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1.
The Sichevita and Poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the Getic Nappe in the South Carpathians. The present work provides SHRIMP age data for the zircon population from a Poniasca biotite diorite and geochemical analyses (major and trace elements, Sr–Nd isotopes) of representative rock types from the two intrusions grading from biotite diorite to biotite K-feldspar porphyritic monzogranite. U–Pb zircon data yielded 311 ± 2 Ma for the intrusion of the biotite diorite. Granites are mostly high-K leucogranites, and biotite diorites are magnesian, and calcic to calc-alkaline. Sr, and Nd isotope and trace element data (REE, Th, Ta, Cr, Ba and Rb) permit distinguishing five different groups of rocks corresponding to several magma batches: the Poniasca biotite diorite (P1) shows a clear crustal character while the Poniasca granite (P2) is more juvenile. Conversely, Sichevita biotite diorite (S1), and a granite (S2*) are more juvenile than the other Sichevita granites (S2). Geochemical modelling of major elements and REE suggests that fractional crystallization can account for variations within P1 and S1 groups. Dehydration melting of a number of protoliths may be the source of these magma batches. The Variscan basement, a subduction accretion wedge, could correspond to such a heterogeneous source. The intrusion of the Sichevita–Poniasca plutons took place in the final stages of the Variscan orogeny, as is the case for a series of European granites around 310 Ma ago, especially in Bulgaria and in Iberia, no Alleghenian granitoids (late Carboniferous—early Permian times) being known in the Getic nappe. The geodynamical environment of Sichevita–Poniasca was typically post-collisional of the Variscan orogenic phase.  相似文献   

2.
The dike belt and separate intrusive bodies of the Abdar–Khoshutula series were formed in the NE-trending linear zone, southwest of the Daurian–Khentei batholith, in the peripheral part of the Early Mesozoic magmatic area, on the western termination of the Mongol–Okhotsk belt. The granitoids of this series are subdivided into following geochemical types: anatectic granitoids of the calc-alkaline and subalkaline series, alkaline rocks, and plumasite rare-metal leucogranites (Li–F granites). The entire series was formed within approximately 12–15 Ma. Its geochemical evolution follows two trends, which correspond to two stages of the granitoid magmatism. The early stage was responsible for the formation of granitoids of two phases of the Khoshutulinsky Pluton and alkaline syenites with similar trace element distribution patterns. However, syenites, as agpaitic rocks, are significantly enriched in Ba, Zr, and Hf. The late stage of the intrusive- dike series resulted in the formation of the dike belt and Abdar Massif of rare-metal granites. These rocks show enrichment in Li, Rb, Cs, Nb, Ta, Sn, and Y, and deep negative anomalies of Ba, Sr, La, and Ce, which are best expressed in the late amazonite–albite granites of the Abdar intrusion and ongonites of the dike belt. The intrusive-dike series in the magmatic areas of different age of Mongolia and Baikal region are characterized by the wide compositional variations, serve as important indicators of mantle-crustal interaction and differentiation of granitoid magmas, and could highlight the nature of zonal areas within the Central Asian Fold Belt. Obtained geochemical data indicate a potential opportunity to concentrate trace and ore components during long-term evolution of the intrusive-subvolcanic complexes, which could be indicators of the evolution of the ore-magmatic systems bearing rare-metal mineralization.  相似文献   

