【摘要】 本文从热力学、物理学、物质结构和高压高温相变的角度对板块俯冲—折返假说的物理基础进行了分析讨论。在实际不均匀固体地球高压高温热力学体系中,地表柯石英超高压变质的非平衡态形成模式比平衡态形成模式有更大的普遍性、多样性;"静态流体地球"模型和静岩压力与深度换算公式,对其中的非平衡态体系,和地表中可能存在的局域准静水压平衡态体系,都不适用。把压力直接换算成地球深度,断言地表矿物柯石英就是产生于上地幔的稳定相的结论,以及回避俯冲原动力,把地表柯石英和金刚石超高压变质物的存在与深俯冲之间划上恒等号,缺乏科学根据。实际不均匀固体地球是一个天然的高压高温体系,为了保存高压高温相柯石英,岩石圈内板块折返冷却速率应与实验室中所进行的保压淬火临界速率具有可比性。从实验室的高压高温相变规律看,如此极端缓慢的板块折返抬升冷却速率很难保持住柯石英。有关影响折返过程保存柯石英的四个重要因素还存在很多矛盾问题。物质中原子扩散和化学反应时间通常落在μs~m s范围,而建立平衡时间在m in~102h之间。在由超高压变质岩的同位素定年法和扩散动力学冷却速率法所得构造变质过程的时间内,己有极其充足的时间在几十千米的有限尺度中,进行扩散反应、产物变质,乃至于建立同位素平衡。由于波速异常成因存在的多解性,板块俯冲—折返通道(轨迹),不应仅由地震层析波速异常图来确定。板块俯冲与折返运动的变化应遵循能量和质量守恒定律,在P—T—t轨迹(通道)中应留下数量较多的俯冲—折返过程陆壳岩石、地幔物质的一次相变或二次相变等产物。回顾板块俯冲—折返假说本身的发展过程,最关键的一步,是忽视了固体地球物质的成分、应力等局部不均匀性所造成的局部高压微区和其它非平衡热力学因素影响等事实,沿用传统的静流体模型及其压力—深度换算公式。从物理基础看,板块深俯冲快折返的"壮观地质事件"的猜想,尚需更多更科学的证据去证实。更多还原

【Abstract】 In the present paper,the physical foundation of the hypothesis of plate subduction—exhumation in the Earth has been analyzed and discussed in the light of thermodynamics,physics,matter-structure and high-temperature high-pressure phase-transformation.For the non-equilibrium high-temperature high-pressure system of the heterogeneous solid Earth,the non-equilibrium state formation modes for the ultrahigh-pressure metamorphism of coesite in the Earth’s crust are more greater universality and diversity than the equilibrium state formation mode which should not be assumed to be the only one.The mode of static fluid Earth and conversion formula of litho-static pressure into depth are valid no longer for the real heterogeneous solid Earth including not only the non-equilibrium state,but also the equilibrium state existing possibly in some localized regions with stable hydrostatic,quasi-hydrostatic pressure in the Earth’s crust.Chopin(1984) has favoured the idea that coesite grew under nearly static(hydrostatic) pressure condition which belonged an equilibrium thermodynamics growth mode,he has opened a coesite ultrahigh pressure metamorphic study of its kind.However,it is lacking in scientific evidence that the subsequent use of conversion formula of litho-static pressure into depth,made the formation pressure ≥2.8GPa of natural coesite translate into 100km directly;and further asserted that the obtained coesite in the Earth’s crust is a stable phase produced from the Earth’s mantle.For the actual inhomogeneity solid earth,the driving force of plate deep subduction already was not the issue of overcoming fluid buoyancy which is driving low-density continental crust rocks to insert into high-density crust—mantle rock,but should resolve the problem of low-density continental crust rocks to penetrate into solid crust—mantle rock with high-density.It is necessary to have a giant,abnormal,and rare driving force for that.From the point of view of physics,it is very hard to subduct solid continental crust rock into solid crust—mantle rock.Chopin firstly evaded the original driving force,and further,drew a constant equal sign without scientific basis between the two events of the coesite and diamond ultrahigh pressure metamorphic rock found in the Earth’s crust and the stable phase produced in the mantle or the deep subduction,and then again rose up to a "paradigm" height that had misled need no original driving force of research.Since the introduction of the hypothesis of plate subduction—exhumation so far,the original driving force of plate subduction—exhumation has always not been resolved.Uneven solid Earth is a natural high-temperature high-pressure system,in order to preserve the coesite,a high-temperature high-pressure phase of quartz,the rapid cooling rate of plate is requested over 40℃ / Ma that should be comparable with the laboratory critical rate of quenching under pressure-keeping(which requires not less than(0.5 ~ 1.0)×102℃ / s),however,there is a huge differential in 1013 order of magnitude for both cases.From the lab