Nature and origin of ultramafic lamprophyres and carbonatites from the borders of the Labrador Sea [Elektronische Ressource] : insights from petrology, geochemistry, and geochronology / Sebastian Tappe

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2005
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

NATURE AND ORIGIN OF ULTRAMAFIC LAMPROPHYRES AND
CARBONATITES FROM THE BORDERS OF THE LABRADOR SEA: INSIGHTS
FROM PETROLOGY, GEOCHEMISTRY, AND GEOCHRONOLOGY
٭
Dissertation
zur Erlangung des Grades
Doktor der Naturwissenschaften

am Fachbereich
Chemie, Pharmazie und Geowissenschaften
der Johannes Gutenberg-Universität Mainz
٭
Sebastian Tappe
geboren am 30. April 1976 in der Hansestadt Stralsund
٭
Mainz, 16. Juni 2005

i

A dissertation submitted to the
Geosciences Institute of the Johannes Gutenberg University Mainz
in fulfilment of the requirements for the degree of
Doctor rerum naturalium





Dekan: xxx
1. Berichterstatter: xxx
2. Berichterstatter: xxx
Tag der mündlichen Prüfung: 18/11/2005


ii CURRICULUM VITAE
Name: Sebastian Tappe
thDate and place of birth: 30 of April 1976 in the Hansestadt Stralsund (Germany)
Nationality: German
Address: Kirchstrasse 10, 55124 Mainz, Germany
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Education:
• Graduated from high-school, August 1994 (Johann Gottfried Herder–Gymnasium,
Stralsund).
• Military Service, October 1994-September 1995 (trained as a tank driver in Basepohl
and Stadtallendorf).
• University of Greifswald, October 1995-Feburary 2001 (Diploma program, German
M.Sc. equivalent, with courses in geology, oceanography, mineralogy, inorganic
chemistry and remote sensing; diploma thesis on “Petrology and Geochemistry of
mafic alkaline volcanics from southern Sweden”).
• Universities of Greifswald/Memorial-Newfoundland/Mainz, May 2001-present (Ph.D.
program; preparation of thesis on “Ultramafic lamprophyre, carbonatite and lamproite
intrusions from Labrador and New Quebec, Canada”).


iii Awards:
th• Best oral presentation by a young scientist at 8 International Kimberlite Conference
held in Victoria, Canada, 2003.
Publications:
Peer-reviewed journal articles
Tappe, S., Foley, S. F. & Pearson, D. G. (2003a). The Kamafugites of Uganda: a
mineralogical and geochemical comparison with their Italian and Brazilian analogues.
Periodico di Mineralogia 72, 51-77.
Tappe, S., Jenner, G. A., Foley, S. F., Heaman, L. M., Besserer, D., Kjarsgaard, B. A. &
Ryan, A. B. (2004a). Torngat ultramafic lamprophyres and their relation to the North Atlantic
Alkaline Province. Lithos 76, 491-518.
Tappe, S. (2004). Mesozoic mafic alkaline magmatism of southern Scandinavia.
Contributions to Mineralogy and Petrology 148, 312-334.
Tappe, S., Foley, S. F., Jenner, G. A. & Kjarsgaard, B. A. (2005). Integrating ultramafic
lamprophyres into the IUGS classification of igneous rocks: rational and implications.
Journal of Petrology 46, 1893-1900.
Extended abstracts
Tappe, S., Obst, K. & Solyom, Z. (2001). Geochemie und Genese der mesozoischen
Schlotbasalte am SW-Rand des Fennoskandischen Schildes (Schonen, Schweden). Terra
Nostra 5/01, 65-68.
Tappe, S., Foley, S. F., Jenner, G. A., Ryan, B., Besserer, D. & Kjarsgaard, B. A. (2003b).
Ultramafic lamprophyre dyke swarm, Torngat Mountains, Quebec and Labrador: Mineralogy
and Geochemistry. Extended Abstracts of the 8th International Kimberlite Conference (7.2.)
iv PREAMBLE
This doctoral thesis embodies selected results of my research at the Universities of Greifswald
and Mainz, as well as at Memorial University of Newfoundland and the University of Alberta
between 2001-2005. It consists of three articles, which have been prepared for publication in
the following international peer-review journals:
Part I (Journal of Petrology, published in September 2005, volume 46, pp. 1893-1900):
• “Integrating ultramafic lamprophyres into the IUGS classification of igneous rocks:
rationale and implications”
Part II (Journal of Petrology, revised version submitted in June 2005):
• “Genesis of ultramafic lamprophyres and carbonatites, Aillik Bay, Canada:
implications for incipient rifting in the Labrador Sea area”
Part III (Lithos, published in October 2004, volume 76, pp. 491-518):
• “Torngat ultramafic lamprophyres and their relation to the North Atlantic Alkaline
Province”

These manuscripts have co-authors, as listed in the table of contents, and their contributions
are indicated in the acknowledgments of this thesis.

