oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Geochemistry and petrography of Early Paleozoic Yusupuleke Tagh rapakivi-textured granite complex, South Altyn: An example for magma mixing
阿尔金造山带南缘岩浆混合作用:玉苏普阿勒克塔格岩体岩石学和地球化学证据

WANG Chao,LIU Liang,ZHANG AnD,YANG WenQiang,CAO YuTing,
王超
,刘良,张安达,杨文强,曹玉亭

岩石学报 , 2008,
Abstract: The calc-alkaline granites of the Yusupuleke Tagh batholiths are associated with abundant mafic magmatic enclaves (MME) and aplite dikes. The granitc complex exhibits excellent evidence for magma mixing and mingling, such as the K-feldspar megacrysts in MME, long prisms of apatite, rapakivi feldspars (plagioclase-mantled K-feldspars), oikocrysts of quarts and feldspar-sphene ocelli. These suggest that mixing process of granitic and more mafic magmas induce the formation of the rapakivi texture. Textural evidence of the rapakivi magmas is better preserved in aplite than in the more deep-seated rapakivi granites formed by slow cooling, that indicate the decompression during crystallization of the magmas may promote the production of the mantled alkali feldspar megacrysts. Geochemical, there are linear arrays in binary diagrams. MME and host granitoids are considered cogenetic, and are hybrid rocks that were produced by the mixing of two components in different proportions. The granites are characterized by high Ga/Al, K2O/Na2O, Fe/Mg and low CaO, and showing A-type granite signatures but the aplites are peraluminous, high Na2O, CaO, similar to more felsic, fractionated A-type granites. Chemical data suggest that the MME originated from the enriched mantle melts, whereas the felsic component was produced by partial melting of preexisting crustal materials. Deep-seated interactions between felsic and mafic magmas were responsible for the common characteristics of both magma suites. The chemical evolution of post-orogenic plutnism indicates mantle-crust interactions at decreasing depths in an actively extending orogen. The distinct composition and rapakivi-texture of the granitoids reflects two stages of hybridization and emplacement at the end of an orogenic cycle.
Surface weathering of rapakivi granite outcrops – implications for natural stone exploration and quality evaluation  [PDF]
H?rm?, Paavo,Selonen, Olavi
Estonian Journal of Earth Sciences , 2008,
Abstract: Implications of surface weathering of rapakivi granite outcrops for natural stone evaluation were studied in the Wiborg rapakivi granite batholith in southeastern Finland. The study was performed as field mapping, comprising the whole batholith and as detailed investigations on selected outcrops. The Wiborg batholith is composed of wiborgite, pyterlite, even-grained rapakivi granite, porphyritic rapakivi granite, porphyry aplite, and gabbro-anorthosite. Wiborgite is the main rapakivi granite type. Weathering affects coarse-grained rapakivi varieties: wiborgite, pyterlite, and porphyritic rapakivi granite. Weathering occurs as surficial weathering of outcrops and randomly along subhorizontal and subvertical fractures, and varies in intensity. In the weathered upper parts of the outcrops the colour of the stone is altered and soundness of the stone diminished, which has a significant impact on the natural stone evaluation. In rapakivi granite areas, subsurface evaluation methods, by which the weathered surface part of the outcrops can be recognized, should always be used. Development of subsurface methods is required in order to make them more applicable in the evaluation of natural stone in areas with weathered rock.
