Ammonium in biotite from metamorphic and granitic rocks of Japan     

Yuuko Itihara  Hiroji Honma 《Geochimica et cosmochimica acta》1979,43(4):503-509

Ammonium contents of biotites from metamorphic and granitic rocks of Japan have been determined, and correlated with the ${}^{18}\text{O}{}^{16}\text{O}$ ratios of the rocks.NH₄ contents of biotites averaged 22 ppm in granitic rocks of non-metamorphic terranes, 67 ppm in granitic rocks in the Ryoke metamorphic belt, and 279 ppm in metamorphosed sedimentary rocks of the Ryoke belt. In granitic rocks, enrichment of NH₄ in biotites is a result of the interaction between the granitic magma and surrounding sedimentary rocks. In metasedimentary rocks, the high NH₄ content in biotites is due to inheritance from original organic material in sedimentary rocks.Biotites from migmatites of the Ryoke belt contain more NH₄ (average, 475 ppm) than those from metasedimentary rocks. This suggests the existence of a metamorphic fluid or anatectic magma enriched in NH₄.  相似文献   

Ammonium in granites and its petrogenetic significance     

《Earth》1999,45(3-4):145-165

Ammonium is present as a trace constituent in all granites, with an average concentration of 45 ppm (NH₄⁺), equivalent to 35 ppm of elemental N. It shows wide variations related to petrography and region, but the only significant correlation between ammonium and other geochemical parameters is that it is most abundant in peraluminous granites and least abundant in peralkaline granites. These variations can be related to (a) the amount of sedimentary material in the magmatic source region, and (b) redox conditions in the source region. The ammonium content of granitic magmas can also be modified by fractionation or contamination. Hydrothermal alteration has a major effect on the ammonium content of granitic rocks, and variation due to this cause may exceed the magmatic variation. Most hydrothermally altered granites are enriched in ammonium as a result of the transfer of ammonium from sedimentary country rocks by the hydrothermal fluids.  相似文献   

Identifying granite sources by SHRIMP U-Pb zircon geochronology: an application to the Lachlan foldbelt   总被引：24，自引：1，他引：23  

Sue Keay  David Steele  William Compston 《Contributions to Mineralogy and Petrology》1999,137(4):323-341

The potential genetic link between granites and their host sediments can be assessed using zircon age inheritance patterns. In the Lachlan fold belt, southeastern Australia, granites and associated high-grade metasedimentary rocks intrude low-grade Ordovician country rock. This relationship is well-exposed in the Tallangatta region, northeast Victoria (part of the Wagga-Omeo Metamorphic Complex). In this region granites (two I-types and two S-types) have intruded during the mid-late Silurian between approximately 410–430 Ma based on the ages of magmatic zircons. The age spectra for inherited zircons from the granites have been compared with those of detrital zircons from the enclosing low- and high-grade metasediments. In broad terms, both for detrital zircons in all four sediments and for inherited zircons in three of the four granites, the dominant ages are early Paleozoic and Late Precambrian, with sporadic older Precambrian ages extending up to 3.5 Ga. The ages of the youngest detrital zircons from the low-grade Lockhart and Talgarno terranes limit the time of sedimentation to ca. 466 Ma or younger. The youngest detrital zircons from two samples of the high-grade Gundowring terrane are 473 Ma, making these sediments Ordovician or younger, not Cambrian as originally suggested. However, the individual age spectra for the four selected metasediments are not well matched when closely examined. The age spectra of the inherited zircons in the granites also do not adequately match those in any of the metasediments. Thus, the metasediments might not be representative of the actual source rocks of the granites. While the exact source of the granites cannot be identified from the analysed samples, the existence of a large population of ca. 495 Ma inherited zircon grains in the S-type granites requires that the granite source contains a significant proportion of Cambrian or younger material. This does not preclude the existence of a Precambrian basement to the Lachlan fold belt but indicates that at the level of S-type magma generation, a Cambrian and/or younger protolith is required. Received: 28 August 1998 / Accepted: 7 July 1999  相似文献   

Origin of biotite-apatite-rich enclaves, Achala batholith, Argentina     

Michael J. Dorais  Raul Lira  Yadong Chen  David Tingey 《Contributions to Mineralogy and Petrology》1997,130(1):31-46

