Perovskite rheological constraints on the depth limit of deep earthquakes in the subduction zone
-
摘要: 本文利用林伍德石、钙钛矿两种矿物在不同差应力下随温度变化的蠕变曲线,通过约束温度条件和板块俯冲引起的弹性应变率,得到了俯冲带670 km深度可能的应力范围. 结果显示,在俯冲带670 km深度基于林伍德石蠕变得到应力大小可能超过100 MPa,而相变为钙钛矿后仅为0.1~10 MPa. 通过分析认为钙钛矿的Si扩散引起的快速应变率使得670 km更深深度的俯冲带无法支持较大的应力,可能是下地幔地震终止的原因,而不需要考虑亚稳态相变导致反裂隙断层的消失或林伍德石分解后超塑性等影响.Abstract: In this study, the stress levels at 670 km depth in the subduction zone were obtained. The creep curves of ringwoodite and perovskite were plotted at different stresses against temperatures. The stress values were obtained from those plots by constraining temperature range and the elastic strain rate caused by slab subduction. Our results showed that in the subduction zone the stress for ringwoodite creep may be over 100 MPa. However, for perovskite, the stress accumulation is only at a level of 0.1~10 MPa. We proposed that the high creep strain rate of perovskite caused by fast Si diffusion rate leads to the low stress accumulating limits at 670 km after the phase transformation from ringwoodite to perovskite. That can account for the depth limit of earthquakes in subdcution zone and there is no need of the transformational faulting caused by the olivine-spinel transformation or superplasticity of ringwoodite dissociation products.
-
Key words:
- Perovskite /
- Deep earthquake /
- Dislocation creep
-
-
[1] Akaogi M, Ito E. Navrotsky A. 1989. Olivine-modified spinel-spinel transitions in the system Mg2SiO4-Fe2SiO4: calorimetric measurements, thermochemical calculation, and geophysical application. J. Geophys. Res., 94(B11), 15671-15685.
[2] Burnley P C, Green H W, Prior D J. 1991. Faulting associated with the olivine to spinel transformation in Mg2GeO4 and its implications for deep-focus earthquakes. J. Geophys. Res., 96: 425-443.
[3] Devaux J P, Fleitout L. 2000. Stresses in a subducting slab in the presence of a metastable olivine wedge. J. Geophys. Res., 106(B6): 13365-13373.
[4] Frohlich C. 1989. The nature of deep focus earthquakes. Annual Rev. Earth Planet. Sci., 17: 227-254.
[5] Gleason G C, Green H W. 2009. A general test of the hypothesis that transformation-induced faulting cannot occur in the lower mantle. Phys. Earth Planet. Inter., 172(1-2): 91-103.
[6] Green H W, Burnley P C. 1989. A new self-organizing mechanism for deep-focus earthquakes. Nature, 341: 733-737.
[7] Green H W, Young T E, Walker D, et al. 1990. Anticrack-associated faulting at very high pressure in natural olivine. Nature, 348: 720-722.
[8] Green H W, Zhou Y. 1996. Transformation-induced faulting requires an exothermic reaction and explains the cessation of earthquakes at the base of the mantle transition zone. Tectonophysics, 256(1-4): 39-56.
[9] Guest A, Schubert G, Gable C W. 2004. Stresses along the metastable wedge of olivine in a subducting slab: possible explanation for the Tonga double seismic layer. Phys. Earth Planet. Inter., 141(4): 253-267.
[10] Helffrich G R, Wood B J. 2001.The Earth's mantle. Nature, 412: 501-507.
[11] Irifune T. 1993. Phase transformations in the Earth's mantle and subducting slabs: Implications for their compositions, seismic velocity and density structures and dynamics. Island Arc, 2(2): 55-71.
[12] Ito E, Sato H. 1991. Aseismicity in the lower mantle by supper plasticity of the descending slab. Nature, 351: 140-141.
[13] Ito E, Takahashi E. 1987. Melting of peridotite at uppermost lower-mantle conditions. Nature, 328:514-517.
[14] Ito E, Takahashi E. 1989. Postspinel transformations in the system Mg2SiO4-Fe2SiO4 and some geophysical implications. J. Geophys. Res., 94(B8): 10637-10646.
[15] Jiang G, Zhao D. 2011. Metastable olivine wedge in the subducting Pacific slab and its relation to deep earthquakes. J. Asia Earth Sci., 42(6):1411-1423.
[16] Karato S, Riedel M R, Yuen D A. 2001. Rheological structure and deformation of subducted slabs in the mantle transition zone: implications for mantle circulation and deep earthquakes. Phys. Earth Planet. Inter., 2001, 127(1-4): 83-108.
[17] King S D, Ita J. 1995. Effect of slab rheology on mass transport across a phase transition boundary. J. Geophys. Res., 100(B10): 20211-20222.
[18] Kirby S H. 1987. Localized polymorphic phase transformations in high-pressure faults and applications to the physical mechanism of deep earthquakes. J. Geophys. Res., 92(B13): 13789-13800.
