Ancient mantle metasomatism in West Ykukite field Northern Yakutia

 

 

 

In the subcratonic lithospheric mantle (SCLM) beneath Leningrad pipe (West Ukukit field), Yakutia garnet thermobarometry allows us to identify seven horizons (paleo subduction slab). Microprobe data for Cr-bearing amphiboles >500 grains from mantle xenoliths and concentrates reveal a broad range of compositions changing from Cr- pargasitic hornblendes to pargasites, edinites, kataforites, К-richterites with increasing pressure determined with new amphibole thermobarometer.  The low pressure (LP) Cr-hornblendes and pargasites compiles the high-temperature branch (90-60 mw/m2) from 3.5 GPa to Moho traced by basaltic cumulates. In the middle part of SCLM edinites mark 35 to 40 mw/m2 geotherms. In the middle part of SCLM edinites mark 35 to 40 mw/m2 geotherms. At high pressures kataforites also vary in thermal conditions. Richterites near the lithosphere base trace both low –and high temperature convective branches.

 Age samples of aillikites estimated by 40Ar/39Ar age using the method described in detail by A. Travin et al. [40]. Quartz ampoules with samples were irradiated in the Cd-coated channel of a reactor (BBP-K type) at the Tomsk Polytechnic Institute. The gradient of the neutron flux did not exceed 0.5% of the sample size. Step-heating experiments were carried out in a quartz reactor with an external heater. The blank for 40Ar (10 min at 1200°C) was not higher than 5×10–10 cm3. Ar was purified using Ti and ZrAl SAES getters. The isotopic composition of Ar was measured on a Micromass Noble Gas 5400 mass spectrometer (analyst Yudin D.S.). The results of the dating of the phlogopite grains and amphiboles occurred in the intergroup with the Phl are shown the (Figure 1). The phlogopie from the spinel lherzolite 2665 Ma corresponding to the final stge of the craton formation. Similar age was determined for the Phl from Udachnaya. The age of the intergrowth of the Amph-Phl from the sample Ol-151 is splitting. The high temperature part with the age 1368Ma may be reffered to the global activization of the plume and accretion magmatism activity found in many World regions [42] including Siberia. The more yanger plateo is close to the 380-400 Ma which is just corresponds to the Devonian plume magmatism? And the small plateau ~210 Ma refer to Triassic The . As well in the sample Ol-112 the older one 370 Ma plateo just give Devonian age. And one of the younger 160 Ma corresponds to the Jurassic stage of kimberlite volcanism.

Presence of the Phl with the 2.6 Ga referring to the major event of the crust generaion corresponding to the beginning of mertasomatic H2O bearing metasomatic processes recorded in the mantle xenoliths in the World proves the common model of the appearance of water in the mantle  at the last stages of the continental growth, The other two peaks  400 -380 Ma and 160 Ma may be referred to the plume kimberlite magmatism and even to the protokimberlite stage (latest one). 

RBRF grant 19-05-00788