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1.
《Gondwana Research》2001,4(3):497-508
Ocellar lamprophyres are reported from Danva, in Sirohi district, Rajasthan which lies in the Pindwara-Watera sector of the South Delhi Fold Belt (SDFB). They intrude mafic metavolcanics and garnetiferous biotite schist of the Ajabgarh Group of the Delhi Supergroup. These lamprophyres are unaltered, show porphyritic and panidiomorphic textures with olivine, clinopyroxene, amphibole, biotite and spinels constituting the phenocryst phase in a ground mass of clinopyroxene, amphibole, mica and analcime. Petrochemically, these lamprophyres can be classified as analcime monchiquite (alkaline lamprophyre), though they have some affinity towards ultramafic lamprophyres and lamproites. Chemistry of the minerals suggests that the clinopyroxenes have a compositional range of diopside and salite, amphiboles are typically kaersutites, biotites are titanium rich and spinels are Al-rich ulvospinels. These minerals plot in discriminant fields of minerals from alkaline and ultramafic lamprophyres.The Danva lamprophyres are characterized by a variety of ocellar features that include (i) porphyritic ocellus with microphenocrysts of kaersutites and biotite in ground mass of analcime, (ii) zoned ocellus with concentric zones of carbonates and analcime and (iii) composite ocellus in which type (i) ocellus enclose the type (ii) ocellus. These ocellar features are interpreted to represent late stage magmatic segregation and magmatic crystallization involving two immiscible magmatic liquids.The Danva lamprophyres are in strike continuity of the Pipela lamprophyres and therefore confirm alkaline magmatism for over 20 kms in SDFB during end-Neoproterozoic tectono-thermal event. The close spatial association of the lamprophyres with Cu-Zn-Au deposits of Danva and Pipela area and the first report of monchiquite with affinity towards ultramafic lamprophyres and lamproites may be significant in gold (and possibly diamond) exploration in the SDFB. 相似文献
2.
A metre-thick ultramafic lamprophyre dyke intrudes the basement of the Tandilia belt at the Sierra Alta de Vela, Argentina. A petrological and geochemical study of this rock and associated small dykes indicates a predominantly calc-alkaline trend. Phlogopite K–Ar dating of the ultramafic lamprophyre gave a minimum age of 1928 ± 54 Ma as a late event of the Transamazonian Orogeny, which is well represented in the basement of the Tandilia belt.An electron microprobe study indicates the presence of phlogopite, albite, chromite and Cr-rich phenocrysts and Cr-free microphenocrysts of diopside as primary minerals. Subsequent to deformation at the contacts with the wall rock, metasomatism generated strongly zoned amphibole (edenite, pargasite, Mg-hastingite and tremolite compositions) and andradite as well as chlorite, sericite, albite, apatite and calcite. The central zone of the lamprophyre is almost undeformed and exhibits some ocellar texture. Geochemical and isotopic signatures of the lamprophyre suggest that its magma source may have previously undergone incompatible element enrichment of the mantle source, representing the original precursor magma for the calc-alkaline dyke series of the Sierra Alta de Vela. 相似文献
3.
