A point based Eulerian definition of rain event based on statistical properties of inter drop time intervals: An application to Chilbolton data     

Massimiliano Ignaccolo  Carlo De Michele 《Advances in water resources》2010

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Silicate‐oxide mineral chemistry of mafic–ultramafic rocks as an indicator of the roots of an island arc: The Chilas Complex,Kohistan (Pakistan)          下载免费PDF全文

Rubina Bilqees  M. Qasim Jan  M. Asif Khan  Brian F. Windley 《Island Arc》2016,25(1):4-27

The Chilas Complex is a major lower crustal component of the Cretaceous Kohistan island arc and one of the largest exposed slices of arc magma chamber in the world. Covering more than 8000 km², it reaches a current tectonic width of around 40 km. It was emplaced at 85 Ma during rifting of the arc soon after the collision of the arc with the Karakoram plate. Over 85% of the Complex comprises homogeneous, olivine‐free gabbronorite and subordinate orthopyroxene–quartz diorite association (MGNA), which contains bodies of up to 30 km² of ultramafic–mafic–anorthositic association (UMAA) rocks. Primary cumulate textures, igneous layering, and sedimentary structures are well preserved in layered parts of the UMAA in spite of pervasive granulite facies metamorphism. Mineral analyses show that the UMAA is characterized by more magnesian and more aluminous pyroxene and more calcic plagioclase than those in the MGNA. High modal abundances of orthopyroxene, magnetite and ilmenite (in MGNA), general Mg–Fe–Al spatial variations, and an MFA plot of whole‐rock analyses suggest a calc‐alkaline origin for the Complex. Projection of the pyroxene compositions on the Wo–En–Fs face is akin to those of pyroxenes from island arcs gabbros. The presence of highly calcic plagioclase and hornblende in UMAA is indicative of hydrous parental arc magma. The complex may be a product of two‐stage partial melting of a rising mantle diaper. The MGNA rocks represent the earlier phase melting, whereas the UMAA magma resulted from the melting of the same source depleted by the extraction of the earlier melt phase. Some of the massive peridotites in the UMAA may either be cumulates or represent metasomatized and remobilized upper mantle. The Chilas Complex shows similarities with many other (supra)subduction‐related mafic–ultramafic complexes worldwide.  相似文献   

Clarifying the distal to proximal tephrochronology of the Millennium (B–Tm) eruption,Changbaishan Volcano,northeast China     

《Quaternary Geochronology》2016

Tephra dispersed during the Millennium eruption (ME), Changbaishan Volcano, NE China provides one of the key stratigraphic links between Asia and Greenland for the synchronization of palaeoenvironmental records. However, controversy surrounds proximal-distal tephra correlations because (a) the proposed proximal correlatives of the distal ME tephra (i.e. B–Tm) lack an unequivocal chronostratigraphic context, and (b) the ME tephra deposits have not been chemically characterized for a full spectrum of element using grain-specific techniques. Here we present grain-specific glass chemistry, including for the first time, single grain trace element data, for a composite proximal sequence and a distal tephra from Lake Kushu, northern Japan (ca. 1100 km away from Changbaishan). We demonstrate a robust proximal-distal correlation and that the Kushu tephra is chemically associated with the ME/B–Tm. We propose that three of the proximal pyroclastic fall units were erupted as part of the ME. The radiocarbon chronology of the Kushu sedimentary record has been utilised to generate a Bayesian age-depth model, providing an age for the Kushu tephra which is consistent with high resolution ages determined for the eruption and therefore supports our geochemical correlation. Two further Bayesian age-depth models were independently constructed each incorporating one of two ice-core derived ages for the B–Tm tephra, providing Bayesian modelled ages of 933–949 and 944–947 cal AD (95.4%) for the Kushu tephra. The high resolution ice-core tephra ages imported into the deposition models help test and ultimately constrain the radiocarbon chronology in this interval of the Lake Kushu sedimentary record. The observed geochemical diversity between proximal and distal ME tephra deposits clearly evidences the interaction of two compositionally distinct magma batches during this caldera forming eruption.  相似文献   

The influence of volcanism on paleoclimate in the northeast of China： Insights from Jinchuan peat, Jilin Province, China   总被引：3，自引：0，他引：3  

Xumei Mao  Shenggao Cheng  Yetang Hong  Yongxuan Zhu  Fenglin Wang 《中国地球化学学报》2009,28(2):212-219

