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C and O stable isotopes and rare earth elements in the Devonian carbonate host rock of the Pivehzhan iron deposit, NE Iran 伊朗东北部Pivehzhan铁矿泥盆系碳酸盐岩储集岩C、O稳定同位素及稀土元素特征
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-06-21 DOI: 10.1344/GEOLOGICAACTA2018.16.2.2
P. N. Tehrani, A. A. Calagari, F. V. Roldan, V. Simmonds, Kamal Siahcheshm
The Pivehzhan iron deposit is located at about 80km southwest of Mashhad, NE Iran. They occur within the Devonian carbonates as lenticular and massive bodies, as well as veinlets of magnetite and iron sulphides, transformed to goethite and haematite by weathering process. The hydrothermal calcite is the most important gangue mineral, which is observed in the form of veins/veinlets and open-space filling. The iron ores are accompanied by some minor elements such as Mn, Ti, Cr, and V and negligible amounts of Co and Ni. The distribution pattern of Rare Earth Elements (REEs) normalized to Post Archean Australian Shale (PAAS), which is characterized by the upward convex, as well as the positive Eu anomalies indicate the activity of reduced and acidic hydrothermal fluids. The negative Ce anomalies of host carbonates, although slight, point to the dominance of anoxic conditions during interaction with hydrothermal fluids. The hydrothermal calcite and quartz coexisting with the iron minerals contain principally fluid, which were homogenized into liquid phase. The homogenization temperature (TH (L-V) ) and the salinity of the analysed fluid inclusions range from 129°C to 270°C and from 0.4wt.% to 9.41wt.% NaCl eq., respectively. The δ 13 C PDB  and  δ 18 O SMOW  values ranges from -2.15‰ to -5.77‰ (PeeDee Belemnite standard, PDB) and from +19.87‰ to +21.64‰ (Standard Mean Ocean Water standard, SMOW) in hydrothermal calcite veinlets occurring with iron minerals and -0.66‰ to -4.37‰ (PDB) and +15.55‰ to +20.14‰ (SMOW) within the host carbonates, respectively. The field relations and petrographic examination along with geochemical and isotopic considerations indicate that the Pivehzhan iron deposit was formed through replacement processes by reducing and acid fluids containing light carbon and oxygen isotopes. Variations in the physico-chemical conditions of hydrothermal fluids and their interaction with carbonates were the most effective mechanisms in the formation of this iron deposit. The potential source of iron was probably the basement magmatic rocks from which iron was leached by hydrothermal solutions.
Pivehzhan铁矿位于伊朗东北部马什哈德西南约80公里处。它们以透镜状和块状体的形式出现在泥盆纪碳酸盐岩中,以及由风化作用转化为针铁矿和赤铁矿的磁铁矿和硫化铁细脉。热液方解石是最重要的脉石矿物,以脉/细脉和开孔充填形式存在。铁矿石中还含有少量的锰、钛、铬和钒等元素,Co和Ni的含量可忽略不计。稀土元素(ree)分布模式归一化到太古宙后澳大利亚页岩(PAAS),呈上凸特征,且Eu正异常表明还原酸性热液的活动。寄主碳酸盐的负Ce异常虽然轻微,但表明在与热液流体相互作用过程中缺氧条件占主导地位。与铁矿物共生的热液方解石和石英主要含流体,均质进入液相。分析的流体包裹体均质温度(TH (L-V))和盐度范围为129°C至270°C, 0.4wt。%至9.41吨。% NaCl eq.。与铁矿物共生的热液方方石细脉中δ 13c PDB值为-2.15‰~ -5.77‰(PeeDee belenite standard, PDB), δ 18o SMOW值为+19.87‰~ +21.64‰(standard Mean Ocean Water standard, SMOW),主碳酸盐中δ 13c PDB值为-0.66‰~ -4.37‰(PDB), δ 18o SMOW值为+15.55‰~ +20.14‰(SMOW)。野外关系、岩石学研究、地球化学和同位素研究表明,皮韦展铁矿床是由含轻碳、轻氧同位素的还原性和酸性流体置换作用形成的。热液流体物理化学条件的变化及其与碳酸盐的相互作用是该铁矿床形成的最有效机制。铁的潜在来源可能是基底岩浆岩,其中铁被热液浸出。
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引用次数: 3