The Achala batholith of Argentina contains very unusual layered enclaves containing up to 30% apatite and 50% biotite in some layers. This modal mineralogy produces bulk-rock compositions that cannot represent liquids, having as little as 29% SiO₂ and up to 8% P₂O₅. Nor can the enclaves represent metasedimentary xenoliths because: (1) none of the Precambrian wall rocks has these compositions; (2) none of the metasedimentary xenoliths present within the batholith shows any degree of transition to the mica-apatite-rich enclaves; (3) the compositions and textures in the enclaves are inconsistent with metasediments; (4) a geochronological study of zircon from an enclave gives an age of 368 ± 2 Ma, the exact age of zircons in the granitic host rocks. For these reasons, we conclude that the enclaves are neither xenoliths of Precambrian wall rocks nor restite of a Precambrian source. The identical age of the enclave and the host granites, coupled with textural, mineralogical, and bulk-rock characteristics of the enclaves, indicates that the enclaves are magmatic segregations, i.e., cumulates. The F-rich nature of the stubby-shaped apatites and biotites indicates a high F content of the magma parental to the enclaves. We infer that the viscosity of the melt was lowered sufficiently to allow cumulates to form in spite of the granitic composition of the melt. Received: 12 December 1996 / Accepted: 11 August 1997  相似文献   

Age,origin, and tectonic implications of Palaeozoic rapakivi granites in the North Qaidam orogen,Northwest China     

《International Geology Review》2012,54(9):1087-1108

Palaeozoic rapakivi granites occur in the western segment of the China Central Orogenic System. Exhibiting typical rapakivi texture, these granites contain magmatic microgranular enclaves of intermediate compositions. SHRIMP zircon U–Pb ages for the granites and enclaves are 433 ± 5 Ma and 433 ± 3 Ma, respectively. The rapakivi granites are magnesian to ferroan, calc-alkalic to alkalic, and are characterized by high FeO_t/(FeO_t + MgO) (0.74–0.91) and Ga/Al ratios, and SiO₂, Na₂O + K₂O and rare earth element (apart from Eu) contents, but low CaO, Ba, and Sr contents. These are typical A-type granite geochemical features. The granites and enclaves exhibit a uniform decrease in TiO₂, CaO, Na₂O, K₂O, FeO, and MgO with increasing SiO₂, and both lithologies have similar trace element patterns. Whole-rock ?_Nd(t) values vary from??9.2 to??8.7 for the granites and from??9.0 to??8.4 for the enclaves, but zircon ?_Hf(t) values vary more widely from??5.8 to??0.2 and??4.6 to +5.1, respectively. Our data suggest that the granites and enclaves have crystallized from different magmas. The granites appear to have been derived from old continental crust, whereas the enclaves required a source having a juvenile component. The spherical shape and undeformed nature of the granites and their geochemical characteristics, coupled with the (ultra)-high pressure metamorphism and evolution of Palaeozoic granitoid magmatism in the North Qaidam orogen, indicate that the rapakivi granites were generated in a post-collisional setting. These rocks are therefore an example of Palaeozoic rapakivi granites emplaced in a post-collisional, extensional orogenic setting.  相似文献   

The abundance of ammonium in the granites of central Spain,and the behaviour of the ammonium ion during anatexis and fractional crystallization     

A. Hall  M. D. Pereira  F. Bea 《Mineralogy and Petrology》1996,56(1-2):105-123

Summary The granites of the Sistema Central Espanol are richer in ammonium than those of most other regions, and have a mean NH₄ ⁺ content of 84 ppm (range = 1–243 ppm). Among the possible causes for the high level of ammonium, a high proportion of organic-rich pelitic protolith and reducing conditions during anatexis are considered to be the most significant. The behaviour of the ammonium ion during magmatic differentiation is discussed by reference to its distribution in the Pedrobernardo layered intrusion: ammonium is depleted in the final liquid fraction, but there is no relative fractionation of NH₄ ⁺ and K⁺. The depletion of the melt in NH₄ ⁺ during crystallization is attributed to its removal by biotite and to a lesser extent by K-feldspar. The behaviour of the ammonium ion during anatexis is discussed with reference to the Peña Negra migmatite complex. It is shown that large amounts of NH₄ ⁺ are present in these high grade metamorphic rocks, and that NH₄ ⁺ is preferentially partitioned into the restite fraction during partial melting. These relationships are attributed to the preferential incorporation of NH₄ ⁺ into potassic host minerals in the order: biotite > muscovite > K-feldspar.

