羌塘赤布张错地区新生代火山岩研究

根据K-Ar同位素年代学研究成果,将赤布张错新生代火山活动划分为3期:第Ⅰ期(40.1~35.1Ma)火山喷发较弱,形成小范围分布的细粒安粗岩和斑状粗面岩;第Ⅱ期(26.5~17.6Ma)火山喷溢最为强烈,形成大面积厚层黑色气孔状安粗岩;第Ⅲ期(5.5~4.61Ma)由潜火山作用形成球粒状、斑状粗面岩岩丘。新生代火山岩系包括高钾钙碱性系列和钾玄岩系列,高钾钙碱性火山岩形成于始新世,属于壳源岩浆系列;钾玄岩系火山岩形成于中新世-上新世,属于幔源岩浆系列。由老到新,岩石系列由高钾钙碱性系列→钾玄岩系列演化,岩性由安粗岩→粗面岩演化。     

Strontium isotopes in Cenozoic volcanic rocks from southeastern Papua New Guinea

Strontium isotope data are presented from 28 rock samples representing four distinct episodes of late Cenozoic volcanism in southeastern Papua. Eocene tholeiitic basalts have initial ⁸⁷Sr/⁸⁶Sr ratios (0.7037) which are higher than those in chemically comparable basalts and are thought to have been enhanced by rock-sea water interaction. Late Cenozoic are trench type volcanoes in the Papuan islands have initial ⁸⁷Sr/⁸⁶Sr ratios which show little variation (0.7041±2) in contrast to those from the contiguous Papua New Guinea mainland (0.7036-0.7054). This isotopic discontinuity does not appear to be due to contamination by immediately underlying sialic metamorphics. High-K trachytes in the Lusancay Islands north of the late Cenozoic are have comparable initial ⁸⁷Sr/⁸⁶Sr ratios. Wide variation (0.703-0.710) in the initial ratios measured in a group of apparently closely related rocks ranging in composition from transitional basalt to peralkaline rhyolite cannot be explained by differences in age or by late magmatic fractionation and continue to pose an enigma.     

青藏高原北部新生代火山岩的成因机制

Based on the electron probeanalyses result of the minerals and the bulk rock composition of the Cenozoic volcanicrocks from Yumen and Hoh Xil lithodistricts on the Qinghai-Tibet Plateau, the formingconditions including temperature and pressure of those rocks are studied.According to thethermodynamics calculation result of the mineral-melt equilibrium,the depth of theasthenosphere superface (about 75～130km) for the northern part of the Qinghai-TibetPlateau during Cenozoic era is suggested. Finally, this paper indicates that the Cenozoicvolcanic rocks in the northern part of the Qinghai-Tibet Plateau mainly consist ofshoshonite series.Their forming temperature is 630～1039℃ and forming pressure isbetween 2.3～4.0 GPa and formed in the intracontinental orogenic belt,where the primarymagma was originated from a particular enriched upmantle and accreted crust-mantle belt ordirectly originated from asthenosphere superface by partial melting of pyrolite.     

青藏高原及邻区新生代火山岩Sr-Nd-Pb同位素特征

笔者在综合分析最近十多年来的Sr、Nd、Pb同位素资料基础上,重点研究了青藏高原及邻区新生代火山岩岩浆源区在时空上的变化规律。结果表明:①冈底斯中段火山岩的岩浆源区逐渐从普通地幔向EMⅡ方向演化;西段晚期火山岩源区的演化方向为俯冲带壳幔混合源→造山带上地壳源→下地壳源。②西羌塘岩浆源区主要为不具富集或亏损的幔源物质;囊谦盆地、大理海东火山岩源区较深,为大洋型软流圈地幔+消减组分混合源;藏北羊湖、雄鹰台鲸鱼湖、西昆仑以及北羌塘巴毛穷宗火山岩的岩浆源区为EMⅡ;鱼鳞山超钾质火山岩为经历了大陆地壳物质强烈交代作用的EMⅡ型岩浆源区;西秦岭火山岩源于亏损地幔,腾冲新生代火山岩源区为受到地壳物质交代的EMⅡ。③西羌塘、可可西里、西昆仑和腾冲新生代火山岩具两种演化趋势——鱼鳞山、普鲁、雄鹰台鲸鱼湖岩区和腾冲火山群向EMⅡ方向演化,而泉水沟、黑石北湖、阿什库勒则分别沿0Ma的地幔上地壳混合线方向演化。④青藏高原及邻区新生代火山岩至少存在4种不同的岩浆源区。     

