The petrology of the Mt Manypeaks Adamellite and associated high‐grade metamorphic rocks near Albany,Western Australia     

N. C. N. Stephenson 《Australian Journal of Earth Sciences》2013,60(4):413-439

The Mt Manypeaks Adamellite is a composite, regionally concordant pluton at least 22 km long and 3 km wide, associated with Precambrian amphibolite facies gneisses of the Albany‐Esperance Block, and situated about 35 km east of Albany, Western Australia. The pluton is surrounded by a granitised aureole, and shows structural and mineralogical harmony with the country rocks. Contacts vary from grada‐tional to sharp. Hence field relations are consistent with syn‐ or late‐kinematic emplacement in the catazone. The normative composition of the pluton corresponds with the thermal trough in the system An‐Ab‐Or‐Q‐H2O at 7 kb PH2O, suggesting an origin involving crystal‐melt equilibria. The pluton is believed to have formed almost in situ by partial anatexis of the country rocks at 700–750°C and a depth of about 25 km during the orogenic episode responsible for regional metamorphism and deformation.  相似文献   

Neoproterozoic granites of the Lajeado intrusive suite,north-center Brazil: A late Ediacaran remelting of a Paleoproterozoic crust     

《Journal of South American Earth Sciences》2013

In north-central Brazil, a number of granite plutons, which intrude Paleoproterozoic gneiss-granulite terrains of the Goiás Massif, crop out along a thermal axis parallel to the Transbrasiliano Lineament. Single zircon lead evaporation ages from three granitic bodies span between 552 and 545 Ma. Sm–Nd model ages (T_DM) vary between 2.1 and 1.7 Ga and negative εNd_{(0.55 Ga)} values between −10 and −13 show that Paleoproterozoic crust was involved in the genesis of these granites. These plutons, which form the Lajeado Intrusive Suite are part of an important Ediacaran magmatic event in central-northern of the Tocantins Tectonic Province, composed of metaluminous to slightly peraluminous granites with geochemical characteristics similar to A-type granites, whose crystallization occurred under low water activity during magmatic emplacement. The granitic intrusive bodies are related to a crustal extensional/transtensional tectonic event at the end of the Neoproterozoic. They may have connection with the granitic plutons of similar age (0.56–0.52 Ga) in northwestern Ceará state, on the other side of the Paleozoic Parnaíba Basin in northwest of Borborema Province, along the Transbrasiliano Lineament.  相似文献   

小兴安岭石林林场A型花岗岩地球化学特征及构造环境     

李超  孙国胜  杨乃峰  孙珍军  杜美艳  敖东 《世界地质》2013,32(1):1-7

根据岩石学及地球化学等特征,对小兴安岭北部石林林场A型花岗岩进行了构造环境研究。石林林场A型花岗岩为高钾钙碱性系列、过铝质岩石,富集大离子亲石元素Rb、Th、U、La、Ce和轻稀土元素。岩石化学成分特点及Na2O--K2O图解表明,花岗岩为铝质A型花岗岩。通过对Nb--Y构造环境判别图解、R1--10 000 Ga/Al判别图解及构造环境讨论表明,石林林场花岗岩形成于陆内拉张环境。  相似文献   

Regional Tectonic Transformation in East Kunlun Orogenic Belt in Early Paleozoic: Constraints from the Geochronology and Geochemistry of Helegangnaren Alkali-feldspar Granite   总被引：4，自引：0，他引：4  

LI Ruibao  PEI Xianzhi  LI Zhuochen  SUN Yu  PEI Lei  CHEN Guochao  CHEN Youxin  LIU Chengjun  WEI Fanghui 《《地质学报》英文版》2013,87(2):333-345