phase change regularity of high-temperature high-pressure,such extremely slow cooling rates of plate exhumation is difficult to keep the living coesite.Conversely,in order to make plate exhumation speed reached laboratory critical cooling rate of keeping coesite quenching under pressure,the speed(in air)of plate exhumation must achieve 10 ~ 20km/s.This meant that to make a huge amount matter with such great speed fast penetrate and exhumation in the solid medium that needs a giant abnormal rare driving force of exhumation,however,from physics viewpoint it is extremely difficult to achieve.In addition,the four important factors put forward by Chopin,influencing the coesite preserve during turn-back process,still exist many problems,and also could not overcome the above paradoxes.The time of atomic diffusion and chemical reaction in solid matter usually falls within the range of μs~ ms,and to create an equilibrium within min ~ 102 h.By the isotopic geochronology of ultrahigh pressure metamorphic rocks and "Frying ice cream" model identification,the time from subduction to exhumation was of 10 ~ 20Ma;and the time from geospeedometry incoming structure metamorphism process was more shorter(< 0.2 Ma).Compared the time of atomic diffusion and chemical reaction of matter with that of results obtained from isotopic geochronology and geospeedometry,there is the same huge orders of magnitude 1017 ~ 20difference between them.From the viewpoint of structure and behavior of materials,in research involving several Ma which is not long to the geological time scale during plate exhumation,and several to tens kilomiters of limited size scale,there should be extremely plenty of time for diffusion,chemical reaction,product metamorphism and exchange with mantle materials to establish isotope equilibrium.The view of "short stay time and fast turn-back speed,without adequate isotope exchange did not reach the isotopic equilibrium"is unbelievable.The hypothesis of plate subduction—exhumation besides must be inspected by the above physical foundation,still needs to be able smoothly to explain the relevant features of coesite in the Earth’s crust.Due to the existence of diversity solutions of wave velocity anomaly genesis,the subduction—exhumation channels(track) should not determine only by seismic wave topographic anomaly map.Plate subduction and exhumation movement is the big event with a big energy and large space changes,and their energy changes should follow the law of conservation of energy.In P—T—t track(channel),the first phase-transformation products produced in obvious and large quantities during the subduction process of continental crust-rocks should be left,and the phase-transformation products occurred by quenching under pressure-keeping,or under low-pressure low-temperature conditions of mantle matter,and the secondary phase-transformation products of continental crust-rocks during the exhumation process should be left also.Similarly,plate subduction—exhumation should comply with the mass-conservation law,P—T—t track(channel) in upper-mantle should appear corresponding continental crust-rocks matter and their phase-transformation products,and around coesite in the Earth’s crust where should exist more mantle-interior materials of up-left.Review the development process of subduction—exhumation hypothesis of itself,the most critical step was neglecting the facts that the localized high-pressure micro-zone induced by local heterogeneity of solid Earth composition,stress and so on,and the influence of other non-equilibrium thermodynamics factors;and adhered to the traditional static fluid Earth model and its pressure—depth conversion formula.From the viewpoint of physical basis,the conjecture of "spectacular geological event" of plate deep-subduction fast-exhumation,still needs more and more scientific evidence to prove.更多还原