Trace elements in olivine:Analysis,geochemical behavior,and case studies
The chemical composition of olivine records valuable information on mantle-derived magma properties,crystallization evolution,and eruption rates.Over the past decade,there have been significant advancements in trace element analysis techniques for olivine,resulting in a wealth of data.This paper systematically reviews the latest research progress in the field of trace element analysis of olivine using electron probe and laser ablation inductively coupled plasma mass spectrometry methods,summarizes the geochemical behaviors of trace elements in olivine,such as the distribution coefficient and diffusion coefficient,analyzes the trace element characteristics of olivine in different rock units around the world,and highlights the research progress of trace elements in olivine from magmatic Ni-Cu deposits.Experimental petrology indicates that the main factors controlling element distribution coefficients in olivine include temperature,pressure,and magma composition,with different trace elements being influenced by different primary factors.The partitioning of most elements in olivine can be predicted by the lattice strain model,whereas Ni,Co,and light rare earth elements are primarily controlled by crystal field effects and crystallization kinetics.The diffusion rates of elements in olivine from the fastest to the slowest are:H and Li(fast)→Fe-Mg-Ni(medium)→Ca(slower)→P-O-Si(very slow).A comparison of trace elements in olivine from different rock units around the world reveals:(1)In volcanic series such as komatiite-picrite-basalt,the Fo value and Ni,Cr,Al,Mn,and other elements of olivine show evolutionary trends,but there is a large overlap between the rock types in binary correlation diagrams and multidimensional analysis methods such as machine learning can greatly improve the classification accuracy;(2)The trace element characteristics of olivine in mantle peridotites and intrusive rocks(crustal cumulates)are similar,making it difficult to distinguish them using single-element indicators like the commonly used Ca depletion;(3)The Ni and Mn contents of olivine in carbonatites differs from other rocks,which may be related to their source and the unique partitioning behavior of elements between olivine and carbonatite melts;(4)There are certain differences in the trace elements of olivine between garnet mantle peridotite and spinel mantle peridotite.The olivine V/Sc ratio and Fe-Mg-Mn-Ca-Ni content are important variables for distinguishing the type and source depth of mantle peridotite.Research progress on trace elements in olivine from magmatic Ni-Cu deposits includes:(1)The re-equilibrium effect during cumulus and post-cumulus stages drives the Ca-Cr-Al elements to migrate to other minerals,resulting in olivine depletion of these elements;(2)Variations in Ni and Co in olivine record the Fe-Ni-Co exchange reactions with sulfides,where a positive correlation between Ni and Co can indicate the presence of sulfides at deeper locations of the intrusion;(3)Ni enrichment(＞5000 x 10-6)or depletion(＜500 × 10-6)in olivine coexisting with sulfides may be related to higher or lower oxygen fugacity.Finally,the paper outlines future research directions and breakthroughs in the field of trace elements in olivine:element behavior during cumulus and post-cumulus stages,multi-element and multi-mineral diffusion to constrain the spatiotemporal evolution of magma,machine learning to discriminate olivine genesis types and mineralization potential of mafic-ultramafic complexes,volatiles and untraditional metal isotopes in olivine.
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维普
