Application of the QUILF thermobarometer to the peralkaline trachytes and pantellerites of the Eburru volcanic complex, East African Rift, Kenya   总被引：1，自引：0，他引：1  

Minghua Ren  Peter A. Omenda  Elizabeth Y. Anthony  John C. White  Ray Macdonald  D.K. Bailey   《Lithos》2006,91(1-4):109-124

The Quaternary Eburru volcanic complex in the south-central Kenya Rift consists of pantelleritic trachytes and pantellerites. The phenocryst assemblage in the trachytes is sanidine + fayalite + ferrohedenbergite + aenigmatite ± quartz ± ilmenite ± magnetite ± pyrrhotite ± pyrite. In the pantellerites, the assemblage is sanidine + quartz + ferrohedenbergite + fayalite + aenigmatite + ferrorichterite + pyrrhotite ± apatite, although fayalite, ferrohedenbergite and ilmenite are absent from more evolved rocks (e.g. with SiO₂ > 71%). QUILF temperature calculations for the trachytes range from 709 to 793 °C and for the pantellerites 668–708 °C, the latter temperatures being among the lowest recorded for peralkaline silicic magmas. The QUILF thermobarometer demonstrates that the Eburru magmas crystallized at relatively low oxidation states (ΔFMQ + 0.5 to − 1.6) for both trachytes and pantellerites. The trachytes and pantellerites evolved along separate liquid lines of descent, the trachytes possibly deriving from a more mafic parent by fractional crystallization and the pantellerites from extreme fractionation of comenditic magmas.  相似文献   

Planation, bauxites and epeirogeny: One or two paleosurfaces on the West African margin?   总被引：3，自引：0，他引：3  

Dominique Chardon  Violaine Chevillotte  Anicet Beauvais  Georges Grandin  Bruno Boulang 《Geomorphology》2006,82(3-4):273-282

Mapping of lateritic bauxites over the West African rifted margin and analysis of the geomorphic properties of these bauxites, combined with available geological data lead to a discussion of the presence of either two Meso-Cenozoic planation surfaces or a single Eocene surface to account for the morphotectonic and paleoclimatic evolution of the Guinean landforms. At large scale, two stepped bauxitic levels are documented. Ongoing or episodic uplift following Gondwana breakup and Meso-Cenozoic climate change are proposed to have allowed the formation and abandonment of an Early mid-Cretaceous surface today preserved as the higher bauxitic level, and the setting of an Eocene planation surface bearing a second generation of bauxites, making the lower bauxitic level. The single Eocene surface hypothesis requires that Paleogene bauxitization preserved large pre-existing relief to explain two stepped bauxitic levels of the same age. The two-surface hypothesis is favored because it would explain rebauxitization of alluvial pebbles of bauxites under the lower lateritic level.  相似文献   

Modification of streaming potential by precipitation of calcite in a sand–water system: laboratory measurements in the pH range from 4 to 12     

Xavier Guichet  Laurence Jouniaux  Nicole Catel 《Geophysical Journal International》2006,166(1):445-460

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Crustal structure across the Grand Banks–Newfoundland Basin Continental Margin – II. Results from a seismic reflection profile     

K. W. Helen Lau  Keith E. Louden  Sharon Deemer  Jeremy Hall  John R. Hopper  Brian E. Tucholke  W. Steven Holbrook  Hans Christian Larsen † 《Geophysical Journal International》2006,167(1):157-170

New multichannel seismic reflection data were collected over a 565 km transect covering the non-volcanic rifted margin of the central eastern Grand Banks and the Newfoundland Basin in the northwestern Atlantic. Three major crustal zones are interpreted from west to east over the seaward 350 km of the profile: (1) continental crust; (2) transitional basement and (3) oceanic crust. Continental crust thins over a wide zone (∼160 km) by forming a large rift basin (Carson Basin) and seaward fault block, together with a series of smaller fault blocks eastwards beneath the Salar and Newfoundland basins. Analysis of selected previous reflection profiles (Lithoprobe 85-4, 85-2 and Conrad NB-1) indicates that prominent landward-dipping reflections observed under the continental slope are a regional phenomenon. They define the landward edge of a deep serpentinized mantle layer, which underlies both extended continental crust and transitional basement. The 80-km-wide transitional basement is defined landwards by a basement high that may consist of serpentinized peridotite and seawards by a pair of basement highs of unknown crustal origin. Flat and unreflective transitional basement most likely is exhumed, serpentinized mantle, although our results do not exclude the possibility of anomalously thinned oceanic crust. A Moho reflection below interpreted oceanic crust is first observed landwards of magnetic anomaly M4, 230 km from the shelf break. Extrapolation of ages from chron M0 to the edge of interpreted oceanic crust suggests that the onset of seafloor spreading was ∼138 Ma (Valanginian) in the south (southern Newfoundland Basin) to ∼125 Ma (Barremian–Aptian boundary) in the north (Flemish Cap), comparable to those proposed for the conjugate margins.  相似文献   