Crystal Chemistry and Geochronology of Thorium-Rich Monazite from Kovela Granitic Complex, Southern Finland  [PDF]
Thair Al-Ani, Pentti H?ltt?, Sari Gr?nholm, Lassi Pakkanen, Nadhir Al-Ansari
Natural Resources (NR) , 2019, DOI: 10.4236/nr.2019.106016
Abstract: Abundant porphyritic granites, including Grt-bearing and Bt-bearing porphyritic granites, and porphyritic potash-feldspar granite (trondhjemite-granitic composition) are widely distributed within the Kovela granitic complex Southern Finland, which associated with monazite-bearing dikes (strong trondhjemite composition). The investigated monazite-bearing dikes are dominated by a quartz + K-feldspar + plagioclase + biotite + garnet + monazite assemblage. The monazite forms complexly zoned subhedral to euhedral crystals variable in size (100 - 1500 μm in diameter) characterized by high Th content. The chemical zoning characterised as: 1) concentric, 2) patchy, and 3) intergrowth-like. Textural evidence suggests that these accessory minerals crystallized at an early magmatic stage, as they are commonly associated with clusters of the observed variations in their chemical composition are largely explained by the huttonite exchange \"\", and subordinately by the cheralite exchange \"\" with proportions of huttonite (ThSiO4) and cheralite [CaTh(PO4)2] up to 20.4% and 9.8%, respectively. Textural evidence suggests that these monazites and associated Th-rich minerals (huttonite/thorite) crystallized at an early magmatic stage, rather than metamorphic origin. The total lanthanide and actinide contents in monazite and host dikes are strongly correlated. Mineral compositions applied to calculate P-T crystallization conditions using different approaches reveal a temperature range of 700
The Shahewan rapakivi-textured granite – quartz monzonite pluton, Qinling orogen, central China: mineral composition and petrogenetic significance  [PDF]
Xiaoxia Wang,Tao Wang,Ilmari Haapala,Xinxiang Lu
Bulletin of the Geological Society of Finland , 2002,
Abstract: The Mesozoic Shahewan pluton consists of four texturally different types of biotite-hornblende quartz monzonite. In the porphyritic types alkali feldspar occurs as euhedral or ovoidal megacrysts that are often mantled by one or more plagioclase shells, and as smaller grains in the groundmass. Quartz, plagioclase (An20–28), biotite, and hornblende occur as inclusions in the alkali feldspar megacrystsand, more abundantly, in the groundmass. Euhedral quartz crystals in the groundmass are not as common and well developed as in typical rapakivi granite. Compared to typical rapakivi granites, the mafic minerals (biotite and hornblende) are rich in Mg and poor in Fe, and the whole rock is low in Si, K, F, Ga, Zr, LREE, Fe/Mg, and K/Na. The rocks of the Shahewan pluton are thus regarded as rapakivi-textured quartz monzonites and granites but not true rapakivi granites.
Magmatic constraints on localization of natural stone deposits in the Vehmaa rapakivi granite batholith, southwestern Finland  [PDF]
Olavi Selonen,Carl Ehlers,Hannu Luodes,Fredrik Karell
Bulletin of the Geological Society of Finland , 2011,
Abstract: The 1580–1570 Ma old Vehmaa rapakivi granite batholith was studied with the aim to define the geological constraints for localization of natural stone deposits in the batholith. The batholith comprises four roughly concentric granite intrusions from the margin inwards: pyterlite, coarse-grained porphyritic rapakivi granite and two types of medium-grained porphyritic rapakivi granite. Also porphyry aplite and even-grained rapakivi granite occur. The batholith has intruded as a succession of pulses of subhorizontal sheet-like intrusions conceivably through repeated cauldron subsidence. Natural stone quarries are confined only to certain intrusions within the batholith. We show that the medium-grained porphyritic granite body in the centre of the batholith comprises two almost identical but different intrusions, with only slightly different appearances: the inner (IG) and the outer (OG) granite. The quarries are confined to the outer intrusion which has an appearance more attractive to the market than that of the inner intrusion. The localization of the natural stone deposits in the Vehmaa batholith is a result of the magmatic history of the batholith, producing intrusions of different appearances with different commercial potential.
Magmatic Rocks of the Karavanke Granitic Massif, Slovenia  [PDF]
Meta Dobnikar,Tadej Dolenec,Breda ?in?-Juhant,Nina Zupan?i?
Geologija , 2000,
Abstract:
Plagioclase-mantled K-feldspar in the Carboniferous porphyritic microgranite of Altenberg-Frauenstein, Eastern Erzgebirge/Krusné Hory  [PDF]
Axel Müller,Reimar Seltmann
Bulletin of the Geological Society of Finland , 2002,
Abstract: The Upper Carboniferous porphyritic microgranite of Altenberg-Frauenstein, formerly known as Granitporphyr (Dalmer 1896) and here abbreviated as GP, forms a 36 km long and up to 18 km wide complex of ring dykes related to the Teplice-Altenberg caldera in the German–Czech border region of the Eastern Erzgebirge/Krusné Hory. The microgranites are characterized by the occurrence of plagioclase-mantled K-feldspar phenocrysts. The microgranite varieties representtwo main stages of intrusion evolved from acid (GP I) to intermediaterocks (GP II) within the intrusion. The most acid rock (GP Icum) occurs as enclaves in GP I and GP II and is interpreted as a cumulate of K-feldspar and quartz phenocrysts. The porphyritic microgranites show field, textural and geochemical evidence suggesting that some of them have formed as a result of interaction between felsic and mafic magmas. Mixing features are abundant in the porphyriticquartz-feldspar-hornblende microgranite (GP II) interpreted as a hybrid rock. They are less discrete in the early phase (GP I) and not obvious in the acid enclaves (GP Icum). This trend seems to reflect a continuous deflation of the magma chamber from the top to the bottom. According to the definition of rapakivi granites after Haapala and R m (1992), the porphyritic microgranite of Altenberg-Frauenstein may be considered as rapakivi granite although ovoid alkali feldspar megacrysts typical of classical rapakivi granites are not recorded.However, due to its Carboniferous age and being the only known granitewith rapakivi texture in the German–Czech part of the Variscan belt, the microgranite of Altenberg-Frauenstein is exceptional.