Gaurav J. Kokandakar Sachin S. Ghodke K. Rathna Laxman B. More B. Nagaraju Munjaji V. Bhosle K. Vijaya Kumar 《Journal of the Geological Society of India》2018,91(2):135-146
Three distinct alkaline magmas, represented by shonkinite, lamprophyre and alkali basalt dykes, characterize a significant magmatic expression of rift-related mantle-derived igneous activity in the Mesoproterozoic Prakasam Alkaline Province, SE India. In the present study we have estimated emplacement velocities (ascent rates) for these three varied alkaline magmas and compared with other silicate magmas to explore composition control on the ascent rates. The alkaline dykes have variable widths and lengths with none of the dykes wider than 1 m. The shonkinites are fine- to medium-grained rocks with clinopyroxene, phologopite, amphibole, K-feldspar perthite and nepheline as essential minerals. They exhibit equigranular hypidiomorphic to foliated textures. Lamprophyres and alkali basalts characteristically show porphyritic textures. Olivine, clinopyroxene, amphibole and biotite are distinct phenocrysts in lamprophyres whereas olivine, clinopyroxene and plagioclase form the phenocrystic mineralogy in the alkali basalts. The calculated densities [2.54–2.71 g/cc for shonkinite; 2.61–2.78 g/cc for lamprophyre; 2.66–2.74 g/cc for alkali basalt] and viscosities [3.11–3.39 Pa s for shonkinite; 3.01–3.28 Pa s for lamprophyre; 2.72–3.09 Pa s for alkali basalt] are utilized to compute velocities (ascent rates) of the three alkaline magmas. Since the lamprophyres and alkali basalts are crystal-laden, we have also calculated effective viscosities to infer crystal control on the velocities. Twenty percent of crystals in the magma increase the viscosity by 2.7 times consequently decrease ascent rate by 2.7 times compared to the crystal-free magmas. The computed ascent rates range from 0.11–2.13 m/sec, 0.23–2.77 m/sec and 1.16–2.89 m/sec for shonkinite, lamprophyre and alkali basalt magmas respectively. Ascent rates increase with the width of the dykes and density difference, and decrease with magma viscosity and proportion of crystals. If a constant width of 1 m is assumed in the magma-filled dyke propagation model, then the sequence of emplacement velocities in the decreasing order is alkaline magmas (4.68–15.31 m/sec) > ultramafic-mafic magmas (3.81–4.30 m/sec) > intermediate-felsic magmas (1.76–2.56 m/sec). We propose that SiO2 content in the terrestrial magmas can be modeled as a semi-quantitative “geospeedometer” of the magma ascent rates. 相似文献
4.
The mafic dykes in Wadi Mandar-Wadi Um Adawi area are as follows: (1) calc-alkaline lamprophyre (i.e., kersantite and spessartite), (2) diabase, and (3) alkaline lamprophyre (i.e., camptonite). The field relations reveal that the emplacement of calc-alkaline lamprophyres preceded the diabase dykes, while alkaline lamprophyres emplaced later than the diabase dykes. Calc-alkaline are basaltic andesite, basaltic trachyandesite to basalt, while the diabase dykes and alkaline lamprophyres are basaltic in composition. These dykes are characterized by metaluminous character. Calc-alkaline lamprophyres and diabase dykes show transitional affinity from calc-alkaline to alkaline, while the alkaline lamprophyres exhibit more strong alkaline character. The mafic dykes were crystallized under temperature 1100–1150 °C and pressure 3–5 kbars in a high oxygen fugacity conditions. Fe-Ti oxides in the dykes are represented by ilmenite and Ti-magnetite. The chemistry of the sulfides hosted in those mafic dykes suggests a magmatic-hydrothermal origin for these minerals. The geochemical behavior of high field strength elements and large ion lithophile elements in these dykes excludes the derivation of diabase or alkaline lamprophyre either by partial melting or fractional crystallization from calc-alkaline lamprophyre. The parental magmatic sources of the studied dykes were generated from crustal material with addition of mantle-derived melt during the post-collisional stage. The mafic dykes in Wadi Mandar-Wadi Um Adawi area were generated from different magmatic sources by partial melting and subsequent fractional crystallization. In addition, the crustal contamination/assimilation process has a prominent role in the magmatic evolution of diabase and alkaline lamprophyre dykes. 相似文献
5.
The southern part of a lamprophyre dyke swarm from West Otago,New Zealand comprises monchiquites and camptonites. Dykes arecompositionally similar to volatile-rich nephelinite or nephelinebasanite, and contain leucocratic ocelli and irregular veinsegregations of nepheline benmoreite composition. Ocelli arecommonly zoned with an upper globule or centrally disposed coreof analcime-carbonate and an alkali feldspar-kaersutite-richlining. Virtually identical zoning is developed in minerals common toboth lamprophyre host and ocellus. Kaersutite is progressivelyenriched in Fe, Mn, Alvi, and Na + K, and depleted in Mg, andTi towards the rim. Titanaugite is concentrically zoned to aegirine-augite,and is sector zoned with prism sectors enriched in Ti and Al(and to a lesser extent in Fe and Na) compared to basal sectors.Brown micas are zoned from titanphlogopite cores to titanbiotiteand titaniferous lepidomelane rims. In monchiquites glass occurs as an intersertal phase and asan ocellus infilling. The glass is phonolitic and contrastssharply with the composition of the ultrabasic host, indicatingthat production of extreme differentiates without intermediatecompositions is possible by fractional crystallization. Identicalglass compositions in both lamprophyre groundmass and ocelluspreclude liquid immiscibility. Instead, it is suggested thatocelli are segregations of residual liquids drawn into gas vesiclesas a consequence of reduction of the vapour phase, volume duringcooling. The analcime-carbonate globule within the ocellus isinterpreted as the condensed vapour phase. At Haast River, in the northern part of the swarm the dyke associationof peridotite, camptonite, trachyte, tinguaite, and carbonatiteis readily explained in terms of this model. Fractional crystallizationof camptonite results in phonolitic late stage liquids which,if separated from the lamprophyre host crystallize as sodalitetinguaites, leaving a more ultrabasic residuum whose compositionis equivalent to damkjernitic peridotite. Vesiculation of thecamptonite results in separation of a volatile phase (fluidimmiscibility) which is carbonate and alkali-rich, the sourceof both carbonatites and the agent responsible for fenitization. 相似文献
6.
