Recently, the Deep Processes and Shallow Responses Research Team of the Department of Geology at Northwestern University conducted a systematic study on the reaction mechanism of melt/peridotite using high-temperature and high-pressure experimental petrology methods, providing a new perspective for the evolution of physical properties and chemical composition of the oceanic lithospheric mantle. The related achievements are as follows: Transformation of Refractory Oceanic Lithospheric Mantle by Reactive Melt Infiltration: An Experimental Study on the Roles of Temperature, Melt Volume and Ascent Velocity” The title was published in the international geological journal Journal of Geophysical Research: Solid Earth. The oceanic lithospheric mantle (OLM) exhibits significant multidimensional heterogeneity in both physical properties (density, seismic velocity) and chemical composition (lithology, elements, isotopes). There have long been two main views in the academic community regarding its causes: one is the difference in the degree of partial melting of the mantle; The second is the infiltration and modification of deep source reaction melt flow. However, the dominant mechanism remains controversial to this day. Monoclinopyroxene plays a dual role in the evolution of OLM: it participates in the melting reaction of mantle peridotite and is a typical product of the metasomatism of the reaction melt flow. Therefore, analyzing its mineral chemical composition is a key breakthrough in clarifying the above controversies. The research team systematically collected data on the composition of natural clinopyroxene from mantle inclusions in deep-sea peridotites and oceanic island basalts representing OLM, and compared it with experimental data on partial melting and data on the replacement of OLM by existing reactive melt flows. The results show (Figure 1a): (1) Even a low degree of partial melting (7.4%) can lead to extreme depletion of Na and Ti content in clinopyroxene (<0.5 wt.%), making it difficult to explain the extremely high Na and Ti content in natural samples; (2) There have been melt flow experiments that can explain the high Ti and low Na characteristics of clinopyroxene, but cannot explain the high Ti and high Na characteristics. Further tracking of the crystallization pressure conditions of previous reaction melt flows revealed (Figure 1b) that related experiments were mostly limited to lower pressure environments of 0.5-1 GPa. The research team speculates that the low pressure environment may have restricted the enrichment of Na in the clinopyroxene crystallized from the reaction melt flow.

Based on the above questions and speculations, the research team systematically conducted reactions and in-situ crystallization experiments between eclogite/rich siliceous pyroxene melts and amphibolite under high pressure conditions of 2 GPa. The experimental variables include different cooling amplitudes (1400 ℃ → 1350 ℃ → 1300 ℃), melt/rock ratios (1:2, 1:1, 2:1), and reaction times (4-48 hours). The aim is to simulate the interaction between mantle plumes and oceanic lithospheric mantle (OLM), systematically explore the effects of temperature, melt flux, and melt migration velocity on metasomatic reactions, and resolve the controversy over the causes of OLM heterogeneity; And based on experimental products, constrain the evolution process of OLM physical properties, and then construct corresponding lithospheric dynamics evolution models. The main insights gained from the study are as follows:

(1) Multiple factors controlling the genesis of clinopyroxene and clinopyroxene have been revealed: during the interaction between the silicon rich reaction melt flow and harzburgite, olivine is dissolved and clinopyroxene ± clinopyroxene is precipitated/crystallized. Monoclinopyroxene crystallizes only under high melt to rock ratio, long reaction time, and low temperature conditions, while clinopyroxene crystallizes under opposite conditions (Figure 2a-b). The differences in the above crystal types are attributed to the dynamic evolution of the melt composition during the interaction between the melt and peridotite - the melt generated by high melt/rock ratio, long reaction time, and low temperature is more enriched in elements such as Ca, Na, Al, Ti, which is conducive to the saturation of clinopyroxene (Figure 2c-d).

(2) It has been confirmed that high-pressure reaction melt flow plays a key role in OLM metasomatism: monoclinic pyroxene formed under 2 GPa conditions exhibits synchronous enrichment of Na and Ti, explaining the origin of Na - and Ti rich monoclinic pyroxene in natural samples (Figure 3a). Meanwhile, the Na/Ti ratio can effectively distinguish the formation pressure of clinopyroxene - high Na/Ti indicates high pressure, while low Na/Ti indicates low pressure (Figure 3b).

(3) characterizes the dynamic evolution process of physical properties of OLM under mantle plume background: when the mantle plume interacts with OLM, the high-temperature reactive melt flow reshapes the mineral composition of OLM through element diffusion and mineral crystallization, thereby changing its overall physical properties. This not only leads to a significant decrease in the seismic wave velocity of the explained OLM (explaining the shallow low velocity anomaly of mature OLM), but also increases its density and causes subsidence; After dismantling, the residual melting of the low-density mantle plume below upwelling, forming local vertical convection, driving the dynamic evolution of the physical and chemical properties of the OLM (Figure 4).

Paper information: Hou, Y.S. (Hou Yongsheng), Li, H. Y. * (Li Hongyan), Zhang, C. * (Zhang Chao), Wang, Y. (Wang Yu),& Xu, Y. G. (2026). Transformation of Refractory Oceanic Lithospheric Mantle by Reactive Melt Infiltration: An Experimental Study on the Roles of Temperature, Melt Volume, and Ascent Velocity. Journal of Geophysical Research: Solid Earth, 131, e2026JB033875 https://doi.org/10.1029/2026JB033875