The Helegangnaren feldspar granite exposed in the eastern part of East Kunlun, is characterized by high concentrations of SiO2 and alkaline, low abundances of Fe, Mg and Ca, metaluminous-weak peraluminous. Trace elements analysis shows that the granite is depleted extremely in Ba, Sr and Eu, and rich in some large-ion lithophile elements and high field strength elements. Besides, the granite has high Ga contents, the values of 104(Ga/Al) vary from 2.50 to 2.77, which is mainly greater than the lower limit of A-type granites (2.6), and is higher than the I- and S-type granites’ average (2.1 and 2.28, respectively). Rare earth element (REE) is characterized by relatively high fractionations of light REE (LREE) and heavy REE (HREE) (LREE/HREE=9.3–13.60, (La/Yb)N=10.92–18.02), pronounced negative Eu anomalies (δEu=0.08–0.13), and exhibits right-dipping gull pattern. Major elements, rare elements and trace elements features show the granite is ascribed to A-type granite and A2 subtype in tectonic genetic type. They are plotted into post-collision or within-plate area in a variety of tectonic discriminations. Geological and geochemical data comprehensively suggest that the granite is formed in a post-collision extensive tectonic setting. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yields a weighted mean age of 425?Ma, belonging to Middle Silurian, which is similar to the age of the post-collision geological events in the region. The differences of magmatic rocks in formation age, rocks assemblage and rocks series systematically indicate that the regional tectonic stress regime in the East Kunlun orogenic belt experienced a major transformation from compress to extension in Middle Silurianin, and the Helegangnaren feldspar granite intruded in the early stage of tectonic transformation.  相似文献   

The AD 1362 Öræfajökull eruption,S.E. Iceland: Physical volcanology and volatile release     

Kirti Sharma  Stephen Self  Stephen Blake  Thorvaldur Thordarson  Gudrun Larsen 《Journal of Volcanology and Geothermal Research》2008

The explosive rhyolitic eruption of Öræfajökull volcano, Iceland, in AD 1362 is described and interpreted based on the sequence of pyroclastic fall and flow deposits at 10 proximal locations around the south side of the volcano. Öræfajökull is an ice-clad stratovolcano in south central Iceland which has an ice-filled caldera (4–5 km diameter) of uncertain origin. The main phase of the eruption took place over a few days in June and proceeded in three main phases that produced widely dispersed fallout deposits and a pyroclastic flow deposit. An initial phase of phreatomagmatic eruptive activity produced a volumetrically minor, coarse ash fall deposit (unit A) with a bi-lobate dispersal. This was followed by a second phreatomagmatic, possibly phreatoplinian, phase that deposited more fine ash beds (unit B), dispersed to the SSE. Phases A and B were followed by an intense, climactic Plinian phase that lasted ∼ 8–12 h and produced unit C, a coarse-lapilli, pumice-clast-dominated fall deposit in the proximal region. At the end of Plinian activity, pyroclastic flows formed a poorly-sorted deposit, unit D, presently of very limited thickness and exposed distribution. Much of Eastern Iceland is covered with a very fine distal ash layer, dispersed to the NE. This was probably deposited from an umbrella cloud and is the distal representation of the Plinian fallout. A total bulk fall deposit volume of ∼ 2.3 km³ is calculated (∼ 1.2 km³ DRE). Pyroclastic flow deposit volumes have been crudely estimated to be < 0.1 km³. Maximum clast size data interpreted by 1-D models suggests an eruption column ∼ 30 km high and mass discharge rates of ∼ 10⁸ kg s^− 1. Ash fall may have taken place from heights around 15 km, above the local tropopause (∼ 10 km), with coarser clasts dispersed below that under a different wind regime. Analyses of glass inclusions and matrix glasses suggest that the syn-eruptive SO₂ release was only ∼ 1 Mt. This result is supported by published Greenland ice-core acidity peak data that also suggest very minor sulphate deposition and thus SO₂ release. The small sulphur release reflects the low sulphur solubility in the 1362 rhyolitic melt. The low tropopause over Iceland and the 30-km-high eruption column certainly led to stratospheric injection of gas and ash but little sulphate aerosol was generated. Moreover, pre-eruptive and degassed halogen concentrations (Cl, F) indicate that these volatiles were not efficiently released during the eruption. Besides the local pyroclastic flow (and related lahar) hazard, the impact of the Öræfajökull 1362 eruption was perhaps restricted to widespread ash fall across Eastern Iceland and parts of northern Europe.  相似文献   

Contrasting origins of Cenozoic silicic volcanic rocks from the western Cordillera of the United States   总被引：2，自引：0，他引：2  

Eric H. Christiansen  Michael McCurry 《Bulletin of Volcanology》2008,70(3):251-267