Petrography and geochemistry of late- to post-Variscan vaugnerite series rocks and calc-alkaline lamprophyres within a cordierite-bearing monzogranite (the Sierra Bermeja Pluton, southern Iberian Massif). 含堇青石二长花岗岩(Sierra Bermeja Pluton,Iberian南部地块)中晚华力西期至后华力西时期的沃涅岩系岩石和钙碱性煌斑岩的岩石学和地球化学。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-06-08 DOI: 10.1344/GEOLOGICAACTA2018.16.3.1
J. Errandonea-Martin, F. Sarrionandia, M. Carracedo-Sánchez, J. G. Ibarguchi, L. Eguiluz
The Sierra Bermeja Pluton (southern Central Iberian Zone, Iberian Massif) is a late-Variscan intrusive constituted by cordierite-bearing peraluminous monzogranites. Detailed field mapping has allowed to disclose the presence of several NE–SW trending longitudinal composite bodies, formed by either aphanitic or phaneritic mesocratic rocks. According to their petrography and geochemistry these rocks are categorised as calc-alkaline lamprophyres and vaugnerite series rocks. Their primary mineralogy is characterised by variable amounts of plagioclase, amphibole, clinopyroxene, biotite, K-feldspar, quartz and apatite. Broadly, they show low SiO2 content (49–56wt.%), and high MgO+FeOt (10–17wt.%), K2O (3–5wt.%), Ba (963–2095ppm), Sr (401–1149ppm) and Cr (87–330ppm) contents. Field scale observations suggest that vaugneritic rocks and lamprophyres would constitute two independent magma pulses. Vaugneritic dioritoids intruded as syn-plutonic dykes, whereas lamprophyres were emplaced after the almost complete consolidation of the host monzogranites. In this way, vaugnerite series rocks would be an evidence for the contemporaneity of crustal- and mantle-melting processes during a late-Variscan stage, while lamprophyres would represent the ending of this stage.
Sierra Bermeja岩体(伊比利亚地块中伊比利亚带南部)是一个由含堇青石过铝二长花岗岩组成的晚瓦里西斯侵入岩。详细的野外测图揭示了几个NE-SW向纵向复合体的存在,这些复合体由隐晶质或显晶质中晶岩形成。根据岩石学和地球化学特征,将其划分为钙碱性煌斑岩系列和辉绿岩系列。其主要矿物学特征为不同数量的斜长石、角闪石、斜辉石、黑云母、钾长石、石英和磷灰石。总体上,它们的SiO2含量较低(49 ~ 56wt.%), MgO+FeOt (10 ~ 17wt.%)、K2O (3 ~ 5wt.%)、Ba (963 ~ 2095ppm)、Sr (401 ~ 1149ppm)和Cr (87 ~ 330ppm)含量较高。野外观测表明,辉长岩和煌斑岩构成两个独立的岩浆脉冲。辉长岩闪长岩是同深裂岩脉侵入的,而煌斑岩是在寄主二长花岗岩几乎完全固结后侵入的。这样,辉长岩系列岩石可以作为瓦里斯坎晚期地壳和地幔熔融过程同时发生的证据,而煌斑岩则代表这一阶段的结束。
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引用次数: 8
Taxonomic revision of the Oligocene percoid fish Oligoserranoides budensis (Heckel, 1856), from the Paratethys and paleobiogeographic comments 根据Paratethys和古生物地理学评论,对渐新世peroide鱼的分类修订(Heckel,1856)
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-03-26 DOI: 10.1344/GEOLOGICAACTA2018.16.1.5
M. Bieńkowska-Wasiluk, M. Pałdyna
Small perch-like fishes from the Oligocene of the Paratethys were traditionally assigned to Serranus budensis (Heckel, 1856). A new morphological study of the holotype and specimens from the Outer Carpathians, Poland, is provided herein. Oligoserranoides budensis (Heckel, 1856), Percoidei incertae sedis, is revised and compared with other small perch-like fishes from the Oligocene Paratethys. Caucasoserranoides morozkiensis, Carpathoserranoides brnoensis, Carpathoserranoides polonicus and Oligoserranoides comparabilis are very similar to O. budensis and further studies are necessary to clarify the validity of those species. O. budensis is compared with the Oligocene-Lower Miocene Pirsagatia sytchevskayae, the Eocene Jimtylerius temnopterus, Ottaviania mariae,O. leptacanthus, Veranichthys ventralis and the Palaeocene Proserranus lundensis. O. budensis shares many characters with the Lutjanoidea, and differs in a toothless palatine. The palaeobiogeography of Oligocene small perch-like fishes in the Paratethys is presented.