Discovery of Paleoproterozoic rapakivi granite on the northern margin of the Yangtze block and its geological significance
LiJuan Zhang,ChangQian Ma,LianXun Wang,ZhenBing She,ShiMing Wang
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-010-4236-7
Abstract: The Huashanguan rapakivi pluton in Zhongxiang, Hubei Province, China, is the first discovered Proterozoic rapakivi pluton in the Yangtze block. Based on field and petrographical observations, a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton. Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts. Alkali feldspars and quartz had two or more generations. Petrochemically, the Huashanguan rapakivi granites were characterized as having high values of Si, K, Fe, Th, U, La, Ga, Ce, Sm and LREE, low values of Ca, Mg, Sr, Nb, Y and HREE, and a negative Eu anomaly. These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites, and had an affinity to A-type granites. LA-ICP-MS U-Pb zircon dating also was conducted. The dating yielded a 207Pb/206Pb weighted mean age of 1851±18 Ma (MSWD =1.2), which represents the age of the pluton emplacement. The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton, and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation. The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block. These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent.
Petrography and geochemistry of the topaz-bearing granite stocks in Artj rvi and S skj rvi, western margin of the Wiborg rapakivi granite batholith  [PDF]
Sari Lukkari
Bulletin of the Geological Society of Finland , 2002,
Abstract: The Artj rvi and S skj rvi granite stocks at the western margin of the Wiborg rapakivi batholith are multiphase rapakivi granite intrusions in which the most evolved phase is topaz-bearing granite. The Artj rvi stock is composed of porphyritic and even-grained biotite granite and even-grained topaz granite, and the S skj rvi stock comprises even-grained biotite granite and porphyritic topazgranite. The granites are metaluminous to peraluminous A-type granites, showing within-plate (WPG) geochemical characteristics. The topaz granites from the Artj rvi and S skj rvi stocks are petrographically and geochemically similar to other topaz-bearing rapakivi granites in Finland. The anomalous geochemistry of the topaz granite is essentially magmatic; postmagmatic reactions have only slightly modified its composition. Greisen veins, some of which are mineralized, are widely found associated with the Artj rvi and S skj rvi stocks.The most characteristic feature of the Artj rvi granite stock is a stockscheider at the roof contact of the topaz granite. The stockscheider is composed of schlieren layering and pegmatite layers parallel to the contact. The most probable mechanism for the formation of the schlieren layering is velocity-gradient sorting parallel to the flow, which led to accumulation of mafic minerals along the upper contact of the topaz granite. Cooling and contraction of the topaz granite formed fractures parallel to the roof contact and the residual pegmatite magmas were injected along the fractures forming pegmatite layers. Textures like graphic intergrowths, aplitic groundmass and fan-shaped alkali feldspar crystals associated with the Artj rvi porphyritic biotite granite and pegmatite indicatecrystallization from undercooled magma. Miarolitic cavities found in the porphyritic biotite granite and topaz granite indicate at least local volatile saturation.
Geodynamics of Dikes in North of Saveh  [PDF]
Mohammad-Hasan Bazoobandi, Mohammad-Ali Arian, Mohammad-Hashem Emami, Gholam-Reza Tajbakhsh, Abdollah Yazdi
Open Journal of Ecology (OJE) , 2015, DOI: 10.4236/oje.2015.59037
Abstract: Dikes can be divided into sheeted, feeder, cone and swarm types based on the origin and the formation. A group of dikes that are formed in dense in a relatively broad zone influenced by a particular tectonic regime are referred to as swarm dikes. Swarm dikes have numerous applications such as locating mantle plume centers, determining areas of longstanding tensions and detection of deformation networks. The purpose of this article is classified swarm dikes of “North of Saveh” based on previous studies. In one study, swarm dikes are classified based on their initial geometry into five types of I, II, III, IV and V. According to this classification, our study has been shown that the dikes in north of Saveh are of type IV. In another study, the swarm dikes are classified into three types: parallel, large radial and small radial. According to the classification, our study has been shown that the dikes of North Saveh are parallel that have arisen by tensions caused by the collision of the Arabian plate and the Central Iran plate. In addition to original tensions in the region, local faults have been effective on the arrangement and the establishment of dikes.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.