3.
The Serra da Providência batholith includes the type area of the homonymous suite, the oldest rapakivi magmatic assemblage in the SW of the Amazonian craton (1.60–1.53 Ga). In the midwest portion of this massif, besides wiborgites/pyterlites and granophyric syenogranites, a leucosyenogranite facies and porphyritic rhyolites constitute new rock varieties recently described in that area. UPb LA-MC-ICP-MS zircon ages of 1574 ± 9 Ma and 1604 ± 3 Ma, respectively, were obtained for these new varieties and confirm their link with the Serra da Providência magmatism, whereas the subvolcanic rocks are older than the main rock varieties and were formed in a precursor event. These granitic facies are metaluminous to peraluminous, alkali-calcic, A2-type, ferroan granites. Their FeOt/(FeOt + MgO) ratios vary from 0.83 to 0.98 and suggest that these rocks were crystallized from oxidized-to reduced-A-type magmas, where the leucosyenogranites and granophyric sienogranites tend to be formed under more reduced conditions. They show fractionated REE patterns with very pronounced to weak negative Eu anomalies. The presence of granophyric textures and miarolitic cavities in equigranular syenogranitic facies suggests that these rocks were formed at shallow crustal depths, lower than 3 km. Three samples of leucosyenogranite have silica contents higher than 75% and low K/Rb ratios (<150), similarly to the tin specialized granites described in the Amazonian craton. Two distinctive groups of mafic rocks were recognized in the study area: porphyritic and equigranular gabbronorites. They correspond to tholeiitic basalts, with #Mg varying from 37 to 41 in porphyritic gabbronorites and 51 to 65 in equigranular gabbronorites. The low to moderate #Mg suggests that these rocks were crystallized from more evolved basaltic magmas. The porphyritic gabbronorites are enriched in TiO2, FeOt, K2O, P2O5 and REE compared to the equigranular gabbronorites that are enriched in MgO and CaO. The porphyritic gabbronorites have significant negative Eu anomalies a feature not observed in the equigranular gabbronorites. Porphyritic gabbronorites geochemical characteristics are similar to calc-alkaline basalts, whereas equigranular gabbronorites are similar to continental basalts. Petrographic, geochemical, and geological data of the felsic facies and the presence of associated mafic rocks corroborate the bimodal and post-collisional character of this magmatism. The occurrence of porphyritic rhyolites associated with shallow level plutonic granites in the Serra da Providência batholith reinforces the similarities between the Rondonian granites and the classical Fennoscandian rapakivi granites.  相似文献   

4.
The paper deals with geological and geochemical studies of granitoids of the Olenek complex in the Olenek uplift of the basement of the northern Siberian craton. The age of these granitoids was earlier estimated at 2036 ± 11 Ma. The granitoids of the Olenek complex correspond in composition to high-alumina quartz diorites, granites, and leucogranites of the normal petrochemical series. According to geochemical and mineralogical characteristics, the quartz diorites can be assigned to granites of the transitional I-S type, and the granites and leucogranites, to S-type granites. The 8Nd(T values in the granites of the Olenek complex vary from -0.2 to + 1.4, and the Nd model age is 2.4-2.5 Ga. The quartz diorite is characterized by 8Nd(T) = + 3.0 and a Nd model age T(DM) = 2.2 Ga. The geochemical characteristics of the granites and leucogranites indicate their formation through the melting of a source of graywacke composition, whereas the quartz diorites resulted, most likely, from the mixing of granitic and basaltic melts. The fact that the granitoids of the Olenek complex intruded the folded rocks of the Eekit Formation but stay virtually undeformed massive bodies suggests that they formed at the postdeformation stage of the regional evolution after the completion of the Paleoproterozoic orogenic events. The intrusion of granitoids marks the completion of the formation of the Early Proterozoic Eekit fold belt on the western (in the recent coordinates) margin of the Birekta terrane of the Olenek superterraine and the final formation of the superterrane structure. At the next stage of magmatism (1.98-1.96 Ga), best pronounced in the uplifts of the basement of the northern Siberian craton, all terranes forming the Anabar and Olenek superterranes assembled into a single structure.  相似文献   

5.
Geochemical and geochronological studies of the main types of granitoids of the Angara-Vitim batholith (AVB) and granites of the Zaza complex in western Transbaikalia were carried out. U-Pb (SHRIMP-II) and Rb-Sr dating yielded the age of autochthonous gneiss-granites of the Zelenaya Griva massif (325.3±2.8 Ma), quartz syenites of the Khangintui pluton (302.3±3.7 Ma) and intruding leucogranites of the Zaza complex (294.4±1 Ma), monzonites of the Khasurta massif (283.7±5.3 Ma), and quartz monzonites of the Romanovka massif (278.5±2.4 Ma). The U-Pb and Rb-Sr dates show that the Late Paleozoic magmatism in western Transbaikalia proceeded in two stages: (1) 340–320 Ma, when predominantly mesocratic granites of the Barguzin complex, including autochthonous ones, formed, and (2) 310–270 Ma, when most AVB granitoids formed. We suggest that at the early stage, crustal peraluminous granites formed in collision geodynamic setting. At the late (main) stage, magmatism occurred in postorogenic-extension setting and was accompanied by the formation of several geochemical types of granitoids: (1) typical intrusive mesocratic granites of the Barguzin complex, similar to those produced at the first stage; (2) melanocratic granitoids (monzonitoids, quartz syenites), which were earlier dated to the early stage of the AVB evolution; (3) leucocratic medium-alkali (peraluminous) granites of the Zaza intrusive complex; and (4) some alkali-granite and syenite intrusions accompanied by alkaline mafic rocks. The diversity of granitoids that formed at the late stage of magmatism was due to the heterogeneous composition of crust protoliths and different degrees of mantle-magma participation in their formation.  相似文献   

