Temperature and Bulk Composition Control on the Growth of Monazite and Zircon During Low-pressure Anatexis (Mount Stafford, Central Australia)   总被引：5，自引：0，他引：5  

RUBATTO  DANIELA; HERMANN  JORG; BUICK  IAN S. 《Journal of Petrology》2006,47(10):1973-1996

The formation, age and trace element composition of zircon andmonazite were investigated across the prograde, low-pressuremetamorphic sequence at Mount Stafford (central Australia).Three pairs of inter-layered metapelites and metapsammites weresampled in migmatites from amphibolite-facies (T 600°C)to granulite-facies conditions (T 800°C). Sensitive high-resolutionion microprobe U–Pb dating on metamorphic zircon rimsand on monazite indicates that granulite-facies metamorphismoccurred between 1795 and 1805 Ma. The intrusion of an associatedgranite was coeval with metamorphism at 1802 ± 3 Ma andis unlikely to be the heat source for the prograde metamorphism.Metamorphic growth of zircon started at T 750°C, well abovethe pelite solidus. Zircon is more abundant in the metapelites,which experienced higher degrees of partial melting comparedwith the associated metapsammites. In contrast, monazite growthinitiated under sub-solidus prograde conditions. At granulite-faciesconditions two distinct metamorphic domains were observed inmonazite. Textural observations, petrology and the trace elementcomposition of monazite and garnet provide evidence that thefirst metamorphic monazite domain grew prior to garnet duringprograde conditions and the second in equilibrium with garnetand zircon close to the metamorphic peak. Ages from sub-solidus,prograde and peak metamorphic monazite and zircon are not distinguishablewithin error, indicating that heating took place in less than20 Myr. KEY WORDS: accessory phases; anatexis; trace element partitioning; U–Pb dating  相似文献   

缅甸弧中部俯冲带下方地幔间断面起伏形态研究     

崔清辉  高原  周元泽  魏荣强  李国辉 《地球物理学报》2022,65(2):471-483

新生代以来,印度板块和欧亚板块发生碰撞形成了喜马拉雅造山带和青藏高原,印度板片在喜马拉雅东构造结处缅甸弧俯冲带进入深部地幔.开展缅甸弧俯冲带下方地幔间断面的研究有助于认识印度大陆岩石圈的碰撞-俯冲过程及其对上地幔结构的影响.本文选用了发生于缅甸弧地区的3个中源地震事件,获取了欧洲和美国阿拉斯加地区多个密集地震台网/台阵...  相似文献   

华北地块北缘晚古生代——早中生代岩浆活动期次、特征及构造背景   总被引：43，自引：0，他引：43  

张拴宏  赵越  刘建民  胡健民  宋彪  刘健  吴海 《岩石矿物学杂志》2010,29(6):824-842

通过对华北陆块北缘近年来获得的晚古生代—早中生代岩浆岩锆石U-Pb及部分39Ar-40Ar测年结果的分析,认为该区晚古生代—早中生代期间至少经历了泥盆纪、早石炭世晚期—中二叠世及二叠纪末—三叠纪等3期明显的岩浆作用过程。泥盆纪岩浆活动时限在400～360Ma左右,岩性主要为碱性岩(正长岩及二长岩),其次为基性-超基性岩、二长闪长岩、碱性花岗岩及流纹岩,出露面积较少。早石炭世晚期—中二叠世岩浆活动时限在330～265Ma左右,岩性主要为闪长岩、石英闪长岩、花岗闪长岩及花岗岩,其次为辉长岩及英云闪长岩。二叠纪末—三叠纪岩浆活动(250～200Ma),岩性主要为钾长花岗岩、二长花岗岩及碱性杂岩,其次为基性-超基性岩及少量中酸性火山岩。华北地块北缘晚古生代—早中生代岩浆岩呈近东西走向的带状分布,其中泥盆纪及早石炭世晚期—中二叠世岩浆岩主要分布在内蒙古隆起上,而二叠纪末—三叠纪岩浆岩分布范围更大,其南界可以到达燕山构造带最南端的蓟县盘山及太行山北段的河北涿鹿矾山地区。这些广泛分布的多期次岩浆活动表明华北地块北缘在晚古生代—早中生代期间经历了复杂的岩浆及构造作用过程。泥盆纪岩浆活动可能与白乃庙岛弧岩带与华北克拉通弧-陆碰撞后的伸展作用有关。早石炭世晚期—中二叠世岩浆活动的形成与古亚洲洋向华北地块的俯冲作用有关。而二叠纪末—三叠纪岩浆活动的形成与华北地块与西伯利亚南缘蒙古增生褶皱带拼合后的伸展及岩石圈拆沉作用有关。  相似文献   

