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1.
Two unusual diamonds were studied from kimberlites from China, which contain both ultramafic and eclogitic mineral inclusions in the same diamond hosts. Diamond L32 contains seven Fe-rich garnets, four omphacites and one olivine inclusion. Four olivine, one sanidine and one coesite were recovered from diamond S32. Both garnet and omphacite inclusions have similar compositions as those from other localities of the world, and show basaltic bulk composition. All the garnet and omphacite inclusions in diamond L32 have positive Eu anomalies (Eu/Eu*1.64 1.79). These observations support the proposal that mantle eclogite is the metamorphic product of subducted ancient oceanic crust. The Mg/(Mg + Fe) ratio of the olivine inclusions from the two diamonds (91-92) are evidently lower than the normal olivine inclusions in diamonds from the same kimberlite pipe (92-95). The following model is proposed for the formation of diamonds with “mixed” mineral inclusions. Ascending diamond-bearing eclogite (recycled oceanic crust) entrained in mantle plumes may experience extensive partial melting, whereas the ambient peridotite matrix remains subsolidus in the diamond stable field. This provides a mechanism for the transport of diamond from its original eclogitic host to an ultramafic one. Subsequent re-growth of diamond in the new environment makes it possible to capture mineral inclusions of different lithological suites. Partial melts of basaltic sources may interact with the surrounding peridotite, resulting in the relatively lower Mg/(Mg + Fe) ratios of the coexisting olivine inclusions from the studied diamonds. Diamonds with “mixed” mineral inclusions demonstrate that plume activity also occurred in the Archean cratons. 相似文献
2.
Rondi M. Davies William L. Griffin Suzanne Y. O''Reilly Tom E. McCandless 《Lithos》2004,77(1-4):99-111
Analyses of mineral inclusions, carbon isotopes, nitrogen contents and nitrogen aggregation states in 29 diamonds from two Buffalo Hills kimberlites in northern Alberta, Canada were conducted. From 25 inclusion bearing diamonds, the following paragenetic abundances were found: peridotitic (48%), eclogitic (32%), eclogitic/websteritic (8%), websteritic (4%), ultradeep? (4%) and unknown (4%). Diamonds containing mineral inclusions of ferropericlase, and mixed eclogitic-asthenospheric-websteritic and eclogitic-websteritic mineral associations suggests the possibility of diamond growth over a range of depths and in a variety of mantle environments (lithosphere, asthenosphere and possibly lower mantle).
Eclogitic diamonds have a broad range of C-isotopic composition (δ13C=−21‰ to −5‰). Peridotitic, websteritic and ultradeep diamonds have typical mantle C-isotope values (δ13C=−4.9‰ av.), except for two 13C-depleted peridotitic (δ13C=−11.8‰, −14.6‰) and one 13C-depleted websteritic diamond (δ13C=−11.9‰). Infrared spectra from 29 diamonds identified two diamond groups: 75% are nitrogen-free (Type II) or have fully aggregated nitrogen defects (Type IaB) with platelet degradation and low to moderate nitrogen contents (av. 330 ppm-N); 25% have lower nitrogen aggregation states and higher nitrogen contents (30% IaB; <1600 ppm-N).
The combined evidence suggests two generations of diamond growth. Type II and Type IaB diamonds with ultradeep, peridotitic, eclogitic and websteritic inclusions crystallised from eclogitic and peridotitic rocks while moving in a dynamic environment from the asthenosphere and possibly the lower mantle to the base of the lithosphere. Mechanisms for diamond movement through the mantle could be by mantle convection, or an ascending plume. The interaction of partial melts with eclogitic and peridotitic lithologies may have produced the intermediate websteritic inclusion compositions, and can explain diamonds of mixed parageneses, and the overlap in C-isotope values between parageneses. Strong deformation and extremely high nitrogen aggregation states in some diamonds may indicate high mantle storage temperatures and strain in the diamond growth environment. A second diamond group, with Type IaA–IaB nitrogen aggregation and peridotitic inclusions, crystallised at the base of the cratonic lithosphere. All diamonds were subsequently sampled by kimberlites and transported to the Earth's surface. 相似文献
3.