6.
利用LA-ICP-MS锆石U-Pb法测得程潮矿区花岗岩成岩年龄为（128.8±0.5） Ma,石英二长斑岩成岩年龄为（128.3±0.5） Ma,闪长岩成岩年龄为（140.0±0.3） Ma,辉绿玢岩成岩年龄为(125.5±0.5) Ma,皆形成于早白垩世。地球化学分析结果显示：花岗质岩为高钾准铝质I型系列;闪长岩和辉绿玢岩为高钾钙碱性系列。各岩体的稀土元素总量较高,轻稀土强烈富集,轻、重稀土元素分异明显,无明显的负铕异常。花岗质岩的微量元素以富集Rb、Th、U、La等元素,贫Ba、Nb、Sr等元素为特点。闪长岩和辉绿玢岩具有相似的微量元素特征,表现为K、La、Nd富集和Ta、Nb、Sr、P、Ti亏损的特点。根据岩体的锆石Hf同位素组成和地球化学特征可知,程潮矿区各岩体可能是岩石圈地幔在部分熔融过程中,混入了不同数量古老下地壳物质的产物。矿区花岗质岩的成岩年龄与程潮Fe矿床的成矿年龄相近,暗示其与矿体有着密切的联系。  相似文献   

7.
《International Geology Review》2012,54(11):1040-1053
The Ordovician Famatinian-age magmatic cordierite-andalusite-bearing Capillitas batholith, in the Pampean Ranges of northwestern Argentina, encompasses a coarsely porphyritic to equigranular two-mica monzogranite with equigranular, fine-grained, late leucogranitic muscovite-rich facies. This batholith exhibits sharp, discordant contacts with low-pressure biotite-andalusite-cordierite schists of the La Cébila Formation, locally developing biotite-cordierite-muscovite-bearing contact hornfels aureoles.

The two-mica monzogranite contains cordierite, andalusite, and sillimanite, although cordierite and andalusite are more abundant in the leucogranitic equigranular facies. These minerals are not homogeneously distributed and the three minerals are found together only locally. The presence of biotite-rich xenoliths with a high amount of anhydrous aluminum silicates (andalusite, sillimanite) and cordierite, exhibiting textures similar to those of the host monzogranites, suggest that, at least in part, they have been incorporated into the magma and reequilibrated. The pressure during emplacement was probably 4 kbar under near-solidus temperature, thus preserving the anhydrous aluminum-silicate stability under high H2O activity.

The major-element data indicate a peraluminous calc-alkalic trend with compositional gaps. They attest to the existence of two distinct magma pulses. The chondrite-normalized REE patterns and multi-element spidergrams point to a probable origin by crustal (metasediment?) anatexis for both pulses. Peraluminous granitic magma cannot be a primary melt of metaluminous quartz-amphibolite, since there is a great geochemical homogeneity of all the granitoids. Igneous xenoliths are absent and the isotopic compositions of the granitoids correspond to those of metasedimentary sources. Both major and trace elements point to a collisional tectonic environment of an inner-continental magmatic arc.  相似文献   

8.
阿巴拉契亚造山带加拿大纽芬兰岛东南部发育一晚泥盆纪阿克利巨型花岗岩基(～2500 km2).该岩基侵位于甘德和阿瓦隆地块的多佛-赫米蒂奇湾巨型断层带之间,内部发育钨-锡-钼矿床及相关的矿化.本文锆石年代学研究显示,岩基中Tolt单元侵位于378±2 Ma,各单元年龄基本一致,为同期岩浆多次侵位的产物.岩基中主要岩石类型...  相似文献   