Two fundamentally different types of silicic volcanic rocks formed during the Cenozoic of the western Cordillera of the United States. Large volumes of dacite and rhyolite, mostly ignimbrites, erupted in the Oligocene in what is now the Great Basin and contrast with rhyolites erupted along the Snake River Plain during the Late Cenozoic. The Great Basin dacites and rhyolites are generally calc-alkaline, magnesian, oxidized, wet, cool (<850°C), Sr-and Al-rich, and Fe-poor. These silicic rocks are interpreted to have been derived from mafic parent magmas generated by dehydration of oceanic lithosphere and melting in the mantle wedge above a subduction zone. Plagioclase fractionation was minimized by the high water fugacity and oxide precipitation was enhanced by high oxygen fugacity. This resulted in the formation of Si-, Al-, and Sr-rich differentiates with low Fe/Mg ratios, relatively low temperatures, and declining densities. Magma mixing, large proportions of crustal assimilation, and polybaric crystal fractionation were all important processes in generating this Oligocene suite. In contrast, most of the rhyolites of the Snake River Plain are alkaline to calc-alkaline, ferroan, reduced, dry, hot (830–1,050°C), Sr-and Al-poor, and Nb-and Fe-rich. They are part of a distinctly bimodal sequence with tholeiitic basalt. These characteristics were largely imposed by their derivation from parental basalt (with low fH₂O and low fO₂) which formed by partial melting in or above a mantle plume. The differences in intensive parameters caused early precipitation of plagioclase and retarded crystallization of Fe–Ti oxides. Fractionation led to higher density magmas and mid-crustal entrapment. Renewed intrusion of mafic magma caused partial melting of the intrusive complex. Varying degrees of partial melting, fractionation, and minor assimilation of older crust led to the array of rhyolite compositions. Only very small volumes of distinctive rhyolite were derived by fractional crystallization of Fe-rich intermediate magmas like those of the Craters of the Moon-Cedar Butte trend. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Characterization of juvenile pyroclasts from the Kos Plateau Tuff (Aegean Arc): insights into the eruptive dynamics of a large rhyolitic eruption     

Caroline Bouvet de Maisonneuve  Olivier Bachmann  Alain Burgisser 《Bulletin of Volcanology》2009,71(6):643-658

Silicic pumices formed during explosive volcanic eruptions are faithful recorders of the state of the magma in the conduit, close to or at the fragmentation level. We have characterized four types of pumices from the non-welded rhyolitic Kos Plateau Tuff, which erupted 161,000 years ago in the East Aegean Arc, Greece. The dominant type of pumice (>90 vol.%) shows highly elongated tubular vesicles. These tube pumices occur throughout the eruption. Less common pumice types include: (1) “frothy” pumice (highly porous with large, sub-rounded vesicles), which form 5–10 vol.% of the coarsest pyroclastic flow deposits, (2) dominantly “microvesicular” and systematically crystal-poor pumices, which are found in early erupted, fine-grained pyroclastic flow units, and are characterized by many small (<50 μm in diameter) vesicles and few mm-sized, irregular voids, (3) grey or banded pumices, indicating the interaction between the rhyolite and a more mafic magma, which are found throughout the eruption sequence and display highly irregular bubble shapes. Except for the grey-banded pumices, all three other types are compositionally identical and were generated synchronously as they are found in the same pyroclastic units. They, therefore, record different conditions in the volcanic conduit leading to variable bubble nucleation, growth and coalescence. A total of 74 pumice samples have been characterized using thin section observation, SEM imagery, porosimetry, and permeametry. We show that the four pumice types have distinct total and connected porosity, tortuosity and permeability. Grey-banded pumices show large variations in petrophysical characteristics as a response to mingling of two different magmas. The microvesicular, crystal-poor, pumices have a bimodal bubble size distribution, interpreted as reflecting an early heterogeneous bubble nucleation event followed by homogeneous bubble nucleation close to fragmentation. Finally, the significant differences in porosity, tortuosity and permeability in compositionally identical tube and frothy pumices are the result of variable shear rates in different parts of the conduit. Differential shear rates may be the result of either: (1) pure shear, inducing a vertical progression from frothy to tube and implying a relatively thick fragmentation zone to produce both types of pumices at the same time or (2) localized simple shear, inducing strongly tubular vesicles along the wall and near-spherical bubbles in the centre of the conduit and not necessarily requiring a thick fragmentation zone.  相似文献   