Just like contemporary sediments, peat itself is a good repository of information about climate change, the effects of volcanic activity on climate change have been truly recorded in peat, since it is a major archive of volcanic eruption incidents. A section of sand was identified as tephra from the Jinchuan peat, Jilin Province, China, for the grains look like slag with surface bubbles and pits, characterized by high porosity, and loose structure with irregular edges and corners. According to the peat characteristics of uniform deposition, the tephra was dated at 2002–1976 a B.P. by way of linear interpolation, so the time of volcanic eruption was 15 B.C.–26 A.D. (the calibrated age). While the geochemical characteristics of tephra in this study are quite the same as those of tephra from the Jinlongdingzi volcano at Longgang and from alkaline basaltic magma, with the contents of SiO₂<55%, and the similar contents to Al₂O₃ and Fe, but the contents of Na₂O>K₂O. We speculated that the tephra in this study came from the Longgang volcano group. Compared with 11 recorded volcanic eruption events as shown on the carbon and oxygen isotope curves of the Jinchuan peat cellulose, it is obviously seen that adjacent or large-scale volcanic eruptions are precisely corresponding to the minimum temperature and humidity. It seems that these volcanic eruptions indeed affected the local climate, leading to the drop of regional temperature and humidity. As a result, there was prevailing a cold and dry climate there, and all these changes can be well recorded in peat. So the comparison of volcanic eruption events with information about climate change developed from peat, can provide strong evidence for the impact of volcanism on climate change.  相似文献   

内蒙古二连浩特北部阿仁绍布地区晚石炭世花岗岩Sr-Yb分类及其成因   总被引：2，自引：1，他引：1  

许立权  鞠文信  刘翠  贺宏云  李满英 《地质通报》2012,31(9):1410-1419

对分布在内蒙古二连浩特北部阿仁绍布地区的晚石炭世花岗岩类,依据Sr、Yb含量,划分为低Sr高Yb型、极低Sr高Yb型和低Sr低Yb型花岗岩3种类型。低Sr高Yb型花岗岩类相对低Si、富Al,Na2O>K2O,稀土元素分馏中等,有或无负Eu异常,Sr含量低,平均为183×10-6,Ba含量较高,平均585×10-6,Y含量高,平均30.06×10-6,Rb/Sr比值较低,平均0.97;极低Sr高Yb型花岗岩富Si、REE,低Al、Sr、Ba,高的Rb/Sr比值(平均为7.47),具明显的负Eu异常等;低Sr低Yb型花岗岩富Si,贫Al、Ca、Mg,重稀土元素(Y、Yb)含量低,Y含量在(7.26～10.6)×10-6之间,平均9.76×10-6,Yb含量在(1.04～1.89)×10-6之间,平均1.44×10-6,δEu=0.64～0.94,具弱负Eu异常,微量元素Ba含量高,Rb/Sr比值低。3种类型的花岗岩类过铝指数(A/CNK)多小于1.0,说明它们均源自变质火成岩的部分熔融。由于源区的深度不同(pT条件不同)和残留的主要矿物相不同,它们的岩石地球化学特征存在差异。极低Sr高Yb型花岗岩形成深度最浅(中上地壳),熔融残留相以斜长石为主;低Sr高Yb型花岗岩类形成于中下地壳,熔融残留相为斜长石和辉石;低Sr低Yb型花岗岩形成深度最深,推测可能形成于加厚下地壳(>40km)底部,熔融残留相为石榴子石、斜长石和角闪石。  相似文献   

全球变化背景下新疆地区气候跃变的可能影响因素分析   总被引：1，自引：0，他引：1  

李稚  李卫红  陈亚宁 《冰川冻土》2011,33(6):1302-1309

基于新疆过去50a气温和降水时间序列长期趋势的研究结果,结合对1986年及附近时段对全球气候产生重大影响的一系列事件（厄尔尼诺、火山爆发、核电站爆炸事故、温室气体增加等）的分析,探讨了1986年新疆气温和降水出现跳跃式变化的原因.具体表现为：当厄尔尼诺现象发生时,常常出现暖冬、早春,在该现象消退过程,往往降水有所增多;...  相似文献   

