country rocks. On a regional scale, the different phases of the Heerenveen batholith describe an overall zonation of central homogeneous granites enveloped by composite, sheeted and sheared margins. This pattern is typical for most of the large 3.1 Ga granite batholiths in the Barberton granitoid-greenstone terrain. We suggest that the sequence of progressively changing emplacement controls and the formation of steady-state magma chambers described here for the Heerenveen batholith may be of wider application to other zoned and/or incrementally assembled batholiths.

Pyrochlore chemistry from the Sokli phoscorite-carbonatite complex, Finland: Implications for the genesis of phoscorite and carbonatite association

The phoscorite-carbonatite complex in the Sokli alkaline-carbonatite massif, northern Finland, comprises five stages of intrusions of phoscorites and carbonatites (P1-C1, P2-C2 and P3-C3 for phoscorites and calcite carbonatites; D4 and D5 for dolomite carbonatites). The phoscorites and calcite carbonatites at Sokli usually occur as pairs with the same mineral assemblages. Pyrochlore is found in the majority of rock types in the Sokli phoscorite-carbonatite complex, shows wide compositional variation and seems to preserve evolution trends of host rocks. Crystallization of pyrochlore begins from the P2-C2 phoscorite and calcite carbonatite and continues up to the latest D5 dolomite carbonatite. Pyrochlore in the early stage P2-C2 rocks has high U and Ta contents. These elements suddenly decrease from the P3-C3 rocks, on the other hand, Th and Ce contents increase. The compositions of the late generations from the D4 and D5 rocks are close to that of an ideal end-member pyrochlore with formula (Ca,Na)2Nb2O6F. The Nb/Ta ratio and F content of pyrochlore increase from P2-C2 to the latest D5 dolomite carbonatite. The composition and evolutionary history of pyrochlore from the phoscorites are distinguished from those of the associated calcite carbonatites. Pyrochlore from the calcite carbonatites shows larger A-cation deficiencies compared to those from the paired phoscorites. Ta and Zr contents are slightly higher in pyrochlore from the calcite carbonatites, whereas Ti is generally higher in pyrochlore from the associated phoscorites. Moreover, pyrochlore from the phoscorites always shows a longer and more complex crystallization history compared to that of the same stage carbonatites. This indicates that the chemical condition was clearly different in the two systems during the crystallization of pyrochlore. Based on these results, together with the previous mineralogical and geochemical studies on the Sokli phoscorite-carbonatite complex, we propose a liquid immiscibility process as the most possible segregation mechanism of the two associated rocks. The composition of pyrochlore in the late dolomite carbonatites is distinct and always lies on the evolutional trend of the earlier varieties. This implies that the dolomite carbonatites are the final magmatic products of the Sokli phoscorite-carbonatite system.

Geology, geochemistry and mineralogy of indium resources at Mount Pleasant, New Brunswick, Canada

Indium-bearing deposits at Mount Pleasant, New Brunswick represent one of two major episodes of mineralization associated with granitic intrusions near the southwest margin of the Late Devonian Mount Pleasant caldera. Porphyry tungsten–molybdenum deposits, with negligible indium content, are associated with the earliest stage of intrusion and represent the first mineralization episode. Indium-bearing vein, replacement and breccia-hosted tin-base metal deposits are associated with a younger stage of intrusion and represent the second episode. The indium-bearing deposits are best developed in an eruptive center at Mount Pleasant referred to as the North Zone; indium resources in this area total 620 t In. The most significant individual deposit is the Upper Deep Tin Zone, which contains 476 t In in indicated and inferred resources totalling 1.7 Mt grading 280 g/t In, along with 0.68% Sn, 2.26% Zn and 0.29% Cu. The indium-bearing tin-base metal deposits occur as sulfide-rich veins, breccias and replacement zones in both granitic rocks and associated volcanic and sedimentary rocks. Sphalerite, chalcopyrite, arsenopyrite and cassiterite are the most abundant ore minerals; a wide variety of other minerals occur in minor to trace amounts including löllingite, native bismuth, bismuthinite, wolframite, molybdenite, tennantite, stannite, kësterite, ferrokësterite, stannoidite, pyrite, galena, bornite, wittichenite and roquesite. Indium correlates most closely with high contents of zinc and copper, reflecting its concentration primarily in sphalerite and, to a lesser degree, in chalcopyrite. Electron-microprobe analyses for indium in sphalerite ranged mainly from < 0.01% to 6.90% In; the highest values were encountered in sphalerite containing abundant inclusions of chalcopyrite. Indium appears to substitute for Zn and Fe according to the coupled substitution CuIn ↔ 2(Zn,Fe), to form solid solution between sphalerite and roquesite. Indium content in chalcopyrite is much lower than in sphalerite; analyses ranged from 0.01% to 0.40% In. Indium-rich sphalerite and associated minerals were deposited at temperatures that varied from 400 °C to less than 200 °C. Indium and associated metals were likely concentrated in magmatic–hydrothermal fluids derived from silicic magma now represented by a large body of granite that underlies Mount Pleasant and that degassed through small cupolas at the top of the magma chamber. Deposition of the metals occurred in response to cooling and dilution of the hot magmatic ore fluids, mainly as a result of mixing with meteoric fluids. This is similar to mechanisms proposed for other indium-bearing tin-polymetallic deposits.

