大陆岩石圈地幔异剥橄榄岩化的证据和意义

异剥橄榄岩化是地幔橄榄岩与硅不饱和熔体发生强烈相互作用的地幔过程。这一过程通常伴随地幔物理-化学性质的显著改变，与克拉通岩石圈减薄和破坏密切相关。本文梳理了前人对异剥橄榄岩化的驱动机理、结构和成分特征及其对大陆稳定性影响等方面的定性认识，并在此基础上通过热力学模拟，刻画了不同属性地幔与熔体在不同温度压力条件下的相互作用过程，目标是为定量限定异剥橄榄岩化的发生条件、物理-化学效应及地球动力学意义。研究显示，异剥橄榄岩化通常会出现磷灰石、角闪石、金云母和碳酸盐等标志性交代矿物，并以斜方辉石被单斜辉石替换为典型特征，还可发育海绵边、熔体囊（已冷却结晶为单斜辉石、橄榄石等细粒矿物）和矿物环带等非平衡结构。热力学模拟表明，熔岩反应过程受原岩、熔体性质以及熔/岩比例的共同控制，不同属性地幔（难熔方辉橄榄岩、饱满二辉橄榄岩）与贫硅（如霞石岩）熔体反应都能生成富单斜辉石橄榄岩，且在较高压力（如2.5GPa和4.0GPa）条件下更容易形成异剥橄榄岩；相比之下，不同性质地幔与富硅（如MORB）熔体反应在任何压力条件下均不能产生异剥橄榄岩。此外，两类熔体参与的熔岩反应均能引起围岩密度逐渐增加，并在高压条件下能导致饱满岩石圈地幔密度超过地幔参考值、达到岩石圈失稳的条件。因此，本文从热力学的角度定量约束了异剥橄榄岩化的发生条件和对岩石圈地幔的影响，为前人提出的橄榄岩-熔体反应能够造成岩石圈地幔减薄和破坏这一概念模型提供了理论实证，对评估大陆稳定性具有重要意义。

Evidence and significance of wehrlitization within continental lithospheric mantle

Wehrlitization refers to the mantle process that mantle peridotite interacts strongly with silica-undersaturated melts. This process usually triggers significant changes in mantle physico-chemical properties and thus is intimately linked to the thinning and destruction of cratonic lithosphere. Here, we first review the mechanism, texture and composition variations on wehrlitization and its impact on continental stability and then quantitatively characterize this process via thermodynamic modeling. It has been shown that wehrlitization may involve both modal and stealth metasomatism that usually introduce apatite, amphibole, phlogopite and carbonate into the peridotite and alter the modal abundance of rock-forming phases at the same time. Besides, non-equilibrium textures, including sponge texture, melt pockets (now presented as finer-grained clinopyroxene, olivine and other accessory minerals) and mineral zoning, are also typical wehrlitization. Thermodynamic modeling shows that the effects from melt impregnation on mantle peridotites are jointly controlled by the nature of the initial rock and the infiltrating melts as well as melt/rock ratio. Reaction with silica-poor (e.g., nephelinitic) melts usually facilitate the formation of clinopyroxene-rich peridotites and eventually wehrlite especially at high pressures (2.5Ga and 4.0GPa), regardless of the initial compositions of the peridotites (e.g., refractory harzburgite or fertile lherzolite). In contrast, the reaction with silica-rich (e.g., MORB) melts cannot produce wehrlite under the possible pressure range of continental lithosphere. Furthermore, the melt-rock reaction will always increase the density of mantle peridotites no matter of the melt compositions. The density of infiltrated fertile mantle may exceed that of the Preliminary Reference Earth Model (PREM), and this will eventually result in lithospheric instability. Collectively, our study quantitatively reveals the preferred physical conditions for wehrlitization and provides a quantitative theoretical framework for the previous conceptual model that peridotite-melt interaction can cause the thinning and destruction of the lithospheric mantle and has significant implications for continental stability.