Young Potassic Rocks

Mantle-derived K-rich melts had intrigued of the founders ofpetrology and many of the later experts in field and experimental geology,because they are sometimes associated with carbonatites and even diamond. Theytend to contain anomalous concentrations of many such elements as K, Rb, Sr, U,F, P, etc. along with Ni, Co, and Cr indicating a mixture of crusts and mantle.For key isotopic indicators like Sr⁸⁶/Sr⁸⁷, O¹⁶/O¹⁸,they show great variability. In addition most of these rocks are young with fewancient examples. Is this real or the result of a sampling problem? Modernobservations leave no doubt that sediments must be subducted on a large scale.There is now evidence that the upper mantle (and perhaps even the lower mantle)is not homogeneous but rather like a fruit cake, and that thermal anomalies inthe mantle resulting from deep mantle plumes or deep subduction, can releasethese unusual rocks clearing the mantle of leftover subduction material. TheYoung Potassic Rocks, written for those  interested in the geochemistry of K-rich meltsfrom the deep Earth, reviews the present state of knowledge of these uniquevolcanic rocks.