Dynamic process analyses of saline intrusion with over-exploitation by coupled flow and dispersive modelling

Understanding of saline intrusion into coastal aquifer is an important issue in management and protection of groundwater resource, which can be well achieved by groundwater modelling. To explain some phenomena of correlation between groundwater level and salinity in observation wells in coastal area, the authors compare the migration velocity of saline particles and transmission velocity of water pressure and derive analytical equations of these two velocities for plane and radial flows. The driving force and resistance of saline intrusion were analysed based on the analytical modelling. The destruction and reconstruction of the equilibrium between fresh water seepage towards sea and saline dispersion to inland were considered as an essence of whole intrusion process. The dynamic process of seepage and dispersion at different stages of saline intrusion were analysed under groundwater over-exploitation. The basic equations of saline intrusion were derived and the mechanism of transitional zone movement was discussed. These constitute coupled seepage–dispersion theory of saline intrusion, which becomes an important supplement to existing theory of saline intrusion. As a case study on saline intrusion in Guangrao County in Eastern China, this theory was applied to predict the development of saline intrusion in the study area.

The memory of volcanic waters: Shallow magma degassing revealed by halogen monitoring in thermal springs of La Soufrière volcano (Guadeloupe, Lesser Antilles)

The halogen contents of thermal waters collected since 1979 at La Soufrière volcano (Guadeloupe, Lesser Antilles) are interpreted as a retarded record of magma degassing pulses dispersed into the hydrothermal system. The further the spring is located from the source, the larger the time delay and the older the event recorded in water chemistry. Using advection–dispersion transport models in porous media, we reconstruct the time-series of degassing pulses for the period 1971–1992 and show that it correlates with the seismic records. The 1975–1977 sismo-volcanic crisis at La Soufrière is thereby interpreted as the result of a magma intrusion at shallow depth (∼3 km) which likely began in approximately 1973 and degassed in a pulsatory regime during ∼15 yr. The recent recrudescence of fumarolic and seismic activity could represent the initial stage of new magma injection. Measurement of halogen contents in hydrothermal waters collected around active volcanoes may provide a powerful tool for detection of the initial stages of magma intrusions.

Compositional variation of Fe−Ti oxides from the Sokli complex, northeastern Finland

