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Gr&#;tter Herman S. Pell Jennifer A. Fitzgerald Catherine E. 《Mineralogy and Petrology》2018,112(2):707-718
Exploration for diamond-bearing kimberlites in the Chidliak project area by Peregrine Diamonds has generated a grid-like till sampling pattern across four discrete areas of interest totalling 402 km2 that is densely populated with research-grade compositional data for 10,743 mantle-derived Cr-pyrope garnets. The available dataset is well suited to statistical analysis, in part due to the relatively unbiased spatial coverage. Previous workers showed empirically that the TiO2 and Mn thermometry (Ti-TMn) attributes of Cr-pyrope populations at the Chidliak project may serve as source-specific “fingerprints”. In this work, we employ a simplified version of the multivariate Mahalanobis distance technique to formally examine the variability of, and differences between, Ti-TMn attributes of Cr-pyrope subpopulations recovered from a Laurentide-age glaciated terrain that also contains 30 known kimberlites within the four areas of interest. We show the simplified Mahalanobis distance approach enables accurate discrimination of Cr-pyrope subpopulations with subtly to distinctly different Ti-TMn attributes, and permits proper demarcation of their respective kimberlite source(s), specifically in areas with straightforward glacial histories. Redistribution and blending of Cr-pyrope subpopulations from known kimberlite sources is also observed, and typifies areas at Chidliak with complex late-glacial histories. Our results support <1 km horizontal scale subtle to obvious variability in the proportions of TiO2-rich and high-temperature (> 1100 °C) Cr-pyropes between closely spaced kimberlite source(s) and also between physically adjacent magma batches within single kimberlite pipes. The local scale variability is attributed to protokimberlite fluid or melt interacting with, and metasomatizing discrete conduits within, the ambient diamond-facies peridotitic mantle at times closely preceding eruption of kimberlite magma batches at Chidliak.
相似文献13.
Late Paleozoic or Permo-Carboniferous Gondwana successions world-wide are marked by widespread and lengthy glaciation (~ 67 Ma), and multiple transitions from Icehouse to Greenhouse state. Mineralogical and compositional changes in sandstones and mudstones of the Gondwana succession in drill hole GDH-45 from the Khalaspir basin of Bangladesh are interpreted in a climatic framework, using the proxies of the Mineralogical Index of Alteration (MIA) and the Chemical Index of Alteration (CIA). Low MIA (< 75) and CIA (< 70) values in the lowermost unit (Unit 1) of the Khalaspir Gondwana sequence indicates minimal chemical weathering of the source and imply cold and dry glacial climatic conditions. Values increase progressively in the overlying Unit 2, suggesting warming and deglaciation. Very high MIA (80–100) and CIA (90–100) values in Unit 3 indicate intense chemical weathering associated with warm and humid climatic conditions in a post-glacial setting. These changes are recorded in both sandstones and mudstones, illustrating the value of acquiring data for a variety of size grades. The stratigraphic changes are also well recorded by progressively decreasing K2O/Al2O3 and increasing Ga/Rb ratios, the combination of which may comprise a new geochemical proxy of climate and weathering. Upward increase in the modal Q / (F + L) and Qp / (F + L) ratios are also consistent with change from cool to warm and humid climate in the source region. The change in climatic conditions within the Khalaspir sequence is also well correlated with the Gondwana successions of other continental blocks, and records the climatic fluctuations and extent of climatic impact in Gondwanaland during the Permo-Carboniferous. 相似文献
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The Devonian–Carboniferous Tsetserleg terrane of Mongolia forms part of the complex Central Asian Orogenic Belt (CAOB). The Tsetserleg terrane consists mainly of clastic sediments, and is situated in the southern Hangay–Hentey Basin. Internally the terrane is divided into the Erdenetsogt (Middle Devonian), Tsetserleg (Middle‐Upper Devonian) and Jargalant (Lower Carboniferous) Formations. Provenance and tectonic setting of the Hangay–Hentey Basin remains controversial, with proposals ranging from passive margin through to island‐arc. A suite of 94 Tsetserleg sandstones and mudrocks was collected with the aim of constraining provenance, source weathering, and depositional setting, using established petrographic and whole‐rock geochemical parameters. Petrographically the sandstones are immature, with average compositions of Q22F14L64, Q14F17L69, and Q18F12L70 in the Erdenetsogt, Tsetserleg, and Jargalant Formations, respectively. Lv/L ratios range from 0.81 to 1.00 (average 0.95), and P/F from 0.68 to 0.93 (average 0.83). Framework compositions indicate deposition in an undissected or transitional arc. Geochemically, the sandstones are classified as greywackes. Geochemical contrasts between sandstone and mudrock averages in each formation are small, with lithotype means for SiO2 ranging only from 65.54 to 68.62 wt.%. These features and weak trends on variation diagrams reflect the immaturity of the sediments. Comparison of elemental abundances with average upper continental crust, major element discriminant scores, and immobile element ratios indicate a uniform average source composition between dacite and rhyolite. The maximum value for the Chemical Index of Alteration in the Erdenetsogt Formation is about 78 after correction for K‐metasomatism, indicating moderate source weathering. Lower maximum values (61 and 63, respectively) in the Tsetserleg and Jargalant Formations indicate they were derived from a virtually unweathered and tectonically active source. Tectonic setting discrimination parameters indicate a continental island‐arc environment, similar to several other CAOB suites of similar age. This arc source may have been built on a continental fragment situated within the Mongol–Okhotsk Ocean during Middle Devonian‐Lower Carboniferous time. 相似文献
