Petrologic and geochemical characteristics of the Krivaja-Konjuh ophiolite complex (NE Bosnia and Herzegovina) [Elektronische Ressource] : petrogenesis and regional geodynamic implications / vorgelegt von Branimir Šegvić

Informations

• Publié par: ruprecht-karls-universitat_heidelberg
• Publié le: 01 janvier 2010
• Nombre de lectures: 41
• Poids de l'ouvrage: 26 Mo

Extrait

Petrologic and geochemical characteristics of
the Krivaja-Konjuh ophiolite complex (NE Bosnia and Herzegovina) ─
petrogenesis and regional geodynamic implications



INAUGURAL-DISSERTATION

zur Erlangung der Doktorwürde der
Mathematisch-Naturwissenschaftlichen Gesamtfakultät
der Ruprecht-Karls-Universität Heidelberg





vorgelegt von
Diplom-Geologe
Branimir Šegvi ć
aus Zadar, Kroatien











Tag der mündlichen Prüfung: 05. Februar 2010












Petrologic and geochemical characteristics of
the Krivaja-Konjuh ophiolite complex (NE Bosnia and Herzegovina) ─
petrogenesis and regional geodynamic implications



INAUGURAL-DISSERTATION

zur Erlangung der Doktorwürde der
Mathematisch-Naturwissenschaftlichen Gesamtfakultät
der Ruprecht-Karls-Universität Heidelberg



vorgelegt von
Diplom-Geologe
Branimir Šegvi ć
aus Zadar, Kroatien




Gutachter:
Prof. Dr. Rainer Altherr (Universität Heidelberg)
Prof. Dr. Alan Woodland (Universität Frankfurt)


Tag der mündlichen Prüfung: 05. Februar 2010





























Mojim roditeljima
(Meinen Eltern)











TABLE OF CONTENTS



ABSTRACT 1

KURZFASSUNG 5

1. INTRODUCTION 9
1.1. Prologue 9
1.2. Aims of dissertation 10
1.3. Structure of the thesis 10

2. GEOGRAPHICAL SETTING 13

3. GEOLOGICAL SETTING 17
3.1. A modern conception of Tethyan ophiolites 17
3.2 The Central Dinaridic Ophiolite Belt (CDOB) 19
3.3. Geology of the Krivaja-Konjuh Ophiolite Complex (KKOC) 21

4. PETROGRAPHY AND MINERAL CHEMISTRY OF THE KKOC ROCKS 27
4.1. Sampling locations 27
4.2. Ultramafic rocks 30
4.2.1. Rock types, textures and structures 30
4.2.1.1. Plagioclase lherzolite 31
4.2.1.2. Spinel lherzolite 33
4.2.1.3. Plagioclase lherzolite with pyroxene streaks 35
4.2.1.4. ase lherzolite with poikiloblastic texture 35
4.2.1.5. Equigranular spinel lherzolite 35
4.2.1.6. Spinel-olivine websterite 35
4.2.1.7. Dunite (cumulate ultramafic rocks) 36
4.2.1.8. Podiform chromitite 36
4.2.1.9. Summary of petrographic features 36
4.2.2. Mineral chemistry 38
4.2.2.1. Olivine 38 4.2.2.2. Orthopyroxene 39 4.2.2.3. Clinopyroxene 44
4.2.2.4. Spinel 47
4.2.2.5. Plagioclase 50
4.2.2.6. Other phases 51

4.3. Metamorphic sole 52
4.3.1. Rock types, textures and structures 52
4.3.1.1. Granoblastic amphibolites 54
4.3.1.1.1. Clinozoisite-sapphirine amphibolite 54
4.3.1.1.2. Corundum amphibolite 54
4.3.1.1.3. Epidote-ilmenite amphibolite 56
4.3.1.1.4. Amphibolite 58
4.3.1.2. Porphyroblastic garnet-diopside amphibolite 59
4.3.1.2.1. Rutile-garnet-diopside amphibolite 59
4.3.1.2.2. Contact Opx-bearing garnet-diopside amphibolite 59
4.3.1.2.3. Titanite-garnet-diopside amphibolite 60
4.3.1.2.4. Garnet-diopside amphibolite 61
4.3.1.3. Garnet-diopside-hypersthene amphibolite 61
4.3.1.3.1. Porphyroblastic garnet-diopside-hypersthene amphibolite 61
4.3.1.3.2. Granoblastic garnet-diopsidei-hypersthene amphibolite 61
4.3.1.4. Diopside-amphibolite gneiss 62
4.3.1.5. Plagioclase-garnet-diopside gneiss 62
4.3.2. Mineral chemistry 68
4.3.2.1. Amphibole 68
4.3.2.2. Garnet 71
4.3.2.3. Plagioclase 73
4.3.2.4. Clinopyroxene 75
4.3.2.5. Orthopyroxene 76
4.3.2.6. Other phases 77

