Crystal fractionation in the friction melts of seismic faults (Alpine Fault, New Zealand)     

Laurence N. Warr  Ben A. van der Pluijm 《Tectonophysics》2005,402(1-4):111

Compositional variations are documented in friction melts along the Hari Hari section of the Alpine Fault, New Zealand, with multiple stages of melt injection into quartzo-feldspathic schists. Intermediate to felsic melts were heterogeneous in composition, but all fractions show a common trend, with a tendency for the younger melt layers and glasses to be more alkali − (Na + K) and Si-enriched, while being depleted in mafic (Fe + Mg + Mn) components. These changes are attributed primarily to crystal fractionation of the melt during transport. Farther traveled molten layers were on the whole less viscous, mostly due to a higher melt-to-clast ratio; however, compositional change, together with a decrease in volatile content, produced a progressively more viscous liquid melt with time. The glass phase is interpreted as a remnant of this high viscosity felsic residual melt that was preserved during final quenching. Following initial failure, the formation of largely phyllosilicate-derived, volatile-rich, lower viscosity melt corresponds with a phase of fault weakening. Subsequent rapid crystal fractionation during melt transport, the loss of volatiles and freezing of residual melt contributed to the strengthening of the fault during seismic slip.  相似文献   

Multiple Foliations Defined by Different Sillimanite Crystal Habits, Partial Melting and the Late Metamorphic Development of the Cannington Ag-Pb-Zn Deposit, Northeast Australia     

Hyeong Soo Kim  Tim H. Bell   《Gondwana Research》2005,8(4):493-509

A succession of foliations defined by different sillimanite-bearing structural fabrics suggests that the macroscopic, isoclinal synform that dominates the geometry of the Cannington Ag-Pb-Zn deposit, northwest Queensland, Australia formed during D₂. The five foliations in this succession, S₁ to S₅, are defined by aligned sillimanite with habits ranging from individual crystals in S₁ through S₄ to clusters of fibrolite in S₅ in both the matrix and as inclusion trails within garnet and gahnite (Zn-rich spinel) porphyroblasts. S₁, S₃ and S₅ formed as sub-horizontal foliations, whereas S_1a, S₂ and S₄ formed sub-vertically. Foliation intersection/inflexion axes (FIAs) within garnet and gahnite porphyroblasts preserve a succession of trends that shifts from W-E to N-S. This succession indicates that this region experienced N-S followed by W-E bulk crustal shortening. N-S shortening occurred during D₁and D_1a, and W-E shortening occurred from D₂ to D₅. Prismatic and rhombic sillimanite produced during D₁-D₄ accompanied prograde metamorphism to ca. 634 62°C and 4.8 1.3 kbar. The coexistence of fibrous, prismatic and rhombic sillimanite resulted from post peak metamorphic reactivation of the early foliations during D₅. The synformal D₂ fold was intensified during D₄ by W-E bulk shortening. Local partial melting occurred after D₁ in the appropriate bulk rock compositions, based on calculation of P-T pseudosections in the chemical systems KFMASH, KFMASHTO, NCKFMASH and MnNCKFMASH. Zn mineralization related to gahnite growth occurred during D₃ through D₄, and was redistributed by partial melting into structural and rheological sites during D₄ and D₅shearing.  相似文献   

Geochemistry of adakitic quartz diorite in the Yamizo Mountains, central Japan: Implications for Early Cretaceous adakitic magmatism in the inner zone of southwest Japan     

Yutaka  Takahashi  Shin-Ichi  Kagashima  Masumi U.  Mikoshiba 《Island Arc》2005,14(2):150-164

Abstract   Small-volume plutons of Early to Late Cretaceous ages are widely distributed in the Yamizo Mountains, central Japan. These plutons consist predominantly of granitoids, classified into hornblende gabbro, quartz diorite, hornblende–biotite granodiorite and coarse-grained biotite granite. The quartz diorite (52–64 wt% of SiO₂) is characterized by a high Sr content (606–769 p.p.m.) associated with a low Y (13–27 p.p.m.) and heavy rare earth element content (Yb content of 1.19–2.13 p.p.m.). On the Sr/Y versus Y diagram, this rock type mainly plots in the adakite and Archean high-Al tonalite, trondhjemite and granodiorite (TTG) field. Together with its initial Sr isotopic ratios, which range from 0.7038 to 0.7046, these data suggest that quartz diorite originated as slab melts. However, geochemical calculations assuming either eclogite or garnet amphibolite as the source material do not support this suggestion. Instead, the chemical compositions of quartz diorite are better explained by the fractional crystallization of hornblende, plagioclase and biotite from a primitive, basaltic melt in a magma chamber. In this case, the formation of the associated hornblende gabbro can also be explained by the accumulation of hornblende and plagioclase. Adakitic rocks of Early Cretaceous ages have also been reported in the Tamba Belt of the inner zone of southwest Japan, located ca 500 km west of the Yamizo Mountains. These rocks can be correlated to the adakitic rocks in the Yamizo Mountains based on the geology, petrography, geochemistry and radiometric ages. Therefore, we propose the possibility that the Early Cretaceous adakitic rocks in the inner zone of southwest Japan were produced by fractional crystallization from basaltic arc magmas generated by a partial melting of metasomatized wedge mantle peridotite.  相似文献   

