DOCSLIB.ORG

Isotope, Trace Element, and Major Element Constraints From

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Isotope, Trace Element, and Major Element Constraints From CHEMICAL STRATIFICATION OF THE CRUST: ISOTOPE, TRACE ELEMENT, AND MAJOR ELEMENT CONSTRAINTS FROM CRUSTALLY CONTAMINATED LAVAS AND LOWER CRUSTAL XENOLITHS by MARY RUTH REID B.S. (Honors), A.B., University of California, Santa Cruz (1979) SUBMITTED TO THE DEPARTMENT OF EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY February 1987 Massachusetts Institute of Technology Signature of Authoi Department of Earth, Atmospheric, and Planetary Sciences November 7, 1986 fi' Certified byCerifid b I.0 - Stanley R. Hart Thesis Supervisor Accepted by Chairman, Department Committee on Graduate Students 2 CHEMICAL STRATIFICATION OF THE CRUST: ISOTOPIC, TRACE ELEMENT, AND MAJOR ELEMENT CONSTRAINTS FROM CRUSTALLY CONTAMINATED LAVAS AND LOWER CRUSTAL XENOLITHS by MARY RUTH REID Submitted to the Department of Earth, Atmospheric, and Planetary Sciences on November 7, 1986 in partial fulfillment of the requirements for the degree of Doctor of Philosophy ABSTRACT The dehydration of the lower crust and the assimilation of crustal materials into ascending magmas are two geologic phenomenon which lead to vertical mass transport and potentially, geochemical stratification of continental crust. LOWER CRUSTAL XENOLITHS, KILBOURNE HOLE This integrated Sr-Nd-Pb isotope study of paragneiss xenoliths from Kilbourne Hole maar, New Mexico, is the first of its kind applied to materials derived directly from the lower crust (6-10 kb). The pelitic paragneisses represent shales incorporated into the lower crust, in themselves exemplifying the importance of tectonic and sedimentary processes to the evolution of the lower crust. Because shales are rich in elements conventionally thought to be depleted in the lower crust, the pelitic paragneisses are an important geochemical reservoir to consider in the lower crust; their response to high grade metamorphism is pertinent to the problem of intracrustal stratification. Sr isochrons determined from layers at a xenolith (decimeter) scale yield -1.6 Ga ages, coeval with metamorphic ages in basement rocks exposed at the surface. Locally, minerals are in isotopic equilibrium as a result of recent reheating of the lower crust related to Rio Grande rifting. Pb isochrons yield discordant ages as a result of this heating but are internally consistent with tectonothermal stability of the crust throughout the remainder of the Precambrian and most of the Paleozoic in spite of proximity to anorogenic plutonism at -1.4 Ga and orogenic activity at -1.0 Ga. Nd isochrons also yield discordant ages suggesting the heretofore unexpected possibility that effective diffusion rates for Nd are faster than Sr under dry crustal conditions. The paragneisses exhibit a wide range in internal composition. A representative Sm/Nd ratio for the paragneisses as a whole is obtained by considerations based on their time-integrated Nd isotope evolution. Other geochemical characteristics of the paragneisses are be correlated to Sm/Nd and a representative major and trace element composition for the paragneisses is determined. Although similar in many respects to typical shales, the paragneisses are significantly depleted in U and Cs and may have been depleted by a factor of -2 in Th and the LREE relative to the protolith during metamorphism. High LREE abundances measured in the feldspars are unlikely to be maintained in the presence of a melt. Consequently, the paragneisses were probably depleted by means other than partial melting. Relative to average crust, the pelitic paragneisses are radiogenic in 87Sr/ 8 6 Sr, are unradiogenic in 2 0 6 Pb/ 20 4 Pb and 2 0 7 Pb/ 2 0 4 Pb, and have 14 3Nd/ 1 4 4Nd similar to middle Proterozoic crust. Existing data also show that they retain the