A mineral and cumulate perspective to magma differentiation at Nisyros volcano,Aegean arc     

Martijn?KlaverEmail authorView author&#;s OrcID profile  Sergei?Matveev  Jasper?Berndt  C.?Johan?Lissenberg  Pieter?Z.?Vroon 《Contributions to Mineralogy and Petrology》2017,172(11-12):95

Lavas and pyroclastic products of Nisyros volcano (Aegean arc, Greece) host a wide variety of phenocryst and cumulate assemblages that offer a unique window into the earliest stages of magma differentiation. This study presents a detailed petrographic study of lavas, enclaves and cumulates spanning the entire volcanic history of Nisyros to elucidate at which levels in the crust magmas stall and differentiate. We present a new division for the volcanic products into two suites based on field occurrence and petrographic features: a low-porphyricity andesite and a high-porphyricity (rhyo)dacite (HPRD) suite. Cumulate fragments are exclusively found in the HPRD suite and are predominantly derived from upper crustal reservoirs where they crystallised under hydrous conditions from melts that underwent prior differentiation. Rarer cumulate fragments range from (amphibole-)wehrlites to plagioclase-hornblendites and these appear to be derived from the lower crust (0.5–0.8 GPa). The suppressed stability of plagioclase and early saturation of amphibole in these cumulates are indicative of high-pressure crystallisation from primitive hydrous melts (≥ 3 wt% H₂O). Clinopyroxene in these cumulates has Al₂O₃ contents up to 9 wt% due to the absence of crystallising plagioclase, and is subsequently consumed in a peritectic reaction to form primitive, Al-rich amphibole (Mg# > 73, 12–15 wt% Al₂O₃). The composition of these peritectic amphiboles is distinct from trace element-enriched interstitial amphibole in shallower cumulates. Phenocryst compositions and assemblages in both suites differ markedly from the cumulates. Phenocrysts, therefore, reflect shallow crystallisation and do not record magma differentiation in the deep arc crust.  相似文献   

The latest geodynamics in Asia: Synthesis of data on volcanic evolution,lithosphere motion,and mantle velocities in the Baikal-Mongolian region     

Sergei Rasskazov  Irina Chuvashova 《地学前缘(英文版)》2017,8(4):733-752

From a synthesis of data on volcanic evolution,movement of the lithosphere,and mantle velocities in the Baikal-Mongolian region,we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi,Baikal,and North Transbaikal transition-layer melting anomalies.This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage(i.e.in the early late Cretaceous) due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker,Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific.At the latest geodynamic stage,Asia was involved in east-southeast movement,and the Pacific plate moved in the opposite direction with subduction under Asia.The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area.These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab.A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab,formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence.The early—middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens.We propose that extension at the Baikal Rift was caused by deviator flowing mantle material,initiated under the moving lithosphere in the Baikal melting anomaly.Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.  相似文献   

Tree wave migration across an elevation gradient in the Altai Mountains,Siberia   总被引：1，自引：1，他引：0  

Viacheslav I. Kharuk  Sergei T. Im  Maria L. Dvinskaya  Kenneth J. Ranson  Il’ya A. Petrov 《山地科学学报》2017,14(3):442-452

The phenomenon of tree waves(hedges and ribbons) formation within the alpine ecotone in Altai Mountains and its response to observed air temperature increase was considered. At the upper limit of tree growth Siberian pine(Pinus sibirica) forms hedges on windward slopes and ribbons on the leeward ones. Hedges were formed by prevailing winds and oriented along winds direction. Ribbons were formed by snow blowing and accumulating on the leeward slope and perpendicular to the prevailing winds, as well as to the elevation gradient. Hedges were always linked with microtopography features, whereas ribbons were not. Trees are migrating upward by waves and new ribbons and hedges are forming at or near tree line, whereas at lower elevations ribbons and hedges are being transformed into closed forests. Time series of high-resolution satellite scenes(from 1968 to 2010) indicated an upslope shift in the position ribbons averaged 155±26 m(or 3.7 m yr~(-1)) and crown closure increased(about 35%–90%). The hedges advance was limited by poor regeneration establishment and was negligible. Regeneration within the ribbon zone was approximately 2.5 times(5060 vs 2120 ha~(-1)) higherthen within the hedges zone. During the last four decades, Siberian pine in both hedges and ribbons strongly increased its growth increment, and recent tree growth rate for 50 year-old trees was about twice higher than those recorded for similarly-aged trees at the beginning of the 20~(th) century. Hedges and ribbons are phenomena that are widespread within the southern and northern Siberian Mountains.  相似文献   