S-wave velocity structure, mantle xenoliths and the upper mantle beneath the Kaapvaal craton   总被引：1，自引：0，他引：1  

Angela Marie Larson  J. Arthur Snoke  David E. James 《Geophysical Journal International》2006,167(1):171-186

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Shear wave splitting changes associated with the 2001 volcanic eruption on Mt Etna     

Francesca Bianco  Luciano Scarf&#;  Edoardo Del Pezzo  Domenico Patanè 《Geophysical Journal International》2006,167(2):959-967

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Geodynamic significance of granitoid magmatism in the southeast Anatolian orogen: geochemical and geochronogical evidence from Göksun–Afşin (Kahramanmaraş, Turkey) region     

Osman Parlak 《International Journal of Earth Sciences》2006,95(4):609-627

In southeast Anatolia, there are number of tectonomagmatic units in the Kahramanmaraş–Malatya–Elazığ region that are important in understanding the geological evolution of the southeast Anatolian orogenic belt during the Late Cretaceous. These are (a) metamorphic massifs, (b) ophiolites, (c) ophiolite-related metamorphics and (d) granitoids. The granitoids (i.e. Göksun–Afşin in Kahramanmaraş, Doğanşehir in Malatya and Baskil in Elazığ) intrude all the former units in a NE–SW trending direction. The granitoid in Göksun–Afşin (Kahramanmaraş) region is mainly composed of granodioritic and granitic in composition. The granodiorite contains a number of amphibole-bearing mafic microgranular enclaves of different sizes, whereas the granite is intruded by numerous aplitic dikes. The granitoid rocks have typical calcalkaline geochemical features. The REE- and Ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, as well as biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The K–Ar geochronology of the granitoid rocks yielded ages ranging from 85.76±3.17 to 77.49±1.91 Ma. The field, geochemical and geochronological data suggest the following Late Cretaceous tectonomagmatic scenario for southeast Anatolia. The ophiolites were formed in a suprasubduction zone tectonic setting whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or late-thrusting (∼90 Ma). These units were then overthrust by the Malatya–Keban platform during the progressive elimination of the southern Neotethys. Thrusting of the Malatya–Keban platform over the ophiolites and related metamorphic rocks was followed by the intrusion of the granitoids (88–85 Ma) along the Tauride active continental margin in the southern Neotethys.  相似文献   

A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt     

沈上越冯庆来  魏启荣张志斌 张虎 《中国地球化学学报》2006,25(3):216-222

1IntroductionThe northern segment of the South LancangjiangBelt refers to the terrain about200km east of theYunxian-Lingcang granite in the South LancangjiangBelt(Fig.1).During the seventh Five-Year Plan peri-od,Mo Xuanxue et al.(1993)undertook the resear…  相似文献   

延边地区中生代火山岩的岩浆源区:来自Sr-Nd同位素和深源捕虏体(晶)的证据   总被引：6，自引：0，他引：6  

赵全国  许文良  靳克  裴福萍 《吉林大学学报(地球科学版)》2005,35(4):416-422

延边地区中侏罗世和早白垩世火山岩中包含有较多的辉石岩捕虏体和角闪石捕虏晶,前者为普通辉石变种,其化学成分类似于中国东部新生代玄武岩中单斜辉石巨晶的成分,具有岩浆堆积成因特征;后者为韭闪石和镁质绿钠闪石变种,其成分类似于中生代晚期玄武岩中角闪二辉石岩包体里的角闪石和新生代玄武岩中的角闪石巨晶.矿物温压计算结果显示,它们形成深度介于25～37km.延边地区中生代火山岩的(87Sr/86Sr)i值介于0.704 3～0.705 0,εNd(t)值介于2.33～4.71,表明岩浆源区应是一套具有亏损性质的新增生的地幔物质.综合上述结果,可以判定延边地区中生代火山岩的原始岩浆应来源于新增生的壳幔过渡带物质的部分熔融,地壳增生事件的时间为新元古代.  相似文献   

大别山造山带前陆深地震反射剖面   总被引：18，自引：0，他引：18       下载免费PDF全文

董树文 高锐李秋生  刘晓春钱桂华黄东定  匡朝阳李三忠管烨  白金贺日政  李朋武 《地质学报》2005,79(5):595-601

在大别山南部和扬子地块前陆实施的深地震反射剖面(140 km)揭示出大别山造山带前陆地壳的精细结构。总体北倾的地壳内部结构与向北缓倾的叠瓦状莫霍面反射揭示出扬子陆块向北俯冲的行迹。莫霍面向北插入大别山造山带下与南大别山地壳内南倾反射震相叠置,构成交叉反射图像,刻画出扬子前陆与大别山造山带的碰撞构造面貌。  相似文献