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91.
Abstract: Djerfisherite occurs intimately intergrown with troilite and pentlandite in gehlenite-spurrite skarn at Kushiro, mainly as inclusions in gehlenite and andradite grains. The mode of occurrence indicates that the djerfisherite formed in the culminated stage of the contact metamorphic-metasomatic process. The chemical compositions of the mineral are approximately represented by a formula of K6 Na(Fe, Ni, Cu)24 S26 Cl with Ni up to 4. 85. It is likely that high temperature condition corresponding to the formation of gehlenite-spurrite skarn as well as low fO2 and fS2 conditions are responsible for the formation of djerfisherite in the potassium-rich chemical environments. 相似文献
92.
Shinsuke Kato Tomokatsu Morota Yasushi Yamaguchi Sei‐ichiro Watanabe Hisashi Otake Makiko Ohtake 《Meteoritics & planetary science》2017,52(9):1899-1915
Mare basalts provide insights into the composition and thermal history of the lunar mantle. The ages of mare basalts suggest a first peak of magma activity at 3.2–3.8 Ga and a second peak at ~2 Ga. In this study, we reassess the correlation between the titanium contents and the eruption ages of mare basalt units using the compositional and chronological data updated by SELENE (Kaguya). Using morphological and geological criteria, we calculated the titanium content of 261 mare units across a representative area of each mare unit. In the Procellarum KREEP Terrane, where the latest eruptions are located, an increase in the mean titanium content is observed during the Eratosthenian period, as reported by previous studies. We found that the increase in the mean titanium content occurred within a relatively short period near approximately 2.3 Ga, suggesting that the magma source of the mare basalts changed at this particular age. Moreover, the high‐titanium basaltic eruptions are correlated with a second peak in volcanic activity near ~2 Ga. The high‐titanium basaltic eruptions occurring during the last volcanic activity period can be explained by the three possible scenarios (1) the ilmenite‐bearing cumulate rich layer in the core‐mantle boundary formed after the mantle overturn, (2) the basaltic material layers beneath the lunar crust formed through upwelling magmas, and (3) ilmenite‐bearing cumulate blocks remained in the upper mantle after the mantle overturn. 相似文献
93.
Subinertial and seasonal variations in the Soya Warm Current revealed by HF ocean radars,coastal tide gauges,and bottom-mounted ADCP 总被引:2,自引:2,他引:0
Naoto Ebuchi Yasushi Fukamachi Kay I. Ohshima Masaaki Wakatsuchi 《Journal of Oceanography》2009,65(1):31-43
Subinertial and seasonal variations in the Soya Warm Current (SWC) are investigated using data obtained by high frequency
(HF) ocean radars, coastal tide gauges, and a bottom-mounted acoustic Doppler current profiler (ADCP). The HF radars clearly
captured the seasonal variations in the surface current fields of the SWC. Almost the same seasonal cycle was repeated in
the period from August 2003 to March 2007, although interannual variations were also discernible. In addition to the annual
and interannual variations, the SWC exhibited subinertial variations with a period of 5–20 days. The surface transport by
the SWC was significantly correlated with the sea level difference between the Sea of Japan and Sea of Okhotsk for both the
seasonal and subinertial variations, indicating that the SWC is driven by the sea level difference between the two seas. The
generation mechanism of the subinertial variation is discussed using wind data from the European Centre for Medium-range Weather
Forecasts (ECMWF) analyses. The subinertial variations in the SWC were significantly correlated with the meridional wind stress
component over the region. The subinertial variations in the sea level difference and surface current delay from the meridional
wind stress variations by one or two days. Sea level difference through the strait caused by wind-generated coastally trapped
waves (CTWs) along the east coast of Sakhalin and west coast of Hokkaido is considered to be a possible mechanism causing
the subinertial variations in the SWC. 相似文献
94.
