Mantle amphiboles from the lithospheric keel of the Siberian Craton: Reconstructions using new thermobarometry and geochemistry

Abstract

Cr-bearing amphiboles frequently occur in the subcratonic lithospheric mantle of Siberian Craton particularly in northern kimberlite fields like West Ukukit, Kuranakh, Kuoika, Kharamai, as well as in the central part of Yakutia – in Alakit and Daldyn fields and in Aldan and Chompolo fields. In the Leningrad pipe of the West Ukukit field, Cr-bearing amphiboles range from Cr-hornblendes to pargasites, edenites, katophorites, and K-richterites, showing an increase in K and Si content, as well as pressure, as determined using the updated amphibole thermobarometer. The P–T estimates for amphiboles are consistent with the results of garnet thermobarometry, supporting the division into seven horizons (interpreted as paleo-subducted slabs).

Typically, the lower to middle pressure levels and the lithospheric boundary are more heated and Fe-rich, which suggests interaction between melts and peridotites within low-pressure traps for hydrous melts.

K-richterites from the lithosphere–asthenosphere boundary exhibit steeply inclined and enriched trace element patterns, characterized by elevated levels of large ion lithophile elements (LILE), Sr, and Rb, along with pronounced negative anomalies in Nb and Pb. The low to middle pressure Na-rich varieties exhibit peaks in Rb, Ba, and Th, but show significantly lower rare earth element (REE) concentrations with marked depressions in the MREE range. Pargasites and hornblendes display concave REE patterns with distinct Eu anomalies, as well as peaks in Ba, U, and Sr and troughs in high field strength elements (HFSE), reflecting subduction-related signatures. Clinopyroxenes show Th, U, and Sr peaks, indicative of plume-related processes. The pargasites and hornblendes show concave REE patterns with Eu anomalies and Ba, U, Sr peaks and troughs in HFSE reflecting subduction-related signs. Clinopyroxenes reveal Th, U, Sr peaks related to plumes. Amphiboles are commonly Cl-bearing and typically associated with subduction-related processes. In the Leningrad pipe, amphibole ages range from 2.67 Ga – indicating early mantle hydration – to 1370, 500, and 370 Ma, which correspond to re-equilibration during major plume events.