Paratethys渐新世的小型类似鲈鱼的鱼类传统上被分配给布氏Serranus budensis(Heckel,1856)。本文对波兰外喀尔巴阡山脉的正模标本和标本进行了新的形态学研究。对布氏寡serranoides budensis(Heckel,1856),incertae sedis Percoidei进行了修订,并与渐新世副特提斯的其他类似鲈鱼的小型鱼类进行了比较。morozkiensis、brnoensis、polonicus和comparabilis的Carpathoseranoides与O.budensis非常相似,需要进一步的研究来澄清这些物种的有效性。布氏O.budensis与渐新世-下中新世Pirsagatia sytchevskaye、始新世Jimtylerius temnopterus、Ottaviania mariae、O。Leptitacnthus、Veranichthys ventralis和古新世Proseranus lundensis。布氏O.budensis与木犀总科有许多共同的特征,不同之处在于没有牙齿的腭。介绍了副特提斯渐新世小型鲈鱼的古生物地理学。
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引用次数: 0
Resolution test of GOCE satellite data applied to density anomalies at crustal and upper mantle levels. 应用于地壳和上地幔密度异常的GOCE卫星数据分辨率测试。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-03-26 DOI: 10.1344/GEOLOGICAACTA2018.16.1.6
M. Peral, Manel Fernàndez, M. Torné
The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission was devised by the European Space Agency to study the Earth’s gravity field with an unprecedented accuracy using gravity gradient data. The goal of this study is to analyze the resolution in terms of size, burial depth and density contrast of anomalous bodies related to geological structures that can be identified from GOCE data. A parametric study is performed by calculating the gravity gradients associated with rectangular prisms with fixed aspect ratio of 9:3:1 and varying the size, burial depth, and density contrast, selecting those structures showing amplitudes and wavelength variations comparable to the accuracy of GOCE data. Results show that the minimum size for crustal anomalies to be resolved for the vertical component of the gravity gradient is 22.5x7.5x2.5km for a Δρ=500kg/m 3 , burial depth of 0km, and at computation height of 255km. To generate a sufficient signal in amplitude and wavelength in all the components, the size of the anomalous body is 270x90x30km. For a body with Δρ=50kg/m 3 and 0km burial depth a minimum size of 41.4x13.8x4.6km is required for the vertical component at a computation height of 255km. In addition, the application to the 3D case of a passive continental margin which broadly resembles the crustal structure of the NW-Iberia shows that the signal of all gravity gradient components is dominated by the crustal thinning associated with the passive continental margins and the corresponding isostatic response.
