Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-25T07:25:55.640Z Has data issue: false hasContentIssue false
  • English
  • Français

Contrasting settings of serpentinite bodies in the northwestern Zagros Suture Zone, Kurdistan Region, Iraq

Published online by Cambridge University Press:  11 July 2011

NABAZ R. H. AZIZ ,
KHALID J. A. ASWAD  and
HEMIN A. KOYI
NABAZ R. H. AZIZ
Affiliation:
Department of Geology, College of Science, Sulaimani University, Kurdistan Region, Iraq
KHALID J. A. ASWAD
Affiliation:
Department of Geology, College of Science, Mosul University, Iraq
HEMIN A. KOYI*
Affiliation:
Department of Earth Sciences, Uppsala University, Uppsala, Sweden
*
†Author for correspondence: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

Protrusions and lenses of serpentinite–matrix mélanges occur at several places along the thrust faults of the Zagros Suture Zone. They separate the lower allochthonous thrust sheet, the ‘Lower Allochthon’ (i.e. Walash–Naopurdan nappe), of Paleocene–Eocene age from sediments of the Arabian platform and the upper thrust sheet of Mesozoic, ophiolite-bearing terranes termed the ‘Upper Allochthon’ (i.e. Gemo–Qandil nappe). The serpentinite–matrix mélanges occur mostly as stretched bodies (slices) on both sides of the Lower Allochthon (Hero, Halsho and Pushtashan (HHP) and Galalah, Qalander and Rayat (GQR)). Their overall chondrite-normalized rare earth element (REE) patterns form two main groups. Group One exhibits enrichment in the total REEs (> 1 × chondrite) whereas the Group Two pattern shows depletion (i.e. < 1 × chondrite). Bulk-rock MORB-normalized profiles of Group Two are almost flat in the MREE–HREE region with flattening profiles in the Gd–Lu range (> 3 times the MORB composition). In comparison with Group One, Group Two has extremely high REE content and displays variable depletions in the moderately incompatible high-field-strength elements (HFSEs) (Zr, Hf, Y) relative to their adjacent REEs. The REEs in the GQR serpentinite–matrix mélanges have a noticeably high LREE content, and a positive Eu anomaly, and their HREE content never reaches more than 1 × chondrite (i.e. < 0.01 to 1 × chondrite). The latter indicates that the hemipelagic sedimentary, melt-like components (i.e. high LREE, U/La, La/Sm and low Ba/Th) control the geochemical peculiarities of this type of serpentinite. The HHP serpentinite–matrix mélanges, however, are either equally divided between the two REE pattern groups (e.g. Hero, Halsho) or inclined towards Group One (e.g. Pushtashan). Contrary to GQR serpentinites, the variation in HHP serpentinite–matrix mélanges spans a compositional spectrum from U/La-rich to more Ba/Th-rich. Such ratio variations reflect the large variation in these two subducted sedimentary components (i.e. carbonate and hemipelagic sediment mix). The obvious differences in the trace element signatures of the GQR and HHP serpentinite–matrix mélanges might be related to plate tectonic parameters such as convergence rate, subduction age and thickness and type of subducted slab. It is more likely that the influx of subducted components to the mantle wedge relied heavily on the composition of the sedimentary inputs. These vary considerably with time from the relatively deepwater hemipelagic sediments (Qulqula Radiolarite Formation) to platform carbonate sediments (Balambo limestone). The trace element signatures of the GQR and HHP serpentinite–matrix mélanges might suggest multi-staging of the allochthonous sheet emplacement on the Arabian platform sediments.

Keywords

serpentiniteZagrosKurdistan Regiontectonicsubduction
Type
THE ZAGROS OPHIOLITES
Information
Geological Magazine , Volume 148 , Issue 5-6: THEMATIC ISSUE: Geodynamic evolution of the Zagros , November 2011 , pp. 819 - 837
Copyright
Copyright © Cambridge University Press 2011