盐湖丰产元素与Zintl化合物(续完)          下载免费PDF全文

贾永忠  景燕  马军  岳都元  Claude Belin  Monique Tillard 《盐湖研究》2011,19(2):63-72

Zintl化合物是以Edward Zintl命名的化合物,是一类由电正性的碱金属或碱土金属与电负性的13族或14族元素形成的特殊金属间化合物。其价键模式可以是离子键、金属键和共价键共存,其中的准金属可以共价键的形式形成各种形式的离子簇,因而其结构复杂多样。这类化合物的部分阴离子簇不仅具有稳定的笼状、层状和链状结构,并且具有特殊的光、电、磁等性能,使得在半导体、催化、电极材料等方面都有应用的前景和发展潜力。介绍了几个特殊Zintl化合物体系,盐湖丰产元素在Zintl化合物中的作用,指出了含有盐湖丰产元素的Zintl化合物的应用前景和方向。  相似文献   

崩岗侵蚀地貌的演变过程及阶段划分   总被引：4，自引：0，他引：4  

张大林  刘希林 《亚热带资源与环境学报》2011,6(2)

崩岗是中国南方一种常见的土壤侵蚀类型,也是一种严重的水土流失方式,多分布于低山丘陵区的花岗岩风化壳之上.崩岗的形成和发展是2个不同的阶段,并始终受到水力和重力的作用.2种外力对比关系的不同使崩岗的演变过程具有明显的阶段性.通过选取适当的指标体现这种规律性,可以对崩岗的发展阶段进一步划分,对崩岗的治理控制具有重要的意义.  相似文献   

中国2007年以来全新世火山地质研究的主要进展     

白志达  徐德斌  许桂玲  王妍 《矿物岩石地球化学通报》2011,30(4):365-374

简要列举了近年来全新世火山地质领域的研究进展,主要涉及新确定的全新世火山、精细喷发序列与喷发频率、高分辨率火山机构多维框架研究、火山碎屑物粒度分布、形貌特征与成因、火山碎屑流、涌流和火山泥石流堆积、降落堆积成因亚类、火山活动与新构造和火山地质遗迹资源、环境及火山灾害。  相似文献   

Explosive volcanic eruptions triggered by cosmic rays: Volcano as a bubble chamber     

Toshikazu Ebisuzaki  Hiroko Miyahara  Ryuho Kataoka  Tatsuhiko Sato  Yasuhiro Ishimine 《Gondwana Research》2011,19(4):1054-1061

Volcanoes with silica-rich and highly viscous magma tend to produce violent explosive eruptions that result in disasters in local communities and that strongly affect the global environment. We examined the timing of 11 eruptive events that produced silica-rich magma from four volcanoes in Japan (Mt. Fuji, Mt. Usu, Myojin-sho, and Satsuma-Iwo-jima) over the past 306 years (from AD 1700 to AD 2005). Nine of the 11 events occurred during inactive phases of solar magnetic activity (solar minimum), which is well indexed by the group sunspot number. This strong association between eruption timing and the solar minimum is statistically significant to a confidence level of 96.7%. This relationship is not observed for eruptions from volcanoes with relatively silica-poor magma, such as Izu-Ohshima. It is well known that the cosmic-ray flux is negatively correlated with solar magnetic activity, as the strong magnetic field in the solar wind repels charged particles such as galactic cosmic rays that originate from outside of the solar system. The strong negative correlation observed between the timing of silica-rich eruptions and solar activity can be explained by variations in cosmic-ray flux arising from solar modulation. Because silica-rich magma has relatively high surface tension (~ 0.1 Nm^?1), the homogeneous nucleation rate is so low that such magma exists in a highly supersaturated state without considerable exsolution, even when located relatively close to the surface, within the penetration range of cosmic-ray muons (1–10 GeV). These muons can contribute to nucleation in supersaturated magma, as documented by many authors studying a bubble chamber, via ionization loss. This radiation-induced nucleation can lead to the pre-eruptive exsolution of H₂O in the silica-rich magma. We note the possibility that the 1991 Mt. Pinatubo eruption was triggered by the same mechanism: an increase in cosmic-ray flux triggered by Typhoon Yunya, as a decrease in atmospheric pressure results in an increase in cosmic-ray flux. We also speculate that the snowball Earth event was triggered by successive large-scale volcanic eruptions triggered by increased cosmic-ray flux due to nearby supernova explosions.  相似文献