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Ammonium in Zentralspanischen Graniten, und das Verhalten des Ammonium-Ions während Anatexis und fraktionierter Kristallisation

Zusammenfassung Die Granite des Sistema Central Espanol sind reicher an Ammonium als die der meisten anderen Regionen, und haben einen durchschnittlichen NH₄ ⁺ Gehalt von 84 ppm (von 1-243 ppm). Der hohe Ammoniumgehalt könme auf einen hohen Anteil peiitischer Ausgangsgesteine, die reich an organischen Material sind, and auf reduzierende Bedingungen während der Anatexis zurückgehen. Das Verhalten des Ammonium-Ions während magmatischer Differentiation wind in Hinblick seiner Verteilung in der geschichteten Intrusion von Pedrobernardo diskutiert: Ammonium ist in der finalen Schmelzfraktion angereichert, aber es gibt keine relative Fraktionierung von NH₄ ⁺ and K⁺. Die Verarmung der Schmelze an NH₄ ⁺ wahrend der Kristallisation geht darauf zurück, daß NH₄ ⁺ von Biotit and in einem geringen Ausmaß von K-Feldspat aufgenommen wird. Das Verhalten des Ammonium-Ions während der Anatexis wird am Peña Negra Migmatit-Komplex diskutiert. Es zeigt rich, daß große Mengen von NH₄ ⁺ in diesen hochgradig metamorphen Gesteinen vorkommen, and das NH₄ ⁺ während teilweiser Aufschmelzung vorzugsweise in der Restit-Fraktion angereichert wird. Diese Beziehungen gehen auf die vorzugsweise Aufnahme von NH₄ ⁺ in Kali-führenden Gastmineralen zurück, and zwar in folgender Ordnung: Biotit > Muskovit > K-Feldspat.

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With 5 Figures  相似文献   

New 40Ar/39Ar age constraints on the timing of magmatic events in the Panagyurishte region, Bulgaria     

Andrea B. Rieser  Franz Neubauer  Robert Handler  Svetlana H. Velichkova  Zivko Ivanov 《Swiss Journal of Geoscience》2008,101(1):107-123

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Proterozoic rapakivi granites from the North Qaidam orogen,NW China: Implications for basement attribution     

《Gondwana Research》2016,29(4):1516-1529

Voluminous Proterozoic (~ 1700 Ma) rapakivi granites occur in several cratons, especially in the northern hemisphere. Similar Proterozoic rapakivi granites have recently been recognized in the Paleozoic North Qaidam orogen, western segment of the China Central Orogenic System (CCOS). SHRIMP zircon U–Pb dating of these granites yielded ages of 1778 ± 17 and 1778 ± 12 Ma. These granites exhibit typical rapakivi textures. They are ferroan, alkalic to alkalic-calc, metaluminous to peraluminous and characterized by high Ga/Al ratios, Na₂O + K₂O and rare earth elements (apart from Eu) contents, but low MgO, CaO and Sr contents. These are typical A-type granite features. Whole-rock ε_Nd(t) values of the granites range from − 6.09 to − 5.74 with Nd model ages of 2762 to 2733 Ma, and their zircon ε_Hf(t) values are from − 8.3 to − 5.2 with two-stage Hf model ages of 2944 to 2800 Ma, suggesting that these rocks were derived from old continental crust. The ages, rapakivi texture and geochemical features suggest that these granites are very close to typical Proterozoic (~ 1700 Ma) rapakivi granites within the North China Craton (NCC) and belong to the group of Proterozoic rapakivi granites of the northern hemisphere. These indicate that part of the basement of the North Qaidam orogen in the western CCOS is similar to that of the NCC or was probably derived from it, and then became involved in the CCOS. This provides new data to solve the dispute on the basement origin in this orogen.  相似文献   

Precambrian terranes in the southwestern framing of the Siberian craton: isotopic provinces,stages of crustal evolution and accretion-collision events     

《Russian Geology and Geophysics》2007,48(1):61-70

We studied geology and main rock assemblages of the Precambrian Kan, Arzybei, and Derba terranes of the Central Asian Fold Belt which border the Siberian craton in the southwest. The Precambrian terranes include three isotopic provinces (Paleoproterozoic, Mesoproterozoic, and Neoproterozoic) distinguished from the Sm-Nd isotope compositions of granitoids, felsic metavolcanics, and metasediments. The terranes formed in three stages of crustal evolution: 2.3–2.5, 0.9–1.1, and 0.8–0.9 Ga. Proterozoic juvenile crust was produced by subduction-related magmatism; it was originally of transitional composition and transformed into continental crust by potassic plutonism as late as the Late Vendian-Cambrian. Terrigenous sediments in the Arzybei and Derba terranes vary in T(DM) Nd model ages from 1.0 to 2.0 Ga. The Nd ages of the underlying metavolcanics and lowest T(DM) of metasediments indicate that terrigenous sedimentation started in the Neoproterozoic. It was maintained by erosion of Mesoproterozoic-Neoproterozoic crust and, to a lesser extent, of Early Precambrian rocks on the craton margin or in Paleoproterozoic terranes. Ar-Ar dating of amphiboles and biotites from metamorphic rocks and U-Pb dating of zircons from granitoids yielded 600–555 and 500–440 Ma, respectively, corresponding to the Vendian and Early Paleozoic stages of nearly synchronous metamorphism and plutonism. Accretion and collision events caused amalgamation of the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic terranes in the Vendian and their collision with the Siberian craton. The lateral growth of the paleocontinent completed in the Late Ordovician.  相似文献   