Mafic and Felsic Magma Interaction in Granites: the Hercynian Karkonosze Pluton (Sudetes, Bohemian Massif) 总被引：12，自引：0，他引：12
The Hercynian, post-collisional Karkonosze pluton contains severallithologies: equigranular and porphyritic granites, hybrid quartzdiorites and granodiorites, microgranular magmatic enclaves,and composite and lamprophyre dykes. Field relationships, mineralogyand major- and trace-element geochemistry show that: (1) theequigranular granite is differentiated and evolved by smalldegrees of fractional crystallization and that it is free ofcontamination by mafic magma; (2) all other components are affectedby mixing. The end-members of the mixing process were a porphyriticgranite and a mafic lamprophyre. The degree of mixing variedwidely depending on both place and time. All of the processesinvolved are assessed quantitatively with the following conclusions.Most of the pluton was affected by mixing, implying that hugevolumes (>75 km3) of mafic magma were available. This maficmagma probably supplied the additional heat necessary to initiatecrustal melting; part of this heat could have also been releasedas latent heat of crystallization. Only a very small part ofthe Karkonosze granite escaped interaction with mafic magma,specifically the equigranular granite and a subordinate partof the porphyritic granite. Minerals from these facies are compositionallyhomogeneous and/or normally zoned, which, together with geochemicalmodelling, indicates that they evolved by small degrees of fractionalcrystallization (<20%). Accessory minerals played an importantrole during magmatic differentiation and, thus, the fractionalcrystallization history is better recorded by trace rather thanby major elements. The interactions between mafic and felsicmagmas reflect their viscosity contrast. With increasing viscositycontrast, the magmatic relationships change from homogeneous,hybrid quartz diorites–granodiorites, to rounded magmaticenclaves, to composite dykes and finally to dykes with chilledmargins. These relationships indicate that injection of maficmagma into the granite took place over the whole crystallizationhistory. Consequently, a long-lived mafic source coexisted togetherwith the granite magma. Mafic magmas were derived either directlyfrom the mantle or via one or more crustal storage reservoirs.Compatible element abundances (e.g. Ni) show that the maficmagmas that interacted with the granite were progressively poorerin Ni in the order hybrid quartz diorites—granodiorites—enclaves—compositedykes. This indicates that the felsic and mafic magmas evolvedindependently, which, in the case of the Karkonosze granite,favours a deep-seated magma chamber rather than a continuousflux from mantle. Two magma sources (mantle and crust) coexisted,and melted almost contemporaneously; the two reservoirs evolvedindependently by fractional crystallization. However, maficmagma was continuously being intruded into the crystallizinggranite, with more or less complete mixing. Several lines ofevidence (e.g. magmatic flux structures, incorporation of granitefeldspars into mafic magma, feldspar zoning with fluctuatingtrace element patterns reflecting rapid changes in magma composition)indicate that, during its emplacement and crystallization, thegranite body was affected by strong internal movements. Thesewould favour more complete and efficient mixing. The systematicspatial–temporal association of lamprophyres with crustalmagmas is interpreted as indicating that their mantle sourceis a fertile peridotite, possibly enriched (metasomatized) byearlier subduction processes. KEY WORDS: Bohemian Massif; fractional crystallization; geochemical modelling; hybridization; Karkonosze 相似文献
7.
