PICO
The North China Craton (NCC) has been affected by the subduction and roll-back of the Paleo-Pacific Plate in the Mesozoic. To study the thinning of the lithosphere and the melting of the NCC, a three-dimensional (3-D) resistivity model of the lithosphere is obtained from a magnetotelluric sounding (MT) deployed in the NCC (Figure 1). In addition, the cause of the low resistivity of the upper mantle of the NCC can be solved by the Nernst-Einstein Equation and the Arrhenius Equation which is used to establish the relationship between the resistivity and temperature. Moreover, the Hashin-Shtrikman (HS) boundary conditions limit the range of electrical conductivity of mixed minerals (Figure 2). Based on the 3D resistivity structure, the temperature and melt fraction model, the lithospheric resistivity of the north of 37.5°N in the Ordos Block (OB), the southern Taihang Uplift (THU) and the Luxi Uplift (LXU) are as low as 1 Ωm which the upper mantle temperature is in the range of 1400 - 1550 °C, and the melt fraction is 1-10% in the high-temperature regions. According to the resistivity model and the thermal state, the westward subduction and roll-back of the Paleo-Pacific Plate provided conditions for upper mantle melting in the LXU and the Bohai Bay Basin (BBB). It also made the Tanlu Fault Zone (TLFZ) and THU channels for the upwelling, and the front of the Paleo-Pacific Plate stagnant slab is blowing the THU. With the remote tectonic stress of the Paleo-Pacific Plate and the Indian Plate, anticlockwise rotation of the OB induced the low resistivity of grabens and rifts around the OB (Figure 3). Moreover, upper mantle volatiles (H2O and CO2) and slight carbonatite melts significantly lower the mantle melting temperature.
* This work was supported by National Natural Science Foundation of China (Grants 41974112 and 40434010) and project SINOPROBE on sub-project SINOPROBE-01.
Reference:
Dong, S..T. Li. (2009). SinoProbe: the exploration of the deep interior beneath the Chinese continent. Acta Geologica Sinica, 83(7), 895-909.
Hirschmann, M. M. (2010). Partial melt in the oceanic low velocity zone. Physics of the Earth and Planetary Interiors, 179(1), 60-71.
Zhao, G..M. Zhai. (2013). Lithotectonic elements of Precambrian basement in the North China Craton: Review and tectonic implications. Gondwana Research, 23(4), 1207-1240.
Figure 1 Simplified s tectonic map of the North China Craton (modified from Zhao and Zhai (2013)); Map of MT profiles and sites, in which blue dots represent MT stations in this study, supported by the “SINOPROBE” project (Dong and Li, 2009). TNCO: Trans-North China Orogen
Figure 2 Schematic diagram of dynamic changes of water and carbon dioxide during heating and melting of upper mantle minerals. NAMs means nominally anhydrous minerals; the “Calculate” in the dashed box is the calculation category of this study; the criterion for determining the interconnection of melts was proposed by Hirschmann (2010).
Figure 3 Schematic diagram of the possible formation mechanisms of the North China Craton inferred from the crustal and upper mantle 3-D resistivity model derived from this research.
How to cite: Li, B. and Ye*, G.: Three-dimensional Lithospheric Resistivity Structure and Thermal State of the North China Craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6901, https://doi.org/10.5194/egusphere-egu23-6901, 2023.
The Belo-Ziminsky alkaline-ultrabasic carbonatite massif contain dolomite, and calcite ankerite carbonatites essential part , syenites, melteigites and iolites cut by aillikite dikes of several generations (Ashchepkov et al., 2020; Doroshkevich et al., 2014-2021 etc). We analyzed >4000 mineral grains by electron microscope in all types of rocks and >230 grains by LA ICP MA All rocks of the massif are derived from one type of mantle melt that was close to aillikite and formed at a level of >5 GPa in the mantle.
According to the nature of the PGE spectra – and by serpentinized xenoliths in aillikites, this melt drained metasomatized enriched peorvskites and hydrogenated mantle and was initially very rich in HFSE. Above, at the level of the crust and the upper part of the mantle, the melt began to separate under liquation. In the lower and middle crust, several (3) magmatic chambers were probably formed sequentially, which separated various carbonate and silicate melts, and from dolomite to ankerite melts, judging by the slope, the number of grains in the source decreased, that is, the melts became less deep and more fractionated.
These trends are reflected both in the composition of pyroxenes from aillikites and in the PTX diagram . All this led to significant variations in rocks and their rare-earth spectra of all rocks
How to cite: Zhmodik, S., Ashchepkov, I., Kiseleva, O., Belyanin, D., Sotnikova, I., Medvedev, N., and Karmanov, N.: Tracing of evolution of carbonatite and silicate melts of the Belo-Ziminsky alkaline-ultrabasic carbonatite massif by mineralogy and geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16857, https://doi.org/10.5194/egusphere-egu23-16857, 2023.
Kimberlitic xenocrysts: garnets, pyroxenes, ilmenites, spinels from Anabar region were analyzed by EPMA and LAICPMS.
Reconstructed mantle sections of t Anabar region published (Ashchepkov et al., 2001; 2016; 2019; 2022 show in general, the relative rarity of sub-Ca pyropes in lower part of the section and the frequency of wehrlite associations in the upper part. Pyroxenite -eclogite lens from 3 to 5 GPa is widely represented in most sections. Ilmenite trends are not long. In several pipes amphiboles from Cr-hornblendes to Cr-richterites were detected.
In the Anabar region (Khardakh and Staro-Rechensky fiedls) The REE patterns of garnets are characterized by high variations in the spectra, with elevated LREE and HFSE minima, peaks of U, Pb, associated with subduction fluid flows. Pyroxenes are characterized by inclined REE spectra of La/Ybn ~15 to 20 and with varying HREE with subduction-related Ba, U, Pb peaks. But pyroxenes with plume related spectrums of with smooth spider diagrams (SD) are often found in pyroxenite lens.
Garnets from the Kuranakh field (Malokuonamskaya, Losi, Trudovaya, Universitetskaya etc) are divided into dunite-garburgite with low REE and LREE enrichment and wehrlite with convex REE maximum Gd, Eu and high concentrations of HREE often enriched in Th , U varying Ta-Nb and always low Zr-Hf. Clinopyroxenes from the Malokuonamskaya pipe often have a local minimum of HREE and variations in the slope and enrichment of the REE spectra. On the CD, the peaks of Ba are varying, they show Ta, Nb enrichment and minima in Zr-Hf.
The garnets from the Universitetskaya pipe are mainly lherzolite-harzburgite with signs of subduction genesis (U peaks), and wide variations of HFSE sometime with Zr–Hf enrichment, due aqueous metasomatism. Clinopyroxenes are generally more diverse in REE spectra, Nb peaks with wide variations of Ba, Th-U and HFSE are common on CD
The Losi dike has a high content of perovskites, with highly enriched spectra with a slope with a decrease in highly charged and Pb and ilmenites with high and inclined REE spectra due to fractionation of proto-kimberlite (essentially carbonatite) melt. The eclogitic minerals with Eu anomalies and peaks of U, Ba and low HFSE are common.
In most mantle sections, ancient subduction sings are recorded in pyrope garnets, an partially adakite metasomatism in pyroxenes. Later they were modified by the action of plume carbonatite melts. The middle pyroxenite-eclogite lens originated as the boundary of the crust in ancient Archaic times. The upper wehrlitic part of the section arose during the melting of the pyroxene lens in the middle part and the migration of melts to the upper part. Protokimberlite metasomatism is not very pronounced. No signs of the supposed delamination of the lithosphere (Griffin et al, 2005) were found in the sections, which was also proved by Opx-Gar thermobarometry under the Duken field (Ashchepkov, 2003). The lower part of the section is depleted so garnet and pyroxenes are rare and reflect low-temperature geotherm.
Grant RBRF 19-05-00788.
How to cite: Kostrovitsky, S., Ashchepkov, I., Medvedev, N., Karmanov, N., and Alymova, N.: Mineralogy and geochemistry of the kimberlite xenocrysts from the Anabar region, Yakutia, Russia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3860, https://doi.org/10.5194/egusphere-egu23-3860, 2023.
Minerals from leucite lamproites of the Murunsky alkaline massif (Vladykin, 2000; 2005; Vladykin, 2009) were analyzed by electron microscopy in the sections of 700 grains of minerals (IGM SB RAS) and LA ICP MS (IIC SB RAS) - 40 grains. Pyroxenes, amphiboles, various micas including varieties of the Ba type, leucites and nephelines, Ba and K feldspars, eudialyte, barite, stroztianite, ilmenites, Cr- spinelides, Ti magnetites, apatites, tourmaline, and various carbonates and sulfides: pyrrhotite, petlandite, chalcopyrite, murunite, smithsonite, galena.
Pyroxenes are divided into 3 groups from diopsides to augites and aegirines, revealing a continuous series of compositions according to MgO (Fig. 1). Amphiboles K-richterites and arfversonites, and Ca-Fe ackermanites. Complete ranges from phlogopites to biotites have been established among micas. The proportion of Ba micas is significant. In the diagram genetic digram (Minchell, 1995 )(Fig. 2) falls into the field of ailikites or orangeites, and lamproites. Leucites and nephelines occurs friquiently. Numerous apatites are characterized by Ca-Sr substitution and noticeable F contents (to 3%). K-type eudialytes and a mineral close to priderite were found.
In the TRE diagrams (Fig.3), pyroxenes are characterized by La-enriched ~200-250 weakly inclined spectra of La/Ybn (2-3) that spread out in the HREE wing. Amphiboles of the K-Na-Ca are characterized show inclined spectra with Ho-Tm depression, LILE peaks elevated Zr, Hf, Y and Ta-Nb minima. The more alkaline amphiboles are characterized by reduced REE concentrations, more elevated Zr-Hf. Ultra-alkaline amphiboles (richterite and arfvedsonite) have higher REE contentswith characteristic U-shaped spectra, very high LILE contents high peaks of Sr, Zr, Hf. Phlogopites have oblique U-shaped spectra with a sharp peak Eu interference Ti. Very high LILE with a peak at Va, Sr, Y, Pb are typical.
Low REE and especially LREE with a peak of Eu are characteristic of leucites. U, Sr, Pb peaks are also characteristic, and HFSE vary. The REE spectra of K-Ba feldspars are similar to those of phlogopite. High peaks of LILE, Sr, Pb, Y are expressed on spiderdiagrams
Judging by the peculiarities of mineral trends, lamproites are the result of low degrees melting under the influence of plume melts of a mantle deeply metasomatized by subduction processes. Pyroxenes are end–to-end minerals, at an early stage their compositions were controlled by fractionation of olivine and then saturated SiO2 silicates. Further fractionation led to enrichment with rare elements P, Sr, F. In amphiboles, the growth of REE was accompanied by the accumulation of Zr, Hf, while Nb, Ta were removed during the deposition of T-magnetite. Grant RBRF 19-05-00788.
How to cite: Ashchepkov, I., Vladykin, N., Sotnikova, I., Medvedev, N., Karmanov, N., and Alymova, N.: Mineralogical and geochemical characteristics of lamproite minerals of the Murunsky massif., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3560, https://doi.org/10.5194/egusphere-egu23-3560, 2023.
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
How to cite: Iudin, D., Ashchepkov, I., Babushkina, S., Oleinikov, O., and Medvedev, N.: Ancient mantle metasomatism in West Ykukite field Northern Yakutia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8651, https://doi.org/10.5194/egusphere-egu23-8651, 2023.