The S-type Ladybird leucogranite suite of southeastern British Columbia: Geochemical and isotopic evidence for a genetic link with migmatite formation in the North American basement gneisses of the Monashee complex   总被引：1，自引：0，他引：1  

Alana M. Hinchey  Sharon D. Carr   《Lithos》2006,90(3-4):223-248

The 62–52 Ma Ladybird granite (LBG) suite is a peraluminous, leucocratic, S-type, quartz monzonitic to granitic suite which occurs as batholiths, stocks, dikes, sills, and pegmatite veins predominantly in the high-grade rocks of the Shuswap complex, in southeastern British Columbia. The emplacement of the LBG was synchronous with the production of abundant migmatites within Thor–Odin dome of the Monashee complex, an exposure of North American basement, exhumed from depths of ca. 26–33 km by Eocene extensional faults. The LBG and the leucosome in migmatites from Thor–Odin dome have similar major and trace element patterns, and are both characterized by zircons which have inherited Precambrian cores. Whole rock Nd isotope compositions show a range of values for the LBG with εNd_{(55 Ma)} values from − 5.0 to − 17.2. The εNd_{(55 Ma)} for the leucosome samples range from − 9.5 to − 23.6, overlapping with those of the granitic suite. These data support the interpretation of a genetic link between formation of the LBG suite and melting of North American basement rocks, such as those exposed in the core of Thor–Odin dome. The leucosome samples have lower high field strength element (HFSE) concentrations and positive Eu anomalies, whereas the LBG samples have higher HFSE concentrations and negative Eu anomalies. The similar trace element characteristics suggest that the leucosome from the migmatites and the LBG are related, whereby most of the leucosome samples are cumulates and the LBG samples represent evolved or residual melts. The initial ⁸⁷Sr/⁸⁶Sr isotope values for both the LBG and leucosome samples have a large range. However, the initial Sr isotopic ratios for the LBG suite are lower than those of the leucosome samples, with ⁸⁷Sr/⁸⁶Sr_{(55 Ma)} ranging from 0.70603 to 0.73688 and 0.74256 to 0.76593, respectively. This isotopic discrepancy suggests either: a) isotopic disequilibrium during partial melting in the mid- to lower crust where the leucosome formed, b) the distribution of Sr during partial melting was controlled by different melt-producing reactions, and/or c) isotopic heterogeneity in the source rocks. At least part of the LBG suite likely formed via melting of North American basement rocks that were dominantly of sedimentary origin. Melting of the Proterozoic supracrustal metasedimentary rocks overlying North American basement may also have contributed to the formation of the different phases of the suite found at the regional scale. However, the abundant leucosomes in the basement rocks of Thor–Odin dome may mark the paths along which anatectic melt migrated in the structurally overlying Ladybird granites of the South Fosthall pluton.  相似文献   

基于偏最小二乘回归的融雪型洪水预报模型   总被引：2，自引：0，他引：2  

覃新闻  李智录  李波 《水文》2006,26(5):38-40

本文采用偏最小二乘回归法对新疆塔什库尔干河流的实测流量资料进行分析,建立了日平均流量的偏最小二乘回归模型,采用建立的模型对2001年日平均流量进行了预报。研究分析表明,结果比较合理,这为融雪型洪水预报提供了一种新的思路和研究方法。  相似文献   