9.
Geochemical, isotopic and age constraints support a comagmatic origin for Ghuweir Mafics and the Feinan A-type granites. The two rocks types, named collectively in this paper as the Feinan Ghuweir Magmatic Suite (FGMS), formed between 556 and 572 Ma ago according to Rb-Sr whole-rock dating. FGMS has low Sr initial ratios, which preclude a significant contribution of much older crust in the magma genesis.The FGMS has a wide range of silica contents, with a gap at 55-65 wt% SiO2. It has a transalkaline to alkaline character; belongs to the medium to high K calc-alkaline series; it ranges from metaluminous to mildly peraluminous character and belongs to the alkali and alkali-calcic series. The Feinan granites and the Ghuweir rhyolites and rhyodacites are classified as A-type granites and belong to group A2 of Eby [Eby, N.G., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic iplications. Geology 20, 641-644].According to geochemical modeling the Ghuweir Mafics were derived from a subduction modified lithospheric mantle by 10% batch modal partial melting of a phlogopite-bearing spinel lherzolite. The intra-suite geochemical variations can be ascribed to fractional crystallization of olivine, pyroxene, and plagioclase. The accumulation of apatite in the most evolved samples is responsible for the high concentrations of REE.The Feinan granites and the Ghuweir rhyolites and rhyodacites were derived from the mafic magma by the fractional crystallization of ≈78% of the original magma to the mineral assemblage olivine+pyroxene+plagioclase+magnetite. The intra-suite geochemical variations in the Feinan A-type granites are due to the fractional crystallization of the mineral phases: amphibole +Na and K-feldspar+apatite +magnetite+zircon+allanite.The FGMS correlates with time-equivalent rocks in many parts of the Arabian-Nubian Shield and the surrounding areas.  相似文献   

10.
Many elongated, lenticular plutons of porphyritic granitoids are distributed mainly near the southern and northern margin of the Chhotanagpur Gneissic Complex （CGC） which belongs to the EW to ENE-WSW tending 1500 km long Proterozoic orogenic belt amalgamat ng the North and South Indian cratonic blocks. The late Grenvillian （1071 ±64 Ma） Raghunathpur porphyritic granitoid gneiss （PGG） batholith comprising alkali feldspar granite, granite, granodiorite, tonalite, quartz syenite and quartz monzonite intruded into the granitoid gneisses of southeastern part of CGC in the Purulia district, West Bengal and is aligned with ENE-WSW trending North Purulia sr~ear zone, Mineral chemistry, geochemistry, physical condition of crystallization and petrogenetic model of Raghunathpur PGG have been discussed for the first time. The petrographic and geochemical features （including major and trace- elements, mineral chemistry and S7Sr/S6Sr ratio） suggest these granitoids to be classified as the shosh- onitic type. Raghunathpur batholith was emplaced at around 800 ~C and at 6 kbar pressure tectonic discrimination diagrams reveal a post-collision tectonic setting while structural studies reveal its emplacement in the extensional fissure of North Purulia shear zone. l＇he Raghunathpur granitoid is compared with some similar granitoids of Europe and China to draw its petrogenetic model. Hybridi- zation of mantle-generated enriched mafic magma and crustal magma at lower crust and later fractional crystallization is proposed for the petrogenesis of this PGG. Mafic magma generated in a post-collisional extension possibly because of delamination of subducting slab. Raghunathpur batholith had emplaced in the CGC during the final amalgamation （~ 1.0 Ga） of the North and South Indian cratonic blocks. Granitoid magma, after its generation at depth, was transported to its present level along megadyke channel, ways within shear zones.  相似文献   