蚌埠地区中生代岩浆作用十分发育, 以酸性岩浆活动为主, 部分地区伴随基性岩脉侵入。本文利用LA-ICP-MS技术, 对蚌埠五河地区煌斑岩中的锆石进行U-Pb同位素定年。研究表明, 该煌斑岩中锆石多成半自形到浑圆状, 多为捕获锆石。锆石U-Pb年龄多集中在3 100 Ma、2 500 Ma和2 000 Ma附近, 少量新生锆石年龄约为156 Ma, 捕获锆石年龄与华北基底的五河杂岩相当吻合, 可能不具有扬子板块俯冲陆壳年代学信息。本次测得煌斑岩的形成年龄为156.1±8.2 Ma, 为晚侏罗世。蚌埠地区普遍存在一期构造变形事件, 表现为由南向北的逆冲推覆。由于煌斑岩脉遭受到逆冲推覆构造的改造, 因此煌斑岩的形成年龄也限定了蚌埠地区推覆构造变形事件的下限。 相似文献
8.
Origin and geodynamic significance of Upper Cretaceous lamprophyres from the Villány Mts (S Hungary)
Summary In the Villány Mts of southern Hungary, ocelli-bearing porphyritic lamprophyre dykes and sills of Upper Cretaceous age occur
sporadically, intruding Mesozoic carbonate rocks. They at places contain metasomatised mantle xenoliths and quartz xenocrysts
of crustal origin. They are moderately fractionated with significant LILE and LREE enrichments and a notable Nb–Ta negative
anomaly. Trace elements indicate that they formed in an intraplate environment by very low degree partial melting of a metasomatised
garnet lherzolite mantle source that was enriched by earlier subduction. Based on petrography, geochemistry and age constraints,
they differ from other Mesozoic basic rocks of the Tisza block (Mecsek Mts and Slavonian basalts); however, they show a significant
geochemical similarity to the Upper Cretaceous lamprophyre dyke swarm from NE Transdanubia (northwestern Hungary) situated
on the Alcapa microplate. Thus we suggest that lamprophyres from the Villány Mts and NE Transdanubia could have originated
from the same or similar enriched asthenospheric mantle sources. 相似文献
9.
A review of the 2500 Ma span of alkaline-ultramafic, potassic and carbonatitic magmatism in West Greenland 总被引：1，自引：0，他引：1
Kimberlites, carbonatites and ultramafic, mafic and potassic lamprophyres have been produced in West Greenland in recurrent events since the Archaean. Five distinct age groups are recognised: Archaean (>2500 Ma). Early Proterozoic (1700–1900 Ma), Middle Proterozoic (Gardar, c. 1100–1300 Ma), Late Proterozoic (600 Ma) and Mesozoic-Tertiary (200-30 Ma) The rocks comprise two large and four small carbonatite occurrences, four kimberlite dyke swarms, one lamproite dyke swarm and one lamproite pipe, one dyke swarm of potassic lamprophyre (shonkinite) and some ten dyke swarms of ultramafic lamprophyre and monchiquite. Geochemical data for the various rock groups are presented. Some of the carbonatites may represent relatively unmodified mantle-derived melts. The kimberlites range from primitive to differentiated compositions, and there are regional differences between kimberlites within Archaean and Proterozoic basement. The ultrapotassic lamproites and shonkinites have strong negative Nb spikes in their trace element spectra. The ultramafic and monchiquitic lamprophyres encompass a large compositional variation; however, several of the dyke swarms have individual chemical characters.
The rocks are very unevenly distributed in West Greenland, indicating a lithospheric control, probably by old weakness zones providing access to the surface. The kimberlites are considered to be mainly of asthenospheric derivation. The regional differences are interpreted in terms of melting with phlogopite as a residual phase, with smaller degrees of melting at deeper levels beneath the Archaean lithosphere than beneath the Proterozoic. The ultrapotassic lamproites and shonkinites occur almost exclusively within a continental collision zone with possible two-way subduction and they are interpreted as mainly of lithospheric derivation, with a contribution from a subducted slab. Data for the other rock types are equivocal.