重力场和稳态海洋环流探测器(GOCE)卫星任务是由欧洲空间局设计的,目的是利用重力梯度数据以前所未有的精度研究地球重力场。本研究的目的是分析GOCE数据中与地质构造相关的异常体的大小、埋深和密度对比的分辨率。通过计算固定长宽比为9:3:1的矩形棱镜的重力梯度,改变尺寸、埋深和密度对比,选择那些振幅和波长变化与GOCE数据精度相当的结构,进行参数化研究。结果表明,在Δρ=500kg/m 3、埋深为0km、计算高度为255km时,重力梯度垂直分量需要解决的地壳异常最小尺寸为22.5x7.5x2.5km。为了在所有分量中产生足够的振幅和波长信号,异常体的大小为270x90x30km。对于Δρ=50kg/ m3,埋深为0km的尸体,计算高度为255km时,垂直分量的最小尺寸要求为41.4 × 13.8 × 4.6km。此外,对与西北伊比利亚地壳结构大致相似的被动大陆边缘三维实例的应用表明,所有重力梯度分量的信号都以与被动大陆边缘相关的地壳减薄及其相应的均衡响应为主。
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引用次数: 2
Digestive structures in Middle Ordovician trilobite Prionocheilus Rouault 1847, from the Barrandian area of Czech Republic. 捷克巴兰地地区中奥陶统三叶虫Prionocheilus Rouault 1847的消化结构。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-03-26 DOI: 10.1344/GEOLOGICAACTA2018.16.1.4
O. Fatka, P. Budil
Remains of a digestive system from a slightly damaged articulated specimen of the comparatively rare bathycheilid trilobite Prionocheilus vokovicensis (Snajdr, 1956) are described for the first time. The specimen comes from the Middle Ordovician Sarka Formation of the Prague Basin and contains the midgut region of the digestive system preserved through the axial region of glabella and six anterior thoracic segments. The anterior-most part of the digestive system is unknown as the anterior glabellar lobes are not preserved in the studied specimen. In the cephalic shield, the remains of two pairs of gut diverticulae are seen in the posterior region of the glabella. Remains of five pairs of small cavities developed in the axis of the first six thoracic segments represent the remains of thoracic gut diverticulae. The discussed specimen possess the first undoubted remain of digestive structures established within the family Bathycheilidae (PŘibyl, 1953).
首次描述了相对罕见的三叶虫Prionocheilus vokovicensis(Snaidr,1956)的一个轻微受损的铰接标本的消化系统残骸。该标本来自布拉格盆地的中奥陶世Sarka组,包含通过眉间轴区和六个前胸段保存的消化系统中肠区。消化系统的最前部是未知的,因为研究标本中没有保存眉间前叶。在头罩中,在眉间后部可见两对肠道憩室的残骸。在前六个胸段的轴线上发育的五对小空腔的残余物代表了胸腔肠道憩室的残余物。所讨论的标本拥有第一个在蝙蝠科内建立的毫无疑问的消化结构遗迹(PŘibyl,1953)。
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引用次数: 3
Organic petrology and geochemistry of mudstones from the lower Shahejie Formation, in the Tanggu area of eastern China: evidence for the presence of an ancient saline lake 中国东部塘沽地区沙河街组下段泥岩的有机岩石学和地球化学:古代盐湖存在的证据
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-03-26 DOI: 10.1344/GEOLOGICAACTA2018.16.1.3
L. Li, G. Yao, M. Cai, Y. Liu
Mudstones in the lower Shahejie Formation, in the Tanggu area of the Huanghua Depression, have been found to contain analcime and ankerite. Hydrothermal sedimentation has been invoked to explain the origin of these two minerals, raising the question of whether hydrothermal activity occurred at a sufficient scale to significantly raise the salinity of the depositional environment. We applied a suite of organic petrological and geochemical methods to directly address this question. Maceral composition, kerogen type, and the distribution of n-alkanes, hopanes, and steranes indicate that the organic matter contained in these mudstones and dolomitic mudstones is mainly derived from algae and bacteria. The dominant acritarch genera, C31R/C30 hopane ratio, gammacerane index, Pr/Ph ratio, and the relationship between Pr/n-C17 and Ph/n-C18 suggest that the mudstones and dolomitic mudstones were deposited in an anoxic, saline lacustrine environment. Tmax, biomarker maturity indices, the thermal alteration index (TAI) and acritarch alteration index (AAI), and vitrinite reflectance all indicate that the organic matter is at an immature to early mature stage. The estimated maximum paleotemperature is close to the present-day burial temperature, and much lower than the homogenization temperature of the analcime veins. Combined with the absence of unresolved complex mixtures on the n-alkane pattern, this suggests that hydrothermal activity had a negligible impact on the salinity and alkalinity of the depositional lake.
