Structural location, composition, and geodynamic nature of diamond-bearing metamorphic rocks of the Kokchetav subduction–collision zone of the Central Asian Fold Belt (northern Kazakhstan)

Abstract

We present data on different aspects of geology, mineralogy, petrology, geochemistry, and geochronology of diamond-bearing metamorphic rocks of the Kumdy-Kol terrane, which show the similarity of their protolith to the sedimentary rocks of the Kokchetav microcontinent. The structural location of the studied objects in the accretion-collision zone evidences that the subduction of the Kokchetav microcontinent beneath the Vendian-Cambrian Ishim-Selety island arc is the main mechanism of transport of graphite-bearing terrigenous-carbonate rocks to zones of their transformation into diamond-bearing metamorphic rocks. The sedimentary rocks of the Kokchetav microcontinent, which are enriched in graphite and iron sulfides and carbonates, contain all components necessary for diamond crystallization in deep-seated subduction zone. This is in agreement with the experimental data and the compositions of fluid-melt inclusions in the minerals of diamond-bearing rocks.

About geological theory

“…The depth where the block halted would amount to about 170 km. This independently derived estimate matches the data of [Buslov et al, 2015]. The transformation of submerged rocks, including siderite, pyrite, and graphite, is favorable for the formation of diamonds within them.…”

“…Conditions that prevailed during the formation of UHP complexes can be conveniently analyzed on an example of the Kokchetav Block in Central Kazakhstan -one of the best-explored complexes. According to recent data [Buslov et al, 2015], the depth to which its rocks subsided -150-200 km -is larger than that of known bodies of similar type.…”

“…It is so far impossible to describe the geological history of the Kokchetav Block, which is part of the Central Asia folded belt, in substantial detail. Literature, however, contains information enabling a reconstruction of the history of the region's development during the period when diamond-bearing rocks formed [Buslov et al, 2015;Khain, 1977;Zhimulev, 2007;and others]. However, some points in the reconstructed history remain at the level of likely assumptions because much of the massif's Riphean sedimentary-volcanic section was destroyed by erosion.…”

Evolution of host‐inclusion systems: a visco‐elastic model

“…(). Finds of other UHPM mineral indicators, such as K‐bearing clinopyroxene (Sobolev & Shatsky, ), supersilicic titanite (Ogasawara et al ., ), Ca–Mg garnet (Sobolev et al ., ) and K‐bearing tourmaline (Shimizu & Ogasawara, ), gave preference to the subduction–exhumation model in explanation of the Kokchetav UHPM complex (Buslov et al ., ; Dobretsov et al ., and references therein). This model and its different modifications are very common for UHPM complexes worldwide.…”

Zircon from diamondiferous kyanite gneisses of the Kokchetav massif: Revealing growth stages using an integrated cathodoluminescence, Raman spectroscopy and electron microprobe approach

“…The Kokchetav massif is a mega-melange zone that consists of a series of units characterised by diverse PT conditions of formation (Dobretsov et al , 1995a,b; 1998; Theunissen et al , 2000; Buslov et al , 2015). The massif is subdivided by the Chaglinka fault zone into two main blocks (diamond-free Kulet and diamondiferous Kumdy-Kol), which in turn include five terranes: Kumdy-Kol; Barchi-Kol; Enbek-Berlyk; Sulu-Tyube; and Kulet (Fig.…”