《International Geology Review》2012,54(11):1340-1369
ABSTRACTLibyan Desert Glass (LDG), rediscovered in modern times in 1932, is an ultrahigh-temperature glass composed of nearly pure SiO2. LDG is found as surface float in Egypt’s Libyan (Western) Desert, its strewnfield defined by the intersection of major faults. Extra-terrestrial components are present in LDG but there is no associated impact crater. LDG is not an impactite, nor do pieces exhibit aerodynamic forms. Extremely viscous silica remained hot long enough to flow several centimetres. Additional constraints on the origin of LDG are imposed by exotic materials found nearby: a dark 30-gram granular micro-diamond mass, mullite-magnetite-silica glass rocks with micro-diamonds, lumps of fine-grained magnetite, titanium filaments, titanium nitride, titanium aluminide, aluminium oxycarbonitride, phosphides, silver, zirconium, zinc, carbonaceous grains, and metal grains coated with carbonaceous materials. The region is underlain by 500–3000 m of flat-lying sandstone composed of quartz grains and little else. To account for LDG and the other unusual materials and nearby outgassing vents, serpentinization is evoked. Products of this complex low-temperature crustal process include serpentine, magnetite, aqueous silica, and great quantities of hydrogen. The hydrogen, produced in Basement rocks beneath the sandstones, may have risen along faults, passing around grains of quartz (with which it does not react) until slowed by tight conditions, perhaps self-sealed by silica produced during serpentinization. Columns of quartz hundreds or thousands of metres high with intergranular spaces filled with H2 (±CH4) may have been established with some hydrogen leaking into the surface domain while still more was produced at depth. Disturbance by occasional impacts or airbursts, large or small, would violently release great columns of pressurized hydrogen, which, ignited, would burn until exhaustion. Such sustained heating events could be repeated. Exotic products might come from materials formed cold in the outer solar system, transformed in a great flickering flame with temperatures perhaps exceeding 1800°C. 相似文献
4.
《地学前缘(英文版)》2020,11(4):1163-1174
Impact diamond is one of perspective natural type of superhard carbon materials,forming huge resources sometimes,such as Popigai impact structure counting the largest diamond storage on the Earth.By present,there are two known types of impact diamonds-after-graphitic and after-coal varieties formed from different carbon precursors.Here we present for the first time a new impact diamond type-diamond fossils,named by "karite",formed about 70 Ma from unmetamorphosed organics in the giant Kara impact crater(Pay-Khoy,Russia).A full complex of the diamond fossil characteristics is described proving its nature and phase state.Karite is presented with supernanocrystalline diamond aggregates,nicely preserves tiny cell morphology and relict features of lignin and cellulose.The diamond fossils are spread widely through the Kara impactites,point to possible wider distribution of impact diamonds within large impact occurrences around the world,can be used for impact modeling,astrobiological and material studies. 相似文献
5.
This paper summarizes advances since 1987 in the application of glacial sediment sampling to mineral exploration (drift prospecting) in areas affected by continental or alpine glaciation. In these exploration programs, clastic glacial sediments are tested by geochemical or mineralogical methods to detect dispersal trains of mineral deposit indicators that have been glacially transported from source by mechanical processes. In glaciated terrain the key sampling medium, till, is produced by abrasion, crushing and blending of rock debris and recycled sediment followed by down-ice dispersal ranging from a few metres to many kilometres. As a consequence of the mid-1980s boom in gold exploration, the majority of case studies and regional till geochemical surveys published in the past decade deal with this commodity. Approximately 30% of Canada and virtually all of Fennoscandia have been covered by regional till geochemical surveys that aid mineral exploration and provide baseline data for environmental, agricultural, and landuse planning. The most profound event in drift prospecting in the last decade, however, has been the early-1990s explosion in diamond exploration which has dramatically increased the profile of glacial geology and glacial sediment sampling and stimulated changes in sampling and analytical methods. 相似文献
6.
A.P Yelisseyev N.P. Pokhilenko J.W. Steeds D.A. Zedgenizov V.P. Afanasiev 《Lithos》2004,77(1-4):83-97
Confocal photoluminescence (PL) and local absorption spectroscopy were used to study the types and spatial distribution of point defects in coated diamonds, the input of which is about 30% in the Snap Lake deposit, Canada. Nitrogen concentration is on the level of several hundreds of ppm in the core, with a nitrogen-poor layer in its outer part, whereas in the coat it is usually several times higher as a result of fast growth. Nitrogen defects in the core are strongly aggregated with N3, B and B′-forms dominating, whereas A-defects are typical of the coat. The rounded shape of the coated diamonds is a result of the combined effect of partial dissolution of the octahedral core and the “abnormal” growth of the coat, which produces a fibrous structure. Analysis of PL and PL excitation spectra showed that structureless yellow-green PL of the coat is likely to be due to nickel-nitrogen complexes with their fine structure broadened in the strain fields. The presence of irradiation/annealing products such as vacancies V0 and nitrogen-vacancy complexes NV−, N2V2 shows that the diamonds studied have undergone post-growth ionizing irradiation with further low-temperature annealing in natural conditions. 相似文献
7.