黄骅坳陷塘沽地区下沙街组泥岩中发现含有方沸石和铁白云石。热液沉积被用来解释这两种矿物的起源,这就提出了一个问题,即热液活动的发生规模是否足以显著提高沉积环境的盐度。我们应用了一套有机岩石学和地球化学方法来直接解决这个问题。宏观组成、干酪根类型以及正构烷烃、hopanes和steranes的分布表明,这些泥岩和白云质泥岩中所含的有机物主要来源于藻类和细菌。优势的顶生岩属,C31R/C30 hopane比值,伽玛组分指数,Pr/Ph比值,以及Pr/n-C17和Ph/n-C18之间的关系表明,泥岩和白云质泥岩沉积在缺氧的盐湖环境中。Tmax、生物标志物成熟度指数、热蚀变指数(TAI)和近热蚀变指标(AAI)以及镜质组反射率均表明有机质处于未成熟至早熟阶段。估计的最高古温度接近现今的埋藏温度,远低于方沸石矿脉的均质温度。再加上正构烷烃模式中不存在未解决的复杂混合物,这表明热液活动对沉积湖的盐度和碱度的影响可以忽略不计。
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引用次数: 2
Hybridization between I-type and S-type granites in the Ordovician Famatinian magmatic arc, Tafí del Valle, Tucumán, NW Argentina. 阿根廷西北部图库曼Tafídel Valle奥陶纪法马汀期岩浆弧中I型和S型花岗岩的杂交。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-03-26 DOI: 10.1344/GEOLOGICAACTA2018.16.1.2
J. P. López, Laura Iudith Bellos, J. Díaz-Alvarado, A. Castro
In the Tafi del Valle region, in northwestern Argentina, several intrusive bodies of lower Paleozoic age were emplaced in the metasedimentary Puncoviscana Formation, belonging to the Sierras Pampeanas. Four intrusive bodies outcrop in the study area: La Ovejeria, El Infiernillo, Loma Pelada and Los Cuartos. La Ovejeria and El Infiernillo intrusive bodies represent the I-type magmatism according to their major element contents and show cotectic evolutions similar to those described by Famatinian I-type batholiths. These moderately peraluminous adakitic trondhjemites have characteristic high Sr/Y ratios and low Fe 2 O 3 +MgO+MnO+TiO 2  contents. They are related to high-pressure conditions at the source, where dehydration melting of basaltic rocks may be involved and garnet is retained in the residue leading to generation of HREE depleted melts. The Loma Pelada granites show characteristics of S-type magmatism (low CaO and MgO, and high SiO 2 and K 2 O contents) typical of granites segregated in the last stages of magmatic differentiation, or anatectic granites. They show an increasing peraluminosity due to garnet entrainment and they are related to the anatectic melts generated in the Puncoviscana Formation. Both the Loma Pelada and Los Cuartos granitoids include samples with intermediate geochemical characteristics that range between those of the El Infiernillo and La Ovejeria and the regional metasedimentary rocks. These characteristics could be explained by assimilation processes involving the I-type intrusive magmas and the metasedimentary host rocks or by hybridization processes between trondhjemitic I-type magmas as La Ovejeria and El Infiernillo and anatectic S-type melts.