内蒙古四子王旗早白垩世钾玄岩的地球化学特征及其形成构造环境   总被引：2，自引：0，他引：2  

李毅吴泰然  罗红玲赵磊 《岩石学报》2006,22(11):2791-2800

内蒙古四子王旗地区发现有一套早白垩世钾玄岩。主量元素、微量元素、稀土元素以及 Sr-Nd 同位素测试结果表明,岩石以低硅(SiO_2含量为48.11%～52.77%)、高钛(TiO_2含量为1.94%～2.77%,平均2.48%)、高钾高碱(K_2O Na_2O 为5.32%～7.02%、K_2O/Na_2O 比值为0.48～1.10)为特征,属于钾玄岩系列。它们富集大离子亲石元素、轻稀土元素,亏损高场强元素,具有微弱的 Eu 负异常(δEu=0.81～0.98),其地球化学特征总体与洋岛玄武岩(OIB)相似。Rb/Nb、Ba/Nb、La/Nb、K/Nb 和 Zr/Nb 比值主要落在 EM I OIB 范围内。~(87)Sr/~(86)Sr 和~(143)Nd/~(144)Nd 比值分别变化在0.7063～0.7077和0.51196～0.51243之间,岩石的 Nd、Sr 同位素组成接近 EM I 地幔端元。随着ε_(Nd)的减小,P_2O_5、Rh、Sr、Ba 和 Zr 逐渐富集,表明四子王旗钾玄岩没有经历明显的地壳物质混染。利用微量元素地球化学原理,推断四子王旗钾玄岩母岩浆源于含金云母地幔橄榄岩减压低度部分熔融。根据其地球化学特征可以认为,四子王旗钾玄岩是华北板块早白垩世岩石圈减薄事件的产物。  相似文献   

The Effects of Small Amounts of H2O, CO2 and Na2O on the Partial Melting of Spinel Lherzolite in the System CaO-MgO-Al2O3-SiO2 {+/-} H2O {+/-} CO2 {+/-} Na2O at 1{middle dot}1 GPa     

LIU  XI; O'NEILL  HUGH ST. C.; BERRY  ANDREW J. 《Journal of Petrology》2006,47(2):409-434

The effects of small amounts of H₂O (<4 wt % in the melt)on the multiply saturated partial melting of spinel lherzolitein the system CaO–MgO–Al₂O₃–SiO₂ ±Na₂O ± CO₂ have been determined at 1·1 GPa inthe piston-cylinder apparatus. Electron microprobe analysisand Fourier transform infrared spectroscopy were used to analysethe experimental products. The effects of H₂O are to decreasethe melting temperature by 45°C per wt % H₂O in the melt,to increase the Al₂O₃ of the melts, decrease MgO and CaO, andleave SiO₂ approximately constant, with melts changing fromolivine- to quartz-normative. The effects of CO₂ are insignificantat zero H₂O, but become noticeable as H₂O increases, tendingto counteract the H₂O. The interaction between H₂O and CO₂ causesthe solubility of CO₂ at vapour saturation to increase withincreasing H₂O, for small amounts of H₂O. Neglect of the influenceof CO₂ in some previous studies on the hydrous partial meltingof natural peridotite may explain apparent inconsistencies betweenthe results. The effect of small amounts of H₂O on multiplysaturated melt compositions at 1·1 GPa is similar tothat of K₂O, i.e. increasing H₂O or K₂O leads to quartz-normativecompositions, but increasing Na₂O produces an almost oppositetrend, towards nepheline-normative compositions. KEY WORDS: H₂O; CO₂; FTIR; hydrous partial melting; mantle melting; spinel lherzolite; system CaO–MgO–Al₂O₃–SiO₂ ± H₂O ± CO₂ ± Na₂O  相似文献   

Petrogenesis of Tertiary Mafic Alkaline Magmas in the Hocheifel, Germany   总被引：5，自引：0，他引：5  

JUNG  CAROLINE; JUNG  STEFAN; HOFFER  EDGAR; BERNDT  JASPER 《Journal of Petrology》2006,47(8):1637-1671

Primitive nephelinites and basanites from the Tertiary Hocheifelarea of Germany (part of the Central European Volcanic Province;CEVP) have high Mg-number (>0·64), high Cr and Nicontents and strong light rare earth element enrichment butsystematic depletion in Rb, K and Ba relative to trace elementsof similar compatibility in anhydrous mantle. Alkali basaltsand more differentiated magmatic rocks have lower Mg-numberand lower abundances of Ni and Cr, and have undergone fractionationof mainly olivine, clinopyroxene, Fe–Ti oxide, amphiboleand plagioclase. Some nephelinites and basanites approach theSr–Nd–Pb isotope compositions inferred for the EAR(European Asthenospheric Reservoir) component. The Nd–Sr–Pbisotope composition of the differentiated rocks indicates thatassimilation of lower crustal material has modified the compositionof the primary mantle-derived magmas. Rare earth element meltingmodels can explain the petrogenesis of the most primitive maficmagmatic rocks in terms of mixing of melt fractions from anamphibole-bearing garnet peridotite source with melt fractionsfrom an amphibole-bearing spinel peridotite source, both sourcescontaining residual amphibole. It is inferred that amphibolewas precipitated in the asthenospheric mantle beneath the Hocheifel,close to the garnet peridotite–spinel peridotite boundary,by metasomatic fluids or melts from a rising mantle diapir orplume. Melt generation with amphibole present suggests relativelylow mantle potential temperatures (<1200°C); thus themantle plume is not thermally anomalous. A comparison of recentlypublished Ar/Ar ages for Hocheifel basanites with the geochemicaland isotopic composition of samples from this study collectedat the same sample sites indicates that eruption of earlierlavas with an EM signature was followed by the eruption of laterlavas derived from a source with EAR or HIMU characteristics,suggesting a contribution from the advancing plume. Thus, theHocheifel area represents an analogue for magmatism during continentalrift initiation, during which interaction of a mantle plumewith the overlying lithosphere may have led to the generationof partial melts from both the lower lithosphere and the asthenosphere. KEY WORDS: alkali basalts; continental volcanism; crustal contamination; partial melting; Eifel, Germany  相似文献   

浙江建德新生代玄武岩源区特征及其成因     

何叶  陈立辉  曾罡  王小均 《高校地质学报》2020,26(3):241-254

中国东南部浙江境内分布有大量新生代板内玄武岩，这些玄武岩的分布受到三条北东—南西向的断裂控制，将浙江玄武岩分为西部、中部、东部三个区域。其中，出露于浙江西部江山-绍兴断裂带的建德玄武岩是浙江境内最古老的新生代玄武岩（约40 Ma）。为进一步认识浙江境内新生代岩浆作用的本质，测定了建德玄武岩的元素组成和Sr、Nd、Hf、Pb同位素组成，并在与浙江境内其它新生代玄武岩对比的基础上，探讨它们之间的成因联系。建德玄武岩为碧玄岩，与浙江西部其它新生代玄武岩一样，碱性程度明显高于浙江中部和东部的新生代玄武岩（以弱碱性的碱性橄榄玄武岩和拉斑玄武岩为主）。这些玄武岩具有较低的SiO₂ (41.3~42.3 wt%）和Al₂O₃（9.70~12.6 wt%）含量，较高的MgO（8.90~15.6 wt%）、CaO（8.92~12.1 wt%）、TiO₂（2.78~3.18 wt%）和Fe₂O₃^T（14.1~16.2 wt%）含量以及较高的Ca/Al（1.02~1.16）比值。不相容微量元素组成上与火成碳酸岩具有亲缘性，即蛛网图上表现为明显的K、Zr、Hf、Ti的负异常（Hf/Hf*=0.74~0.77, Ti/Ti*=0.70~0.74），同时具有高的Zr/Hf比值（48.5~50.1），表明其地幔源区含有碳酸盐组分。建德玄武岩具有亏损的Sr-Nd-Hf同位素组成（⁸⁷Sr/⁸⁶Sr=0.7032~0.7034, εNd=5.85~5.95, εHf=7.78~8.56）和较高的²⁰⁶Pb/²⁰⁴Pb（18.491~18.554）、²⁰⁷Pb/²⁰⁴Pb（15.488~15.518）和²⁰⁸Pb/²⁰⁴Pb（38.387~38.523）比值。相比浙江中部和东部玄武岩，浙江西部玄武岩及建德玄武岩具有更高的碱含量、不相容微量元素含量、La/Yb比值和更明显的K、Zr、Hf、Ti负异常，表明浙江西部玄武岩是碳酸盐化地幔低程度熔融的产物。浙江新生代玄武岩的Ti/Ti*与Ba/Th、K/La比值之间较好的正相关性表明其源区存在两端元混合的特征。其中，以浙江西部玄武岩（包括建德玄武岩）为代表的地幔端元是由含碳酸盐的再循环洋壳熔融产生的碳酸盐熔体与亏损地幔反应形成的碳酸盐化地幔，以较低的Ba/Th、K/La和Ti/Ti*比值为特征。以浙江东部玄武岩为代表的地幔端元具有和碳酸盐化地幔端元互补的、较高的Ba/Th、K/La和Ti/Ti*比值，代表熔融残余的再循环洋壳。因此，浙江新生代玄武岩的地幔源区是不均一的，这种不均一性主要是由具有成因联系的两种端元组分所控制。  相似文献   

风电场风机覆冰期预报方法     

许杨  陈正洪 《气象科技》2021,49(6):923-929

采用Makkonen结冰增长模型镶嵌冰表面辐射融化模型建立适用于风机覆冰的预报模型，基于WRF耦合CALMET综合模式预测结果和风机性能参数驱动模型，进行风机覆冰开始和结束时间的预报。以湖北通山九宫山风电场为研究对象，对2012年12月至2013年12月期间监测到19次风机覆冰进行分析，分别采用提前1 d、提前2 d、提前3 d三种预报方案开展覆冰起止时间的预报，发现该模型对风机覆冰具有一定的提前预警能力，且越临近覆冰发生时间，预报准确性越高。  相似文献