Quenched mafic inclusions in ≤2200 years B.P. deposits at Augustine Volcano,Alaska     

《International Geology Review》2012,54(11):1241-1270

Origins and positions of gold fields and ores, particularly of placers, in the Yana-Kolyma area and elsewhere in the Northeast, as indicated by the morphostructural analysis and the behavior of gold in endogenic and exogenic processes. – V.P. Sokoloff.  相似文献   

Nature and origin of Mesozoic granitoids and associated mineralization in the Sanjiang Tethys Orogeny,SW China: the Xiuwacu complex example     

《International Geology Review》2012,54(7):795-820

ABSTRACT

The magmatic generation for the Late Triassic–Early Jurassic (~215–200 Ma) and Early Cretaceous–Late Cretaceous (~108–79 Ma) post-collisional granites in the Sanjiang Tethys orogeny remain enigmatic. The Xiuwacu complex, located in the southern Yidun Terrane, consists of biotite granite with a weight mean ²⁰⁶Pb/²³⁸U age of 199.8 ± 2.5 Ma, aplite granite of 108.2 ± 2.3 Ma, monzogranite porphyry of 80.8 ± 1.0 Ma, and diorite enclaves of 79.2 ± 0.9 Ma and 77.9 ± 0.8 Ma. The Late Triassic biotite granites show I-type granite affinities, with high SiO₂ contents, high Mg^# values, high zircon δ¹⁸O values, and negative whole-rock ?Nd(t) values, indicating a predominant ancient crustal source with the input of juvenile materials. Their fractionated REE patterns and concave-upward middle-to-heavy REE patterns require garnet-bearing amphibolite as the melt source. The Cretaceous highly fractionated aplite granites and monzogranite porphyries have relatively high SiO₂ contents, high (Na₂O + K₂O)/CaO ratios, high zircon δ¹⁸O values, and enriched whole-rock Sr–Nd isotopic signatures, suggesting that their parent magmas were likely originated from the ancient middle- to lower crust. Their significant negative Eu anomalies and obvious depletions in Nb, Sr, and Ti demonstrate that the Cretaceous granitic magmas had experienced more fractionation than the Late Triassic felsic magmas. The Late Cretaceous diorite enclaves show low SiO₂ contents, high Mg^# values, and high zircon δ¹⁸O values, suggesting that they were probably derived from the partial melting of subcontinental lithospheric mantle enriched by the Late Triassic subduction. The Late Triassic–Early Jurassic and Early Cretaceous–Late Cretaceous magmatism witnessed the post-collisional setting and intraplate extensional setting in response to the slab break-off and lithospheric-scale transtensional faulting, respectively. The partial melting of subduction-modified lithospheric mantle or/and residual sulphide cumulates within the lower crust during the origination of Late Cretaceous magmas could have provided metals for the formation of Xiuwacu deposit.  相似文献   

Evidence of Magma Mixing in the 'Daly Gap' of Alkaline Suites: a Case Study from the Enclaves of Pantelleria (Italy)   总被引：4，自引：0，他引：4  