Toshiyuki Kurihara Kazuhiro Tsukada Shigeru Otoh Kenji Kashiwagi Minjin Chuluun Dorjsuren Byambadash Bujinlkham Boijir Sersmaa Gonchigdorj Manchuk Nuramkhan Masakazu Niwa Tetsuya Tokiwa Gen’ya Hikichi Takafumi Kozuka 《Journal of Asian Earth Sciences》2009,34(2):209-225
Recent mapping projects undertaken in Central Mongolia have revealed the widespread occurrence of radiolarian chert within a Paleozoic accretionary complex. We present the results of the first detailed tectonostratigraphic and radiolarian biostratigraphic investigations of the Gorkhi Formation in the Khangai–Khentei belt of the Central Asian Orogenic Belt.The Gorkhi Formation consists of sandstone shale, alternating sandstone and shale of turbidite affinity and chert with small amounts of siliceous shale, basalt, limestone, and clast-bearing mudstone. Radiolarian chert that is completely devoid of terrigenous clastic material is commonly associated with underlying basalt (sedimentary contact) and with conformably overlying siliceous shale and turbidite deposits. The tectonic stacking of basalt–chert and chert–turbidite successions is the most remarkable structural feature of the formation.The recovery of moderately well-preserved radiolarians and conodonts from red chert led to the recognition of four radiolarian assemblages that have a combined age range from the latest Silurian (Pridolian) to the Late Devonian (Frasnian). No age control exists for the siliceous shale, shale, and sandstone, although they are considered to be latest Devonian or slightly younger on the basis of stratigraphic relationships with underlying chert.The Gorkhi Formation has previously been interpreted as a thick sedimentary basin deposit overlying an unexposed Archean–Neoproterozoic basement; however, the stratigraphy within individual tectonic slices clearly corresponds to that of an ocean plate stratigraphy of an accretionary complex generated by the trenchward movement of an oceanic plate. From the lowermost to uppermost units, the stratigraphy comprises ocean floor basalt, pelagic deep-water radiolarian chert, hemipelagic siliceous shale, and terrigenous turbidite deposits. The biostratigraphic data obtained in the present study provide corroborating evidence for the existence of an extensive deep-water ocean that enabled the continuous sedimentation of pelagic chert over a period of nearly 50 million years. These data, together with structural data characterized by tectonic repetition of the stratigraphy, indicate that these rocks formed as an accretionary wedge along an active continental margin, possibly that of the Angara Craton. The mid-oceanic chert was probably deposited in the Northern Hemisphere portion of the Paleo–Pacific Ocean that faced the Angara Craton and the North China–Tarim blocks. Thus, we propose that subduction–accretion processes along the Paleo–Pacific rim played an important role in the accretionary growth of the active continental margin of the Angara Craton, directly influencing the evolution of the Central Asian Orogenic Belt. 相似文献
95.
96.
97.
Shun Nomura Giovanni De Cesare Mikito Furuichi Yasushi Takeda Hide Sakaguchi 《国际泥沙研究》2022,37(3):299-306
A turbidity current is a turbulent, particle-laden gravity current that is driven by density differences resulting from the presence of suspended sediment particles. The current travels downslope, bearing a large amount of sediment over a great distance, and forms fluvial and submarine bedforms. Knowledge of the spatio-temporal deposition profile of turbidity-deposited sediment is important for a better understanding of sediment transport by turbidity currents. In the current study, the depositi... 相似文献
98.
Bulletin of Earthquake Engineering - Many reinforced concrete (RC) frame buildings in Nepal were significantly damaged by the 7.8 magnitude (Mw) earthquake in Nepal on April 25, 2015. To contribute... 相似文献
99.
Determination of reaction kinetics using grain size: An application for metamorphic zircon growth
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The reaction kinetics of metamorphic minerals can be subdivided into interface‐ and diffusion‐controlled kinetics. The discrimination of reaction kinetics is crucial for estimating reaction rates. Here, we propose a new and simple method for discriminating reaction kinetics. This method requires measuring only the initial and final grain sizes during growth. The reaction kinetics is inferred from different plotted arrays of initial vs. final grain sizes after the mineral growth. Using metamorphic zircon, we take detrital core sizes as the initial sizes and post‐metamorphic grain sizes as the final sizes. The application of the method to the subduction‐related high‐pressure Nagasaki metamorphic complex in Japan shows that this metamorphic zircon grew under interface‐controlled kinetics even at the relatively low temperature of 440°C. This method is potentially applicable to other minerals that have time‐markers, such as chemical zoning or internal structures that are captured at a given point in time during growth. 相似文献
100.