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Agard, P., Jolivet, L., Vrielynck, B., Burov, E. & Monié, P. 2007. Plate acceleration: the obduction trigger? Earth and Planetary Science Letters 258, 428–41.CrossRefGoogle Scholar
Aswad, K. J. 1999. Arc–continent collision in northeastern Iraq as evidenced by Mawat and Penjwin Ophiolite Complexes. Raffidain Journal of Science 10, 51–61.Google Scholar
Aswad, K. J. A., Aziz, N. R. H. & Koyi, H. A. 2011. Cr-spinel compositions in serpentinites and their implications for the petrotectonic history of the Zagros Suture Zone, Kurdistan Region, Iraq. Geological Magazine, doi: 10.1017/S0016756811000422.Google Scholar
Aswad, K. J. & Elias, E. M. 1988. Petrogenesis, geochemistry and metamorphism of spilitized subvolcanic rocks of the Mawat Ophiolite Complex, NE Iraq. Ofiolitti 13, 95–109.Google Scholar
Aziz, N. R. H., Elias, E. M. & Aswad, K. J. 2011. Rb–Sr and Sm–Nd isotope study of serpentinites and their impact on the tectonic setting of Zagros Suture Zone, NE-Iraq. Iraqi Bulletin of Geology and Mining 7, 67–75.Google Scholar
Boudier, F. & Nicolas, A. (eds). 1988. Special Issue: The Ophiolites of Oman. Tectonophysics 151, 1–401.Google Scholar
Elliott, T., Plank, T., Zindler, A., White, W. & Bourdon, B. 1997. Element transport from slab to volcanic front at the Mariana arc. Journal of Geophysical Research 102, 14991–15019.Google Scholar
Ernst, W. G., Maruyama, S. & Wallis, S. 1997. Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust. Proceedings of the National Academy of Sciences of the United States of America 94, 9532–7.CrossRefGoogle ScholarPubMed
Gerya, T. V. &. Stöckhert, B. 2002 Exhumation rates of high pressure metamorphic minerals in subduction channels: the effect of rheology. Geophysical Research Letters 29, 1261, doi: 10.1029/2001GL014307, 4. pp.CrossRefGoogle Scholar
Govindaraju, K. 1995. 1995 working values with confidence limits for twenty-six CRPG, ANRT and IWG-GIT geostandards. Geostandards Newsletter 19 (Special Issue), 1–32.CrossRefGoogle Scholar
Guillot, S., Hattori, K. H., De Sigoyer, J., Nagler, T. & Auzende, A.-L. 2001. Evidence of hydration of the mantle wedge and its role in the exhumation of eclogites. Earth Planetary Science Letters 193, 115–27.CrossRefGoogle Scholar
Hermann, J., Miintener, O. & Scambelluri, M. 2000. The importance of serpentinite mylonites for subduction and exhumation of oceanic crust. Tectonophysics 327, 225–38.CrossRefGoogle Scholar
Hilairet, N., Reynard, B., Wang, Y., Daniel, I., Merkel, S., Nishiyama, N. & Petitgirard, S. 2007. High pressure creep of serpentine, interseismic deformation, and initiation of subduction. Science 318, 1910–13.CrossRefGoogle ScholarPubMed
Hofmann, A. W. 1988. Chemical differentiation of the earth: the relationship between mantle, continental crust, and oceanic crust. Earth and Planetary Science Letters 90, 297–314.CrossRefGoogle Scholar
Horodyskyj, U., Lee, C. T. A. & Luffi, P. 2009. Geochemical evidence for exhumation of eclogite via serpentinite channels in ocean-continent subduction zones. Geosphere 5, 426–8.CrossRefGoogle Scholar
Jassim, S. Z. & Buday, T. 2006. Units of the unstable shelf and the Zagros Suture, Chapter 6. In Geology of Iraq (eds Jassim, S. Z. & Goff, J. C.), pp. 71–90. Brno, Czech Republic: Dolin, Prague and Moravian Museum.Google Scholar
Jassim, S. Z., Suk, M. & Waldhausrova, J. 2006. Magmatism and metamorphism in the Zagros Suture, Chapter 17. In Geology of Iraq (eds Jassim, S. Z. & Goff, J. C.), pp. 212–31. Brno, Czech Republic: Dolin, Prague and Moravian Museum.Google Scholar
King, R. L., Bebout, G. E., Moriguti, T. & Nakamura, E. 2006. Elemental mixing systematics and Sr-Nd isotope geochemistry of mélange formation: obstacles to identification of fluid sources to arc volcanics. Earth and Planetary Science Letters 246, 288–304.CrossRefGoogle Scholar
