petrology of ultramafic and related rocks along iraqi zagros thrust zone

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polymorphs; however slight chemical differences do distinguish them from one another (Winter, 2001; Mohammad and Maekawa, 2007). Antigorite, the most chemically and structurally distinct type within the three species, tends to be stable at higher temperatures than the other two phases of serpentine (Raymond, 2002; Mohammad and Maekawa, 2007). Because of their structural differences, quantitative x-ray diffraction can be used to distinguish the different varieties of serpentine present in a given body of rock. Serpentinization often occurs within subduction zone because ocean water in a trench has the ability to seep down into the mantle wedge causing hydration of ultramafic minerals into serpentine. However, serpentinization also occurs on the ocean floor as a result of the reaction between ocean water and basalt formed at mid-ocean ridges (Winter, 2001, Gaetani et. al., 1998). Different degrees of serpentinization can occur even within a single rock body, with the highest degrees of metamorphism typically found in association with fractures and cracks, along which water can more easily travel (Gaetani et.al., 1998). Serpentinization can be isochemical (constant chemistry) or allochemical (constant volume). During isochemical serpentinization, the bulk composition of the rock plus the introduced water is not changed. The isochemical serpentinization reaction between peridotite and water typically results in a net increase in volume because of the less structurally condensed nature of serpentine with respect to olivine and pyroxene. As a result of this volume increase, serpentinization can cause extensive internal fracturing within a rock body (see reaction 1). Allochemical serpentinization occurs as a constant volume process in which large positively charged ions such as Mg 2+ , Ca 2+ , Fe 2+ , and Si 4+ , are released into solution during the serpentinization process, and transported away by fluids (see reaction 2) 7
Reaction 1: Isochemical serpentinization Olivine + silica in solution Serpentinite 3Mg 2 SiO 4 + H 4 SiO 4 + 2H 2 O 2Mg 3 Si 2 O 5 (OH) 4 (131cc) introduced (220cc) Reaction 2: Allochemical serpentinization Olivine + water solution (Raymond, 2002) serpentine + Mg ion + hydroxyl ion + silica in 5Mg 2 SiO 4 +10H 2 O 2Mg 3 Si 2 O 5 (OH) 4 + 4Mg 2+ + 8(OH) +H 4 SiO 4 (219 cc) introduced (220 cc) removed in solution (Raymond, 2002) 1-1-3-2 Ultrahigh-pressure metamorphism (UHP) Recently exsolution microstructures in minerals have been identified in ultrahigh-pressure (UHP) ultramafic rocks from several orogenic belts including Western Gneiss Region, Norway; Alpe Arami, Switzerland; Centeral Sulawies, Indonesia; Dabie-Sulu UHP terrane in East-Centeral China (Smith, 1988; Dobrzhinetskaya et al., 1996; Harcker et al., 1997; Zhang and Liou 1998; Zhang et al., 1999). The most common exsolution features in olivine from UHP garnet peridotite are ilmenite lamella or rods; magnetite lamella is minor. Exsolution lamella in diopside includes K-feldspar, ilmenite, Mg-Al-Cr titanomagnetite, and garnet. Quartz lamellae is also found in both omphacite and diopside. Exsolution lamellae in garnet includes both Al-pyroxene and rutile rods. Exsolution lamellae in UHP minerals may have formed during nearly isothermal decompression, in contrast to exsolution with falling temperature in primary igneous minerals. Mineral exsolution from breakdown of a solidsolution phase is a subsolidus reaction. A principle characteristic of UHP solid-solution phases, such as majoritic garnet and supersilicic clinopyroxene, is the substitution of sixfold coordinated Si for Al, Fe and Mg in octahedral sites. For example, the tschermakite substitution of [2 Al 8
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 and 22: ocks of the belt. These attributes
Page 23: 1-1-3 Metamorphism of ultramafics M
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 (
Page 76 and 77:
involves loss and gain of CaO, SiO
Page 78 and 79:
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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