坦桑尼亚伦圭新生代火山岩的地球化学特征及岩石成因

伦圭新生代火山岩位于东非裂谷西支最南端,已有的大量地质与地球化学证据表明伦圭火山岩是典型的碱性双峰式火山岩,其SiO2含量在46％～56％之间出现明显的间断.基性火山岩和酸性火山岩均表现出富集轻稀土元素,轻、重稀土元素强烈分馏,无明显Eu异常的特征.基性岩大离子亲石元素Rb、Ba、Th、U、Sr富集,高场强元素Zr、H...     

青藏高原北部黑石北湖新生代钾质火山岩的成因

昆仑岩带新生代钾质火山活动是青藏高原北缘深部动力学过程的重要记录。有关岩浆源区的性质和岩浆产生的机制一直存在较大的认识分歧。阐述了昆仑岩带黑石北湖钾质火山岩的岩石学和地球化学特征,并与西昆仑康西瓦和泉水沟新生代火山岩进行了成因对比分析。研究表明,昆仑火山岩带玄武质岩石的K2O和Na2O含量变化较大,从钠质过渡到钾质,硅碱图显示玄武质初始岩浆向钾质安粗岩方向演化。黑石北湖火山岩的高场强元素和Sr、Nd同位素组成显示岩浆源区具有EMⅡ的性质。岩石LREE的强烈富集和HREE的强烈分馏指示岩浆来自富集型含石榴子石地幔源区。不相容元素K/Nb、Ba/La等比值具有岛弧火山岩与OIB型玄武岩的过渡特征,指示源区为曾遭受软流圈流（熔）体交代的古俯冲地幔楔。     

青藏高原北部黑石北湖新生代钾质火山岩的成因

昆仑岩带新生代钾质火山活动是青藏高原北缘深部动力学过程的重要记录。有关岩浆源区的性质和岩浆产生的机制一直存在较大的认识分歧。阐述了昆仑岩带黑石北湖钾质火山岩的岩石学和地球化学特征,并与西昆仑康西瓦和泉水沟新生代火山岩进行了成因对比分析。研究表明,昆仑火山岩带玄武质岩石的K2O和Na2O含量变化较大,从钠质过渡到钾质,硅碱图显示玄武质初始岩浆向钾质安粗岩方向演化。黑石北湖火山岩的高场强元素和Sr、Nd同位素组成显示岩浆源区具有EMⅡ的性质。岩石LREE的强烈富集和HREE的强烈分馏指示岩浆来自富集型含石榴子石地幔源区。不相容元素K/Nb、Ba/La等比值具有岛弧火山岩与OIB型玄武岩的过渡特征,指示源区为曾遭受软流圈流（熔）体交代的古俯冲地幔楔。     

Petrography of Cenozoic volcanic rocks of Egypt (UAR)

The detailed petrographical characters of Cenozoic volcanic rocks of Egypt are given. Two pétrographic provinces have been identified: Abu Zaabal-Abu Rawash-Qatrani province and Cairo-Suez-El-Bahnasa-Tahna province. The rocks of the first one are doleritic basalts, while those of the second one are typical basalts. The weathering of the doleritic basalt, as especially observed in quarries, was also studied.

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Zusammenfassung Der detaillierte petrographische Charakter von känozoischen vulkanischen Gesteinen aus Ägypten wird dargestellt. Zwei petrographische Provinzen sind identifiziert worden: die Abu Zaabal-Abu Rawash-Qatrani-Provinz und die Cairo-Suez-El-Bahnasa-Tahna-Provinz. Die Gesteine der ersten sind doleritische Basalte, während die der zweiten typische Basalte sind. Die Verwitterung der doleritischen Basalte, insbesondere in Steinbrüchen beobachtet, wird ebenfalls dargestellt.