Except for the Archaean rocks, the age groups can be related to major geotectonic events. The Early Proterozoic group is related to continental collision at 1850 Ma and subsequent rifting; the Middle Proterozoic group is related to continental rifting (Gardar) and the Mesozoic group is likewise related to continental rifting prior to continental break-up in the Tertiary. The 600 Ma kimberlites and carbonatite are envisaged as cratonic, extra-rift activity in relation to continental break-up and formation of the Iapetus ocean further south, perhaps with a common cause in a broad, impinging mantle plume. 相似文献
10.
The igneous rocks of the Katzenbuckel, Southwest Germany, represent a unique and unusual alkaline to peralkaline association within the European Volcanic Province. The magmatic activity can be subdivided into two main phases. Phase I comprises the main rock bodies of phonolite and nepheline syenite, which were later intruded by different peralkaline dyke rocks (tinguaites and alkali feldspar syenite dykes) of phase II. The dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late-stage pneumatolytic activity causing autometasomatic alterations.
As is typical for alkaline to peralkaline igneous rocks, early mafic minerals of phase I rocks comprise olivine, augite and Fe–Ti oxides, which are substituted in the course of fractionation by Na-amphibole and Na-pyroxene. For the early magmatic stage, calculated temperatures range between 880 and 780 °C with low silica activities (0.4 to 0.6) but high relative oxygen fugacities between 0.5 and 1.9 log units above the FMQ buffer. Even higher oxygen fugacities (above the HM buffer) are indicated for the autometasomatic alteration, which occurred at temperatures between 585 and 780 °C and resulted in the formation of pseudobrookite and hematite.
The unusually high oxygen fugacities (even during the early magmatic stage) are recorded by the major element compositions of the mafic minerals (forsterite content in olivine between 68 and 78 mol%, up to 6.2 wt.% ZrO2 and 8.5 wt.% TiO2 in clinopyroxene), the unusual mineral assemblages (pseudobrookite, freudenbergite) and by the enrichment of Fe3+ in the felsic minerals (up to 2.8 wt.% Fe2O3 in alkali feldspar and up to 2.6 wt.% Fe2O3 in nepheline). These observations point to a metasomatically enriched and highly oxidized lithospheric mantle as a major source for the Katzenbuckel melts. 相似文献
11.
Alok Kumar Praveer Pankaj K. Koteswara Rao 《Journal of the Geological Society of India》2016,87(2):127-131
A singular outcrop of a lamproite dyke is located ~1.5 km south-west of Chintalapalle village at the NW margin of the Cuddapah basin, eastern Dharwar craton, southern India.. The dyke trends E-W and is emplaced within the granitic rocks belonging to the peninsular gneissic complex. The lamproite dyke has a porphyritic to weakly porphyritic texture comprising microphenocrysts of sanidine, and potassic richterite set in a groundmass rich in carbonate, and chlorite with rutile and titanate as accessory phases. This new occurrence of lamproite is located mid-way between the well-known Narayanpet kimberlite field towards the west and the Ramadugu and Vattikod lamproite fields in east. The Chintalapalle lamproite dyke, together with those from Vattikod, Ramadugu, Krishna and Cuddapah basin lamproite fields, constitute a wide spectrum of ultrapotassic magmatism emplaced in and around the Palaeo-Mesoproterozoic Cuddapah basin in southern India. 相似文献
12.
大湖-秦南钼矿床位于小秦岭金矿田北矿带,属于东秦岭钼钨成矿带小秦岭-外方山成矿亚带。其矿床类型为含钼石英脉型,与小秦岭北矿带含金石英脉空间上伴生。根据野外地质观察、PIMA测试等结果,对大湖-秦南含钼石英脉的产出、矿石结构构造、蚀变特征进行了研究。含钼石英脉为奶白色,易碎,发育蜂窝状、团块状、角砾状构造。角砾成分为太华群片麻岩角砾、细脉状浸染状辉钼矿化的中生代花岗斑岩角砾等。蚀变有钾化、硅化、绢云母化、高岭土化以及硬石膏化等。根据野外地质特征,蚀变可分为早期钾化+硅化+绢云母化+黄铁矿化+辉钼矿化,晚期为硅化+高岭土化+硬石膏化等。含钼石英脉中的围岩角砾或多或少地发育高岭土化。辉钼矿化主要充填于石英脉的裂隙和蜂窝中。根据包裹体显微测温数据推测含钼石英脉的成矿温度为134～463℃。含钼石英脉中的δ18 O石英值为10.7‰～11.5‰,δDH2O为-96‰～-110‰;这一特征反映了既有岩浆水,也有变质水和天水的参入,高岭土δ18 O为0.1‰～2.3‰,反映了热液成因。黄铁矿δ34S值为-5.778‰～-7.841‰,以富含轻硫为特征,反映了其形成时有生物硫参入。在此基础上,通过区域地质分析,讨论了高岭土化的成因,进而认为大湖-秦南含钼石英脉很可能是与秦岭造山带在245～211Ma全面陆陆碰撞过程有关的花岗斑岩侵位形成的斑岩型钼矿体,在后期金矿形成时,在酸性热液淋滤下进一步富集。 相似文献
13.