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This paper briefly presents a numerical code which simulates the evolution of galaxies belonging to rich clusters. The evolutionary model considers both, cluster dynamics and galaxy photometry, taking into account the galaxy-cluster interactions (collisional stripping, merging and ram-pressure stripping by the ICM) and the intrinsic galaxy evolution. We use different initial mass distributions for galaxies and we briefly discuss the influence of the initial segregation in mass on the evolution of the photometrical properties.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
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Gabriella De Lucia Bianca M. Poggianti Alfonso Aragón-Salamanca Simon D. M. White Dennis Zaritsky Douglas Clowe Claire Halliday Pascale Jablonka Anja von der Linden Bo Milvang-Jensen Roser Pelló Gregory Rudnick Roberto P. Saglia Luc Simard 《Monthly notices of the Royal Astronomical Society》2007,374(3):809-822
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The Hangay–Hentey belt is situated in the central Northern Mongolia, and forms part of the Central Asian Orogenic Belt (CAOB). It is internally subdivided into seven terranes, the largest of which are the neighbouring Ulaanbaatar and Tsetserleg terranes. These coeval terranes are mainly composed of Silurian–Devonian accretionary complexes and Carboniferous turbidites. Proposals for their depositional setting range from passive margin through to island arc. A suite of 19 Ulaanbaatar terrane sandstones and mudrocks (Gorkhi and Altanovoo Formations) were collected with the aim of constraining their provenance, source weathering, and depositional setting based on whole-rock major and trace element data, and for comparison with the neighbouring Tsetserleg terrane. New REE analyses were also made of 35 samples from the Ulaanbaatar and Tsetserleg terranes. Geochemically the Ulaanbaatar sandstones are classed as wackes, and most of the mudstones as shales. Geochemical parameters suggest an immature source, similar to that of the Tsetserleg terrane. Geochemical contrasts between sandstones and mudrocks in the Ulaanbaatar sediments are small, and trends on element – Al2O3 variation diagrams are weak. Comparison with average upper continental crust (UCC), major element discriminant scores, and immobile element ratios (Th/Sc, Zr/Sc, Ce/Sc, Ti/Zr) indicate a uniform average source composition between dacite and rhyolite. Maximum Chemical Index of Alteration value in the Ulaanbaatar terrane is ∼65 after correction for K-metasomatism, indicating minimal weathering in a tectonically active source, similar to that of the Tsetserleg terrane. REE data in both terranes show moderate LREE enrichment and flat HREE segments, with negative Eu anomalies somewhat less than those in UCC and PAAS. Chondrite-normalized patterns are very similar to that for average Paleozoic felsic volcanic rock, supporting the relatively felsic source indicated by immobile trace element ratios. Tectonic setting discriminants (K2O/Na2O–SiO2/Al2O3, La–Th–Sc, Th–Sc–Zr) indicate an evolved continental island arc (CIA; A2) environment for both terranes, similar to several other CAOB suites of similar age. This common arc source was situated within the Mongol-Okhotsk Ocean during Silurian–Lower Carboniferous time. The present-day Aleutian arc is a possible modern analogue of the depositional setting. 相似文献
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The space Fresnel Interferometric Imager, originally proposed to the ESA Cosmic Vision plan, is an innovative concept providing enhanced capabilities in terms of spatial resolution and dynamical range. In this paper we describe some of the most promising applications of the Fresnel Interferometric Imager concept in extragalactic studies. There are two different topics where the FII could make major progress. The first one is the mapping of star-formation in galaxies, from the local universe to ??75?C85% look back time, based on the first version of FII which is optimized for the UV and optical domains. The second topic is a test case for a subsequent improved version of FII, with a larger collecting area and optimized for the near-IR, focusing on the physical properties of the first galaxies. 相似文献
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Hydropeaking power production has the potential to pose serious challenges towards hydrology, water quality and ecology in the downstream water bodies. The effects of such abrupt changes of flow in hyporheic exchange have been explored in a few cases in the literature. This paper extends previous works with a study of finer time resolution in a river of a smaller size and with different climatic characteristics, adding to the current knowledge of peaking‐hyporheic interactions. A high‐frequency logging field experiment measuring hyporheic flow and temperature was conducted on a ~30 × 20 m gravel bar frequently exposed to dry conditions because of fast and abrupt flow changes. This study demonstrates that hyporheic processes are sensitive to hydropeaking with respect to rates of change, durations and temperature. Differences BETWEEN individual events, seasons, watering and dewatering processes and positions in the river bed that can be potentially relevant to ecology were investigated. Understanding the complexity of those processes at the fine scale from the physical point of view is both important for the judgement of potential ecological impacts and for the future management of such regulated systems. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献