11.
Located in the Luonan county, Shaanxi Province, northwest China, Jinduicheng, Shijiawan and Huanglongpu molybdenum deposits constitute the most important molybdenum mineralized district in China. Among these three deposits, the Jinduicheng and Shijiawan molybdenum deposits are connected spatially and genetically with granitoid porphyry (124 ± 6 Ma, K-Ar biotite), and consist of disseminated-veinlet ores. Geochemical studies of rare earth elements (REE) furnish further evidence for understanding the rock- and ore-forming processes of these two porphyry molybdenum deposits and their related granitoid rocks. The REE distribution in molybdenum ore, granitoids and their Middle Proterozoic meta-volcanic wall rocks is discussed. The similarities between the REE signatures of the Shijiawan molybdenum-bearing monzogranite porphyry and the neighbouring Laoneushan monzogranite (130 ± 5 Ma, K-Ar biotite) show that they were produced at the same evolutional stage of granitoid magma derived mainly from crustal anatexis. The Shijiawan biotite monzogranite porphyry may be an apophysis of the Laoneushan granitoid batholith. Compared to the Shijiawan monzogranite porphyry, the Jinduicheng molybdenum-bearing granite porphyry is characterized by a high content of HREE, and depletion in LREE. The unique REE patterns indicates that the molybdenum-bearing granite porphyry was formed by thermogravitation diffusion of a granitoid magma. The slight depletion of REE abundance in the altered granitoid porphyry and meta-volcanic wall rocks shows that leaching of REE occurred during breakdown of the primary mineral assemblage, and crystallization of secondary minerals. The high REE content of molybdenum ore represented re-deposition of the mobilized molybdenum and REE.  相似文献   

12.
In the central segment of the Ribeira belt, southeast Brazil, several foliated porphyritic granitic bodies intrude high-grade migmatitic gneisses of the Andrelândia and Juiz de Fora domains and Embú Complex. Results of geological, geochemical and geochronological investigations of the Maromba, Pedra Selada, Serra do Lagarto and Funil porphyritic I-type granites provide profound similarities, except for the distinct geochemical behavior of the Funil Granite, perhaps related to a different crustal source. These granitoids show similar structural, textural and mineralogical features. Pb-evaporation of single zircons provided ages of 586 ± 6, 579.6 ± 6.3, 586.3 ± 4.8 and 584 ± 5 Ma for the granites, respectively, coincident with the syn-collision I episode of the central Ribeira belt. The intrusion of I-type porphyritic granitoids coeval with the main collisional event has not often been reported in the geological literature. The most common syn-collisional granitic magmatism has normally an S-type signature or even a slightly peraluminous I-type character. However, the occurrence of coeval I- and S-type syn-tectonic granites along the central Ribeira belt, as observed in the investigated area and discussed in this paper is noteworthy.  相似文献   

13.
The Late Paleozoic intraplate magmatism of the Selenga-Vitim structural zone of the Baikal region (Khamar-Daban Range) produced granitoids of different geochemical types: palingenic calc-alkaline granitoids, subalkaline monzogranites, and rare-metal Li-F granitoids and their subvolcanic analogues. Subalkaline and rare-metal granitoids occur in the periphery of the Late Paleozoic magmatic zone. Rare metal granite magmatism is manifested in this region as nearly N-S trending intrusive-dike belts comprising multiphase intrusions (Kharagul, Urugudei, and Bitu-Dzhida massifs) with an exposed area of ∼10 km2 and an age of formation from 311 to 321 Ma and series of accompanying dikes. The early phases of the intrusions are made up of biotite granites usually with fluorite, which are changed during the late stage by typical topazbearing rare-metal amazonite-albite granites. In the subvolcanic facies, thicker subalkaline dikes of monzonite porphyry, granite porphyry, and elvan are changed by ongonites, topaz rhyolites, and topazites, which occasionally serve as cement in eruptive and fluid-explosive breccias. The development of multiphase intrusions from early biotite granites to late amazonite-albite granites with Li-F mica was accompanied by an increase in SiO2 and, especially, Na2O contents, whereas the level of (FeO + Fe2O3), CaO, and K2O declined. Geochemical evolution includes an increase in the same direction in the contents of F, Li, Rb, Cs, Sn, Be, Ta, and Pb and a decrease in Ba, Sr, Zn, Zr, Th, and U. Similar evolution is also characteristic of the subvolcanic rocks, which emphasizes the genetic relation of the whole intrusive-dike complex of the Khamar-Daban province. Significant differences were detected in the distribution of K, Ba, Sr, and Zr between the calc-alkaline granitoids and rare-metal Li-F granites. The continental crust-normalized patterns of the raremetal granites show positive anomalies for Li, Rb, Nb, and Pb. The rare-metal Li-F granites could not be produced by palingenesis only, and their formation required specific conditions causing extensive accumulation of characteristic trace elements. During the evolution of granite melts, Li, Rb, Ta, Nb, Sn, W, and F are extensively accumulated in late intrusive phases, which indicates an important role of the processes of magmatic and fluid-magmatic differentiation during their formation. The composition and isotope geochemical characteristics of the supposed magma source material correspond to the ancient Precambrian continental crust with a mean model age of more than 1200 Ma.  相似文献   