松辽盆地东南隆起区营城组柱状节理流纹岩特征和成因   总被引：4，自引：1，他引：3  

李金龙  王璞珺  郑常青  唐华风  吴颜雄  边伟华 《吉林大学学报(地球科学版)》2007,37(6):1131-1138

松辽盆地东南隆起区下白垩统营城组出露柱状节理流纹岩。柱状节理属于原生构造节理,岩相为火山通道相次火山岩亚相-侵出相,柱体排列方式为近水平式、倾斜式、近直立式,截面为不规则的四方柱、五方柱、六方柱,柱体规模属于中小型,流纹岩中常发育隐爆角砾结构。通过对柱状节理流纹岩成分及结构构造的研究,表明本区的流纹岩柱体直径与其对应的显微组构斑晶大小成正比例相关。柱状节理的成因是熔岩冷却收缩形成的,由于受到种种内外因素制约,形成的柱状节理形态各异。  相似文献   

福建永泰云山碱性流纹岩的厘定及其地质意义   总被引：4，自引：0，他引：4  

邱检生  王德滋 《地质论评》2000,46(5):520-529

福建永泰云山破火山石帽山群第三旋回顶部的霏细流纹岩含有霓石、钠铁闪石等碱性铁镁矿物。化学成化富硅、富碱,碱性指数（ＡＫＩ值）大于０．９０,Ｒｂ、Ｔｈ、Ｚｒ、Ｇａ等元素的含量高,Ｇａ／Ａｌ值大;贫钙、镁、铝和过渡族元素,轻、重稀土比值较小,并具有显著的负铕异常。在Ｋ２Ｏ－Ｎａ２Ｏ及以Ｇａ／Ａｌ值为基础的多种判别图上均投影在Ａ型花岗岩区。上述特征与其邻近的魁歧典型碱性花岗岩相似,也可与国外有关典型碱性  相似文献   

古亚洲洋俯冲板片断离与后造山伸展：贺根山缝合带火山岩年代学和地球化学证据   总被引：1，自引：0，他引：1  

王金芳  李英杰  李红阳  董培培 《地质学报》2020,94(12):3561-3580

本文以出露于贺根山缝合带迪彦庙蛇绿混杂岩北侧的乌兰拜其白音高老组流纹岩- 粗面岩为研究对象,通过野外地质调查和岩石学、地球化学、锆石U- Pb年代学研究,探讨岩石成因类型、构造环境和古亚洲洋俯冲板片断离与后造山伸展过程。岩石地球化学研究表明, 乌兰拜其地区白音高老组流纹岩具有较高的SiO 2、Al 2O 3、K 2O和Na 2O+K 2O含量,以及较高的Ga/Al比值,相对贫CaO、MgO、Sr、Ba、Eu、Ti和P,稀土元素配分曲线为右倾海鸥式分布,负铕异常显著。该区粗面岩属于钾玄岩系列,具有高碱(Na 2O+K 2O)、高K 2O、高Al 2O 3、低TiO 2,富集Rb、Ba、U和轻稀土元素, 亏损 Nb、Ta 和 Ti,稀土元素配分曲线为右倾式分布。岩石学和岩石地球化学特征表明,乌兰拜其地区白音高老组流纹岩为迪彦庙- 白音布拉格蛇绿混杂岩带早白垩世后造山A型花岗岩浆的喷出相- A型流纹岩,其形成于后造山伸展构造环境;粗面岩为后造山型钾玄质火山岩,与洋壳俯冲作用有关,形成于俯冲板片断离- 后造山伸展构造背景。流纹岩和粗面岩锆石LA- ICP- MS U- Pb同位素测年,获得206Pb/238U加权平均年龄分别为140. 4±1. 2Ma和134. 9±1. 1Ma,表明白音高老组流纹岩- 粗面岩喷发于早白垩世,反映了贺根山缝合带早白垩世后造山A型花岗岩浆- 钾玄质岩浆作用事件。结合贺根山缝合带的壳幔电性结构特征和晚古生代蛇绿岩- 岛弧岩浆岩、中生代后造山A型岩浆岩的时空分布与演化关系,认为根山缝合带三叠纪- 早白垩世后造山伸展岩浆作用与古亚洲洋俯冲板片断离作用有关,提出了该区后造山A型花岗岩浆- 钾玄质岩浆作用的俯冲板片断离- 后造山伸展地球动力学模式。  相似文献