The Woods Point dyke swarm comprises hundreds of narrow, subparallel igneous dykes and dozens of pipe-shaped dyke bulges within strongly deformed early Palaeozoic turbidites of the Melbourne trough. Porpylitic alteration accompanied dyke emplacement and was followed by microfracturing induced by high fluid pressures, involving CO2 of magmatic origin, as the dykes solidified. Further stress caused through-going faults having ladder and other patterns. Isotopic studies suggest that metamorphically or geothermally-derived solutions filled the faults and other fractures with quartz and carbonate and altered immediately adjacent dyke rock. However earlier-formed vein and wall rock carbonates retained their magmatic isotopic composition. Fluid inclusions indicate vein deposition began at approximately 400°C with salinities up to 9 weight percent NaCl. Nine sulfide minerals and gold were deposited in the veins after ankerite, sericite and albite, while quartz deposition continued through all stages. Sulfur isotopic determinations indicate the vein sulfur could not have been derived from adjacent sedimentary rocks, nor exclusively from the dykes. Metamorphic waters of marine origin is a viable source for sulfur. Saline and CO2-rich alkaline solutions reacted with the dyke wall rocks and probably evolved chemically prior to deposition of gold. Vug carbonates deposited by meteoric water that leached vein carbonates mark the end of vein formation.Present Adress: 631 Station Street, North Carlton 3054, Victoria, Australia 相似文献
14.
Shoshonitic lamprophyre dykes and their relation to mesothermal Au---Sb veins at Hillgrove, New South Wales, Australia 总被引：5，自引：0，他引：5
The Hillgrove mineral field, in the southern part of the New England Orogen of northeastern New South Wales, Australia, contains numerous mesothermal Au---Sb vein systems. Calc-alkaline (shoshonitic) lamprophyre (CAL) dykes are also associated with mineralisation with dilational lode structures acting as conduits for dyke intrusion, which has occurred before and after major quartz-stibnite veining. Dykes include minette and vogesite compositions and were emplaced in the late Permian (247–255 Ma), at the same time as regionally extensive I-type magmatism in the New England Orogen. Least-altered dykes are enriched in Mg, K, Ba, Rb, Sr, Zr, Th, Cr and Ni relative to I-type intrusives although chemical affinities are evident between lamprophyres and the more mafic members of the high-K Moonbi Plutonic Suite.
Hillgrove lamprophyres are commonly enriched in Sb, As, Hg, Au, W and Bi with respect to average CAL compositions. Evidence indicates this is most likely due to contamination of magma during intrusion through mineralised structures, rather than a primary magmatic feature. Partially resorbed xenocrystic stibnite occurs in dykes which have intruded lode structures, probably facilitated by the low melting point of stibnite (550°C) and its incorporation into the magma. Carbon and oxygen isotopic data from carbonates in least-altered, post-lode lamprophyres are indistinguishable from carbonate in altered dykes and veins, implying that hydrothermal interaction continued after dyke intrusion. Although it is unlikely that lamprophyre dykes have been a direct source for mineralisation at Hillgrove, the close temporal and spatial relation of dykes, mesothermal Au---Sb veins and I-type intrusions are interpreted to be manifestations of the post-collisional setting and influx of mantle-derived heat and partial melts into the New England Orogen during the late Permian. 相似文献
15.