在阿根廷西北部的Tafi del Valle地区,属于Sierras Pampeanas的变质沉积Puncoviscana组中侵位了几个下古生代的侵入体。研究区有四个侵入体露头:La Ovejeria、El Infiernillo、Loma Pelada和Los Cuartos。La Ovejeria和El Infiernillo侵入体根据其主要元素含量代表I型岩浆作用,并显示出类似于法马汀I型岩基所描述的共晶演化。这些中等过发光的adakitic黄铁矿具有高的Sr/Y比和低的Fe2O3+MgO+MnO+TiO2含量。它们与源头的高压条件有关,在高压条件下,可能涉及玄武岩的脱水熔融,石榴石保留在残留物中,导致HREE贫化熔体的产生。Loma Pelada花岗岩表现出S型岩浆作用的特征(低CaO和MgO,高SiO2和K2O含量),这是在岩浆分化的最后阶段分离的花岗岩或深熔花岗岩的典型特征。它们显示出由于石榴石夹带而增加的过光度,并且它们与Puncoviscana地层中产生的深熔熔体有关。Loma Pelada和Los Cuartos花岗质岩石都包括具有中等地球化学特征的样本,其范围介于El Infiernillo和La Ovejeria以及区域变质沉积岩的样本之间。这些特征可以通过涉及I型侵入岩浆和变质沉积宿主岩的同化过程来解释,也可以通过La Ovejeeria和El Infiernillo等三方I型岩浆与深熔S型熔体之间的杂交过程来解释。
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引用次数: 5
1.90-1.88Ga arc magmatism of central Fennoscandia: geochemistry, U-Pb geochronology, Sm-Nd and Lu-Hf isotope systematics of plutonic-volcanic rocks from southern Finland 芬诺斯坎迪亚中部1.90-1.88Ga弧岩浆作用:芬兰南部深部火山岩地球化学、U-Pb年代学、Sm-Nd和Lu-Hf同位素系统
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2018-01-01 DOI: 10.1344/GEOLOGICAACTA2018.16.1.1
Jaakko Kara, M. Väisänen, Å. Johansson, Y. Lahaye, H. O’Brien, O. Eklund
The earliest Svecofennian magmatism in southern Finland has been dated at 1.90-1.88Ga. As an example of this, the Orijarvi (ca. 1.89Ga) and Enklinge (ca. 1.88Ga) volcanic centres comprise bimodal plutonic batholiths surrounded by volcanic rocks of comparable ages and chemical compositions. Here, we report geochemical and Sm-Nd isotope data from intrusive and extrusive samples, combined with zircon U-Pb and Lu-Hf isotopes for granodiorites from both study areas. The samples range from gabbros to granites and indicate a subduction-related continental margin setting. The zircons from the Orijarvi granodiorite define an age of 1892±4Ma whereas the Enklinge granodiorite yields an age of 1882±6Ma. Several inherited ages of 2.25-1.95Ga as well as younger ages of 1.86-1.80Ga were found in the Enklinge granodiorite. The initial e Nd values from the mafic rocks from both locations fall in the range +1.1 to +2.9 whereas the felsic rocks exhibit initial e Nd values of -0.4 to +1.2. The magmatic zircons from the Orijarvi and Enklinge granodiorites show average initial e Hf values of -1.1 (at 1892Ma) and zero (at 1882Ma), respectively, each with a spread of about 7 e-units. The initial e Hf values for the inherited zircons from Enklinge range from +3.5 to +7.6 with increasing age. The Sm-Nd data indicate that the mafic rocks were derived from a “mildly depleted” mantle source while the felsic rocks show larger crustal contribution. Also, the variation in e Hf values indicates minor mixing between mildly depleted mantle derived magmas and crustal sources. U-Pb ages and Hf isotopes for inherited zircons in the Enklinge granodiorite suggest the presence of juvenile Svecofennian “proto-crust” at depth.