Stratigraphy,structure and geochronology of ore leads in the Matsitama Schist belt of Northern Botswana     

P.G. Coomer  M.P. Coward  B.C. Lintern 《Precambrian Research》1977,5(1):23-41

The Matsitama schist belt in northeastern Botswana comprises an area of metasediments, notably quartzites, limestones, shales and amphibolites that are bounded by granites and gneisses. The belt lies southwest of the Rhodesian cration and north of the Limpopo mobile belt.Stratigraphic, structural and lead isotopic evidence indicates that the Matsitama metasediments are equivalent to the Shashi metasediments in the Limpopo belt. There is strong evidence that the Matsitama and Shashi metasediments stratigraphically underlie volcanic rocks of the Tati belt which have been correlated with Archaean schist belts of about 2700 Ma of Rhodesia. Therefore, the Matsitama and Shashi rocks are at least as old as the schist belts of the Rhodesian craton and may represent a shallow-water facies that occurs only in the Limpopo area.There is no structural evidence that the Matsitama and Shashi metasediments were deposited unconformably on basement rocks, although the presence of gneiss, amphibolite and ironstone pebbles in a Matsitama conglomerate, as well as the presence of orthoquartzites, shows the existence of a basement source region. However, the surrounding granites intrude the Matsitama and Shashi metasediments and all underwent several deformation phases.The structural history of the Matsitama rocks can be described in terms of five phases of deformation. The main cleavage-producing deformation phase, F₂, folded the rocks into a major synform and intensely deformed them. Before this, however, the rocks had been folded and thrust so that part of the succession shows downward-facing F₂ structures and there are possibly repetitions of the stratigraphy due to imbrication. Structures of the F₃ and F₄ phases fold the main cleavage but locally are sufficiently intense to modify the shape of the finite strain ellipsoid. There is a major ductile shear zone of F₄ age, south of which F₄ folds are tight, while to the north, F₄ deformation is negligible. All of these structures can be correlated with deformation phases in the Tati schist belt to the east and in the northern part of the Limpopo mobile belt.Lead isotope evidence suggests that mineralization in the Matsitama metasediments occurred at least 2200 Ma ago, and that leads from Dihudi/Thakadu and Messina, in the centre of the Limpopo belt, underwent a two-stage history of events at 2600–2700 Ma and 2000–2100 Ma ago, agreeing with other geochronological evidence. The leads from Matsitama and Messina are isotopically distinct from leads from the Rhodesian schist belts, which show evidence of transfer to the crust some 3500 Ma ago. The absence of this 3500 Ma-old lead from the Matsitama and Messina environments may indicate different crustal conditions and possibly the absence of the Rhodesian-type early basement.  相似文献   