5. GEOCHEMISTRY OF KKOC ROCKS 81
5.1. Ultramafic rocks 81
5.1.1. Peridotites 81
5.1.2. Olivine websterites and dunites 93
5.2. Metamorphic sole 97

6. DISCUSSION 107
6.1. Geothermobarometry 107
6.1.1. Introduction 107
6.1.2. Peridotites 110
6.1.2.1. Geothermometers 110
6.1.2.2. Geobarometer 112
6.1.3. Metamorphic rocks113
6.1.3.1. Geothermometers 113
6.1.3.2. Geobarometers 117
6.2. Petrogenesis of peridotitic rocks 127
6.2.1. Mantle peridotites 127
6.2.1.1. Composition and equilibration of KKOC upper mantle 127

6.2.1.2. Nature of upper mantle dynamics 131
6.2.1.3. KKOC geotectonic setting and regional implications 135
6.2.2. Pyroxenites, dunites, and chromitites 140
6.3. Petrogenesis of metamorphic rocks 150
6.3.1. Protolith and its original geotectonic setting 150
6.3.2. Conditions and model of metamorphosis 157
6.3.2.1. Metamorphic evolution recorded in petrographic
characteristics 157
6.3.2.2. Mineral assemblages and P-T conditions of metamorphosis 160
6.3.2.3. P-T-t path of metamorphosis 164
6.3.2.4. Geodynamic significance of metamorphism 166

7. CONCLUSIONS 169

8. REFERENCES 173



APPENDIX 193

A. Materials 193
B. Analytical techniques 195
C. Mineral chemistry 201
D. Bulk-rock geochemistry 298


















ABSTRACT
Based on its petrological and geochemical characteristics, the Krivaja-Konjuh Ophiolite
Complex (KKOC) and the surrounding ophiolitic mélange make an integral part of the Central
Dinaridic Ophiolite Belt (CDOB) of the Internal Dinarides. The Jurassic ultramafic and mafic
sequences form about 80 % of the KKOC, whereas the rest belongs to the metamorphic
sole, which is found concentrating in the northwestern and southern margins. Due to the
emplacement processes, the main peridotite mass is reported to possess a highly
dismembered block-like structure.
The KKOC ultramafic rocks, comprising lherzolites, pyroxenites, dunites, along with rocks
from the metamorphic sole and chromitites were subjected to an extensive analytical
investigation, which included electron micrope probe analysis (EMPA), secondary electron
microscopic (SEM) studies, x-ray fluorescence (XRF) analysis and inductively coupled
plasma mass spectrometry (ICP-MS), in order to reveal their mineralogical, geochemical and
petrological characteristics.
The lherzolitic modal mineralogy consists of olivine, orthopyroxene, clinopyroxene, spinel
and occasionally plagioclase. Most of the analysed samples are characterised by a mantle
porphyroclastic texture and a foliated structure. With respect to clear differences in modal
mineralogy, as well as in phase and bulk-rock chemistry, one is able to distinguish two main
varieties among the KKOC lherzolites. The first one renders spinel lherzolites, whilst the
second variety is known as plagioclase lherzolites.
Geothermometric estimations yielded the main equilibration range, for both spinel and
plagioclase lherzolites, to range from 809 to 1012 °C (T1). The Fe-Mg exchange between
olivine and spinel provided a temperature range of 550 to 682 °C (T2), which is found to be
indicative for subsolidus reequilibration processes. Using the oceanic and rift-ridge
geotherms, the equilibration pressures extending from 1.2 to 2.0 GPa (ca. 40-65 km depth)
were inferred for T1 temperatures. The final equilibration level marked by the T2
temperatures happened under pressures below 1.0 GPa.
Numerous geochemical parametres are pointing to the KKOC lherzolites as fertile solid
residues, which, before metamorphism, underwent low to moderate degrees of MOR melting.
The mineral chemistry of spinel and the REE normalisation levels (relative to chondrite)
yielded an average batch melting degree of ~ 7.7 % for spinel lherzolites. Based on this
estimation and constant values of melt production rate and depth of melting onset, the KKOC
oceanic crust thickness is calculated, having being around 5.4 km. This crustal thickness
would imply a ridge spreading rate of 32 mm/year, which defines the KKOC ridge system to
have been relatively slow-spreading (< 55 mm/year). The modern analogues of such MOR
settings exist in the Northern Atlantic and the Indian Ocean. The most-eastern segment of
the KKOC is, however reported to deviate from the MOR fertile geochemistry.
The occurrence of pargasitic amphibole, coupled with a Cr-enriched spinel, call for
enhanced mantle melting (~ 15 %) in a SSZ-type of setting. Contrary to the amphibole
formation in a SSZ mantle wedge, geochemical evidences clarify the growth of plagioclase
through sub-solidus equilibration (T2) and melt metasomatism of the lithospheric mantle at a
MOR-type setting. It can be concluded that the main part of the KKOC lherzolites presents a
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