芬兰南部最早的斯韦芬尼期岩浆活动时间为1.90-1.88Ga。作为一个例子,Orijarvi(约1.89Ga)和Enklinge(约1.88Ga)火山中心由双峰深成岩基组成,周围是年龄和化学成分相当的火山岩。在此,我们报告了侵入和挤压样品的地球化学和Sm-Nd同位素数据,并结合两个研究区花岗闪长岩的锆石U-Pb和Lu-Hf同位素。样品范围从辉长岩到花岗岩,表明与俯冲有关的大陆边缘环境。奥里雅维花岗闪长岩的锆石年龄为1892±4Ma,而恩克林格花岗闪长岩的锆石年龄为1882±6Ma。在恩克林格花岗闪长岩中发现了几个2.25 ~ 1.95 ga的继承年龄和1.86 ~ 1.80 ga的继承年龄。两个地区基性岩的初始e - Nd值均在+1.1 ~ +2.9之间,而长英质岩的初始e - Nd值为-0.4 ~ +1.2。Orijarvi和Enklinge花岗闪长岩岩浆锆石的平均初始e Hf值分别为-1.1 (1892Ma)和0 (1882Ma),分布约为7 e-单位。Enklinge继承锆石的初始Hf值随年龄的增加在+3.5 ~ +7.6之间。Sm-Nd数据表明,基性岩来源于“轻度衰竭”的地幔源,而长英质岩则表现出较大的地壳贡献。此外,e Hf值的变化表明轻度枯竭的地幔源岩浆与地壳源岩浆之间存在少量混合。Enklinge花岗闪长岩中继承锆石的U-Pb年龄和Hf同位素表明,深部存在幼年七芬尼期“原壳”。
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引用次数: 10
Experimental early crystallization of K-feldspar in granitic systems : implications on the origin of magmatic fabrics in granitic rocks 花岗质体系中钾长石的实验早期结晶:对花岗质岩石岩浆组构成因的启示
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2017-12-18 DOI: 10.1344/GEOLOGICAACTA2017.15.4.2
J. Díaz-Alvarado
One of the most outstanding characteristics of some granodioritic to granitic rocks is the presence of K-feldspar megacrysts. For instance, granodiorites and monzogranites of the Spanish Central System batholith present variable amounts of large (up to 10cm in length) euhedral K-feldspar crystals. The porphyritic textures, the euhedral shape, the alignment of plagioclase and biotite inclusions and the magmatic fabrics point to a magmatic origin for these megacrysts. This work presents a phase equilibria study in a high-K 2 O granodioritic system. A series of experiments were conducted with a granodioritic composition (GEMbiot) to study the crystallization sequence at the emplacement conditions in the Gredos massif, i.e. 4 H 2 O wt.% and 0.4GPa. Experimental results show that orthopiroxene is the liquidus phase at 1010oC, which reacts with the H 2 O-rich melt to stabilize biotite between 980 and 940oC. Plagioclase crystallizes at around 910oC, and K-feldspar crystallizes in the matrix between 750 and 700oC when the crystal fraction is around 0.5. However, at 850 oC, a pelite-doped experiment shows euhedral K-feldspar (≈5vol%) in both the reactive xenolith domain together with cordierite and the granodioritic domain, where the K 2 O wt.% rise from 4.5 in the normal experiment to 5.9 in the doped experiment. These results suggest that the bulk-assimilation process promotes the bulk and heterogeneous K 2 O enrichment in a huge granodioritic magma volume, which triggers an early crystallization of K-feldspar megacrysts. Because of this early crystallization of the megacrysts, the magmatic foliations defined by K-feldspar megacrysts are formed during and after the emplacement processes and are highly influenced by tectonic kinematics.