Constraints on the origin of Damaran granites by Rb/Sr and δ18O data     

U. Haack  J. Hoefs  E. Gohn 《Contributions to Mineralogy and Petrology》1982,79(3):279-289

The mean (⁸⁷Sr/⁸⁶Sr) and mean (⁸⁷Rb/⁸⁶Sr) ratios of the intrusive granites from the North and South of the Orogen's Central Zone plot on straight lines. These are interpreted as areal isochrons indicating the time of last Sr isotope homogenization 526 and 571 Ma ago in the respective source rocks.Initial (⁸⁷Sr/⁸⁶Sr) and mean (⁸⁷Rb/⁸⁶Sr) ratios of approximately coeval granites of the main magmatic pulses in the North (470 Ma) and in the South (520 Ma) line up along isochrons suggesting that in both cases 60 Ma passed after the homogenization in the protolith before large scale intrusions took place.The data require that the intrusions have preserved the Rb/Sr ratios of their source rocks permitting only very little assimilation or fractionation.The source rocks in the North and South had rather unradiogenic Sr 526 and 571 Ma ago, respectively. At R_i0.7066 all presently known Damaran metasediments and metavolcanics as well as the basement must be excluded as the protoliths. A hypothetical source with a large proportion of low (⁸⁷Sr/⁸⁶Sr) volcanic material is required. In the center, on the other hand, the Sr isotope ratios are more radiogenic and derivation from common Damaran metasediments is a distinct possibility.The total rock ¹⁸O values show an unusual spread from 7.1 to 15.2, the majority being very heavy. This excludes granulites and requires sediments or heavily altered volcanics as source rocks. A plot of ¹⁸O vs. initial Sr isotope ratios of the granites from the center which could have been derived from Damaran metasediments has a very clear negative slope. No trend is visible for the southern granites. Of the northern granites the older group shows a negative, the younger group a positive correlation. This is interpreted as indicating mainly altered volcanics (perhaps spilites) for the older and a mixture of volcanogenic and metasedimentary rocks as the source for the younger group. The high ¹⁸O values show that the granites are crustal remelts.  相似文献   

Geochemistry and geochronology of the rapakivi granites and associated rocks in the midwest portion of the Serra da Providência composite batholith,SW of Amazonian craton,Rondônia,Brazil     

《Journal of South American Earth Sciences》2016

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   

北京密云元古宙常州沟组之下环斑花岗岩古风化壳岩石的发现及其碎屑锆石年龄   总被引：18，自引：1，他引：17  

和政军  牛宝贵  张新元  赵磊  刘仁燕 《地质通报》2011,30(5):798-802

在北京密云地区,最近发现环斑花岗岩(脉)上发育有古风化壳,并被长城系常州沟组砂岩覆盖。风化壳物质的组成主要为来自环斑花岗岩的原地风化残留物和粗碎屑岩,采用SHRIMP和LA-ICP-MS方法,分别获得环斑花岗岩古风化壳碎屑岩的碎屑锆石U-Pb年龄值为(1682±20)Ma、(1708±6)Ma等,与相邻的密云环斑花岗岩年龄相同。这套古风化壳碎屑岩的存在和测年结果显示,长城系常州沟组的底界年龄应小于1682Ma。  相似文献   

西藏当惹雍错吉松环斑花岗岩的发现及地质意义          下载免费PDF全文

陈振华  刘云  李均良 《沉积与特提斯地质》2006,26(2):16-20

在1∶25万区域地质调查工作中,于当惹雍错中部的吉松一带发现环斑花岗岩,获同位素K-Ar法年龄45.3Ma,时代为始新世。吉松环斑花岗具特殊的卵状环斑结构,K2O Na2O含量较高,K2O>Na2O;稀土元素含量高,具明显的铕亏损,为造山型环斑花岗岩,形成于青藏高原陆内碰撞造山晚期的后碰撞环境。  相似文献   

Recognition of Early Paleozoic Magmatisms in the Supposed Proterozoic Basements of Zhalantun, Great Xing’an Range, NE China     

QIN Tao  GUO Rongrong  ZANG Yanqing  QIAN Cheng  WANG Yan  SI Qiuliang  SUN Wei  MA Yongfei 《《地质学报》英文版》2019,93(5):1434-1455

The Zhalantun terrane from the Xing'an massif, northeast China, was used to be considered as Proterozoic basements. However, amounts of detrital zircon ages from the meta-sedimentary rocks deny the existence of Precambrian basements recently. Notably, magmatic rocks were barely reported to limit the exact ages of the Zhalantun basements. In this study, we collected rhyolite, gabbro and quartz diorite for zircon in-situ U-Pb isotopic dating, which yield crystallization ages of ～505 Ma, ～447 Ma and ～125 Ma, respectively. Muscovite schist and siltstone define maximum depositional ages of ～499 Ma and ～489 Ma, respectively. Additionally, these dated supracrustal rocks and plutons also yield ancient detrital/xenocryst zircon ages of ～600–1000 Ma, ～1600–2220 Ma, ～2400 Ma, ～2600–2860 Ma. Based on the whole-rock major and trace element compositions, the ～505 Ma rhyolites display high SiO_2 and alkaline contents, low Fe_2O_3T, TiO_2 and Al_2O_3, and relatively high Mg O and Mg#, which exhibit calc-alkaline characteristics. These rhyolites yield fractionated REE patterns and negative Nb, Ta, Ti, Sr, P and Eu anomalies and positive Zr anomalies. The geochemistry, petrology and Lu-Hf isotopes imply that rhyolites were derived from the partial melting of continental basalt induced by upwelling of sub-arc mantle magmas, and then experienced fractional crystallization of plagioclase, which points to a continental arc regime. The ～447 Ma gabbros exhibit low Si O2 and alkaline contents, high Fe2 O3 T, Ti O2, Mg O and Mg#. They show minor depletions of La and Ce, flat MREE and HREE patterns, and negative Nb, Ta, Zr and Hf anomalies. Both sub-arc mantle and N-MORB-like mantle were involved in the formation of the gabbros, indicative of a probable back-arc basin tectonic setting. Given that, the previously believed Proterozoic supracrustal rocks and several plutons from the Zhalantun Precambrian basements were proved to be Paleozoic to Mesozoic rocks, among which these Paleozoic magmatic rocks were generally related to subduction regime. So far, none Proterozoic rocks have been identified from the Zhalantun Precambrian basement, though some ～600–3210 Ma ancient detrital/xenocryst zircons were reported. Combined with ancient zircon ages and newly reported ～2.5 Ga and ～1.8 Ga granites from the south of the Zhalantun, therefore, the Precambrian rocks probably once exposed in the Zhalantun while they were re-worked and consumed during later long tectonic evolutionary history, resulting in absence of Precambrian rocks in the Zhalantun.  相似文献   