[19] Kirby S H, Durham W B, Stern L A. 1991. Mantle phase changes and deep-earthquake faulting in subudcting lithosphere. Science, 252: 216-225.
[20] Kirby S H, Stein S, Okal E A, et al. 1996. Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere. Rev. Geophys., 34(2): 261-306.
[21] Kohlstedt D L. The role of water in high-temperature rock deformation. In: Keppler H and Smyth J R ed. Water in Nominally Anhydrous Minerals, Reviews in Mineralogy and Geochemistry, 2006, 62: 377-396.
[22] Koper K D, Wiens D A. 2000. The waveguide effect of metastable olivine in slabs. Geophys. Res. Lett., 27(4), 581-584.
[23] Marton F C, Shankland T J, Rubie D C, et al. 2005. Effects of variable thermal conductivity on the mineralogy of subducting slabs and implications for mechanisms of deep earthquakes. Phys. Earth Planet. Inter., 149(1-2): 53-64.
[24] Minear J, Toks?z M. 1970. Thermal regime of a downgoing slab and new global tectonics. J.Geophys. Res., 75: 1397-1419.
[25] Negredo A M, Valera J L, Carminati E. 2004. TEMSPOL: a Matlab thermal model for deep subduction zones including major phase transformations. Comp. & Geosci., 30(3): 249-258.
[26] Peacock S M. Thermal and petrologic structure of subduction zones. In Bebout G E, Scholl D W, Kirby S H, et al. ed. Subduction: Top to Bottom, AGU Geophysical Monograph 96, Washington D C, 1996, 119-133.
[27] Peacock S M. Thermal structure and metamorphic evolution of subducting slabs. In: Eiler J M ed. Inside the Subduction Factory, AGU Geophysical Monograph 138, Washington D C, 2003, 7-22.
[28] Presnall D C, Phase diagrams of Earth-forming minerals. In: Ahrens T J ed. Mineral Physics and Crystallography: A Handbook of Physical Constants. American Geophysical Union, Washington D C, 1995.
[29] Rubie D C, Ross C R. 1994. Kinetics of the olivine-spinel transformation in subducting lithosphere: experimental constraints and implications for deep slab processes. Phys. Earth Planet. Inter., 86(1-3): 223-241.
[30] Schmeling H, Monz R, Rubie D C. 1999. The influence of olivine metastability on the dynamics of subduction. Earth Planet. Sci. Lett., 165(1): 55-66.
[31] Scholz C H. The Mechanics of Earthquakes and Faulting. Cambridge University Press: 2nd version, 2002.
[32] Shimojuku A, Kubo T, Ohtani E, et al. 2009. Si and O diffusion in (Mg,Fe)2SiO4 wadsleyite and ringwoodite and its implications for the rheology of the mantle transition zone. Earth Planet. Sci. Lett., 284(1-2): 103-112.
[33] Stein C A, Stein S. 1992. A model for the global variation in oceanic depth and heat flow with lithospheric age. Nature, 359: 123-129.
[34] Stein S, Stein C A. 1996. Thermo-mechanical evolution of oceanic lithosphere: implications for the subduction process and deep earthquakes. Subduction from top to bottom. Geophys. Monogr., 95: 1-17.
[35] Tetzlaff M, Schmeling H. 2000. The influence of olivine metastability on deep subduction of oceanic lithosphere. Phys. Earth Planet. Inter., 120(1-2): 29-38.
[36] Toksöz M, Minear J, Julian B. 1971. Temperature field and geophysical effects of a downgoing slab. J. Geophys. Res., 76, 1113-1138.
[37] Turcotte D, Schubert G. 1973. Frictional heating of the descending lithosphere. J. Geophys. Res.,78: 5876-5886.
[38] Wang S G, Liu Y J, Ning J W. 2011. Relationship between the growth rate of forsterite phase transformation and its water content and the existing depth of metastable olivine.Chinese J. Geophys. (in Chinese), 54(7): 1758-1766.
[39] Weertman J, Weertman J R. 1975. High temperature creep of rocks and mantle viscosity. Annual Rev. Earth Planet. Sci., 3: 293-315.
[40] Wiens D A. 2001. Seismological constraints on the mechanism of deep earthquakes: temperature dependence of deep earthquake source properties. Phys. Earth Planet. Inter., 127(1-4): 145-163.
[41] Xu J, Yamazaki D, Katsura T, et al. 2011. Silicon and Magnesium diffusion in a single crystal of MgSiO3 perovskite. J. Geophys. Res., 116(B12): B12205.
[42] Ye G Y, Lou X T, Wang Y B, et al. 2008. A group of distinct seismic phases that could be used to detect metastable olivine. Chinese J. Geophys. (in Chinese), 51(4): 1165-1171.
-
计量
- 文章访问数: 1103
- PDF下载数: 1623
- 施引文献: 0
下载: