Geochemistry and petrogenesis of late Ediacaran (605–580 Ma) post-collisional alkaline rocks from the Katherina ring complex,south Sinai,Egypt     

《Journal of Asian Earth Sciences》2014

The Katherina ring complex (KRC) in the central part of south Sinai, Egypt, is a typical ring complex of late Neoproterozoic age (605–580 Ma). It was developed during the final tectono-magmatic stage of the north Arabian–Nubian Shield (ANS) during evolution of the Pan-African crust. The KRC includes Katherina volcanics, subvolcanic bodies, ring dykes and Katherina granitic pluton. The Katherina volcanics represent the earliest stage of the KRC, which was subsequently followed by emplacement of the subvolcanic bodies and ring dykes. The Katherina granitic pluton depicts as the latest evolution stage of the KRC that intruded all the early formed rock units in the concerned area. The Katherina volcanics are essentially composed of rhyolites, ignimbrite, volcanic breccia and tuffs. Mineralogically, the peralkaline rhyolites contain sodic amphiboles and aegirine. The rhyolite whole rock chemistry has acmite-normative character. The subvolcanic bodies of the KRC are represented by peralkaline microgranite and porphyritic quartz syenite. The ring dykes are semicircular in shape and consist mainly of quartz syenite, quartz trachyte and trachybasalt rock types. The Katherina subvolcanic rocks, volcanic rocks as well as the ring dykes are alkaline or/and peralkaline in nature. The alkaline granitic pluton forms the inner core of the KRC, including the high mountainous areas of G. Abbas Pasha, G. Bab, G. Katherina and G. Musa. These mountains are made up of alkaline syenogranite and alkali feldspar granite. The mantle signature recorded in the KRC indicates a juvenile ANS crust partial melting process for the generation of this system. The evolution of the KRC rocks is mainly dominated by crystal fractionation and crustal contamination. Mineral geothermometry points to the high temperature character of the KRC, up to 700–1100 °C.  相似文献   

新疆乌什塔拉地区晚泥盆世火山岩地球化学特征及构造意义     

王鲲鹏  樊双虎  彭小华 《西北地质》2014,(2):23-29

乌什塔拉地区晚泥盆世火山岩产于破城子组中下段,位于南天山造山带中部,主要由一套酸性火山岩和中性火山岩-沉积岩组成;岩性主要为英安斑岩、流纹斑岩及少量安山岩,呈北西向展布。对岩石地球化学研究,表明破城子组火山岩属钙碱性准铝-过铝质系列;富集轻稀土元素,相对亏损重稀土元素,具有弱的Eu(平均为0.68)负异常;大离子亲石元素(K、Rb、Th等)明显富集,高场强元素相对亏损,具有明显的Ba、Nb、Ta、P、Ti负异常,且Th/Ta(9.04~14.37)值较高,Ta/Yb(0.27~0.69)值较低,暗示其具有陆缘岛弧火山岩的特征。87 Sr/86 Sr为0.713 14~0.725 07,比值较高,反映岩浆演化过程中有地壳物质的混染。结合南天山造山带的构造演化特征,认为晚泥盆世破城子组火山岩形成于活动大陆边缘环境。  相似文献   

Geochemical constraints on the genesis of the Pb–Zn deposit of Jalta (northern Tunisia): Implications for timing of mineralization,sources of metals and relationship to the Neogene volcanism     

《Chemie der Erde / Geochemistry》2014,74(4):601-613

The occurrence of Pb–Zn deposits of Jalta district (northern Tunisia) as open space fillings and cements and breccia in the contact zones between Triassic dolostones and Miocene conglomerates along or near major faults provides evidence of the relationship between the mineralization and tectonic processes. Pb isotopes in galena from the deposits yielded average ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.821, 15.676 and 38.837, respectively, implying a well-mixed multi-source upper crustal reservoir of metals. Magmatism and compressional tectonism during the Alpine orogeny favored Pb–Zn mineralization in the Jalta district. The enrichment in Pb, Zn, Cd and Co of the Triassic carbonates and enrichments in Pb, Zn and Cd in Triassic clayey shales is associated with hydrothermal alteration around faults. Alunite in the deposit has δ³⁴S values (−2.5 to −1.5‰ VCDT), which could have been formed at and above the water table in a kind of steam-heated environment, where fluids containing H₂S mixed with fluids containing K and Al. The H₂S could have been produced by TSR of sulfates at high temperature at depth and then leaked upward through deep-seated faults, whereas the K and Al could have been acid-leached from Miocene volcanic rocks.  相似文献   

赣南龙南地区余田群玄武岩SHRIMP锆石U-Pb年龄及其地质意义   总被引：3，自引：2，他引：1  

项媛馨  巫建华 《地质通报》2012,31(5):716-725

江西南部余田群由双峰式火山岩组成,分布在近EW向展布的三南-寻乌断裂带的临江、东坑、白面石、菖蒲等火山盆地之中。SHRIMP锆石U-Pb定年结果显示:东坑盆地余田群最下部玄武岩的年龄为194.4Ma±2.0Ma,菖蒲盆地余田群最上部玄武岩的年龄为191.9Ma±2.2Ma。这2个年龄结果,一方面指示余田群的地质时代属早侏罗世早期,另一方面说明玄武岩和长英质火山岩的年龄一致,且与剖面层序吻合,属典型的双峰式火山岩组合。余田群双峰式火山岩地质时代的厘定,为江西南部早侏罗世早期处于拉张构造环境提供了年代学证据。同时,菖蒲盆地玄武岩中存在2571~2225Ma残留锆石或捕获锆石,为江西南部可能存在新太古代晚期—古元古代的基底提供了旁证。  相似文献   

大别山北缘西段双桥中生代火山岩地球化学及锆石U-Pb同位素年代学   总被引：1，自引：0，他引：1  

杨梅珍  曾键年  任爱琴  陆建培  覃永军  李法岭 《岩石矿物学杂志》2012,31(2):133-144

首次对大别山北缘西段(河南省境内)中生代火山岩进行了锆石原位U-Pb同位素测年。结果表明,罗山县双桥火山岩集中区石英安山岩锆石LA-ICP-MS U/Pb年龄为133.1±1.5 Ma,与大别东段中生代火山岩主体毛坦厂组的时代一致,属早白垩世,稍早于或与大别山区大规模花岗岩岩基侵位时代相同;与长江中下游地区的宁芜和庐枞盆地火山岩喷发时间同步,可能同属中国东部中生代巨量岩浆活动的重要组成部分,与太平洋板块斜向俯冲引起的大陆岩石圈重力不稳而产生的拆沉导致岩石圈强烈减薄深部动力学过程相联系。大别山西段早白垩世火山岩属高钾钙碱性系列粗安岩-英安岩-流纹岩组合。中酸性火山岩显示轻稀土元素富集、重稀土元素强烈亏损、弱或基本无负Eu异常的稀土元素配分模式以及高Sr低Yb特征,反映岩浆部分熔融源区残余有石榴石,说明当时存在加厚的成熟陆壳。高(87Sr/86Sr)i(0.707 56)、极低的εNd(t)(-20.1)和大离子亲石元素富集、高场强元素Nb、Ta明显亏损,显示岩浆源区的壳源性质。以上特征反映大别山地区该时期岩石圈伸展程度和软流圈上涌规模远不如长江中下游同时期以幔源为主的中基性火山岩发育的宁芜和庐枞地区。  相似文献   

Genetic Mechanism of Dolomitization in Fengcheng Formation in the Wu‐Xia area of Junggar Basin,China     

ZHU Shif  ZHU Xiaomin  NIU Huapeng  HAN Xuefang  ZHANG Yueqian  YOU Xincai 《《地质学报》英文版》2012,86(2):449-461

The dolomitic rocks of the Fengcheng Formation are considered to be formed under special geologic conditions, and are significant hydrocarbon reservoir rocks in the Wu-Xia area in the Junggar Basin. Analyses of petrologic characteristics and stable isotope composition indicate that the dolomitizing host rock is volcanic and the dolomitizing fluids probably consists of brine from shore-shallow lakes with great evaporation and salinity in the Fengcheng Formation, which have formed under arid climatic conditions, as well as residual Mg-rich seawater from the underlying Jiamuhe Formation and Carboniferous. Dust tuff in the area has significant plagioclase content. Anorthite and labradorite hydrolysis by CO2 can be coupled with calcite precipitation. Late Mg-rich brine percolated and replaced calcite formed in the early time, which lead to precipitate dolostones with different occurrences, such as graniphyric, random bedded or lumpy. The diagenetic dolostones with different occurrences resulting from particular formation conditions occurred in different tectonic settings. The dolomitizing fluid has been driven by the thermal convection flow generated by volcanic eruptions. At the same time, the overthrusts of the Wu-Xia growth fault?have speeded up the flow of deep Mg-rich water upwards, and induced the water to quickly?penetrate and horizontally migrate in the strata. Fracture is the major and the most important reservoir space in dolomitic reservoir of the Fengcheng Formation. Fracture and fault plays a decisive role in controlling the formation of dolostone and the distribution of favorable reservoirs. The deliverability of oil and gas is determined by the development and match relations of dissolved pores and fractures to a certain degree.  相似文献   

Late Ordovician island‐arc volcanic rocks,northern Capertee Zone,Lachlan Fold Belt,New South Wales     

P. F. Carr  C. L. Fergusson  J. W. Pemberton  G. P. Colquhoun  S. I. Murray  J. Watkins 《Australian Journal of Earth Sciences》2013,60(3):319-330

The Cape Hoskins volcanoes form part of the Quaternary volcanic island arc that extends from Rabaul in the east to the Schouten Islands in the west, and they overlie the northerly dipping New Britain Benioff Zone. The products of the volcanoes range in composition from basalt to rhyolite, and are normative in quartz and hypersthene. They contain phenocrysts of plagioclase and subordinate augite, hypersthene, and in most samples iron‐titanium oxides; some samples also contain olivine or quartz or both, and some pumice contains hornblende and, rarely, biotite.

Chemical analyses of 29 volcanic rocks are presented; 22 were also analysed for 17 minor elements — Rb, Ba, Sr, Pb, Zn, Cu, Zr, Y, Ni, Co, Sc, Cr, V, Ga, B, U, and Th.

Chemically the rocks have many of the characteristics of the ‘island arc tholeiitic series’, but do not show a pronounced relative enrichment in iron and appear to be relatively enriched in Sr. Compared with volcanic rocks from the northern part of the Willaumez Peninsula, they are lower in K (but not Na), Ti, Rb, Ba, Zr, Pb, Th, Ni, and probably also V, Cu, and Zn: these differences are attributed to the greater depth of the Benioff Zone beneath the Willaumez Peninsula. The more basic of the Cape Hoskins rocks are similar in most respects to lavas of comparable composition from Ulawun volcano to the east.  相似文献   

Kenn Plateau off northeast Australia: a continental fragment in the southwest Pacific jigsaw     

N. F. Exon  P. J. Hill  Y. Lafoy  C. Heine  G. Bernardel 《Australian Journal of Earth Sciences》2013,60(4):541-564

The submarine Kenn Plateau, with an area of about 140 000 km², lies some 400 km east of central Queensland beyond the Marion Plateau. It is one of several thinned continental fragments east of Australia that were once part of Australia, and it originally fitted south of the Marion Plateau and as far south as Brisbane. It is cut into smaller blocks by east- and northeast-trending faults, with thinly sedimented basement highs separated by basins containing several kilometres of sediment. In the Cretaceous precursor of the Kenn Plateau, Late Triassic to Late Cretaceous basins probably rested unconformably on Palaeozoic to Triassic rocks of the New England Fold Belt. Rift volcanism was common on the northern plateau and was probably of Early Cretaceous age. Late Cretaceous extension and breakup were followed by Paleocene drifting, and the Kenn Plateau moved to the northeast, rotated 30° anticlockwise and left space that was filled by Tasman Basin oceanic basalts. During these events, siliciclastic sediments poured into the basins from the continental mainland and from locally eroding highs. After a regional Late Paleocene to Early Eocene unconformity, siliciclastic sedimentation resumed in proximal areas. In deep water, radiolarian chalks were widely deposited until biosiliceous sediment accumulation ended at the regional Late Eocene to Early Oligocene unconformity, and warming surface waters led to accumulation of pure biogenic carbonates. Calcarenite formed in shallow water on the margins of the subsiding plateau from the Middle Eocene onward. Some seismic profiles show Middle to Late Eocene compression related to New Caledonian obduction to the east. Hotspots formed parts of two volcanic chains on or near the plateau as it moved northward: Late Eocene and younger volcanics of the Tasmantid chain in the west, and Late Oligocene and younger volcanics of the Lord Howe chain in the east. As the volcanoes subsided, they were fringed by reefs, some of which have persisted until the present day. Other reefs have not kept up with subsidence, so guyots formed. The plateau has subsided 2000 m or more since breakup and is now subject solely to pelagic carbonate sedimentation.  相似文献   

Geochemical and isotopic evidence for the age,orogenic setting and petrogenesis of the Nychum Volcanic association,North Queensland     

J.C. Bailey  W.R. Morgan  L.P. Black 《Australian Journal of Earth Sciences》2013,60(3-4):375-393

Rb‐Sr and K‐Ar age determinations agree with palaeobotanical evidence in assigning an age of 270 Ma (Lower Permian) to the Nychum Volcanics, North Queensland. Geological and geochemical evidence (moderate ‐REE, La/Yb, Th, Zr/Y, Hf/Yb, Sc/Ni) indicate that the volcanics were erupted on a thin, active continental margin. Five magma groups are present: high‐alumina basalts, andesite‐dacites, acid rocks, tholeiitic andesites, and pitchstone with a high La/Yb ratio. The high‐alumina basalts and calc‐alkaline andesites have a parent‐daughter (source rock‐partial melt) relationship. The acid rocks share high HREE, Zr, Hf, Zn, Sc, Fe/Mg and low Al with, and may be fractionated from, the tholeiitic subduction‐zone andesites. Low‐pressure fractional crystallisation is evident in all five magma groups.  相似文献   

The age and tectonic significance of the Warraweena Volcanics and related rocks,southern Thomson Orogen     

A. C. Hack  R. C. Dwyer  G. Phillips  S. Whalan  H.-Q. Huang 《Australian Journal of Earth Sciences》2013,60(7-8):1071-1096

Abstract

Magmatic-textured zircon from medium- to high-K calc-alkaline Warraweena Volcanics (WV) in two drill holes have yielded concordant U–Pb dates of 417?±?3.5 and 414?±?4.0?Ma and are interpreted as maximum emplacement ages. The Warraweena volcanics were previously considered to be either Neoproterozoic or Macquarie arc equivalents. Whole-rock εNd_t values of these volcanics are +4.5 and +4.8. Along strike of the drill holes, Devonian zircon U–Pb ages (411?±?5.5?Ma) were obtained from coherent S-type rhyolite flows that have highly negative εNd_t values (–7.9 and –7.8). These are a component of the Oxley volcanics. The ages of the Warraweena and Oxley volcanics are identical within uncertainty.

The Oxley volcanics (OV) are interbedded with predominantly fine- to medium-grained metasedimentary and so imply a Lower Devonian deposition age for these host rocks. Based on their geophysical characteristics, the metasediments are widely distributed. These metasedimentary rocks yield a wide range of maximum depositional ages, from Early Devonian to earliest Ordovician–latest Cambrian, similar to the Cobar Basin. The absence of complex fabric development typical of Ordovician supracrustal rocks in the region, and conformity with the OV where observable suggest the widespread sedimentation was synchronous with rift-related volcanism in the Early Devonian.

Regionally, the WV is temporally, geochemically and isotopically (εNd values) similar to the calc-alkaline Louth Volcanics located over 100?km to the southwest of the WV. Louth Volcanics define a complexly folded belt in geophysical data. Other potentially correlative Early Devonian igneous rocks occur in the nearby Cobar Superbasin and elsewhere in the eastern Lachlan Orogen and are considered to represent the products of a post-orogenic, nascent continental back-arc rift system.  相似文献