The impact of summer temperature changes on vegetation development in Ireland during the Weichselian Lateglacial Interstadial     

Nelleke van Asch  Wim Z. Hoek 《第四纪科学杂志》2012,27(5):441-450

We analysed pollen from a sediment core from Fiddaun, a small Lateglacial lake basin in western Ireland. Results reflect the general Lateglacial vegetation development in Ireland, as reconstructed from other pollen records. The Fiddaun diagram shows a number of short‐lived regressive vegetation phases during the Interstadial. The close similarity between two pollen records from the same region (Fiddaun and Lurga) indicates that these fluctuations probably reflect regional rather than local changes. Comparison with a previously published climate reconstruction, based on a chironomid‐inferred mean July air temperature reconstruction, lithology, and oxygen and carbon isotopes of lake marl from the Fiddaun record, allowed us to establish the relationship between summer temperature and vegetation changes. Results reveal that two temporary regressive shifts in the pollen record correspond to cold oscillations, which have been correlated to Greenland Interstadial 1b and 1d. It seems that the first cold oscillation (GI‐1d) had the most distinct effect on vegetation in Ireland. In contrast, it appears that the transition from Juniperus shrubland and Empetrum heath to grassland, which is estimated at ～13.7 ka BP, was not caused by decreasing summer temperatures, as no substantial change is observed in the climate proxies. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Modelling seismic wave propagation in a two‐dimensional cylindrical whole‐earth model using the pseudospectral method     

Yanbin Wang  Hiroshi Takenaka  Takashi Furumura † 《Geophysical Journal International》2001,145(3):689-708

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Inferred attenuation from site effect-correctedT phases recorded on the island of Hawaii     

S. Koyanagi  K. Aki  N. Biswas  K. Mayeda 《Pure and Applied Geophysics》1995,144(1):1-17

Coda site amplification factors are used to eliminate the site effect from records of three circum-PacificT phases recorded by the Hawaiian Volcano Observatory (HVO) network on the island of Hawaii. ObservedT-phase amplitudes across the island generally decrease with increasing distance from the conversion point where acoustic waves in the SOFAR channel become seismic waves propagating through the crust. However, the decay of the observedT-phase signal across the island is not regular in regions of dense station coverage, in particular, the Kilauea caldera region. We divide the maximum observedT-phase amplitudes at a given station by the coda site amplification factor obtained for the same station and frequency band (3.0Hz); the distribution of these amplitudes reveals a smooth pattern over the entire island. The distance over which the site effect-correctedT-phase amplitude decreases by one-half, combined with the apparent velocity of propagation ofT phases across the island, allows for an approximate determination of near-surfaceQ over much of the island of Hawaii. We found a region of lowQ in the Kilauea summit area (Q≈30) and east rift zone (Q≈60) with considerably higherQ in the Kaoiki and northern portions of the island (Q≈150 to 200). The lowQ values obtained in the Kilauea summit region and east rift zone are significantly lower than estimates of codaQ in the same region, suggestingT phases may be sampling the earth's near-surface properties.  相似文献   

Occurrences of hydrous and carbonate phases in ultrahigh-pressure rocks from east-central China: Implications for the role of volatiles deep in cold subduction zones   总被引：3，自引：0，他引：3  