relatively high 6180 of their precursors. In contrast, isotopic data for orthogneisses from Kilbourne Hole indicate that they are unradiogenic in 87 Sr/ 8 6 Sr and may be more variable, albeit largely unradiogenic, in 14 3Nd/14 4Nd. Consequently, representative isotope characteristics for the lower crust as a whole depend on the relative proportion of these different lithologies. If pelitic paragneisses are present at geologically reasonable 10-20% abundance levels in the lower crust, they reduce the heat flux required of the subcontinental mantle by up to 50%. They increase 8 7 Sr/ 8 6Sr by up to 0.006 and incompatible elements abundances by 20-100% over previous estimates for the lower crust. On the other hand, the unradiogenic Pb isotopic signature of the lower crust, previously suspected from studies of granulites exposed at the surface, is confirmed. CRUSTAL ASSIMILATION, KODIAK ISLAND, ALASKA, AND PARICUTIN VOLCANO, MEXICO Crustal assimilation in two disparate tectonic settings is examined in order to understand its nature and timing. The Ghost Rocks volcanics (GRV) of Kodiak Island, Alaska are early Tertiary submarine basalts and andesites which erupted in a near-trench setting. Subduction of the Kula-Farallon spreading center beneath the Kodiak accretionary prism is proposed as the ultimate source of the GRV on the bases of tectonic considerations and MORB-like isotopic and trace element signatures in the basalts. Andesites which are conformably overlain by the basalts have less radiogenic Nd isotope signatures and arc-like chemical affinities. Inversion of selected trace element characteristics in light of the Nd isotope data shows them to be the product of mixing between the basalts and sediments of the accretionary prism. The lavas of Paricutin volcano, a cinder cone in Mexico, exhibit linear trends in isotopic and incompatible element ratios consistent with crustal assimilation. However, they exhibit a tripartite trend in elemental abundances over time and more mafic lavas are richer in many of the incompatible elements than those which have undergone greater amounts of crustal assimilation. This is suggested to reflect the diachronous interplay of crystal fractionation with crustal 4 assimilation. Ratios between the U-series nuclides are not appreciably affected by crustal assimilation although 2 2 6 Ra is significantly enriched over 2 30 Th and 2 10 Pb. Since the trend in 2 26 Ra abundance with time is correlated with that inferred to be the result of crustal assimilation, crustal assimilation must have occurred subsequent or consequent to Ra enrichment, or within the last 8000 years. If the 2 1 0Pb- 2 2 6 Ra disequilibria arose from Ra enrichment, crustal assimilation could have occurred within years of eruption. Thesis Supervisor - Dr. Stanley R. Hart Professor of Geology and Geochemistry TABLE OF CONTENTS Title Page 1 Abstract 2 Table of Contents 5 List of Figures 9 List of Tables 13 Acknowledgments 14 Prelude 16 Introduction 17 Chapter 1. Variable Scales of Sr-Nd-Pb Isotopic Equilibrium 18 and tectonothermal evolution of the lower crust, Kilbourne Hole, New Mexico Introduction 19 Thermal considerations in the study of the lower crust 22 Geologic context 27 Sample descriptions 28 Analytical scheme 29 Sample preparation 29 Analytical techniques 29 Results 32 Sr isochrons 34 Nd isochrons 38 Pb isochrons 38 Discussion 48 Nd equilibrium - Sr disequilibrium: isotopic response to 48 equilibration Summary of the geochronology 52 Possible evidence for lack of xenolith-scale equilibration 56 from the Precambrian to the Tertiary Implications for thermal state and evolution of the lower crust 60 State of the lower crust: intensive properties (P,T,pH 20) 60 Tectonothermal evolution of the lower crust since the 62 Precambrian Rio Grande rifting 62 Ancestral Rocky Mountains 63 Llano orogeny 64 Anorogenic magmatism 65 1.6 - 1.9 crust-forming event 66 Conclusions 67 References 70 Chapter 2. Where Do Rare Earth Elements Reside in the Lower Crust? 