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101.
Andrey A. Gurenko Kaj A. Hoernle Alexander V. Sobolev Folkmar Hauff Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2010,159(5):689-702
The Canary Island primitive basaltic magmas are thought to be derived from an HIMU-type upwelling mantle containing isotopically
depleted (NMORB)-type component having interacted with an enriched (EM)-type component, the origin of which is still a subject
of debate. We studied the relationships between Ni, Mn and Ca concentrations in olivine phenocrysts (85.6–90.0 mol.% Fo, 1,722–3,915 ppm
Ni, 1,085–1,552 ppm Mn, 1,222–3,002 ppm Ca) from the most primitive subaerial and ODP Leg 157 high-silica (picritic to olivine
basaltic) lavas with their bulk rock Sr–Nd–Pb isotope compositions (87Sr/86Sr = 0.70315–0.70331, 143Nd/144Nd = 0.51288–0.51292, 206Pb/204Pb = 19.55–19.93, 207Pb/204Pb = 15.60–15.63, 208Pb/204Pb = 39.31–39.69). Our data point toward the presence of both a peridotitic and a pyroxenitic component in the magma source.
Using the model (Sobolev et al. in: Science 316:412–417, 2007) in which the reaction of Si-rich melts originated during partial
melting of eclogite (a high pressure product of subducted oceanic crust) with ambient peridotitic mantle forms olivine-free
reaction pyroxenite, we obtain an end member composition for peridotite with 87Sr/86Sr = 0.70337, 143Nd/144Nd = 0.51291, 206Pb/204Pb = 19.36, 207Pb/204Pb = 15.61 and 208Pb/204Pb = 39.07 (EM-type end member), and pyroxenite with 87Sr/86Sr = 0.70309, 143Nd/144Nd = 0.51289, 206Pb/204Pb = 20.03, 207Pb/204Pb = 15.62 and 208Pb/204Pb = 39.84 (HIMU-type end member). Mixing of melts from these end members in proportions ranging from 70% peridotite and 30%
pyroxenite to 28% peridotite and 72% pyroxenite derived melt fractions can generate the compositions of the most primitive
Gran Canaria shield stage lavas. Combining our results with those from the low-silica rocks from the western Canary Islands
(Gurenko et al. EPSL 277:514–524, 2009), at least four distinct components are required. We propose that they are (1) HIMU-type
pyroxenitic component (representing recycled ocean crust of intermediate age) from the plume center, (2) HIMU-type peridotitic
component (ancient recycled ocean crust stirred into the ambient mantle) from the plume margin, (3) depleted, MORB-type pyroxenitic
component (young recycled oceanic crust) in the upper mantle entrained by the plume, and (4) EM-type peridotitic component
from the asthenosphere or lithosphere above the plume center. 相似文献
102.
Trace elements in garnets and chromites: Diamond formation in the Siberian lithosphere 总被引:1,自引:0,他引:1
W.L. Griffin N.V. Sobolev C.G. Ryan N.P. Pokhilenko T.T. Win E.S. Yefimova 《Lithos》1993,29(3-4):235-256
Proton-microprobe analyses of trace elements in garnet and chromite inclusions in diamonds (DI) from the Mir, Udachnaya, Aikhal and Sytykanskaya kimberlites in Yakutia, CIS, provide new insights into the processes that form diamond. Equivalent data on garnet and chromite concentrates from these pipes yield information on the thermal state and chemical stratification of the Siberian lithosphere. Peridotite-suite diamonds from Yakutia have formed over a temperature interval of ca. 600°C, as measured by Ni and Zn thermometry on garnet and chromite inclusions in diamonds. Individual diamonds contain inclusions recording temperature intervals of >400°C; ranges of >100°C are common. Diamond formation followed a severe depletion event(s), and a separate enrichment in Sr. Comparison of temperatures on DI garnet and spinel with temperatures derived from diamondiferous harzburgites, exposed inclusions in boart and concentrate minerals suggests that the diamond-containing part of the lithosphere has cooled significantly since the Siberian diamonds crystallized. The peridotite-suite diamonds probably formed mainly in response to one or more relatively short-lived thermal events, related to magmatic intrusion. The northern part of the Daldyn-Alakit district may have had a typical cratonic geotherm at the time of diamond formation, and during kimberlite intrusion. The southern part of the district, and the Malo-Botuobiya kimberlite field, probably had a relatively low geotherm (ca. 35 mW/m2). The vertical distribution of garnet and chromite types indicates that the mantle above 120 km depth is dominated by lherzolites, whereas the deeper parts of the lithosphere are a mixture of lherzolites and more depleted harzburgites and dunites. 相似文献
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107.