Kogiso, T., Tatsumi, Y. & Nakano, S. 1997. Trace element transport during dehydration processes in the subducted oceanic crust: 1. Experiments and implications for the origin of ocean island basalts. Earth and Planetary Science Letters 148, 193–205.CrossRefGoogle Scholar
Lindquist, E. S. & Goodman, R. E. 1994. The strength and deformation properties of a physical model melange. In Proceedings of the first North American Rock Mechanics Symposium (Narms) (Austin, Texas): (eds Nelson, P. P. & Laubach, S. E.), pp. 843–50. Rotterdam: A.A. Balkema.Google Scholar
Liu, X. & O'neill, H. StC. 2000. The effect of Cr2O3 on partial melting relations in the model mantle system CMAS-Cr2O3. In Australian National University Research School of Earth Sciences Annual Report 2000, pp. 104–5.Google Scholar
Niu, Y. 2004. Bulk-rock major and trace element compositions of abyssal peridotites: implications for mantle melting, melt extraction and post-melting processes beneath mid-ocean ridges. Journal of Petrology 45, 2423–58.Google Scholar
Niu, Y. & Hekinian, R. 1997. Basaltic liquids and harzburgitic residues in the Garrett Transform: a case study at fast-spreading ridges. Earth and Planetary Science Letters 146, 243–58.Google Scholar
Nicolas, A. 1989. Structures of ophiolites and dynamics of oceanic lithosphere. Dordrecht: Kluwer Academic, 368 pp.Google Scholar
Nicolas, A., Ildefonse, B. Boudier, F., Lenoir, X. & Ben Ismail, W. 2000. Dike distribution in the Oman-United Arab Emirates ophiolite. Marine Geophysical Researches 21, 269–87.CrossRefGoogle Scholar
Patino, L. C., Carr, M. J. & Feigenson, M. D. 2000. Local and regional variations in Central American arc lavas controlled by variations in subducted sediment input. Contributions to Mineralogy and Petrology 138, 265–83.CrossRefGoogle Scholar
Plank, T. & Langmuir, C. H. 1993. Tracing trace elements from sediment input into volcanic output at subduction zones. Nature 362, 739–42.CrossRefGoogle Scholar
Salters, V. J. M., Longhi, J. E. & Bizimis, M. 2002. Near mantle solidus trace element partitioning at pressures up to 3.4 GPa. Geochemistry, Geophysics, Geosystems (G3) 3, 1038, doi:10.1029/2001GC000148, 23 pp.Google Scholar
Stern, R. J., Kohut, E. J., Bloomer, S. H., Leybourne, M., Fouch, M. & Vervoot, J. 2006. Subduction factory processes beneath the Guguan cross-chain, Mariana Arc: no role for sediments, are serpentinites important? Contributions to Mineralogy and Petrology 151, 202–21.CrossRefGoogle Scholar
Schmidt, M. W. & Poli, S. 1998. Experimentally based water budgets for dehydrating slabs and consequences for arc magma generation. Earth and Planetary Science Letters 163, 361–79.CrossRefGoogle Scholar
Schwartz, D. P., Stenner, H. D., Costa, C., Smalley, R., Ellis, M. & Velasco, M. 2001. Paleoseismology at the end of the world: initial observations of the Fagnano Fault, Tierra Del Fuego, Argentina. Seismological Research Letters 72, 265.Google Scholar
Sun, S. S. & McDonough, W. E. 1989. Chemical and isotopic systematics of ocean basalt: implications for mantle composition and processes. In Magmatism in the Ocean Basins (eds Saunders, A. D. & Norry, M. J.), pp. 313–45. Geological Society of London, Special Publication no. 42.Google Scholar
Wunder, B., Baronnet, A. & Schreyer, W. 1997. Ab-initio synthesis and TEM confirmation of antigorite in the system MgO-SiO2-H2O. American Mineralogist 82, 760–4.CrossRefGoogle Scholar
You, C.-F., Castillo, P. R., Gieskes, J. M., Chan, L. H. & Spivack, A. J. 1996. Trace element behavior in hydrothermal experiments: implications for fluid processes at shallow depths in subduction zones. Earth and Planetary Science Letters 140, 41–52.Google Scholar