Petrogenesis of Proterozoic Lamproites and Kimberlites from the Cuddapah Basin and Dharwar Craton, Southern India 总被引：9，自引：3，他引：9
CHALAPATHI RAO N. V.; GIBSON S. A.; PYLE D. M.; DICKIN A. P. 《Journal of Petrology》2004,45(5):907-948
Proterozoic mafic potassic and ultrapotassic igneous rocks emplacedin the Cuddapah Basin and Dharwar Craton of the southern Indianshield are among the earliest recorded on Earth. Lamproitesintrude the basin and its NE margin, whereas kimberlites intrudethe craton to the west of the basin. Kimberlites occur in twospatially separate groups: the non-diamondiferous Mahbubnagarcluster that was emplaced at 1400 Ma and is of a similar ageto the Cuddapah lamproites, and the predominantly diamondiferousAnantapur cluster, emplaced at 相似文献
8.
T. Gasparik 《Physics and Chemistry of Minerals》2002,29(3):170-180
Multianvil experiments were carried out at 10–15 GPa and 1600–1700 °C to match the compositions of majoritic garnet inclusions
from diamonds, and to determine the compositions of other phases potentially coexisting with these inclusions in the source.
Most experiments produced coexisting majoritic garnet, diopsidic clinopyroxene, one or more (Mg,Fe)2SiO4 polymorphs, and quenched carbonatic melt. The experimental garnets had relatively high Ca and Fe contents similar to the
observed Ca and Fe contents of the inclusions. The resulting Si contents confirmed that the depth of origin of the inclusion
with the highest Si content did not exceed 410 km, thus none of the majoritic garnet inclusions found so far originated in
the transition zone (410–660 km). The evidence from inclusions and experiments is consistent with the presence of an eclogite
layer occurring globally between 200 and 410 km. Compositional variations observed among more than 100 majoritic garnet inclusions
with their Si content, which is a measure of pressure and depth, are consistent with the origin of the eclogite layer by crystal
fractionation in a magma ocean. The compositions of olivine coexisting with majoritic garnet in the experimental products
had the average Fe/(Fe + Mg) ratios between 0.16 and 0.28. Inclusions with such high Fe contents have not been found; the
Fe/(Fe + Mg) ratio of the olivine inclusions in diamonds usually varies between 0.05 and 0.09. Hence, the mantle between 200
and 410 km may not contain olivine. In the absence of olivine, the discontinuity at 410 km is most likely a chemical boundary
between the 200-km-thick eclogite layer and a more mafic transition zone.
Received: 15 March 2001 / Accepted: 14 September 2001 相似文献
9.
10.
《Geoforum》2015
This study examines the political uses of “conflict diamond” discourse in global debates about commodity certification and socially responsible mining in Zimbabwe. Engaging critical literature on “conflict-free” corporate branding initiatives, the study focuses on representations of conflict in Marange, in Zimbabwe’s eastern highlands. In 2006, a diamond rush in Marange drew in tens of thousands of artisanal miners from across Zimbabwe as well as foreigners, and the government initiated military crackdowns in 2008. In a highly contested vote in 2009, the international government delegates who comprised the voting members in the Kimberley Process Certification System (KPCS) ruled that conflict in Marange did not meet the KPCS definitions of “conflict diamond.” The study examines discourses of key stakeholders in the multinational diamond industry, human rights organizations, policymakers as well as artisanal miners in Zimbabwe between 2006 and 2014. The article argues that advocacies against diamond certification as well as advocacies favouring certification both tended to overlook the interests of artisanal miners, focusing narrowly on certain forms of conflict while associating artisanal mining with illicitness. The Marange case illustrates how conventional discourses on “conflict diamonds” not only obscure the complex nature of conflicts in contemporary capitalist accumulation processes; they also risk contributing to new forms of structural violence. This analysis highlights the need to pay careful attention to how global commodity certification discourses inter-relate with political agendas at multiple scales. The study draws attention to dilemmas for geographers when portraying the interests of marginalized groups in – and affected by – the diamond mining sector. 相似文献