14.
We studied the geologic position, mineralogy, petrography, chemical composition, and age of granitoids of the Gamov batholith located in the Heilongjiang-Grodekovo terrane, southern Primorye (Russia). The studies have revealed four intrusive rock phases, from gabbro to leucogranites, in the massif. U-Pb zircon dating of tonalites of phase II and leucogranites of phase IV (254 ± 4 and 259 ± 2 Ma, respectively) shows that the intrusion of granitoids took place in the Late Permian without a significant gap in time. Structural investigations gave evidence for the intrusion in the E-W compression setting. Geochemical studies have revealed granitoids of strongly different compositional types in the intrusive massif: gabbroids, quartz diorites and tonalites with characteristics of low-alumina TTG, calc-alkalic granodiorites and I-type granites, and moderately alkaline leucogranites. The obtained data, together with the results of previous research into the Permo-Triassic granitoids of southern Primorye, reject their formation as a result of the evolution of the Solonker oceanic structures and suggest a more intricate tectonic scenario, which calls for additional study.  相似文献   

15.
The Sergipano belt is the outcome of collision between the Pernambuco-Alagoas Domain (Massif) and the São Francisco Craton during Neoproterozoic assembly of West Gondwana. Although the understanding of the Sergipano belt evolution has improved significantly, the timing of emplacement, geochemistry and tectonic setting of granitic bodies in the belt is poorly known. We recognized two granite age groups: 630–618 Ma granites in the Canindé, Poço Redondo and Macururé domains, and 590–570 Ma granites in the Macururé metasedimentary domain. U–Pb SHRIMP zircon ages for granites of first age group indicated ages of 631 ± 4 Ma for the Sítios Novos granite, 623 ± 7 Ma for the Poço Redondo granite, 619 ± 3.3 Ma for the Lajedinho monzodiorite, and 618 ± 3 Ma for the Queimada Grande granodiorite. These granitoids are dominantly high-K calc-alkaline, magnesian, metaluminous, mafic enclave-rich (Queimada Grande and Lajedinho), or with abundant inherited zircon grains (Poço Redondo and Sitios Novos). Geochemical and isotope data allow us to propose that Sítios Novos and Poço Redondo granites are product of partial melting of Poço Redondo migmatites. Sr-Nd isotopes of the Queimada Grande granodiorite and Lajedinho monzodiorite suggest that their parental magma may have originated by mixing between a juvenile mafic source and a crustal component that could be the Poço Redondo migmatites or the Macururé metasediments. Other 630–618 Ma granites in the belt are the mafic enclave-rich Coronel João Sá granodiorite and the Camará tonalite in the Macururé sedimentary domain. These granites have similar geochemical and isotopic characteristics as the Lajedinho and Queimada Grande granitoids. We infer for the Camará tonalite and Coronel João Sá granodiorite that their parental magmas have had contributions from mafic lower crust and felsic upper crust, most probably from underthrust São Francisco Craton, or Pernambuco-Alagoas Domain. The younger 590–570 Ma granite group is confined to the Macururé metasedimentary domain. Although these granites do not show typical features of S-type granites, their U–Pb age, field relationships, geochemical and Sr-Nd data suggest that their parental magmas have originated from high degree melting of the Macururé micaschists. Field observations support a model in which the Macururé domain, limited by the Belo Monte-Jeremoabo and São Miguel do Aleixo shear zones, behaved as a ductile channel flow for magma migration and emplacement during the Neoproterozoic, very much like the channel flow model proposed for emplacement of leucogranites in the Himalayas.  相似文献   