J. G. Liou    R. Y. Zhang  W. G. Ernst 《Island Arc》1995,4(4):362-375

Abstract Minor epidote-zoisite, phengite, glaucophane, nyböite, talc, magnesite, and dolomite occur as matrix phases or as mineral inclusions in some ultrahigh-pressure (UHP) rocks from the Dabie-Sulu terrane. Some of these phases contain inclusions of coesite or coesite pseudomorphs and appear to have been in equilibrium with coesite at the time of formation. Their occurrences in the UHP rocks together with experimentally determined and calculated phase relations indicate that they are stable at mantle depths in relatively low-temperature environments. Because of the apparently dry nature of subducted continental protoliths of the Yangtze craton, small amounts of volatile components at depths exceeding 50 km along a cold subduction zone may have been stored mainly by these hydrous and carbonate phases. These minerals, in addition to some dense hydrous magnesian silicates, act as important carriers for H₂O and CO₂ recycled at mantle depths. Available petrological and geochemical data support limited or no fluid flow in this region. At very high pressures and low temperatures, the subducted sialic crust evidently served as a desiccating agent. Partial melting of the subducting slab, therefore, may not have occurred, and near absence of volatile expulsion from the subducting slab to the overlying mantle wedge + continental crust may have inhibited large-scale partial melting, accounting for the lack of a typical contemporaneous calc-alkaline magmatic arc.  相似文献   

Petrology of gabbroic xenoliths in 1960 Kilauea basalt: crystalline remnants of prior (1955) magmatism     

R. V. Fodor  R. B. Moore 《Bulletin of Volcanology》1994,56(1):61-73

The 1960 Kapoho lavas of Kilauea’s east rift zone contain 1–10 cm xenoliths of olivine gabbro, olivine gabbro-norite, and gabbro norite. Textures are poikilitic (ol+sp+cpx in pl) and intergranular (cpx+pl±ol±opx). Poikilitic xenoliths, which we interpret as cumulates, have the most primitive mineral compositions, Fo_82.5, cpx Mg# 86.5, and An_80.5. Many granular xenoliths (ol and noritic gabbro) contain abundant vesicular glass that gives them intersertal, hyaloophitic, and overall ‘open’ textures to suggest that they represent ‘mush’ and ‘crust’ of a magma crystallization environment. Their phase compositions are more evolved (Fo_80–70, cpx Mg# 82–75, and An_73–63) than those of the poikilitic xenoliths. Associated glass is basaltic, but evolved (MgO 5 wt%; TiO₂ 3.7–5.8 wt%). The gabbroic xenolith mineral compositions fit existing fractional crystallization models that relate the origins of various Kilauea lavas to one another. FeO/MgO crystal–liquid partitioning is consistent with the poikilitic ol-gabbro assemblage forming as a crystallization product from Kilauea summit magma with ∼8 wt% MgO that was parental to evolved lavas on the east rift zone. For example, least squares calculations link summit magmas to early 1955 rift-zone lavas (∼5 wt% MgO) through ∼28–34% crystallization of the ol+sp+cpx+pl that comprise the poikilitic ol-gabbros. The other ol-gabbro assemblages and the olivine gabbro-norite assemblages crystallized from evolved liquids, such as represented by the early 1955 and late 1955 lavas (∼6.5 wt% MgO) of the east rift zone. The eruption of 1960 Kapoho magmas, then, scoured the rift-zone reservoir system to entrain portions of cumulate and solidification zones that had coated reservoir margins during crystallization of prior east rift-zone magmas. Received: January 7, 1993/Accepted: November 23, 1993  相似文献   

Seismic wave propagation in complex crust-upper mantle media using 2-D finite-difference synthetics   总被引：1，自引：0，他引：1  

S. O. Hestholm  E. S. Husebye  B. O. Ruud 《Geophysical Journal International》1994,118(3):643-670

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Investigations of S_n and P_n phases in the area of the upper Rhine Graben and northern Switzerland     

T. Plenefisch  S. Faber  K.-P. Bonjer 《Geophysical Journal International》1994,119(2):402-420

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