75 Chapter 3. An Isotopic Profile of Early Proterozoic Crust: 86 Progress Report on Crustal Xenoliths from southern New Mexico Introduction 87 Review of oxygen isotope data for Kilbourne Hole xenoliths 89 Results 90 Rb - Sr 90 Kilbourne Hole 90 Potrillo Maar 96 Sm - Nd 96 U - Pb 102 Th - Pb 105 Discussion and interpretation 106 Review of isotopic data for supracrustal rocks and ores of 106 New Mexico Representative characteristics, crustal prehistories, and 110 the effects of granulite metamorphism Orthogneisses 111 Paragneisses 113 Likely duration of crustal prehistory 113 Representative Sm/Nd and Th/Pb characteristics of the 118 pelitic paragneisses Sm - Nd 119 Th - Pb 120 7K3 121 Comparison to other granulite localities 122 Summary and conclusions 128 Compositional stratification and the effect of granulite 128 metamorphism Duration of crustal prehistory and role of tectonics in 129 evolution of the lower crust References 132 Chapter 4. Geochemical Constraints on the Contribution of 136 Metasedimentary Rocks to the Lower Crust: Paragneiss Xenoliths from Kilbourne Hole, New Mexico Introduction 137 Sample descriptions 140 Analytical techniques 141 Major elements 141 Evidence for a shale protolith 141 Internal compositional variation - possible origins and 147 implications Correlation with Sm-Nd: Major element composition of the 157 representative pelitic paragneiss (RPP) Summary of the major element characterstics 161 Trace element systematics 162 Sm and Nd 164 Paragneisses 164 Protolith 164 U and Th 167 Paragneisses 167 Protolith 168 Sr and Pb 174 Paragneisses 174 Protolith 174 K, Rb, and Cs 177 Summary and discussion of the trace element data 180 The REE revisited: Considerations and complications in 182 characterizing
Load more

Recommended publications
  • Neoproterozoic Glaciations in a Revised Global Palaeogeography from the Breakup of Rodinia to the Assembly of Gondwanaland
    Sedimentary Geology 294 (2013) 219–232 Contents lists available at SciVerse ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo Invited review Neoproterozoic glaciations in a revised global palaeogeography from the breakup of Rodinia to the assembly of Gondwanaland Zheng-Xiang Li a,b,⁎, David A.D. Evans b, Galen P. Halverson c,d a ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia b Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109, USA c Earth & Planetary Sciences/GEOTOP, McGill University, 3450 University St., Montreal, Quebec H3A0E8, Canada d Tectonics, Resources and Exploration (TRaX), School of Earth and Environmental Sciences, University of Adelaide, SA 5005, Australia article info abstract Article history: This review paper presents a set of revised global palaeogeographic maps for the 825–540 Ma interval using Received 6 January 2013 the latest palaeomagnetic data, along with lithological information for Neoproterozoic sedimentary basins. Received in revised form 24 May 2013 These maps form the basis for an examination of the relationships between known glacial deposits, Accepted 28 May 2013 palaeolatitude, positions of continental rifting, relative sea-level changes, and major global tectonic events Available online 5 June 2013 such as supercontinent assembly, breakup and superplume events. This analysis reveals several fundamental ’ Editor: J. Knight palaeogeographic features that will help inform and constrain models for Earth s climatic and geodynamic evolution during the Neoproterozoic. First, glacial deposits at or near sea level appear to extend from high Keywords: latitudes into the deep tropics for all three Neoproterozoic ice ages (Sturtian, Marinoan and Gaskiers), al- Neoproterozoic though the Gaskiers interval remains very poorly constrained in both palaeomagnetic data and global Rodinia lithostratigraphic correlations.