N.M.S. Rock 《Earth》1977,13(2):123-169
Lamprophyres are porphyritic dyke-rocks, readily recognisable in the field, which seemed to have become enveloped in petrological mystery because of their scattered and often contradictory literature. Important characteristics common to all members of this extremely heterogeneous group are suggested to include their intrusion at a late stage in any igneous event, the presence of essential amphibole or biotite coupled with peculiar chemistry, and their lack of felsic phenocrysts. Panidiomorphic texture is usual, though by no means exclusive to lamprophyres.At least four lamprophyre subgroups may be recognised; these are quite distinct in petrology, chemistry, paragenesis and petrogenesis although individual members of each subgroup are closely similar. Thealkaline lamprophyre subgroup is considered in detail: new definitions ofcamptonite andmonchiquite are proposed which are believed to reconcile majority usage whilst accomodating existing analytical data; the termouachitite is reassessed andfourchite suggested to be superfluous;sannaite, an alkali feldspar-rich alkaline lamprophyre, may be more abundant than its frequency within the literature implies — some “minettes” and “vogesites” are more correctly termed sannaite, particularly those occurring in carbonatite complexes.Camptonites most probably represent alkali basalt magmas which became unusually hydrous through influence of an alkaline pluton, and then evolved at relatively low pressures. Varied evidence is considered to suggest that the nearly isotropic base in monchiquites typically consists of altered glass rather than analcime; where analcime is present it probably formed along with zeolites by secondary processes. “Monchiquitic” is not an appropriate synonym for “analcime-bearing”, as in some literature. Field, chemical and statistical evidence is taken to suggest that many monchiquites are either chilled heteromorphs of camptonites or camptonitic magmas which crystallised under high CO2 activities. Liquid immiscibility seems to be more extensively developed in camptonites and monchiquites than in any other igneous rocks, and is probably governed by their hydrous state.The genetic connotations of lamprophyre names, asserted early in their history but later questioned, are here modified but reaffirmed: broadly minettes and related lamprophyres connote post-orogenic granites or mildly potassic (shoshonitic) alkaline rocks, alkaline lamprophyres connote alkali basalts or sodic alkaline rocks, and alnoites connote carbonatites. 相似文献
16.
Torngat ultramafic lamprophyres and their relation to the North Atlantic Alkaline Province 总被引：3，自引：0，他引：3
Sebastian Tappe George A. Jenner Stephen F. Foley Larry Heaman Dean Besserer Bruce A. Kjarsgaard Bruce Ryan 《Lithos》2004,76(1-4):491-518
Geological mapping and diamond exploration in northern Quebec and Labrador has revealed an undeformed ultramafic dyke swarm in the northern Torngat Mountains. The dyke rocks are dominated by an olivine-phlogopite mineralogy and contain varying amounts of primary carbonate. Their mineralogy, mineral compositional trends and the presence of typomorphic minerals (e.g. kimzeyitic garnet), indicate that these dykes comprise an ultramafic lamprophyre suite grading into carbonatite. Recognized rock varieties are aillikite, mela-aillikite and subordinate carbonatite. Carbonatite and aillikite have in common high carbonate content and a lack of clinopyroxene. In contrast, mela-aillikites are richer in mafic silicate minerals, in particular clinopyroxene and amphibole, and contain only small amounts of primary carbonate. The modal mineralogy and textures of the dyke varieties are gradational, indicating that they represent end-members in a compositional continuum.
The Torngat ultramafic lamprophyres are characterized by high but variable MgO (10–25 wt.%), CaO (5–20 wt.%), TiO2 (3–10 wt.%) and K2O (1–4 wt.%), but low SiO2 (22–37 wt.%) and Al2O3 (2–6 wt.%). Higher SiO2, Al2O3, Na2O and lower CO2 content distinguish the mela-aillikites from the aillikites. Whereas the bulk rock major and trace element concentrations of the aillikites and mela-aillikites overlap, there is no fractional crystallization relation between them. The major and trace element characteristics imply related parental magmas, with minor olivine and Cr-spinel fractionation accounting for intra-group variation.