The phoscorite-carbonatite complex at Sokli, northeastern Finland, is composed of five stages of intrusions of phoscorites and carbonatites (P1-C1, P2-C2, P3-C3 phoscorites and calcite carbonatites, D4 and D5 dolomite carbonatites) which are cut by numerous lamprophyric dikes. Magnetite is ubiquitous in all constituent rock units of the complex and frequently associates with ilmenite. Most ilmenite intergrowths from the Sokli phoscorite-carbonatite complex occur as internal and/or external granules (composite type exsolutions) or sandwich type exsolution lamellae in the host magnetites. Discrete ilmenite crystals are found only in P3 and C3. On the other hand, ilmenites in the ultramafic lamprophyres occur as discrete crystals as well as trellis and sandwich type exsolution lamellae or composite type exsolutions in magnetite. Electron microprobe analyses reveal that magnetite of the Sokli complex belongs essentially to the magnetite-ulvospinel solid solution series with a small proportion of magnesioferrite. The compositions of magnetite from the Sokli phoscorite-carbonatite complex vary systematically from stage to stage with increasing Fe2+/(Fe2++Mg) ratio, and decreasing Al, Mn and Ti contents. Magnetite from the ultramafic lamprophyre is characterized by large compositional ranges owing to the large amount of mantle-derived xenocrysts. Some grains are particularly high in Cr (up to 21.0 wt.% Cr2O3). Aluminous magnesian titanomagnetites are also found, but most magnetites in the ultramafic lamprophyres are pure magnetite. The compositional variation of ilmenite from the Sokli complex is mainly caused by the substitution of Fe2+ into Mg and Mn, and partly Ti into Nb. Mg-and Mn-rich ilmenites in the early stage P1-C1 rocks evolve towards pure FeTiO3 composition in the latest D5 dolomite carbonatite. Ilmenites from the ultramafic lamprophyres are relatively poor in Mn compared to those from the phoscorite-carbonatite complex. In the coexisting magnetite and ilmenite, Mg and Mn cations preferentially partition into ilmenite rather than magnetite. In spite of the mineralogical and geochemical contrasts between the phoscorites and associated carbonatites, compositions of Fe−Ti oxide minerals from the two paired rocks at a given stage are basically the same, and evolve systematically from stage to stage. This supports the hypothesis that the phoscorites and conjugate carbonatites are derived from common parental melts. Furthermore, the intrusions of the Sokli phoscorite-carbonatite complex are considered to have either crystallized from successive batches representing a continuum in time and magmatic evolution, or that the P1-C1 parental magma has simply differentiated to form the later stage rocks.

Viscous fingering during replenishment of felsic magma chambers by continuous inputs of mafic magmas: Field evidence and fluid-mechanics experiments

Research Article| January 01, 2005 Viscous fingering during replenishment of felsic magma chambers by continuous inputs of mafic magmas: Field evidence and fluid-mechanics experiments D. Perugini; D. Perugini 1Department of Earth Science, University of Perugia, Piazza Università, 06100, Perugia, Italy Search for other works by this author on: GSW Google Scholar G. Poli G. Poli 1Department of Earth Science, University of Perugia, Piazza Università, 06100, Perugia, Italy Search for other works by this author on: GSW Google Scholar Geology (2005) 33 (1): 5–8. https://doi.org/10.1130/G21075.1 Article history received: 29 Jul 2004 rev-recd: 01 Oct 2004 accepted: 01 Oct 2004 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D. Perugini, G. Poli; Viscous fingering during replenishment of felsic magma chambers by continuous inputs of mafic magmas: Field evidence and fluid-mechanics experiments. Geology 2005;; 33 (1): 5–8. doi: https://doi.org/10.1130/G21075.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Vegetation Island outcrops (Terra Nova Intrusive Complex, Antarctica) offer a unique example of the replenishment of a felsic magma chamber fossilized at the initial stages of intrusion of a mafic magma. The morphology of interfaces between the mafic and the felsic magma ranges from rounded to finger-like, and their quantification by means of fractal dimension indicates a wide variability of morphological complexity. Fluid-mechanics experiments of viscous fingering have been performed by injecting water + glycerin solutions with different viscosity ratios into pure glycerin using the Hele-Shaw cell. The fact that interface morphologies between the injected and the host fluid are identical to those observed on outcrops indicates that the latter shows the development of viscous fingering processes during the initial stages of intrusion of the mafic magma into the felsic magma chamber. The fractal dimension of the simulated structures was measured, and a very good exponential empirical relationship between the logarithm of viscosity ratio and fractal dimension has been derived. The empirical relationship is used to estimate viscosity ratios of natural structures by using measured values of fractal dimension. Results indicate that in the same magmatic system, a wide range of viscosity ratio existed between the two magmas. These results are used to reconstruct the mechanism of replenishment of the felsic magma chamber as characterized by continuous heating of the resident felsic magma by continuous inputs of the mafic magma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.