Post-Brasiliano (Pan-African) high-K granitic magmatism in Central Brazil: the role of late Precambrian-early Palaeozoic extension   总被引：1，自引：0，他引：1  

Mrcio M. Pimentel  Reinhardt A. Fuck  Carlos JosSouza de Alvarenga 《Precambrian Research》1996,80(3-4)

In western Goiás, Brazil, the emplacement of large, high-K postorogenic granites and associated small gabbro-dioritic intrusions, followed immediately after the last deformational events of the Brasiliano-Pan-African orogeny at 600 Ma. Well-fitted whole-rock Rb---Sr isochrons indicate ages which suggest two discrete intrusive events: the older between 588 and 560 Ma and the younger between 508 and 485 Ma. The older granites display general petrographic and geochemical characteristics of highly differentiated calc-alkaline I-type granitoids, whereas the younger intrusions are more alkaline, similar to A-type granites.Initial ⁸⁷Sr/⁸⁶Sr ratios vary from 0.703 to 0.710 and initial Nd isotope ratios yield ε_Nd(T) values in the range between −4.0 and +3.0. There are no major differences in initial isotopic compositions between the two granite groups, suggesting that the parental magmas for both groups of rocks mostly originated by refusion of crustal sources isotopically similar to the 940-640 Ma basement arc-type metatonalites-metagranodiorites and associated arc metavolcanics.The major and trace element compositional differences between the two granite groups is explained in terms of modifications in the melting conditions within the crust, with younger melts being produced by the refusion of anhydrous, depleted crustal sources left after the extraction of previous batches of more hydrated calc-alkaline magmas. The heat input required to promote extensive remelting of the continental crust was, most likely, provided by mantle-derived mafic magmas that invaded and probably underplated the crust, during uplift and extension.The two intrusive events are bimodal in nature and are interpreted as shallow-level extension-related events associated with regional uplift and denudation occurring just after two orogenic pulses at the end of the Proterozoic and early Palaeozoic, the older at 600 Ma and the younger between 550 and 510 Ma. The onset of the granite magmatism at 590 Ma, shortly post-dating the Brasiliano orogeny (600 Ma), is broadly coeval with the initial stages of sedimentation of the terrigenous and carbonatic rocks of the ensialic Paraguay Belt in Brazil and its correlative in Bolivia, the Tucavaca Belt, which probably correspond to rift deposits related to the break up of Laurentia from Gondwana at the end of the Proterozoic and beginning of the Palaeozoic. Granites of the younger group cut the deformational structures of the Paraguay Belt metasediments and pre-date, by between 40 and 20 Ma, the initial stages of subsidence and sedimentation of the Paraná Basin.  相似文献   

Age of intrusion and rapid cooling of the Frankenstein gabbro (Odenwald,SW-Germany) evidenced by40Ar/39Ar and single-zircon207Pb/206Pb measurements     

Herbert Kirsch Dipl.-Geol.  Dr. Bernd Kober  Prof. Dr. Hans Joachim Lippolt 《International Journal of Earth Sciences》1988,77(3):693-711