The Torngat ultramafic lamprophyres have a Neoproterozoic age and are spatially and compositionally closely related with the Neoproterozoic ultramafic lamprophyres from central West Greenland. Ultramafic potassic-to-carbonatitic magmatism occurred in both eastern Laurentia and western Baltica during the Late Neoproterozoic. It can be inferred from the emplacement ages of the alkaline complexes and timing of Late Proterozoic processes in the North Atlantic region that this volatile-rich, deep-seated igneous activity was a distal effect of the breakup of Rodinia. This occurred during and/or after the rift-to-drift transition that led to the opening of the Iapetus Ocean. 相似文献
17.
秦岭地区蚀变煌斑岩型金矿的发现及金的预富集研究 总被引：7，自引：1，他引：6
秦岭地区煌斑岩广泛分布,大部分蚀变煌斑岩型金矿发现于微成盆地南侧。本文对煌斑岩金的预集提出了认识,深入研究蚀变煌斑岩型金矿中金的预富集和成矿特征有望扩大在秦岭地区的找金前景。 相似文献
18.
山东铜岭金矿的矿体定位构造 总被引：1，自引：0，他引：1
铜岭金矿位于山东省乳山市东南部,产在三佛山斑状二长花岗岩中,为含金石英脉型金矿。在三佛山岩体边部发育弧形脉岩群,铜岭金矿就位于该弧形脉岩群的弧顶外端,走向ＮＷ,与区内脉岩群垂直,据此提出铜岭金矿受三佛山岩体构造控矿的看法。铜岭金矿矿体的定位还受蚀变带宽度变化的影响,往往产于蚀变带狭缩处与膨大处的转换部位。铜岭金矿矿石金品位及矿体厚度在走向和倾向上均呈串珠状或波状变化。 相似文献
19.
Field Evidence of Magma Mixing from Microgranular Enclaves Hosted in Palaeoproterozoic Malanjkhand Granitoids, Central India 总被引：5，自引：0，他引：5
The Malanjkhand granitoids (MG) pluton (about 1500 sq km) occurs in the Balaghat district of Madhya Pradesh. The MG (~2400 Ma) represent an episode of Palaeoproterozoic felsic magmatism in Central India and hosts potential Cu (±Mo±Au) deposits. The enclaves hosted in MG can be broadly classified into two categories: microgranular enclaves (dark-coloured, fine-grained magmatic) and xenoliths of country rocks. The microgranular enclaves (ME) may be rounded, ellipsoidal, discoid, elongated, lenticular or tabular, and their size commonly reaches up to 2 metres across. The ME have sharp and in places, diffuse contacts with their host granitoids. The shape and size of ME indicate contemporaneous flow and mingling of partly crystalline felsic-mafic magmas. Some ME exhibit dark crenulated margins giving them a pillow-like form that has been attributed to undercooling of a ME magma as globules intruded into a granitoid magma. The presence of corroded felsic and mafic minerals (xenocrysts) in ME is interpreted as the result of mechanical transfer during the mafic-felsic magma interaction and mixing event. Mafic minerals (biotite) rim the quartz xenocrysts giving rise to ocellar texture, which exhibit signatures of resorption under hybrid (enclave) magma conditions. All these features suggest an origin for the calc-alkaline intermediate granitoid magma in Malanjkhand involving a magma mixing process. 相似文献
20.
M. S. Rao 《Journal of the Geological Society of India》2018,91(1):5-8
Pyrite containing appreciable content of cobalt (up to 5.61 wt%) and minor amounts of nickel (up to 0.70 wt%) is being reported from electron microprobe studies in a lamprophyre dyke from the Sidhi complex, Mahakoshal belt, Central India. However, cobalt and nickel are conspicuously absent from the associated chalcopyrite reflecting that in a pyrite-chalcopyrite association these elements are preferentially sequestered in pyrite. The microprobe analysis of pyrite grains reveal that their Fe content is variable (40.62 to 46.02 wt%) and reciprocally related to cobalt and nickel concentrations implying the presence of latter as solid solution in the structure of pyrite. The cobalt contents of the pyrite are comparable to those (up to 3.21 wt%) reported from the cobaltbearing pyrites of the Kalyadi copper deposits of Dharwar craton of southern India. Co:Ni (16.05 average) in the studied pyrite appears to be more consistent with a magmatic, rather than a hydrothermal, origin. However, further studies are in progess. This study highlights that besides gold and diamond, lamprophyres are also important carriers of cobalt when available in the magmatic system. 相似文献