Petrology of Whiteschists and Associated Rocks at Mautia Hill (Tanzania): Fluid Infiltration during High-Grade Metamorphism?   总被引：2，自引：0，他引：2  

JONS  NIELS; SCHENK  VOLKER 《Journal of Petrology》2004,45(10):1959-1981

Talc–kyanite schists (whiteschists), magnesiohornblende–kyanite–talc–quartzschists and enstatite–sapphirine–chlorite schistsoccur at Mautia Hill in the East African Orogen of Tanzania.They are associated with metapelites and garnet–clinopyroxene–quartzmetabasites. Geobarometry (GASP/GADS equilibria) applied tothe latter two rock types indicates a peak pressure of P = 10–11kbar. These results are confirmed by the high fO₂ assemblagehollandite–kyanite–quartz and late-stage manganianandalusite that contains up to 19·5 mol. % Mn₂SiO₅. Maximumtemperatures of T = 720°C are inferred from late-stage yoderite+ quartz. A clockwise P–T evolution is constrained byprograde kyanite inclusions in metapelitic garnet and late-stagereaction rims of cordierite between green yoderite and talcthat reflect conditions at least 3–4 kbar below the peakpressure. Oxidizing conditions are recorded throughout the metamorphichistory of the whiteschists and chlorite schists, as indicatedby the presence of haematite coexisting with pseudobrookiteand/or rutile. Increasing water activity near peak pressuresis thought to have led to the breakdown of the high-pressureassemblages (Tlc–Ky–Hem and Mg-Hbl–Ky–Hem)and the subsequent formation of certain uncommon minerals, e.g.yellow sapphirine, Mn–andalusite, green and purple yoderite,piemontite and boron-free kornerupine. The proposed increasein water activity is attributed to fluid infiltration resultingfrom the devolatilization of underlying sediments during metamorphism. KEY WORDS: fluid infiltration; high-pressure amphibolite facies; East African Orogen; Pan-African; whiteschist  相似文献   

The Petrology of Basanite-Tephrite Intrusions in the Erongo Complex and Implications for a Plume Origin of Cretaceous Alkaline Complexes in Namibia   总被引：2，自引：0，他引：2  

TRUMBULL  R. B.; BUHN  B.; ROMER  R. L.; VOLKER  F. 《Journal of Petrology》2003,44(1):93-112

Basanite intrusions from the Early Cretaceous Erongo complex,Namibia, have compositions consistent with near-primary mantlemelts derived from a depth of at least 100 km. These rocks providea key reference for the mantle component(s) involved in breakup-relatedmagmatism in this region. Initial Sr–Nd–Pb isotoperatios of the Erongo basanites and associated tephrites andphonotephrites (⁸⁷Sr/⁸⁶Sr = 0·70425–0·70465;  相似文献   

冬季由印缅来的低槽对于华南天气的影响   总被引：10，自引：0，他引：10  

陶诗言 《气象学报》1953,24(1):172-192

在长江以南做天气预告的人,大致都觉到长江以南的天气不容易预告好。因为江南冬季的天气,常常是在阴沉沉的低云或浓雾笼罩之下,完全睛朗的日子比较少。一般说来,冬季江南天气变化的规律,远不如华北那麽容易握掌,除开寒潮天  相似文献   

中纬度对流层上部的能量变化     

叶笃正  徐淑英 《气象学报》1953,24(1):193-203

能量在大气中是一个主要的因素,大气中一切的现象之所以能发生,都是因为大气有适当的能量的供给和变化。大气中能量的式样很多,不同式样的能力有不同的重要性,研究各种式样的能力的多寡和它的变化是很有意义的,因为大气环流  相似文献   

Spatial Distribution of Carbonaceous Aerosol in the Southeastern Baltic Sea Region (Event of Grass Fires)     

Vadimas Dudoitis  Steigvilė Byčenkienė  Kristina Plauškaitė  Carlo Bozzetti  Roman Fröhlich  Genrik Mordas  Vidmantas Ulevičius 《Acta Geophysica》2016,64(3):711-731

The aerosol chemical composition in air masses affected by large vegetation fires transported from the Kaliningrad region (Russia) and southeast regions (Belarus and Ukraine) during early spring (March 2014) was characterized at the remote background site of Preila, Lithuania. In this study, the chemical composition of the particulate matter was studied by high temporal resolution instruments, including an Aerosol Chemical Speciation Monitor (ACSM) and a seven-wavelength aethalo-meter. Air masses were transported from twenty to several hundred kilometres, arriving at the measurement station after approximately half a day of transport. The concentration-weighted trajectory analysis suggests that organic aerosol particles are mainly transported over the Baltic Sea and the continent (southeast of Belarus). Results show that a significant fraction of the vegetation burning organic aerosol is transformed into oxidised forms in less than a half-day. Biomass burning aerosol (BBOA) was quantified from the ACSM data using a positive matrix factorization (PMF) analysis, while its spatial distribution was evaluated using air mass clustering approach.  相似文献   

Enabling collaborative GeoVisual analytics: Systems,techniques, and research challenges          下载免费PDF全文

Gustavo Adolfo García‐Chapeton  Frank Olaf Ostermann  Rolf A. de By  Menno‐Jan Kraak 《Transactions in GIS》2018,22(3):640-663

Collaboration across disciplines is recognized as one of the great challenges for research in visual analysis of geographic information (GeoVisual Analytics, GVA). Considering the increasing availability of geodata and the complexity of analytical problems, the need to advance the support for collaborative work is becoming more pressing and prominent. This article contributes to this objective by reviewing the state‐of‐the‐art of the support for collaborative work in GVA systems and by identifying research challenges and proposing strategies to address them. We conducted a systematic review, resulting in the identification of 13 collaborative systems, 6 distinct collaborative techniques, and 3 research challenges. We conclude that GVA is moving toward more effective support of multidisciplinary and cross‐domain collaborative analysis. However, to materialize this potential, research is needed to improve the support for hybrid collaborative scenarios, cross‐device collaboration, and support for time‐critical and long‐term analysis.  相似文献   

Can an atmospherically forced ocean model accurately simulate sea surface temperature during ENSO events?     

By A. BIROL KARA  HARLEY E. HURLBURT  CHARLIE N. BARRON  ALAN J. WALLCRAFT  E. JOSEPH METZGER 《地球，A辑:动力气象学与海洋学》2010,62(1):48-61

The performance of an atmospherically forced ocean general circulation model (OGCM) in simulating daily and monthly sea surface temperature (SST) is examined during the historical El Niño Southern Oscillation (ENSO) events during the time period 1993–2003. For this purpose, we use the HYbrid Coordinate Ocean Model (HYCOM) configured for the North Pacific north of 20°S at a resolution of ≈9 km. There is no assimilation of (or relaxation to) SST data and no date-specific assimilation of any data type. The ability of the model in simulating temporal variations of SST anomalies is discussed by comparing model results with two satellite-based SST products. The HYCOM simulation gives a basin-averaged monthly mean bias of 0.3 °C and rms difference of 0.6 °C over the North Pacific Ocean during 1993–2003. While the model is able to simulate SST anomalies with mean biases  <0.5 °C  in comparison to observations during most of the ENSO events, limitations in the accuracy of atmospheric forcing (specifically, net short-wave radiation) have some influence on the accuracy of simulations. This is specifically demonstrated during the 1998 transition period from El Niño to La Niña, when a record large SST drop of  ≈7 °C  occurred in the eastern equatorial Pacific Ocean.  相似文献