    [Show full text]
  • The Western Amazonia Igneous Belt
    Journal of South American Earth Sciences 96 (2019) 102326 Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames The Western Amazonia Igneous Belt T ∗ Gilmar José Rizzottoa, , Cléber Ladeira Alvesa, Francisco Sene Riosa, Márcia Aparecida de Sant’Ana Barrosb a Geological Survey of Brazil (CPRM), Rua 148, nº 485, 74170-110, Goiânia, Goiás, Brazil b Institute of Geosciences of the Federal University of Mato Grosso, Rua 44, No. 41, CEP 78.068-505, Cuiabá, Mato Grosso, Brazil ARTICLE INFO ABSTRACT Keywords: The Western Amazonia Igneous Belt (WAIB) occupies the northern part of South American continent, and a total Amazonian craton area close to 125,000 km2. The belt is composed dominantly by volcano-plutonic felsic rocks (Juruena super- Bimodal magmatism suite, Teles Pires suite and Colíder group) and has dominant alkali-calcic, metaluminous to peraluminous, fer- Underplating rous, geochemical characteristics, similar to A-type granites. The Silicic members are represented by granites and Teles pires suite rhyolitic-rhyodacitic volcanic rocks, mafic members by gabbroic rocks and diabase dykes. Intermediate rocks are rare. Local magma mingling and hybridization are present in several areas. The assemblage of silicic and basic rocks of WAIB was formed between c. 1825 and 1757 Ma. The presence of inherited zircons, from 1875 to 2050 Ma, as well as some Archean ages in the granitic and volcanic rocks from the WAIB, are suggestive of derivation by melting of pre-existing crustal basement (Ventuari-Tapajós Province). This hypothesis is also corroborated by bimodal magmatism and by several model-ages of granites, felsic volcanic rocks and mafic plutonic rocks, with TDM ranging from 2.0 to 2.3 Ga, and εNd value, varying from −3.90 to +2.52.
    [Show full text]
  • Geochemistry and Tectonic Significance of Late Paleoproterozoic A-Type Granites Along the Southern Margin of the North China
    www.nature.com/scientificreports OPEN Geochemistry and tectonic signifcance of late Paleoproterozoic A-type granites along the southern margin of the North China Craton Yan Wang1, Yi-Zeng Yang1*, Wolfgang Siebel2, He Zhang1, Yuan-Shuo Zhang1 & Fukun Chen1 The Longwangzhuang pluton is a typical example of Paleoproterozoic A-type granite intrusions at the southern margin of the North China Craton. This pluton is composed of arfvedsonite granite and minor aegirine–augite granites. Samples from both granite types display similar zircon U-Pb ages with 207U-206Pb ages of 1612 ± 19 Ma [mean square weighted deviation (MSWD) = 0.66] and 1609 ± 24 Ma (MSWD = 0.5), respectively. The granites exhibit similar high silica (SiO2 = 71.1–73.4 wt.%), high alkaline (Na2O + K2O = 8.10–9.26 wt.%, K2O/Na2O > 1), and low Al2O3 (11.8–12.8 wt. %) contents and metaluminous to weakly peraluminous bulk chemistry. The chemical variations of the Longwangzhuang pluton suggest the efects of mineral fractionation. In addition, all samples show typical characteristics of A-type granites, such as high 10000Ga/Al ratios (4.10–7.28), high FeOtot/(FeOtot + MgO) ratios (0.88– 0.99), and high Zr (484–1082 ppm), Ce (201–560 ppm), and Y (78–156 ppm) contents. The εNd(t) values 206 204 207 204 208 204 and the ( Pb/ Pb)t, ( Pb/ Pb)t, and ( Pb/ Pb)t ratios of the arfvedsonite granite samples vary from −4.6 to –5.3, 15.021 to 17.349, 15.241 to 15.472, and 33.206 to 36.905, respectively, and those for the aegirine–augite granite sample amount at −0.2, 14.421, 15.175, and 33.706.