The Frankenstein gabbro complex in the northern Odenwald/FR Germany is one of the Hercynian plutonic bodies of the Saxothuringian zone in the Variscan belt.⁸⁷Sr/⁸⁶Sr isotopic investigations on pyroxene,⁴⁰Ar/³⁹Ar age determinations on hornblendes, plagioclases, biotites and pyroxenes and²⁰⁷Pb/²⁰⁶Pb dating on single zircon crystals have been carried out. The⁸⁷Sr/⁸⁶Sr initial ratio of the gabbro (0.70380) indicates uncontaminated derivation of the magma from the mantle. The results on hornblendes, plagioclases and zircons establish the isotopic age of intrusion and the mode of cooling. Pyroxene and biotite data indicate disturbed K-Ar systems of these minerals. The average ages of the hornblendes (363±7 Ma), of the plagioclases (359±3 Ma) and of the zircons (362 ±9 Ma) agree within the 1-sigma levels and constrain the early history of the plutonic intrusion at the turn from Devonian to Carboniferous times. These minerals must have been cooled below their closure temperatures within a time-interval shorter than the error margins of 10 Ma. The ages therefore are, unlike those of the neighbouring Bergsträßer Odenwald, not long-time cooling ages due to largescale and slow geological uplift of the crustal segment. Instead, they will closely estimate the time of intrusion of the Frankenstein pluton into a shallow crustal level. The hiatus of about 20 Ma compared to the average ages of the crystalline rocks of the Bergsträßer Odenwald in the south characterizes the mafic Frankenstein pluton as a separated unit of the Odenwald crystalline, and underlines the importance of the Carboniferous tectonic fault zone in-between. The present data set clearly demonstrates the importance of the applied combination of methods and techniques to constrain the history of intrusion and cooling of mafic plutonic rocks.  相似文献   

Mineralogy,geochemistry, and genesis of co-genetic granite-pegmatite-hosted rare metal and rare earth deposits of the Kawadgaon area,Bastar craton,Central India     

Yamuna Singh  P. S. C. Pandit  Sanjay Bagora  P. K. Jain 《Journal of the Geological Society of India》2017,89(2):115-130

Co-genetic pegmatites associated with the granite of the Kawadgaon area in the Bastar craton, Central India, contain a wide range of ore minerals of Nb, Ta, Be, Sn, Zr, Ti, and REE, including columbite-tantalite, ixiolite, pseudo-ixiolite, wodginite, tapiolite, microlite, fersmite, euxenite, aeschynite, beryl, cassiterite, monazite, xenotime, zircon, ilmenite, triplite, and magnetite. There is a distinct vertical zonation between the rare metal and tin pegmatites in apical parts of the host granite. Geochemically, these are LCT-S type, beryl-columbite-phosphate pegmatites that have notably high contents of SiO₂ (av. 73.80%), Rb (av. 381 ppm), and Nb (av. 132 ppm). The investigated granites probably were derived from the melting of older crustal rocks, as indicated by a high initial ⁸⁷Sr/⁸⁶Sr isotopic ratio, and the major-element geochemistry of the granites and pegmatites. Plots of mol. CaO/(MgO+FeO^t) vs. mol. Al₂O₃/(MgO+FeO^t) suggest that the source rock was pelitic metasediments. Based on the available data, it is postulated that the derivation of pegmatites from the parent granite occurred shortly after granite emplacement in the late Archaean-early Proterozoic (~2500 Ma). The K/Rb, Ba/Rb, and Rb/Sr ratios of the felsic bodies reveal that a substantial part of the granite formed from evolved melts, and further fractionation produced the co-genetic pegmatites and associated rare metal and rare earth deposits.  相似文献   

Geochemistry and Tectonomagmatic Affinities of the Mozambique Belt Intrusive Rocks in Matuu-Masinga Area, Central Kenya     

C.M. Nyamai  N. Opiyo-Akech  S.J. Gaciri  H. Fujimaki 《Gondwana Research》1999,2(3):387