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Résumé Le caractère détaillé pétrographique de roches volcaniques cénozoiques d'Egypte est démontré. On a identifié deux provinces pétrographiques: la province Abu Zaabal-Abu Rawash-Qatrani et la province Caire-Suez-El-Bahnasa-Tahna. Les roches de la première sont des basaltes doléritiques, tandis que celles de la deuxième sont des basaltes typiques. L'altération des basaltes doléritiques, en particulier observée dans des carrières, a aussi été étudiée.

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. : Abu Zaabal-Abu Rawash- Qatrani, a -Cairo-Suez-EI Bahnasa-Tana. , — . .

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Dedicated to Professor Dr. A.Rittmann on the occasion of his 75th birthday     

K—Ar Geochronology and Evolution of Cenozoic Volcanic Rocks in Eastrn China

Cenozoic volcanic rocks widespread in eastern China constitute an important part of the circum-Pacific volcanic belt.This paper presents more than 150K-Ar dates and a great deal of petrochemical analysis data from the Cenozoic volcanic rocks distributed in Tengchong,China‘s southeast coast,Shandong,Hebei,Nei Monggol and Northeast China.An integrated study shows that ubiquitous but uneven volcanic activities prevailed from the Eogene to the Holocene,characterized as being multi-eqisodic and multicycled.For example,in the Paleocene(67-58Ma),Eocene(57-37.5Ma),Miocene(22-18,16-19Ma),Pliocene(8-3Ma),and Early Pleistocene-Middle Pleistocene(1.2-0.5Ma) there were upsurges of volcanism,while in the Oligocene there was a repose period.In space,the older Eogene volcanic rocks are distributed within the region or in the central part of the NE-NNE-striking fault depression,while the younger Neogene and Quaternary volcanic rocks are distributed in the eastern and western parts.Petrologically,they belong essentially to tholeiite-series and alkali-series basalts,with alkalinity in the rocks increasing from old to youg.The above regularities are controlled by both global plate movement and regional inherent tectonic pattern.     

Trace Element Geochemistry of Cenozoic Volcanic Rocks in Shandong Province

The Cenozoic volcanic rock of Shandong Province are mainly alkalic and strongly alkalic basaltic rocks.The Contents of major and trace elements including transitional,incompatible and rare-earth elements were determined.The chemical characterisitics of major and trace elements indicate that these basaltic rocks were derived from a mantle source and probably represent a primary magma,I,e.,unmodifiecd partical melts of mantle peridotite in terms of Mg values,correlatione between P2O5 and Ce,Sr,Ni and Rb concentrations,mantle xenoliths,etc.The abundances of trace elements vary systematically from west to east.The compatible transition elements such as Co,Ni,and Cr show a remarkable depletion,whereas the incompatible and rare-earth elements are abundant as viewed from the chondrite-nor-malized patterns.The chemical composition and correlation are consistent with the tectonic setting.According to the batch and fractional partial melting theory,the trace element contents of Shandong volcanic rocks can be calculated from the two-component mixing model.     

泰国Phetchabun盆地Wichian Buri次盆新生界火山岩岩性识别及岩相展布特征

新生界火山岩是泰国Phetchabun盆地Wichian Buri次盆的主要含油气岩系,但因火山岩喷发环境复杂,喷发期次频繁,造成火山岩岩性复杂,识别难度较大,岩相展布不清,这些因素严重制约着油气的进一步勘探和开发。通过岩心、岩石薄片、测井及地震等资料分析,总结了研究区火山岩的岩性特征,并提出相应的识别方法,同时对火山岩的发育期次和岩相展布进行了研究。结果表明:①研究区火山岩类型丰富,从基性岩至酸性岩、熔岩至火山角砾岩都有发育,以偏碱性玄武岩为主; ②自然伽马、密度及光电吸收界面指数测井对火山岩成分变化最为敏感,成像测井可以提供火成岩的结构和构造信息,两者结合可准确地识别火山岩岩性; ③结合测井和地震响应特征,研究区新生界火山岩为3期喷发的产物,可识别出火山通道相、溢流相、爆发相和火山沉积相等岩相类型,并预测其分布规律。研究成果为研究区火山岩的岩性识别提供了有效手段,并明确了岩相展布特征,可为研究区的油气勘探和开发提供一定的依据。     

