petrology of ultramafic and related rocks along iraqi zagros thrust zone

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Typical ophiolite sequences are composed of a thin layer of deep-sea sediments, overlying a sequence of basaltic pillow lavas, sheeted dike complexes, foliated to layered gabbro, and finally an ultramafic complex, which can have an exposed thickness of up to 7 km. This ultramafic section of ophiloite can vary in composition, however, it is most commonly dominated by varieties of peridotite typically associated with the mantle such as harzburgite (olivine and orthopyroxene rich), lherzolite (olvine, orthopyroxene, and clinopyroxene rich), and wehrlite (olivine and clinopyroxene rich), and dunite (olivine rich). 1-1-2-3 Replacive ultramafics Another non-cumulate mechanism for the formation of ultramafic rocks involves the replacement of pyroxene minerals with olivine through chemical reactions between a silica-poor magma and a pyroxene-rich host rock (Kubo, 2002). This replacement occurs as the process that silica-poor magma rises through the mantle and saturates pyroxene-rich mantle lherzolite or harzburgite during its ascent. As silica-rich minerals generally have a lower melting temperature than silica-poor minerals, the pyroxene minerals are partially dissolved by the magma, leaving behind olivine in place of pyroxene (Kubo, 2002). Because replacive processes have only recently been defined, there are few studies which focus on the extent to which replacement plays a role in the formation of dunites (Kubo, 2002). At this time, replacive processes are thought to occur most commonly in the transition zone of ophiolite sequences, between ultramafic tectonite and ultramafic cumulate units (Arai, 1994). 5
1-1-3 Metamorphism of ultramafics Metamorphism of ultramafic rocks occurs both at depth and near the surface of the earth during tectonic uplift and emplacement. Because the mantle is under high lithostatic pressure, most mantle rocks have been partially metamorphosed even before their uplift and emplacement (Winter, 2001). Chemical alteration and metamorphism of rocks in the upper mantle are associated with partial melting, fractional crystallization of partially melted magmas, and localized ductile deformation. The primary metamorphic features are difficult to distinguish from features caused by subsequent metamorphism during exhumation stage. The distinctions, however, can be made by geochemical and petrologic analysis to reveal the presence or absence of high pressure mantle mineral fabrics and chemical compositions (Raymond, 2002, Gaetani et al, 1998, Jameieson, 1981). For example, olivine grains which were originally formed in the mantle would be expected to show evidence of ductile deformation. Therefore, the presence of undulatory extinction or zoning in large olivine grains in ultramafic tectonites is often interpreted as an indication of the absence of recrystallization. Accordingly, chemistry of olivine grains with undulatory extinction in ultramafic tectonites is often interpreted as reflecting the composition of the rocks as they existed in the mantle before exhumation (Winter, 2001, Raymond, 2002, Downes, 2001). 1-1-3-1 Serpentinization Metamorphism of ultramafic rocks during uplift and emplacement commonly involves serpentinization, a process by which water is introduced into the system, causing recrystallization of ultramafic minerals into serpentine (Gaetani et. al, 1998). Serpentine Mg 3 Si 2 O 5 (OH) 4 is a metamorphic phyllosilicate with monoclinic, triclinic, orthorhombic or hexagonal structure, depending on the mineral species and environment of crystallization. The three main varieties of serpentine are lizardite, chrysotile, and antigorite (Nesse, 1999). These species are practically 6
Page 1 and 2: PETROLOGY OF ULTRAMAFIC AND RELATED
Page 3 and 4: We certify that we read this thesis
Page 5 and 6: ABSTRACT Four main ultramafic rock
Page 7 and 8: CONTENTS Chapter 1: Background, Aim
Page 9 and 10: Chapter 7: Conclusions and Recommen
Page 11 and 12: Figure 3 - 10: Field photograph of
Page 13 and 14: albite - tremolite zone, E = albite
Page 15 and 16: Figure 6 - 19: Time-paragenesis, al
Page 17 and 18: Table 6 - 2: Representative microna
Page 19 and 20: 1 BACKGROUND 1-1 Ultramafic rocks U
Page 21: ocks of the belt. These attributes
Page 25 and 26: Reaction 1: Isochemical serpentiniz
Page 27 and 28: 1-2-2 Jadeitites Jadeitite is compo
Page 29 and 30: In combining the new data on the se
Page 31 and 32: 2-1 Regional geology The Iraq Zagro
Page 33 and 34: 2-1-1 Geology of Penjwin area 2-1-1
Page 35 and 36: of Luta-Rash. Volcanic rocks are ex
Page 37 and 38: and a sandstone unit of the Paleoce
Page 39: Fig. 2-1: Tectonic subdivision of I
Page 42 and 43: Fig. 2-4: Field photograph of Gimo
Page 45 and 46: Chapter 3 Petrology of ultramafic r
Page 47 and 48: 3-1-2 Harzburgite Harzburgite is th
Page 49 and 50: 3-1-6 Serpentinite Two types of ser
Page 51 and 52: small amount of ilmenite. Hornblend
Page 53: In places, it is surrounded by fine
Page 62 and 63: 4 Mineralogy and mineral chemistry
Page 64 and 65: compositions with Mg-number ranging
Page 66 and 67: 4-3-4 Hydrous phases Hydrous phases
Page 68 and 69: Fig 4 -3: Compositions of chromian
Page 70 and 71: Fig 4 -6: Compositions of chromian
Page 72 and 73:
Chapter 5 Discussions 55
Page 74 and 75:
the tectonite region of the graph (
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involves loss and gain of CaO, SiO
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Fig. 5 - 1: Chromian spinel composi
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Fig. 5-3: Cr-number in spinel vs. F
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Chapter 6 Related rock 65
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plagioclase (Figs. 6 - 2 G,H) and z
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Plagioclase and ilmenite are the or
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2 CaAl 2 Si 2 O 8 (anorthite) + Na
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apatite grains, characterized by bl
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the rim. Estimated pressure - tempe
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16 clinozoisite + H 2 O. (16) From
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metamorphism. It was also formed du
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Fig. 6 - 2: Photomicrographs and im
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Fig. 6 - 4: Backscattered electron
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Fig. 6 - 7: Line scan profile acros
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Fig. 6 - 9: Line scan profile of pa
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Fig. 6 - 11: (A) Backscatter electr
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Fig. 6 - 13: Field of the approxima
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Fig. 6 - 15: Whole rock chemical co
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Fig. 6 - 17: Whole rock chemical co
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Fig. 6 - 19: Time-paragenesis, albi
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1 Conclusions 1. The Iraqi Zagros T
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2 Recommendations for further works
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Arai, S., 1987. An estimation of th
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Chakhmouradian, A.R., Reguir, E.P.,
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Evans, B.W., Frost, B.R., 1975. Chr
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Kamenetsky, V., Crawford, A. J., an
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Morand, V.J., 1990. High chromium a
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Watson, E.B., Wark, D. A. and Thoma
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Table 4 - 1: Representative microna
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Table 4 -11: Representative microna
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Table 4 -13: Representative microna
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Research public activity Peer-revie
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petrology of ultramafic and related rocks along iraqi zagros thrust zone

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