Y2K and Other Stories     

Sergei A. Gourevitch  Dale Kyle 《GPS Solutions》1999,3(1):2-4

GPS technology will face not one but two critical rollover dates over the next eight months. One is the millennium (Y2K) rollover. The other is the GPS week 1024 rollover also known as the GPS End of the Week (EOW). Each rollover dat has the potential to cause severe problems in GPS receivers and related software. This article expolres the reasons why these dates are a problem and describes choices that must be made as to their solution. The paper also describes some verification methods that may be used to test GPS receivers and software. ? 1999 John Wiley & Sons, Inc.  相似文献   

Amplitude,frequency and drivers of Caspian Sea lake-level variations during the Early Pleistocene and their impact on a protected wave-dominated coastline     

Elisabeth L. Jorissen  Hemmo A. Abels  Frank P. Wesselingh  Sergei Lazarev  Vusala Aghayeva  Wout Krijgsman 《Sedimentology》2020,67(1):649-676

The Caspian Sea, the largest isolated lake in the world, witnessed drastic lake-level variations during the Quaternary. This restricted basin appears very sensitive to lake-level variations, due to important variations in regional evaporation, precipitation and runoff. The amplitude, frequency and drivers of these lake-level changes are still poorly documented and understood. Studying geological records of the Caspian Sea might be the key to better comprehend the complexity of these oscillations. The Hajigabul section documents sediment deposited on the northern margin of the Kura Basin, a former embayment of the Caspian Sea. The 2035 m thick, well-exposed section was previously dated by magneto-biostratigraphic techniques and provides an excellent record of Early Pleistocene environmental, lake-level and climate changes. Within this succession, the 1050 m thick Apsheronian regional stage, between ca 2·1 Ma and 0·85 Ma, represents a particular time interval with 20 regressive sequences documented by sedimentary and palaeontological changes. Sequences are regressing from offshore to coastal, lagoonal or terrestrial settings and are bounded by abrupt flooding events. Sediment reveals a low energy, wave-dominated, reflective beach system. Wave baselines delimiting each facies association appear to be located at shallower bathymetries compared to the open ocean. Water depth estimations of the wave baselines allow reconstruction of a lake-level curve, recording oscillations of ca 40 m amplitude. Cyclostratigraphic analyses display lake-level frequency close to 41 kyr, pointing to allogenic forcing, dominated by obliquity cycles and suggesting a direct or indirect link with high-latitude climates and environments. This study provides a detailed lake-level curve for the Early Pleistocene Caspian Sea and constitutes a first step towards a better comprehension of the magnitude, occurrence and forcing mechanisms of Caspian Sea lake-level changes. Facies models developed in this study regarding sedimentary architectures of palaeocoastlines affected by repeated lake-level fluctuations may form good analogues for other (semi-)isolated basins worldwide.  相似文献   

白令海北部陆坡23 ka以来古生产力变化及其对海冰扩张的响应     

宋腾飞  王宏雷  陈漪馨  李朝新  朱爱美  白亚之  石学法  Gorbarenko Sergei  Bosin Aleksandr  刘焱光 《海洋学报》2018,40(5):90-106

本文基于白令海北部陆坡ARC6-B11岩心的沉积物粒度、颜色反射率、有机碳/氮含量和高分辨率化学元素XRF扫描数据,结合底栖和浮游有孔虫AMS14C测年资料,重建了研究区23 ka以来至中全新世的沉积记录,重点研究了海冰的扩张变化对生产力和沉积物输入的影响。研究结果显示,末次盛冰期白令海北部陆坡受到海冰南向扩张的影响而生产力较低,沉积物中砂粒级和冰筏碎屑（IRD）含量较高。HS 1时期由于受到常年冰的覆盖,沉积物中砂粒级和IRD含量存在低值,沉积物中较高的总有机碳（TOC）含量受陆源有机质的影响较大,异常的TOC含量峰值主要受到低海平面和海冰形成过程产生的富氧水团控制下的高浓度细粒物质携带的陆源有机质的快速沉积作用的影响,难以作为反映白令海古生产力的替代指标。B/A暖期和全新世生产力较高,在B/A暖期存在Ca/Ti峰值现象,Ca/Ti峰值现象的产生与碳酸盐补偿深度增加有关,水体通风条件的改变可能起到一定的作用,也不能忽视颗石藻对其产生的潜在影响。  相似文献