Petrogenesis, Sampling Depth, Thermal and Redox Evolution of Spinel Peridotite Xenoliths From Jiaohe, NE China: Insights From Trace Elements in All Rock‐Forming Silicate Minerals

Abstract

AbstractOlivine and orthopyroxene (Opx) are the most abundant minerals in lherzolitic to harzburgitic peridotites, and their compositions represent an important—and sometimes only—source of information for the origin and physicochemical evolution of the subcontinental lithospheric mantle (SCLM). We report a high‐quality in situ trace element data set for Opx and olivine of well‐characterized spinel‐peridotite xenoliths, including eight lherzolites and four harzburgites, which were entrained in the Cenozoic basalts from Jiaohe, NE China. While the lherzolites and harzburgites show contrasting evolution involving various metasomatic agents, reflected in different trace element relationships, both experienced early cooling followed by recent (pre‐entrainment) heating, as unraveled by a combination of mineral thermometers with inherently different diffusion rates. The sampling depth of spinel‐facies peridotites is obtained by olivine‐spinel thermobarometry, taking into account post‐melting subsolidus processes and pre‐emplacement thermal disturbance, using an empirical correction for the Ca content in olivine, which yields a pressure range of 1.1–2.0 GPa. The V contents (92–116 μg/g) and V/Sc ratios (5.7–6.4) in lherzolitic Opx are higher than those in harzburgitic Opx (V: 56–76 μg/g; V/Sc: 3.4–5.9), qualitatively reflecting the reducing and oxidizing effect, respectively of refertilization versus metasomatic interaction with a small‐volume melt. Thus, comparative thermobarometry, together with trace element systematics of Opx and olivine can be effective tools to reveal the architecture, chemical, thermal, and redox evolution of the shallow SCLM, as sampled by spinel peridotite xenoliths.