FERLA  PAOLO; MELI  CARMELINA 《Journal of Petrology》2006,47(8):1467-1507

The island of Pantelleria consists of trachytes, pantelleritesand minor mildly alkaline basalts. Rocks of intermediate composition(falling in the so-called ‘Daly Gap’) such as mugearites,benmoreites and mafic trachytes occur only in the form of enclavesin trachytes and pantellerites inside the main caldera of theisland (Caldera ‘Cinque Denti’), which collapsedduring the ‘Green Tuff’ ignimbrite eruption at 50ka. The enclaves include volcanic, subvolcanic and intrusiverock types. The enclaves in host trachyte contain traces ofglass; devitrified glass occurs within enclaves in host pantellerites.Minerals in the enclaves show regular compositional variationswith whole-rock silica content. Glass present in the medium-grainedsamples is interpreted to be the result of incipient melting.The major and trace element compositions of the enclaves showregular and linear variations between an evolved mafic magma(hawaiite) and a felsic end-member similar to the ‘GreenTuff’ trachyte. Fractional crystallization modelling ofcompatible and incompatible trace elements (V, Ni, Zr, La, Sm,Lu, Nb, Y, Th) does not reproduce the observed trends. Rocksof intermediate composition within the ‘Daly Gap’can be explained only by magma mixing between an already differentiatedmafic magma (hawaiite) and an anorthoclase-rich trachytic meltin the lower and higher parts, respectively, of a stratifiedmagmatic chamber. Medium-grained enclaves are interpreted asthe result of fragmentation of solidified mixing layers in theroof of the magma chamber during the eruption of the ‘GreenTuff’, when the collapse of the caldera took place. Diffusioncalculations suggest a residence time of <5 days for theenclaves in their host magmas. KEY WORDS: Daly Gap; enclaves; magma mixing; Pantelleria  相似文献   

民国时期川黔交界地区插花地清理拨正研究     

杨斌 《地理研究》2011,30(10):1921-1929

民国29～35年（1940～1946年）,国民政府对川黔交界地区的插花地进行了清理拨正。清理拨正可大别为两个阶段：一是川黔两省自行清理拨正（1940～1944年）,二是内政部主持下的清理拨正（1945～1946年）。清理拨正成效较为明显,不仅进行了实地会勘,而且形成了会议决议,川黔交界地区8县17乡镇的33个插花地问题...  相似文献   

MAIN STREET TRANSFORMED: COMMUNITY SENSE OF PLACE FOR NONMETROPOLITAN TOURISM BUSINESS DISTRICTS     

《Urban geography》2013,34(7):609-639

This case study applies the segment approach to investigate community sense of place for a small-town tourism business district (TBD). A stratified random sample of residents from Galena, Illinois (population 3,647), is analyzed to identify personal values and behaviors most closely associated with sense of place for downtown. Despite Galena's extreme orientation to tourism, natives and middle-class newcomers generally were found to be equally, and highly, involved with their TBD. Consequently, respondents claimed sentiments of "at-homeness" (or sense of place) for downtown regardless of their duration of residence. However, natives and newcomers collectively valued downtown for different reasons. One implication is that sense of place for downtown can translate into local agency-based projects and interest groups that promote or oppose the transformation of place. In turn, community cohesiveness can be threatened through the process of transforming a historic downtown into a TBD. [Key words: tourism business district (TBD), sense of place, downtown redevelopment, main street, small town.]  相似文献   

Enclaves and ethnic ties: The local impacts of Singaporean cross‐border tourism in Malaysia and Indonesia     

Mark P. Hampton 《Singapore journal of tropical geography》2010,31(2):239-253

Cross‐border tourism is often proposed by governments as an incentive for economic growth, but critics have suggested that its impacts are, in fact, overplayed. This paper presents research in the Indonesia‐Malaysia‐Singapore Growth Triangle (IMS‐GT). It examines the broad economic impacts of Singaporean cross‐border tourism on local host communities in two locations: Kukup, a traditional Malaysian fishing village in Johor, southern Peninsular Malaysia, and Bintan in Riau Islands Province in western Indonesia. The study found that cross‐border tourism generated income, employment and some local economic linkages. In Kukup clear economic benefits with increased income and employment were unevenly distributed between ethnic groups. The Bintan enclave development had some linkages to the island economy but was reliant on immigrant labour. Cross‐border ethnic ties, particularly Chinese, also played an important role in the growth of tourism in the IMS‐GT. The paper shows that cross‐border tourism can be a useful addition to more conventional forms of international tourism within national tourism planning and could lead to significant economic benefits for local communities.  相似文献   

The You Yangs batholith in Southeastern Australia,the sources of its magmas and inferences for local crustal architecture     

J. D. Clemens 《Australian Journal of Earth Sciences》2019,66(2):247-264

The 365-Ma You Yangs batholith is a mainly I-type monzogranitic body, containing rocks with both clinopyroxene and hornblende, but with a 2–2.5?km-wide rim of S-type rocks. In places, the margins of the intrusion wedge out laterally. A laccolithic shape may explain there being only low-grade contact metamorphism of the Ordovician metasedimentary wall rocks. The chemical and isotopic characteristics of the granitic rocks suggest that the magmas formed by partial melting of a source that contained some meta-igneous rocks but was dominated by chemically immature metasedimentary types, to impart an evolved Sr isotope signature (⁸⁷Sr/⁸⁶Sr_t?=?0.70877–0.71066 for the main monzogranitic rocks), combined with relatively non-radiogenic εNd_t (–2.4 to –1.9). Crystal fractionation played little role in shaping the compositions of the granitic magmas, with the main variations interpreted to be source-inherited. Igneous-textured microgranular enclaves (IMEs) are prominent in the monzogranitic rocks. The IMEs probably had an ultimate enriched-mantle source, and their magmas did not mix significantly with the crustally derived granitic host magmas. The characteristics of the monzogranitic rocks hosting the enclaves suggest the possibility that an unrecognised metasediment-dominated terrane of ancient arc crust may be present beneath the Bendigo Zone.  相似文献   

西藏中拉萨地块西段左左乡晚侏罗世-早白垩世花岗岩年代学、地球化学与岩石成因     

齐宁远  赵志丹  唐演  闫晶晶  石卿尚  刘栋  朱弟成  SHEIKH Lawangin 《岩石学报》2019,35(2):405-422

近年来对青藏高原中拉萨地块西部中生代岩浆作用的源区、成因和演化等问题的研究较少。本文针对中拉萨地块西部噶尔县左左乡两个中酸性岩体进行了岩石学、锆石U-Pb年代学、微量元素和锆石Hf同位素,以及主量元素和微量元素地球化学研究。左左乡北侧岩体寄主花岗闪长岩和闪长质包体获得同期(163Ma和160Ma)的年龄,属于晚侏罗世;南侧岩体花岗岩年龄为142～147Ma,属于早白垩世。北侧与南侧的中酸性岩石均属于准铝质-弱过铝质高钾钙碱性I型花岗岩,富集大离子亲石元素和轻稀土元素,亏损高场强元素。晚侏罗世岩体寄主岩具有较为富集的锆石Hf同位素成分(ε_(Hf)(t)=-16.8～-13.6),可能来源于古老下地壳的部分熔融;包体具有相似的Hf同位素成分(ε_(Hf)(t)=-15.7～-13.6),结合晚侏罗世寄主岩与包体较高的MgO(4.13%～6.90%)、Cr(146×10~(-6)～370×10~(-6))和Ni(31×10~(-6)～113×10~(-6))含量,说明包体代表的中基性岩浆可能源于古老富集地幔的熔融,并且在晚侏罗世寄主花岗闪长岩与闪长质包体所代表的两种岩浆间发生过充分的岩浆混合作用。南侧早白垩世花岗岩具有较负且变化范围大的ε_(Hf)(t)值(-8.2～-4.8和-3.8～+0.2),指示早白垩世岩浆活动中有更多亏损地幔物质或新生地壳物质的加入,并且亏损地幔物质或新生地壳物质与拉萨地块古老地壳物质熔融形成的酸性岩浆发生了岩浆混合,经历岩浆混合后中酸性岩浆又发生了角闪石、长石的分离结晶,最终形成南侧早白垩世岩体的一系列中酸性岩石。研究区早白垩世亏损地幔物质或新生地壳物质的增多可能与南向俯冲的班公湖-怒江板片的回转有关。  相似文献   

