Titel
Alakit and Daldyn kimberlite fields, Siberia, Russia: Two types of mantle sub-terranes beneath central Yakutia?
Autor*in
I.V. Ashchepkov
Institute of Geology and Mineralogy SD RAS
Autor*in
A.M. Logvinova
Institute of Geology and Mineralogy SD RAS
Autor*in
T. Ntaflos
Institute of Geochemistry SD RAS
... show all
Abstract
Mineral data from Yakutian kimberlites allow reconstruction of the history of lithospheric mantle. Differences occur in compositions of mantle pyropes and clinopyroxenes from large kimberlite pipes in the Alakit and Daldyn fields. In the Alakit field, Cr-diopsides are alkaline, and Stykanskaya and some other pipes contain more sub-calcic pyropes and dunitic-type diamond inclusions, while in the Daldyn field harzburgitic pyropes are frequent. The eclogitic diamond inclusions in the Alakit field are sharply divided in types and conditions, while in the Daldyn field they show varying compositions and often continuous Pressure–Temperature (P–T) ranges with increasing Fe# with decreasing pressures. In Alakit, Cr-pargasites to richterites were found in all pipes, while in Daldyn, pargasites are rare Dalnyaya and Zarnitsa pipes. Cr-diopsides from the Alakit region show higher levels of light Rare Earth Elements (LREE) and stronger REE-slopes, and enrichment in light Rare Earth Elements (LREE), sometimes Th-U, and small troughs in Nb-Ta-Zr. In the Daldyn field, the High Field Strength Elements HFSE troughs are more common in clinopyroxenes with low REE abundances, while those from sheared and refertilized peridotites have smooth patterns. Garnets from Alakit show HREE minima, but those from Daldyn often have a trough at Y and high U and Pb. PTXfO2 diagrams from both regions show similarities, suggesting similar layering and structures. The degree of metasomatism is often higher for pipes which show dispersion in P–Fe# trends for garnets. In the mantle beneath Udachnaya and Aykhal, pipes show 6–7 linear arrays of P–Fe# in the lower part of the mantle section at 7.5–3.0 GPa, probably reflecting primary subduction horizons. Beneath the Sytykanskaya pipe, there are several horizons with opposite inclinations which reflect metasomatic processes. The high dispersion of the P–Fe# trend indicating widespread metasomatism is associated with decreased diamond grades. Possible explanation of the differences in mineralogy and geochemistry of the mantle sections may relate to their tectonic positions during growth of the lithospheric keel. Enrichment in volatiles and alkalis possibly corresponds to interaction with subduction-related fluids and melts in the craton margins. Incorporation of island arc peridotites from an eroded arc is a possible scenario.
Stichwort
ThermobarometryGeochemistryDaldynAlakitCratonLithosphere
Objekt-Typ
Sprache
Englisch [eng]
Persistent identifier
https://phaidra.univie.ac.at/o:869185
Erschienen in
Titel
Geoscience Frontiers
Band
8
Ausgabe
4
Seitenanfang
671
Seitenende
692
Verlag
Elsevier BV
Erscheinungsdatum
2017
Zugänglichkeit
Rechteangabe
© 2016, China University of Geosciences (Beijing) and Peking University

Herunterladen

Universität Wien | Universitätsring 1 | 1010 Wien | T +43-1-4277-0