S. Tappe
University of Mainz
June 2005

v TABLE OF CONTENTS


CURRICULUM VITAE ............................................................................................................III
PREAMBLE .................................................................................................................................V
SUMMARY................................................................................................................................VII
ACKNOWLEDGMENTSX

PART I: “INTEGRATING ULTRAMAFIC LAMPROPHYRES INTO THE IUGS
CLASSIFICATION OF IGNEOUS ROCKS: RATIONALE AND IMPLICATIONS” ........1
(S. Tappe; S.F. Foley; G.A. Jenner & B.A. Kjarsgaard)

PART II: “GENESIS OF ULTRAMAFIC LAMPROPHYRES AND CARBONATITES,
AILLIK BAY, CANADA: IMPLICATIONS FOR INCIPIENT RIFTING IN THE
LABRADOR SEA AREA” .........................................................................................................19
(S. Tappe; S.F. Foley; G.A. Jenner; L.M. Heaman; B.A. Kjarsgaard; R.L. Romer; A. Stracke
& J. Hoefs)

PART III: “TORNGAT ULTRAMAFIC LAMPROPHYRES AND THEIR RELATION
TO THE NORTH ATLANTIC ALKALINE PROVINCE” .................................................116
(S. Tappe; G.A. Jenner; S.F. Foley; L.M. Heaman; D. Besserer; B.A. Kjarsgaard & B. Ryan)



vi SUMMARY
The ultramafic lamprophyre (UML) group of igneous rocks comprises potassic, silica
undersaturated members with essential phlogopite/biotite phenocrysts or macrocrysts and >
90 vol.% mafic minerals (including carbonate and apatite), some of which are
characteristically enriched in Al and Ti. UML are globally widespread but represent only a
minor component of continental extension-related magmatism. They are commonly
associated with carbonatites forming dyke swarms or central complexes at rift margins.
However, volumetrically significant UML magma production occurred at the borders of the
Labrador Sea predominantly during the Late Neoproterozoic (~ 610-550 Ma), making it an
ideal area for studying the genesis of this poorly understood magma type and the geodynamic
conditions under which melting occurred.
Previous attempts to decipher the genesis of UML were often hampered by cumbersome
nomenclature systems which caused confusion with other ultramafic rock groups such as
kimberlites. As a consequence, UML were commonly regarded as varieties of kimberlites and
their potential as an indicator of ancient rifting episodes became lost. For this reason, a
simplified UML classification is introduced enabling the correct identification and
subdivision of UML within the IUGS nomenclature system from which they were omitted
entirely in the year 2002. As a first result, the new classification mechanism allows a more
rigorous classification of the Late Neoproterozoic alkaline ultramafic intrusives from northern
Labrador/Quebec and West Greenland as UML and shows that they are not kimberlites as
often referred to in the literature. The existence of a large UML province to either side of the
Labrador Sea remained unrecognized in previous studies because of an inconsistently applied
nomenclature to the dyke rocks from the widespread UML localities and, more importantly,
the lack of detailed petrologic and geochemical characterization and the poorly known age
distribution of rock types. Any genetic model for this UML province has to include a
geodynamic scenario of incipient rifting in an area of thick cratonic lithosphere, which is in
stark contrast to kimberlite magma production within the interior of stable Archean cratons.
A model is developed for the Aillik Bay intrusive suite (central-east Labrador), which is one
of the best exposed and compositionally most diverse UML occurrences at the Labrador Sea
coast. It comprises a variety of UML (aillikite, mela-aillikite, damtjernite) and dolomite-
bearing carbonatite types ranging in age between ~ 590-555 Ma (U-Pb perovskite ages). On
vii 87 86the basis of their overlapping Sr/ Sr ratios (0.70369-0.70662) and initial ε values (+0.1 to i Nd
+1.9) all of these coeval rock types can be related to a single parental magma type. The
carbonate-rich aillikite variety is closest to this primary magma composition, which most
likely formed in a metasomatized garnet peridotite mantle at the base of the cratonic
lithosphere (4-6 GPa, as indicated by the presence of diamonds and relevant published
experimental studies).
Since the geochemical data indicate disequilibrium between the volatile-rich “metasomatic”
component and fertile garnet peridotite under the above outlined pressure conditions, the
volatiles are best considered part of a vein assemblage stabilized within a comparatively cold
lithospheric mantle. The metasomatic incompatible element enriched component was
introduced as small melt frac