16.
Two stages of granitic magmatism occurred during the Pan-African evolution of the Kerala Khondalite Belt (KKB) in southern India. Granitic gneisses were derived from porphyritic granites, which intruded prior to the main stage of deformation and peak-metamorphism. Subsequently, leucogranites and leucotonalites formed during fluid-absent melting and intruded the gneiss sequences. Monazites from granitic gneisses, leucogranites and a leucotonalite were investigated by conventional U-Pb and electron microprobe dating in order to distinguish the different stages of magma emplacement. U-Pb monazite dating yielded a wide range of ages between 590–520 Ma which are interpreted to date high-grade metamorphism rather than magma emplacement. The results of this study indicate that the KKB experienced protracted heating (>50 Ma) at temperatures above 750–800 °C during the Pan-African orogeny. The tectonometamorphic evolution of the study area is comparable to southern Madagascar which underwent a similar sequence of events earlier than the KKB. The results of this study further substantiate previous assertions that the timing of high-grade metamorphism in East Gondwana shifted from west to east during the Late Proterozoic.  相似文献   

17.
The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.  相似文献   

18.
《International Geology Review》2012,54(11):1284-1295
Late Cretaceous–early Tertiary granites in the Gyeongsang Basin have distinctly different bulk-rock compositions. Calc-alkaline I-type metaluminous granites display petrographic features implying magma mixing, whereas A-type granites are hypersolvus and peralkaline. I-type plutons mainly consist of enclave-rich granodiorites and enclave-poor porphyritic granites typified by abundant plagioclase phenocrysts; these granitoids contain various mafic clots and magmatic/microgranular enclaves (MMEs). A-type bodies are perthitic alkali-feldspar granites characterized by interstitial annite + riebeckite-arfvedsonite. New SHRIMP-RG zircon U–Pb age dating of an I-type enclave-poor porphyritic granite and an A-type alkali-feldspar granite yielded ages of 65.7 ± 0.7 and 53.9 ± 0.3 million years, respectively. Based on prior geochronologic data and these contrasting ages of granitic magma genesis, SE Korea may have evolved tectonically from latest Cretaceous compression to late Palaeocene extension (i.e. orogenic collapse). The later part of the 66–54 Ma magmatic gap apparently includes the time of tectonic inversion in the SE Korean Peninsula, a far-field effect of the collision of the Indian subcontinent with Eurasia. This process is also reflected in the 69–52 Ma NNE-trending Eurasian apparent polar wandering path.  相似文献   

19.
为探讨广西岑溪地区糯垌岩体及其岩石包体的成因,对糯垌岩体的岩石包体进行详细的岩相学、LA—ICP—MS锆石U—Pb年代学和地球化学分析。岩相学研究表明糯垌岩体的岩石包体主要为斑状黑云母钾长花岗岩、黑云斜长片麻岩、黑云二长片麻岩、二长变粒岩、钾长变粒岩和花岗闪长岩,按成因分为捕掳体和残浆包体两类。斑状黑云母钾长花岗岩包体(样品F16—7—6)和黑云斜长片麻岩包体(样品F16—13—4)的LA—ICP—MS锆石U—Pb定年结果分别为(152. 3±2. 2) Ma和(252. 7±4. 4)Ma;斑状黑云母钾长花岗岩与寄主岩石形成时代一致,黑云斜长片麻岩与大冲花岗闪长岩的侵位时代一致。岩石包体和寄主岩石在hark图解、稀土元素配分曲线和微量元素蛛网图中具有相似的演化趋势,表明寄主岩石经历了一定程度的同化混染作用。  相似文献   

20.
新疆西准噶尔花岗岩类的时代及其成因   总被引：40，自引：0，他引：40       下载免费PDF全文
在西准噶尔地区存在两期不同成因的花岗岩类,一期为与弧后盆地封闭有关的海西中期(305—320Ma)、以小岩体产出的花岗闪长岩-石英闪长岩;另一期为后造山的海西晚期(240—280Ma)的以巨大岩基形式产出的碱长花岗岩。  相似文献   

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