排序方式： 共有9条查询结果，搜索用时 15 毫秒
1
1.
2.
3.
Alakit and Daldyn kimberlite fields,Siberia,Russia:Two types of mantle sub-terranes beneath central Yakutia? 总被引：1，自引：1，他引：0
I.V. Ashchepkov A.M. Logvinova T. Ntaflos N.V. Vladykin S.I. Kostrovitsky Z. Spetsius S.I. Mityukhin S.A. Prokopyev N.S. Medvedev H. Downes 《地学前缘(英文版)》2017,8(4):671-692
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,Crpargasites 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 Yand high U and Pb.PTX/O2 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. 相似文献
4.
Solov’eva L. V. Kalashnikova T. V. Kostrovitsky S. I. Ivanov A. V. Matsuk S. S. Suvorova L. F. 《Doklady Earth Sciences》2017,475(1):822-827
Mantle xenoliths containing phlogopite and phlogopite–amphibole mineralization from kimberlites of the Kuoika field have been studied. Such xenoliths were found in two series of rocks: magnesian (Mg) pyroxenite–peridotite and Fe-type phlogopite–ilmenite hyperbasite. The 40Ar/39Ar phlogopite age (1600–1800 Ma) and Re–Os and oxygen isotope data in rocks and minerals of the first series of rocks allow us to suggest that Phl–Amph metasomatism of the lithospheric mantle under the Birekte block and its accretion to the Siberian craton occurred in the subduction zone. The second series of rocks is comagmatic to potassium ultramafites and mafites, finding in the Siberian Platform. The phlogopite ages (870–850 Ma) from Phl–Ilm ultramafites corresponds to the beginning of the breakup of the supercontinent Rodinia and is close to ancient age datings of the alkaline ultramafic-carbonatite Tomtor massif. Phlogopite from xenoliths with garnet is much younger in age (500–600 Ma).
相似文献5.
6.
S.I. Kostrovitsky V.G. Malkovets E.M. Verichev V.K. Garanin L.V. Suvorova 《Lithos》2004,77(1-4):511-523
The megacryst suite of the Grib kimberlite pipe (Arkhangelsk province, Russia) comprises garnet, clinopyroxene, magnesian ilmenite, phlogopite and garnet-clinopyroxene intergrowths. Crystalline inclusions, mainly of clinopyroxene and picroilmenite, occur in garnet megacrysts. Ilmenite is characterized by a wide range in the contents of MgO (10.6–15.5 wt.%) and Cr2O3 (0.7–8.3 wt.%). Megacryst garnets show wide variations in Cr2O3 (1.3–9.6 wt.%) and CaO (3.6–11.0 wt.%) but relatively constant MgO (15.4–22.3 wt.%) and FeO (5.2–9.9 wt.%). The pyroxenes also show wide variations in such oxides as Cr2O3, Al2O3 and Na2O (0.56–2.95; 0.86–3.25; 1.3–3.0 wt.%, respectively). The high magnesium and chromium content of all these minerals puts them together in one paragenetic group. This conclusion was confirmed by studies of the crystalline inclusions in megacrysts, which demonstrate similar variations in composition. Low concentration of hematite in ilmenite suggests reducing conditions during crystallization. P–T estimates based on the clinopyroxene geothermobarometer (Contrib. Mineral. Petrol. 139 (2000) 541) show wide variations (624–1208 °C and 28.8–68.0 kbars), corresponding to a 40–45 mW/m2 conductive geotherm. The majority of Gar-Cpx intergrowths differ from the corresponding monomineralic megacrysts in having higher Mg contents and relatively low TiO2. The minerals from the megacryst association, as a rule, differ from the minerals of mantle xenoliths, but garnets in ilmenite-bearing peridotite xenoliths are compositionally similar to garnet megacrysts. The common features of trace element composition of megacryst minerals and kimberlite (they are poor in Zr group elements) suggest a genetic relationship. The origin of the megacrysts is proposed to be genetically connected with kimberlite magma-chamber evolution on the one hand and with associated mantle metasomatism on the other. We suggest that, depending on the primary melt composition, different paragenetic associations of macro/megacrysts can be crystallized in kimberlites. They include: (1) Fe–Ti (Mir, Udachnaya pipes); (2) high-Mg, Cr (Zagadochna, Kusova pipes); (3) high-Mg, Cr, Ti (Grib pipe). 相似文献
7.