The results of SEST millimeter observations of the molecular cloud G345.01+1.79 are presented. Spectra of CH3OH, SO2, SiO, HCO+, C18O, C33S, C34S, HCN, and DCN lines have been obtained. Mapping of the cloud in CH3OH, SiO, and C34S lines indicates that the maximum integrated intensity in the SiO and C34S lines and in low-excitation CH3OH transitions coincide with the northern group of methanol masers, while the corresponding maximum for high-excitation CH3OH transitions coincides with the southern methanol-maser group. The physical parameters are estimated from the quasi-thermal CH3OH lines under the large-velocity-gradient approximation, and their distribution on the sky derived. The density and temperature are higher toward the southern group of methanol masers than in the northern group. This may indicate that star formation is in an earlier stage of evolution in the northern than toward the southern group. A maser component can be distinguished in 14 (of 71) CH3OH lines. We have detected for the first time weak, probably maser, emission in the CH3OH lines at 148.11, 231.28, 165.05, 165.06, and 165.07 GHz. A blue wing is clearly visible in the CH3OH, SiO, C18O, and SO2 lines. The emission in this wing is probably associated with a compact source whose velocity is characteristic of the CH3OH maser emission in the southern group of masers. 相似文献
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110.
Nikolay Bonev Jean-Pierre Burg Zivko Ivanov 《International Journal of Earth Sciences》2006,95(2):318-340
The tectonic evolution of the Rhodope massif involves Mid-Cretaceous contractional deformation and protracted Oligocene and Miocene extension. We present structural, kinematic and strain data on the Kesebir–Kardamos dome in eastern Rhodope, which document early Tertiary extension. The dome consists of three superposed crustal units bounded by a low-angle NNE-dipping detachment on its northern flank in Bulgaria. The detachment separates footwall gneiss and migmatite in a lower unit from intermediate metamorphic and overlying upper sedimentary units in the hanging wall. The high-grade metamorphic rocks of the footwall have recorded isothermal decompression. Direct juxtaposition of the sedimentary unit onto footwall rocks is due to local extensional omission of the intermediate unit. Structural analysis and deformational/metamorphic relationships give evidence for several events. The earliest event corresponds to top-to-the SSE ductile shearing within the intermediate unit, interpreted as reflecting Mid-Late Cretaceous crustal thickening and nappe stacking. Late Cretaceous–Palaeocene/Eocene late-tectonic to post-tectonic granitoids that intruded into the intermediate unit between 70 and 53 Ma constrain at least pre-latest Late Cretaceous age for the crustal-stacking event. Subsequent extension-related deformation caused pervasive mylonitisation of the footwall, with top-to-the NNE ductile, then brittle shear. Ductile flow was dominated by non-coaxial deformation, indicated by quartz c-axis fabrics, but was nearly coaxial in the dome core. Latest events relate to brittle faulting that accommodated extension at shallow crustal levels on high-angle normal faults and additional movement along strike-slip faults. Radiometric and stratigraphic constraints bracket the ductile, then brittle, extensional events at the Kesebir–Kardamos dome between 55 and 35 Ma. Extension began in Paleocene–early Eocene time and displacement on the detachment led to unroofing of the intermediate unit, which supplied material for the syn-detachment deposits in supra-detachment basin. Subsequent cooling and exhumation of the footwall unit from beneath the detachment occurred between 42 and 37 Ma as indicated by mica cooling ages in footwall rocks, and extension proceeded at brittle levels with high-angle faulting constrained at 35 Ma by the age of hydrothermal adularia crystallized in open spaces created along the faults. This was followed by Late Eocene–Oligocene post-detachment overlap successions and volcanic activity. Crustal extension described herein is contemporaneous with the closure of the Vardar Ocean to the southwest. It has accommodated an earlier hinterland-directed unroofing of the Rhodope nappe complex, and may be pre-cursor of, and/or make a transition to the Aegean back-arc extension that further contributed to its exhumation during the Late Miocene. This study underlines the importance of crustal extension at the scale of the Rhodope massif, in particular, in the eastern Rhodope region, as it recognizes an early Tertiary extension that should be considered in future tectonic models of the Rhodope and north Aegean regions. 相似文献