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同系温度为晶体材料的绝对温度(T)与其熔点(T_m)的比值,是对比晶体流变强度的重要参数之一.橄榄石(Mg,Fe)_2Si O_4的熔点随含铁量和含水量的增加而降低,随压力增加而升高,高压下橄榄石的相变可导致熔点随压力发生不连续变化.本文对前人的铁橄榄石(Fe2Si O_4)熔融实验结果进行校正,确定铁橄榄石-γ相Fe2Si O_4-熔体的三联点位于6.4GPa和1793K.然后使用广义混合律建立了常压至6.4GPa,无水橄榄石的固相线和液相线与含铁量和压力的关系.橄榄石T/T_m随深度的变化可用于定性对比具有不同热状态和橄榄石成分的上地幔流变强度,T/T_m=0.5的深度界定了上地幔从半脆性变形到完全塑性变形的转换深度.克拉通岩石圈地幔的橄榄石T/T_m显著低于造山带和伸展盆地,一直到岩石圈-软流圈边界才与周围地幔趋于一致(T/T_m>0.66),表明克拉通的岩石圈强度较高.此外,使用T/T_m分析橄榄石的变形实验结果,发现含水量对橄榄石组构的影响与压力密切相关,但是水对橄榄石流变强度的弱化作用及其与橄榄石同系温度的关系尚需进一步研究.低于6.4GPa(<200km),T/T_m控制了橄榄石[100]和[001]位错滑移的转变.在上地幔10~-(12)~10~-(15)s~(-1)的应变速率和低应力条件下,橄榄石[100](010)位错滑移系(A型组构)的稳定域为T/T_m>0.55~0.60.T/T_m<0.55~0.60时,[001]位错滑移更易于发生,低T/T_m使橄榄石的主控位错滑移系转变为[001](100),形成C型组构.这与天然变形的橄榄岩普遍发育橄榄石A型组构,而超高压变质带中经历了深俯冲的橄榄岩发育橄榄石C型组构一致.而[001](010)位错滑移系(B型组构)受T/T_m和应力的共同影响.因此,橄榄石的同系温度建立了将变形实验结果外延到上地幔流变的桥梁.克拉通地区的上地幔地震波各向异性需要一个四层模型来拟合:上层为残留的A型组构,中间为B型组构,岩石圈-软流圈边界为新生的A型或B型组构,以及Lehmann不连续面之下以扩散蠕变为主的软流圈地幔.对橄榄石组构转变机制的认识是通过地震波各向异性追踪上地幔含水量的分布和地幔流动的关键.
The homoclinic temperature is one of the important parameters for comparing the rheological strength of crystalline materials with the ratio of the absolute temperature (T) to the melting point (T_m) .The melting point of olivine (Mg, Fe) _2SiO_4 varies with the iron content and water content Increases and decreases with the increase of pressure, and the phase transition of olivine under high pressure can lead to the discontinuous change of melting point with pressure.In this paper, the results of the melting experiment on Fe 2 Si O 4 were corrected and the content of fayalite -γ phase Fe2Si O 4 melt is located at 6.4 GPa and 1793 K. The generalized mixing law is then used to establish the pressure to 6.4 GPa. The solidus and liquidus phases of the anhydrous olivine are related to the iron content and pressure . The variation of olivine T / T_m with depth can be used to qualitatively contrast the rheological strength of the upper mantle with different thermal states and olivine components and the depth of T / T_m = 0.5 defines the transition from semi-brittle to complete plastic deformation of the upper mantle Depth.The peridotite T / T_m of the cratonic lithospheric mantle was significantly lower than that of the orogenic belt and extensional basin until the lithosphere-asthenosphere boundary converged with the surrounding mantle (T / T_m> 0.66), indicating that the craton Lithosphere strength is higher. In addition, olivine is analyzed using T / T_m It is found that the influence of water content on the olivine structure is closely related to the pressure, but the weakening effect of water on the rheological strength of olivine and its relationship with the olivine temperature need to be further studied.Under 6.4GPa (< 200km) and T / T_m controlled the transition of the olivine [100] and [001] dislocation slips.In the upper mantle, the strain rates of 10 ~ - (12) ~ 10 ~ - (15) s ~ Under the condition of low stress, [001] dislocation of olivine [010] dislocation slip system (type A structure) is T / T_m> 0.55 ~ 0.60.T / T_m <0.55 ~ 0.60 Sliding is more likely to occur, and the low T / T_m transforms the host dislocation slip system of olivine to [001] (100), forming a C-type structure, which is consistent with the natural peridotite formation of olivine type A Structure, while the ultra-high pressure metamorphic belt experienced a deep subduction peridotite C-type structure of olivine development consistent with the [001] (010) dislocation slip system (B-type structure) by T / T_m and stress together Therefore, the temperature of the olivine’s syngeneic establishes a bridge that deforms the results of the deformation experiment into the upper mantle.The seismic wave anisotropy of the upper mantle in the cratonic region requires a four-layer model to fit: the upper A-type group Structure, the middle of the B-type structure , The lithosphere-asthenosphere boundary is a newborn A-type or B-type structure, and asthenosphere-dominated asthenospheric mantle beneath the Lehmann discontinuity.The understanding of the olivine structure transition mechanism is based on seismic waves The key to anisotropy tracking the distribution of mantle moisture content and mantle flow.