I.V. Ashchepkov N.V. Vladykin T. Ntaflos H. Downes R. Mitchell A.P. Smelov N.V. Alymova S.I. Kostrovitsky A. Ya Rotman G.P. Smarov I.V. Makovchuk Yu.B. Stegnitsky E.N. Nigmatulina O.S. Khmelnikova 《Gondwana Research》2013,23(1):4-24
Regularities of the mantle structure beneath the Siberian Craton were determined using the monomineral thermobarometry and common Opx-Gar methods. Samples were taken from 80 pipes from the Siberian Craton and in comparison 70 pipes from worldwide kimberlites. The largest pipes contain several dunite layers in the lower part of lithospheric mantle which are responsible for the diamond grade. The lithospheric mantle consists of two major parts divided at a depth of 4.0 GPa by a pyroxenite layer. Major intervals determined for the mantle beneath Udachnaya and Mir are: 1) 8.0–6.5 GPa harzburgites, eclogites and dunitic veins; 2) 6.5–5.5 GPa sheared peridotites, low-Cr pyroxenites, dunites; 3)in 5.5–4.0 GPa interval there are 4–6 layers of harzburgitic paleoslabs; 4) 4.0–3.5 GPa the pyroxenites lens; 5) upper layered Sp-Gar peridotite sequence including a trap of basaltic and other silicate melt cumulates at 3.0–2.0 GPa. The lithospheric mantle beneath seven different tectonic terrains in Siberia is characterized by TRE geochemistry and major elements of peridotitic clinopyroxenes. The mantle in Magan terrain contains more fertile peridotites in the South (Mir pipe) than in North (Alakit) which were metasomatized by subduction-related melts producing Phl and Cpx about 500–800 Ma ago. Daldyn terrain is essentially harzburgitic in the west part (abyssal peridotite) but in the east in Upper Muna (East Daldyn terrain) the mantle is more differentiated and in general more oxidized. The Markha terrain (Nakyn) contains depleted but partly refertilized harzburgites, subducted pelitic material and abundant eclogites. Circum-Anabar mantle is ultradepleted in the lower part but in the upper regions it has been fertilized by fluid-rich melts very enriched in incompatible elements. The P-Fe# diagrams (and other components) reveal different structure of mantle columns in each terrain. They are subvertical for the mantle sampled by Devonian pipes. Beneath Mesozoic pipes the mantle has been affected by melt percolation caused by the Siberian Superplume which created continuous Fe-enrichment in the upper part. The models of continent growth and evolution are briefly discussed. In general the geothermal regime and mantle heating is negatively correlated with the thickness of lithosphere. The sheared peridotites under Udachnaya and other kimberlite pipe are likely to have formed after the intrusion of protokimberlite volatile rich (hydrous) melts and hydraulic fracturing. This mechanism is responsible for the origin of asthenospheric lenses.Progressive melting especially in the pervasive zones may be responsible for the creation of 3-4 upper asthenospheric lens near mostly before 4.0 GPa which may be accompanied by mantle diapirism. Such a lens is the trap for the kimberlites in Siberia in Mesozoic time and in rifted intracontinental areas and margins. 相似文献
8.
Solov’eva L. V. Kostrovitsky S. I. Kalashnikova T. V. Ivanov A. V. 《Doklady Earth Sciences》2019,486(1):537-540
Doklady Earth Sciences - The article describes the petrography and mineralogy of xenoliths ilmenite-phlogopite containing deformed and granular peridotites from the Udachnaya-Eastern pipe. The age... 相似文献
9.
S. I. Kostrovitsky L. V. Solov’eva D. A. Yakovlev L. F. Suvorova G. P. Sandimirova A. V. Travin D. S. Yudin 《Petrology》2013,21(2):127-144
Major and rare-earth element data on Cr-poor megacrystic suite from Yakutian kimberlites were generalized. Sr-Nd isotopes were studied in garnet, clinopyroxene, and phlogopite megacrysts as well as in garnet and clinopyroxene from deformed xenoliths. It was shown that Sr-Nd composition of these minerals is similar to that in the least altered diamondiferous kimberlites. The crystallization age of megacrystic minerals was determined by Rb-Sr isochron and Ar-Ar (for phlogopite megacrysts) methods. Obtained data indicate that crystallization of Cr-poor megacrystic suite began at the prekimberlitic stage and continued to the pipe emplacement. It was established that garnets from coarse-porphyric deformed lherzolites and megacrysts are similar in major and rare-earth element compositions and were derived from a common asthenospheric source. However, the distribution of incompatible elements and P-T estimates of crystallization cannot be explained by hypothesis of fractional crystallization of garnet megacrysts. It is suggested that megacrystic assemblage crystallized directly in asthenospheric melt. En route to the surface, this melt caused a metasomatic reworking of lithospheric mantle, on the one hand, and was enriched in Mg and Cr owing to the contamination by lithospheric material, on the other hand. 相似文献
1