    [Show full text]
  • Fifth International Dyke Conference
    FIFTH INTERNATIONAL DYKE CONFERENCE Abstracts and Programme NAL DYKE TIO C A O N N R F E E T R N I E N H C T F E I F 5 IDC F D I N L A N 31 July - 3 August 2005, Pohtimolampi Wilderness Hotel - Polar Circle - Rovaniemi - Finland FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND FIFTH INTERNATIONAL DYKE CONFERENCE "Dyke swarms - time markers of crustal evolution" Pohtimolampi Wilderness Hotel - Polar Circle - Rovaniemi - Finland 31 June – 3 August 2005 ABSTRACTS AND PROGRAMME edited by Jouni Vuollo Geological Survey of Finland P.O. Box 77, FIN-96101 Rovaniemi Satu Mertanen Geological Survey of Finland P.O. Box 96, FIN-02151 Espoo ISBN 951-690-926-4 i FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND Reference (an example): Alaabed S., 2005. Intrusion types of the mantle sequence of the northern Semail ophiolite (UAE Section). In: Vuollo, J. and Mertanen, S. (eds.), 5th International Dyke Conference, 31 July – 3 August 2005, Rovaniemi, Finland, Abstracts and Programme, p. 1. ii FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND Welcome from the Organising Committee Welcome to Rovaniemi! We are very pleased to host you here as a participant of the Fifth International Dyke Conference (IDC- 5). The conference will bring together specialists in volcanology, tectonics, structural geology, petrology, geochemistry, geochronology, and geophysics to present progress made in the last years in various subjects related to dykes and other sheeted intrusions. An important part of the meeting are the pre- and post-conference excursions to the southern and eastern Finland and to the Kola Peninsula, Russia.
    [Show full text]
  • The Rhyacian El Cortijo Suture Zone: Aeromagnetic Signature and Insights for the Geodynamic Evolution of the Southwestern Rio De La Plata Craton, Argentina
    Geoscience Frontiers 5 (2014) 43e52 Contents lists available at SciVerse ScienceDirect China University of Geosciences (Beijing) Geoscience Frontiers journal homepage: www.elsevier.com/locate/gsf Research paper The Rhyacian El Cortijo suture zone: Aeromagnetic signature and insights for the geodynamic evolution of the southwestern Rio de la Plata craton, Argentina Carlos J. Chernicoff a,b,*, Eduardo O. Zappettini b, Javier Peroni b a Council for Scientific and Technical Research (CONICET), Argentina b Argentine Geological-Mining Survey (SEGEMAR), Argentina article info abstract Article history: The amalgamation of the southern Río de la Plata craton involves two possibly coeval Rhyacian sutures Received 21 September 2012 associated with the Transamazonian orogeny, rather than a single one as previously envisaged, i.e. the El Received in revised form Cortijo suture zone and the Salado suture. We circumscribe the Tandilia terrane to the region between 20 March 2013 these two sutures. Accepted 15 April 2013 The El Cortijo suture zone runs along a roughly WNW oriented magnetic low aligned along the Available online 7 May 2013 southern boundary of the Tandilia terrane, i.e. boundary between the Tandilia and Balcarce terranes. This extensive magnetic low, ca. 300 km long, and ca. 90 km wide, would be caused by demagnetization Keywords: El Cortijo suture zone associated with shearing. At a more local scale, the trend of the El Cortijo suture zone often turns e Rhyacian toward the E W. At this scale, WNW trending tholeiitic dykes of Statherian age are seen to cut the Río de la Plata craton Rhyacian El Cortijo suture zone. Spatially associated with the El Cortijo suture zone, there are small Aeromagnetics magnetic highs interpreted to be related to unexposed basic bodies of ophiolitic nature related to those forming part of the El Cortijo Formation.
    [Show full text]
  • Physics of the Earth and Planetary Interiors 176 (2009) 143–156
    Physics of the Earth and Planetary Interiors 176 (2009) 143–156 Contents lists available at ScienceDirect Physics of the Earth and Planetary Interiors journal homepage: www.elsevier.com/locate/pepi Review Supercontinent–superplume coupling, true polar wander and plume mobility: Plate dominance in whole-mantle tectonics Zheng-Xiang Li a,∗, Shijie Zhong b a The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia b Department of Physics, University of Colorado, Boulder, Colorado 80309, USA article info abstract Article history: Seismic tomography has illustrated convincingly the whole-mantle nature of mantle convection, and the Received 27 November 2008 lower mantle origin of the African and Pacific superplumes. However, questions remain regarding how Received in revised form 28 April 2009 tectonic plates, mantle superplumes and the convective mantle interplay with each other. Is the formation Accepted 1 May 2009 of mantle superplumes related to plate dynamics? Are mantle plumes and superplumes fixed relative to the Earth’s rotation axis? Answers to these questions are fundamental for our understanding of the inner Keywords: workings of the Earth’s dynamic system. In this paper we review recent progresses in relevant fields Supercontinent and suggest that the Earth’s history may have been dominated by cycles of supercontinent assembly Superplume True polar wander and breakup, accompanied by superplume events. It has been speculated that circum–supercontinent Mantle dynamics subduction leads to the formation of antipodal superplumes corresponding to the positions of the super- Plate tectonics continents. The superplumes could bring themselves and the coupled supercontinents to equatorial positions through true polar wander events, and eventually lead to the breakup of the supercontinents.
    [Show full text]
  • The Circum-Mediterranean Anorogenic Cenozoic Igneous Province ⁎ Michele Lustrino A,B, , Marjorie Wilson C
    Earth-Science Reviews 81 (2007) 1–65 www.elsevier.com/locate/earscirev The circum-Mediterranean anorogenic Cenozoic igneous province ⁎ Michele Lustrino a,b, , Marjorie Wilson c a Dipartimento di Scienze della Terra, Università degli Studi di Roma La Sapienza, P. le A. Moro, 5, 00185 Rome, Italy b CNR-Istituto di Geologia Ambientale e Geoingegneria (IGAG) c/o Dipartimento di Scienze della Terra, Università degli Studi di Roma La Sapienza, P. le A. Moro, 5, 00185, Rome, Italy c Institute of Geophysics and Tectonics, School of Earth and Environment, Leeds University, Leeds, LS2 9JT, UK Received 18 April 2005; accepted 1 September 2006 Available online 24 January 2007 Abstract During the Cenozoic widespread anorogenic magmatism, unrelated to recent supra-subduction zone modification of its mantle source, developed within the Mediterranean and surrounding regions; this is referred to collectively as the CiMACI (Circum- Mediterranean Anorogenic Cenozoic Igneous) province. On the basis of a comprehensive review of published and new major and trace element and Sr–Nd–Pb isotopic data (more than 7800 samples) for the magmatic rocks, a common sub-lithospheric mantle source component is identified for most of the region. This has geochemical affinities to the source of HIMU oceanic island basalts and to the European Asthenospheric Reservoir (EAR) and the Low Velocity Component (LVC) of previous workers; we refer to this as the Common Mantle Reservoir (CMR). Global and local seismic tomography studies of the mantle beneath the CiMACI province have revealed a range of P- and S- wave velocity anomalies, some of which have been related to the presence of mantle plumes.
    [Show full text]
  • Upper Mantle Flow in the Western Mediterranean ⁎ Giuliano F
    Earth and Planetary Science Letters 257 (2007) 200–214 www.elsevier.com/locate/epsl Upper mantle flow in the western Mediterranean ⁎ Giuliano F. Panza a,b, , Reneta B. Raykova c,1, Eugenio Carminati d, Carlo Doglioni d a Dipartimento di Scienze della Terra, Università degli Studi di Trieste, Via E. Weiss 4, 34127 Trieste, Italy b The Abdus Salam International Centre for Theoretical Physics, Earth System Physics Section, strada Costiera 11, 34014 Trieste, Italy c Geophysical Institute of BAS, Acad. G. Bonchev str. blok 3, 1113 Sofia, Bulgaria d Dipartimento di Scienze della Terra, Università La Sapienza, P.le Aldo Moro 5, 00185 Roma, Italy Received 20 July 2006; received in revised form 18 January 2007; accepted 18 February 2007 Available online 27 February 2007 Editor: R.D. van der Hilst Abstract Two cross-sections of the western Mediterranean Neogene-to-present back-arc basin are presented, in which geological and geophysical data of the TRANSMED Project are tied to a new shear-wave tomography. Major results are i) the presence of a well stratified upper mantle beneath the older African continent, with a marked low-velocity layer between 130–200 km of depth; ii) the dilution of this layer within the younger western Mediterranean back-arc basin to the north, and iii) the easterly raising of a shallower low-velocity layer from about 140 km to about 30 km in the Tyrrhenian active part of the back-arc basin. These findings suggest upper mantle circulation in the western Mediterranean back-arc basin, mostly easterly-directed and affecting the boundary between upper asthenosphere (LVZ) and lower asthenosphere, which undulates between about 180 km and 280 km.
    [Show full text]
  • Anorogenic Magmatism, Plate Motion and Atlantic Evolution
    Anorogenic magmatism, plate motion and Atlantic evolution R. M. MACINTYRE SUMMARY Emplacement of carbonatites at o--I5, 25, 40, 6o-70, I3o Ma (and possibly 8o and xoo Ma) may coincide with major changes in plate motion. This suggests a common triggering mechanism which previously may have operated at intervals of about 23 ° Ma. I. Introduction As nN INTVRCONN~CTED MESH of rigid lithospheric plates embraces the earth, changes in rate or direction of motion of one plate may inevitably affect adjacent plates. Such changes have sometimes been associated with the significant marginal development of basic rocks whose ages provide a means of testing global synchro- nism. However, these rocks are generally unsuitable for precise age determination studies and their relatively rapid disappearance by subduction and erosion makes another approach desirable. The magmatism associated with plate margins and intraplate rifts is associated with regional crustal swells probably derived from deep forceful disturbances (Le Bas I97I ). On the continents these conditions favoured the development of nephelinitic, carbonatitic and kimberfitic rocks. Occasionally geosutures formed and separation occurred, with new spreading axes and oceanic crust, prolific volcanism, coast-parallel dykes and new continental margins determined by the pre-existing rifts. In Africa alkaline igneous rocks and carbonatites are con- centrated in regions of swelling (Bailey x964, Campbell Smith I956, King & Sutherland I96o ) and a close relationship exists between the swelling and their emplacement (Le Bas I97i ). Their ages may therefore indicate when the process responsible for the swellings operated and allow the synchroneity of its action to be examined. With this approach the precision is improved as these rocks are suited to the application of several radiometric methods.
    [Show full text]
  • Hydrothermal Mineral Deposits
    CHAPTER NINE 9 INDIRECT LINKS: HYDROTHERMAL MINERAL DEPOSITS 9.1 Introduction In Chapters 2, 3 and 4 we have examined how doming of the crust, its rupturing and formation of a rift basin are processes that can be linked to mantle plumes. The East African Rift System, and its Red Sea and Gulf of Aden extensions are a modern example of this phenomenon; the Mid­ Continent Rift System in North America is an ancient example. Another ancient example is the Damara-Ribeira rift systems, which subsequently evolved to ocean floor spreading, resulting in the separation of South America from southwestern Africa (Damara hotspot junction, discussed in Chapter 4). "Deposits formed in continental hot spots, rifts and aulacogens" are discussed by Mitchell and Garsan (1981), who included mineral deposits associated with intracontinental hotspots, such as Sn, Nb and U in peralu­ minous and peralkaline granites, REE in carbonatite; deposits associated with intracontinental rifts and aulacogens, such as REE, U and P in carbo­ natite and alkaline complexes, diamonds in kimberlite and porphyry Mo in biotite granite; stratabound Cu (e.g. Kupferschiefer in Europe, Copperbelt in central Africa), stratabound Pb-Zn-Ag (e.g. Sullivan in Canada, Mt. Isa and McArthur River in Australia), lacustrine brines and evaporites (East African lakes), polymetallic hydrothermal veins in granite (e.g. Mid­ continent Rift System in North America). The Great Dyke and Bushveld lgneous Complex, discussed in Chapter 8 of this book, are also included in the rifts and aulacogen settings ofMitchell and Garsan (1981). Sawkins (1990) devoted a chapter to "Intracontinental hotspots, anoro­ genic magmatism and associated metal deposits", in which he included Sn in anorogenic granites, Fe-Ti in anorthosite, Ni-Cu-PGE in layered intru­ sions (e.g.