某些花岗闪长岩至花岗质岩石最显著的特征之一是钾长石巨晶的存在。例如,西班牙中央体系岩基的花岗闪长岩和二长花岗岩呈现出不同数量的大(长度可达10cm)自面体钾长石晶体。斑岩结构、自面体形状、斜长石和黑云母包裹体的排列以及岩浆组构表明这些巨晶的岩浆起源。本文介绍了高k2o花岗闪长岩体系的相平衡研究。采用花岗闪长岩组成(GEMbiot)进行了一系列实验,研究了Gredos地块侵位条件(4 h2o wt.%, 0.4GPa)下的结晶序列。实验结果表明:1010oC时,正辉石为液相相,与富h2o熔体在980 ~ 940oC时发生反应,使黑云母稳定。斜长石在910oC左右结晶,k长石在750 ~ 700oC之间结晶,晶体分数在0.5左右。而在850℃时,掺入褐铁矿的实验中,在与堇青石反应的捕虏体域和花岗闪长岩域均发现自面体K-长石(≈5vol%),其k2o wt.%从正常实验的4.5上升到掺入实验的5.9。这些结果表明,体同化作用促进了巨大花岗闪长岩岩浆体中k2o的体非均质富集,从而引发了钾长石巨晶的早期结晶。由于巨晶的早期结晶作用,以钾长石巨晶为定义的岩浆岩片理形成于侵位过程中和侵位过程之后,并受到构造运动学的高度影响。
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引用次数: 1
Spinels of Variscan olivine hornblendites related to the Montnegre granitoids revisited (NE Spain): petrogenetic evidence of mafic magma mixing 重新考察与黑山花岗质岩石有关的华力西橄榄角闪岩的尖晶石(西班牙东北部):镁铁质岩浆混合的岩石成因证据
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2017-11-22 DOI: 10.1344/GEOLOGICAACTA2017.15.4.5
G. Galán, P. Enrique, L. Butjosa, M. Fernández-Roig
Olivine hornblendites (cortlandtites) form part of the Montnegre mafic complex related to late-Variscan I-type granitoids in the Catalan Coastal Ranges. Two generations of spinel are present in these hornblendites: Spl1 forms euhedral crystals included in both olivine and Spl2. Spl2 forms euhedral to anhedral crystals associated with phlogopite and fibrous colourless amphibole forming pseudomorphs after olivine. Compositions of Spl1 are picotite-Al chromite (Fe#: 77.78-66.60; Cr#: 30.12-52.22; Fe3+/R3+: 6.99-21.89; 0.10< TiO2%<0.62). Compositions of Spl2 are pleonaste (Fe#: 37.86-52.12; Cr#: 1.00-15.45; Fe3+/R3+: 0.31-5.21; TiO2%<0.10). The two types of spinel follow a CrAl trend, mainly due to the substitution (Fe2+)-1Cr-1= MgAl, which is interpreted as the result of mixing between two different mantle-derived melts. The compositions of early Spl1 crystals included in olivine are characteristic of Al-rich basalts. More aluminous Spl2 would result from reaction of olivine with a less evolved, Al and K-rich mantle-derived melt after new refilling of the magma chamber or channel. As a whole, spinels from similar examples of Variscan olivine hronblendites also follow a CrAl trend with high Fe# and starting at higher Cr# than other trends of this type. Cr# heterogeneity in the early spinels from these Variscan hornblendites would be inherited from the variable Al content of the mafic melts involved in their genesis.
橄榄岩角闪岩(cortlandite)是与加泰罗尼亚海岸山脉晚华力西期I型花岗岩有关的黑山镁铁质杂岩的一部分。这些角闪石中存在两代尖晶石:Spl1形成包含在橄榄石和Spl2中的自形晶体。Spl2形成自形到反角体晶体,与金云母和纤维状无色角闪石有关,在橄榄石之后形成假晶。Spl1的成分为皮铝-铬铁矿(Fe#:77.78-66.60;Cr#:30.12-52.22;Fe3+/R3+:6.99-21.89;0.10
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引用次数: 3
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Geologica Acta
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