冈底斯岩浆弧东段沉积岩的早新生代变质作用及构造意义

青藏高原南部冈底斯岩浆弧形成于中生代以来新特提斯洋俯冲和新生代印度与欧亚大陆碰撞过程中。岩浆弧东部出露的中—新生代变质岩是研究大陆地壳组成、生长和再造的理想窗口。本文选择早新生代的变质沉积岩——石榴子石矽线石云母片岩和石榴子石黑云母片麻岩进行了岩石学和锆石U-Pb年代学研究。研究结果表明,石榴子石矽线石云母片岩由石榴子石、黑云母、白云母、斜长石、钾长石、矽线石、石英和金红石组成,峰期变质条件为730～750℃和0.78～0.81GPa。片岩和片麻岩中的锆石由继承的碎屑核和变质边组成,变质边给出的~(206)Pb/~(238) U年龄为51～72Ma,继承碎屑核给出的~(206) Pb/~(238) U(或~(207) Pb/~(206) Pb)年龄在314～3286 Ma之间,并具有340Ma、550Ma、1100～1200Ma、1500～1600Ma和1800Ma年龄峰值,表明这些变质岩的原岩可能形成于晚石炭世。本文研究表明,冈底斯弧东段的古生代沉积岩在早新生代的碰撞造山过程中被埋藏到约25km深的中-下地壳,经历了角闪岩相变质作用和部分熔融,由此导致了岩浆弧中-下地壳组成和同碰撞岩浆岩化学成分的变化。     

Petrogenesis of the Cenozoic volcanic rocks from the northern part of Qinhai-Xizang (Tibet) plateau

Based on electron probe analyses of the minerals and bulk composition of the Cenozoic volcanic rocks from Yumen and Hoh Xil lithodistricts, Qinghai-Xizang plateau, the forming conditions including the temperature and pressure of those rocks are studied in this paper. According to the thermodynamic calculation results of mineral-melt equilibrium, the depth of the asthenosphere superface (about 75 – 130 km) for the northern part of the Qinghai-Xizang plateau during the Cenozoic is suggested. Finally, this paper indicates that the Cenozoic volcanic rocks in the northern part of the Qinghai-Xizang plateau mainly consist of shoshonite series. Their forming temperature is 630 – 1039°C and forming pressure is between 2.3 – 4.0 GPa. The rocks were formed in the intracontinental orogenic belt, of which the primary magma was originated from a particular enrichment upper mantle and accreted crust-mantle belt or directly from asthenospheric superface as a result of partial melting of pyrolite. The project was supported by the National Natural Science Foundation of China (No. 49234080), the Geological Sectional Foundation of MGMR (No. 8506201, 8506207) and the Science Foundation of Northwest University (97NW23).     

Formation of the Late Cenozoic volcanic complexes of the Lesser Caucasus

The paper considers the role of the lithospheric mantle and asthenosphere during the Late Cenozoic collision volcanism of the Lesser Caucasus. The results of petrogeochemical studies show that the products of volcanism of the West Volcanic Zone of Armenia and the calc-alkaline andesite–dacite–rhyodacite complex of the Neogene Kelbadzhar and Karabakh plateaus were formed from an enriched source in a suprasubduction setting. Late Pliocene–Quaternary moderately alkaline and alkaline volcanic rocks of the Lesser Caucasus differ in petrogeochemistry from suprasubduction volcanic rocks. In trace element contents and patterns, they are similar to rocks formed from an enriched mantle source. Comparative analysis of the geological and geophysical data suggests the model of lithospheric slab break-off of the thickened lithosphere as the triggering mechanism for Late Cenozoic magmatism of the Lesser Caucasus.     