    [Show full text]
  • Caracterización Del Vulcanismo Carbonatítico De Catanda (Angola)
    Caracterización del vulcanismo carbonatítico de Catanda (Angola) Marc Campeny Crego ADVERTIMENT . La consulta d’aquesta tesi queda condicionada a l’acceptació de les següents condicions d'ús: La difusió d’aquesta tesi per mitjà del servei TDX ( www.tdx.cat ) i a través del Dipòsit Digital de la UB ( diposit.ub.edu ) ha estat autoritzada pels titulars dels drets de propietat intel·lectual únicament per a usos privats emmarcats en activitats d’investigació i docència. No s’autoritza la seva reproducció amb final itats de lucre ni la seva difusió i posada a disposició des d’un lloc aliè al servei TDX ni al Dipòsit Digital de la UB . No s’autoritza la presentació del seu contingut en una finestra o marc aliè a TDX o al Dipòsit Digital de la UB (framing). Aquesta rese rva de drets afecta tant al resum de presentació de la tesi com als seus continguts. En la utilització o cita de parts de la tesi és obligat indicar el nom de la persona autora. ADVERTENCIA . La consulta de esta tesis queda condicionada a la aceptación de las siguientes condiciones de uso: La difusión de esta tesis por medio del servicio TDR ( www.tdx.cat ) y a través del Repositorio Digital de la UB ( diposit.ub.edu ) ha sido autorizada por los titulares de los derechos de propiedad intelectual únicamente par a usos privados enmarcados en actividades de investigación y docencia. No se autoriza su reproducción con finalidades de lucro ni su difusión y puesta a disposición desde un sitio ajeno al servicio TDR o al Repositorio Digital de la UB .
    [Show full text]
  • Idc5 Pre Excursion.Pdf
    FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND FIFTH INTERNATIONAL DYKE CONFERENCE "Dyke swarms - time markers of crustal evolution" Pohtimolampi Wilderness Hotel - Polar Circle - Rovaniemi - Finland 31 June – 3 August 2005 PRE-CONFERENCE FIELD TRIP A GUIDEBOOK: Southern and Central Finland edited by Luttinen, A.V. Department of Geology P.O.Box 64, FIN-00014 University of Helsinki Vuollo, J.I. Geological Survey of Finland P.O.Box 77 FIN-96101 Rovaniemi ISBN 951-690-927-2 FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND Organising Committee Dr. Jouni Vuollo (Geological Survey of Finland) Dr. Satu Mertanen (Geological Survey of Finland) Prof. Olav Eklund (University of Turku) Prof. Eero Hanski (University of Oulu) Dr. Hannu Huhma( Geological Survey of Finland) Dr. Pentti Hölttä (Geological Survey of Finland) Dr. Arto Luttinen (University of Helsinki) Prof. Tapani Rämö (University of Helsinki) Dr. Saku Vuori (Geological Survey of Finland) IDC5 Congress Office Ms. Marja-Leena Porsanger & Ms. Päivi Mäkikokkila (Rovaniemi-Lapland Con- gresses, University of Lapland) Sponsors Scientific Geological Survey of Finland Large Igneous Provinces Commission University of Oulu University of Helsinki University of Turku Technical sponsors Geological Survey of Finland University of Oulu University of Helsinki University of Turku Tulikivi Kivikeskus Financial sponsors Academy of Finland Geological Survey of Finland City of Rovaniemi & Municipality of Rovaniemi European Diamonds PLC Scandinavian Gold Limited Kiviteollisuusliitto FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND Table of contents Introduction i Itinerary and stop descriptions ii Proterozoic mafic dyke swarms of southern and central Finland 1 1.
    [Show full text]