西藏甲玛铜多金属矿床暗色包体岩石成因:对岩浆混合和成矿的启示   总被引：1，自引：1，他引：0  

张泽斌  唐菊兴  唐攀  陈国良  张忠坤  高昕  杨阳 《岩石学报》2019,35(3):934-952

岩浆混合作用的研究对揭示壳幔相互作用,探讨成岩成矿过程具有重要意义。甲玛矿区位于冈底斯成矿带东段,为超大型斑岩-矽卡岩型铜多金属矿床,矿区内的中酸性岩浆岩中普遍发育暗色包体,对其中的暗色包体中的闪长质包体开展详细的岩相学、岩石地球化学、Hf同位素地球化学及U-Pb同位素地质年代学等方面研究以期查明岩石成因,为岩浆混合作用和成矿作出启示,完善甲玛成岩成矿模型。岩相学观察表明,闪长质包体及寄主岩浆岩中存在多种反映岩浆混合作用的典型组构,如长石-石英熔蚀结构、石英镶边结构、长石交代筛状结构、长石反环带结构、磷灰石针柱状结构等,锆石LA-ICP-MS UPb同位素定年结果显示,包体形成时代(15. 3±0. 3Ma)与中酸性寄主岩石在误差范围内一致,也符合了岩浆混合作用的存在。闪长质包体化学成分上类似高Mg埃达克岩(MgO=3. 53%～6. 62%,Sr/Y=20～57,(La/Yb)N=51～64),具有低SiO_2(52. 44%～59. 45%),高K_2O(3. 19%～5. 62%),高相容元素(Ni=86×10~(-6)～146×10~(-6); Cr=102×10~(-6)～228×10~(-6))的特征,∑REE高于中酸性寄主岩浆岩,且轻重稀土分异明显((LREE/HREE)N=21～23),富集LILE(Rb=189×10~(-6)～284×10~(-6),Sr=498×10~(-6)～658×10~(-6),Ba=1247×10~(-6)～1378×10~(-6)),相对亏损HFSE(Nb、Ta、Ti),在稀土元素配分图及微量元素蛛网图中闪长质包体介于冈底斯带碰撞后时期的超钾镁铁质岩(来源于富集的岩石圈地幔)与甲玛中酸性寄主岩浆岩(主要来源于加厚新生下地壳)之间,Hf同位素(ε_(Hf)(t)=-0. 9～4. 6)同样也介于超钾镁铁质岩与花岗闪长斑岩(代表中酸性寄主岩浆)之间。这些特征说明闪长质包体是富集的岩石圈地幔部分熔融形成的镁铁质岩浆与加厚新生下地壳部分熔融形成的中酸性岩浆发生混合的产物,同时指示了东冈底斯带中新世时期也存在岩石圈地幔伸展对流减薄事件,以及证实了南拉萨地体广泛分布的高钾埃达克质岩在形成过程中,伴随着与富集岩石圈地幔来源的超钾镁铁质岩浆发生不同程度混合。此外,富集的岩石圈地幔部分熔融形成的镁铁质岩浆的混入,将会为中酸性岩浆系统加入大量的水和金属物质,这也是控制甲玛超大型斑岩-矽卡岩型矿床形成的关键因素。  相似文献   

The Formation of Yanshanian Granitic Magma in Dabie Mountains: Dehydration or Aquifer Melting -with Tiantangzhai and Jiuzihe Granites as Examples     

WANG Qiang  ZHAO Zhenhua  QIU Jiaxiang  WANG Renjing  XU Jifeng Guangzhou Institute of Geochemistry  Chinese Academy of Sciences  Guangzhou P.R.C  China University of Geosciences  Wuhan  P.R.C 《Continental Dynamics》2001,(2)

l. IntroductionFluid, especially water is very important to thefOrmation of I--type and S-type granitic magmas,evel1 under high temperature (for example, l000 "C).Some researches suggest that dehydration melting ofhydrous minerals (muscovite, biotite and amphiboIe)under high temperature is the main mechanism ofdeep crustal anatexis (Clemens et al., l987, Skierlie,l993, WoIf et al., l995, Johannes, l996), and themain modeIs of the formation of granitic magmas inthe orogenic belt. Howevef, t…  相似文献