The Matuu-Masinga study area, located about 70 km north-east of Nairobi, is predominantly underlain by rocks of the Neoproterozoic Mozambique Belt (MB) of Kenya. The rocks vary from medium to high grade gneisses and granulites, that are intruded by granites, anorthosites, diorites and gabbros. Important high-grade tectonothermal events in the belt took place between about 845 and 715 Ma B.P. The subsequent cooling and uplift of the basement has been traced by K-Ar dates on biotites, which range between 438 and 528 Ma. The belt has been inferred to mark the sites for several superimposed Proterozoic subduction zones and collisional sutures (Muhongo, 1998, and references therein).The general structural trend in the survey area varies from NNW-SSE to NW-SE direction, with westerly dips and localized concentric trends around granitoid intrusions. Competent mafic lensoidal layers that have undergone ductile deformation and associated with rotated boudins and displaced micro-faults define a sinistral sense of shear. The several shear zones, cleavage patterns, boudins and thinning suggest severe strains.The mafic and granitic rocks are interpreted to be mainly metaluminous to slightly peraluminous. Geochemical data and field studies suggest that the granites are of calc-alkaline origin. The discriminant diagrams suggest a dominantly island arc-tectonic setting with subordinate within plate environment.Rb-Sr whole-rock age of 558 ± 16 Ma is given on the granite from Mavoloni hills, Matuu area. From the low initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70398, the age is interpreted to indicate the time of emplacement for granite magma from a deep crustal or upper mantle material.The gabbroic and granitic rocks in Matuu-Masinga area, with high Ba (av. 1331 ppm) and Zr (av. 370 ppm) contents, are interpreted to have contained hornblende and biotite mineral assemblage phases that had a relatively high distribution coefficients for Ba and Z. The relatively high concentration of Cu (188–5810 ppm, av. 1960 ppm) and Zn (88–264 ppm, av. 155 ppm) in the mafic rocks of the study area invokes further exploration of their ore minerals.  相似文献   

Co-development of Jurassic I-type and A-type granites in southern Hunan,South China: Dual control by plate subduction and intraplate mantle upwelling     

Hua Kong  Huan Li  Qian-Hong Wu  Xiao-Shuang Xi  Jeffrey M. Dick  Jillian Aira S. Gabo-Ratio 《Chemie der Erde / Geochemistry》2018,78(4):500-520

Two types of spatially and temporally associated Jurassic granitic rocks, I-type and A-type, occur as pluton pairs in several locations in southern Hunan Province, South China. This paper aims to investigate the genetic relationships and tectonic mechanisms of the co-development of distinct granitic rocks through petrological, geochemical and geochronological studies. Zircon LA-ICPMS dating results yielded concordant U–Pb ages ranging from 180 to 148 Ma for the Baoshan and Tongshanling I-type granodiorites, and from 180 to 158 Ma for the counterpart Huangshaping and Tuling A-type granites. Petrologically, the I-type granodiorites consist of mafic minerals such as hornblende whereas the A-type granites are dominated by felsic minerals (e.g., quartz, K-feldspar and plagioclase). Major and trace element analyses indicate that the I-type granodiorites have relatively low SiO₂ (64.5–71.0%) and relatively high TiO₂ (0.28–0.51%), Al₂O₃ (13.8–15.5%), total FeO (2.3–4.7%), MgO (1.3–2.6%) and P₂O₅ (0.10–0.23%) contents, and the A-type granites are characterized by high concentrations of Rb (212–1499?ppm), Th (18.3–52.6?ppm), U (11.8–33.6?ppm), Ga (20.0–36.6?ppm), Y (27.1–134.0?ppm) and HREE (20.3–70.0?ppm), with pronounced negative Eu anomalies (Eu/Eu*?=?0.01–0.15). Moreover, the I-type granodiorites are classified as collision-related granites emplaced under a compressional environment, whereas the A-type granites are within-plate granites generated in an extensional setting. Zircon Hf isotopic compositions vary substantially for these granitic rocks. The I-type granodiorites are characterized by relatively young Hf model ages (T_DM1?=?1065–1302 Ma, T_DM^C =1589–2061 Ma) and moderately negative εHf(t) values (–5.9 to –11.5), whereas the A-type granites have very old model ages (T_DM1?=?1454–2215 Ma, T_DM^C?=?2211–2974 Ma) and pronounced negative εHf(t) values (–15.8 to –28.3). These petrochemical and isotopic characteristics indicate that the I-type granodiorites may have been derived from a deep source involving mantle-derived juvenile (basaltic) and crustal (pelitic) components, whereas the A-type granites may have been sourced from melting of meta-greywacke in the crust. This study proposes that the pressure and temperature differences in the source regions caused by combined effects of intra-plate mantle upwelling and plate subduction are the major controlling factors of the co-development of the two different types of magmas. Crustal anatexis related to lithospheric delamination and upwelling of hot asthenosphere under a high pressure and temperature environment led to the formation of the I-type magmas. On the other hand, the A-type magmas were formed from melting of the shallower part of the crust, where extensional stress was dominant and mantle-crust interaction was relatively weak. Rifts and faults caused by mantle upwelling developed from surface to depth and successively became channels for the ascending I- and A-type magmas, resulting in the emplacement of magmas in adjacent areas from sources at different depths.  相似文献