Geochemical Characteristics of Cenozoic Basaltic High-K Volcanic Rocks from Maguan Area, Eastern Tibet

The major element, trace element and Nd-Sr isotopic composition of Cenozoic basaltic volcanic rocks from the Maguan area, eastern Tibet, indicates that the volcanic rocks are enriched in alkalis, especially K (K2O up to 3.81%) and depleted in Ti (TiO2 = 1.27%-2.00%). These rocks may be classified as two groups, based on their Mg# numbers: one may represent primary magma (Mg# numbers from 68 to 69), and the other, the evolved magma(Mg# numbers from 49 to 57). Their REE contents are very high (∑REE = 155.06-239.04μg/g). Their REE distribution patterns are of the right-inclined type, characterized by LREE enrichment [(La/Yb)N =12.0-19.2], no Ce anomaly (Ce/Ce*=1.0), and weak negative Eu anomaly (Eu/Eu*=0.9). The rocks are highly enriched in Rb, Sr and Ba (59.5-93.8μg/g, 732-999 μg/g, and 450-632 g/g, respectively), high in U and Th (1.59-2.31μg/g and 4.73-8.16 μg/g, respectively), and high in Nb, Ta, Zr and Hf (70-118 μg/g,3.72-5.93 μg/g, 215-381 μg/g, and 5.47-9.03 μg/g, respectively). In the primitive mantle-normalized incompatible element spidergram, Nb, Ta, Zr, Hf and P show positive anomalies, whereas Ba, Ti and Y show negative anomalies. The 87Sr/86Sr ratios range from 0. 704029 to 0.704761; 143Nd/144Nd from 0. 512769 to 0. 512949; and εNd from 2.6 to 6.1. These geochemical features might suggest that the potential source of the basaltic high-K volcanic rocks in the Maguan area is similar to the OIB-source mantle of Hawaii and Kergeulen volcanic rocks.     

Isotopic evidence for the origin of Cenozoic volcanic rocks in the Pinacate volcanic field, northwestern Mexico

Six volcanic rocks, reconnaissance samples representing most of the temporal and compositional variation in the Pinacate volcanic field of Sonora and Arizona, are characterized for major element and Nd---Sr isotopic compositions. The samples consist of basanite through trachyte of an early shield volcano, and alkali basalts and a tholeiite from later craters and cinder cones. With the exception of the trachyte sample, which has increased ⁸⁷Sr/⁸⁶Sr due to crustal effects, all ⁸⁷Sr/⁸⁶Sr values fall between 0.70312 and 0.70342, while ε_Nd values are all between + 5.0 and + 5.7. Clinopyroxene in a rare spinel-lherzolite nodule derived from the uppermost mantle beneath the field has ⁸⁷Sr/⁸⁶Sr of 0.70320 but ε_Nd of + 8.8, three ε_Nd units higher than the volcanic rocks. Both the volcanic rocks and the nodule record the presence of asthenospheric, rather than enriched lithospheric mantle beneath Pinacate. This is consistent with one or both of (a) proximity of Pinacate to the Gulf of California spreading center and (b) presence of similar asthenospheric mantle signatures in volcanic rocks over a wide contiguous area of the southwestern USA. We consider the comparison to other southwestern USA magma sources as the more relevant alternative, although a definite conclusion is not possible at this stage.     

可可西里湖地区新生代火山岩同位素地球化学特征及火山成因、源区性质讨论

在青藏高原腹地可可西里地区发育一套新生代碱性、高钾钙碱性——钾玄岩火山岩类,由于该时期正是亚洲大陆内部岩石圈发生剧烈变形,青藏高原强烈隆升的重大变革时期,火山岩的形成在这些重大事件中扮演什么角色?很值得探讨。通过对区内火山岩Rb、Sr、Sm、Nd、Pb同位素的研究,在火山岩的岩浆来源、成因等方面获得了大量信息。研究表明:新生代火山岩主要来源于富集 型地幔区,部分为具极高εSr和极低εNd的酸性火山岩,它是与区内钾质熔岩同源的晚期分异产物;碱性火山岩在成因上与板内初始裂谷有关。研究成果为青藏高原特有的"壳-幔混合层"的形成提供了证据。