Regional and local lithospheric mantle heterogeneity under the northern fields of the Yakutian kimberlite province
Abstract
The heterogeneity of the lithospheric mantle beneath the Siberian platform has become a widely accepted fact (Sobolev, 1976; Griffin et al, 1999; Tychkov et al., 2008; Ashchepkov et al., 2010-2016). We studied the indicator minerals composition from most kimberlite pipes of the northern Yakutian fields (Chomurdakh, Ogoner-Yuryakh, West-Ukukit, Kuyoka, Molodinsky, Toluopsky). Here we pay attention to the TiO2 in garnets - an indicator parameter of mantle heterogeneity. The majority of kimberlite pipes in northern barren fields as well as in southern diamondiferous Yakutian fields, are dominated by low-Ti garnet (TiO2 <0.2%), which corresponds predominantly high-Mg and, respectively, low-Ti lithospheric mantle substrate. The garnet compositions in kimberlites from Chomurdakh and Ogoner-Yuryakh fields show that more than 50% of all heavy fraction garnets are the Ti-rich (> 0.2% TiO2). TiO2 in garnets correlates with REE, Rb, Nb, Zr and Hf. Thus, there are lithospheric mantle "blocks" which undergone metasomatic transformations by a high-Ti fluid enriched by incompatible elements. The local heterogeneity of the lithospheric mantle under the Kuyoka field was established after garnet composition trends studying. Garnet compositions plotted in Cr2O3-CaO show two different trends: 1) lherzolite paragenesis trend, dominating in the Kuyoka field; and 2) lherzolite-wehrlite paragenesis trend steep crossing wehrlite paragenesis field (an anomalous trend after Tychkov, 2008). The second trend was established for spatially adjacent Muza, Tokur and Irina pipes (north-eastern part of the Kuyoka field) as well as for Jila 87/2, Jila 79, Dyanga and Raduzhnaya kimberlite bodies (eastern part of the Kuyoka field). Notably that some pipes of these two groups have Cr-rich garnets related to diamondiferous dunite-harzburgite paragenesis. In this case, the eastern kimberlite pipes of the Kuyoka field are standout by presence of Cr-rich garnets with the unusual lherzolite-verlite paragenesis trend and diamond potential prospects. Possibly, that lithospheric mantle under east zone of Kyoika field preserved the primary mantle heterogeneity. The work was carried out using the equipment of the Centre of collective usage "Isotope-geochemical research" of Institute of Geochemistry, Siberian branch of Russian Academy of Scitnces. The reported study was partially supported by RFBR, research project No. II.2P / IX.130-5.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2018
- Bibcode:
- 2018EGUGA..20..240K