了解全新世的温度变化能为理解目前日益突出的全球变暖、评估未来全球气候变化给出重要的参考。在这项研究中,基于长江下游南漪湖沉积岩芯深度为0~450cm中161个样品的brGDGTs代用指标,对过去12.0ka的大气温度进行重建,以进一步深化对全新世温度变化的理解。发现湖泊周边土壤与湖泊沉积物brGDGTs分子组成存在显著差异:土壤以brGDGTs-Ⅰ系列为主,占到总比重的80%以上,计算得的MBT'5ME平均值为0.81;湖泊表层和柱状沉积物的brGDGTs分子组成更相似,其brGDGT-Ⅰ和brGDGT-Ⅱ分别为43%、48%和62%、35%,对应的MBT'5ME平均值分别为0.44和0.62,因此认为湖泊沉积物brGDGTs主要为自生来源,进而选用基于MBT'5ME的湖泊温度经验计算式进行古温度的重建。重建的南漪湖年均大气温度自12.0 ka B.P.以来变化范围为13.8~22.4℃,根据变化趋势,可以分为4个阶段:①阶段,早全新世(约12.0~8.2 ka B.P.),温度变化范围为15.1~20.6℃,属低温阶段;②阶段,中全新世(约8.2~6.0 ka B.P.),温度为16.8~20.0℃,为稳定高温阶段;③阶段,中晚全新世(约6.0~3.0 ka B.P.),温度为13.8~19.4℃,快速降温阶段;④阶段,晚全新世(约3.0 ka B.P.以来),温度在17.4~22.4℃,快速升温阶段。通过对比其他古气候记录,可以得到以下结论:长江下游地区在约12.0~8.2 ka B.P.时期温度变化主要受高纬度冰川残留的影响,为低温时期;在约8.2~6.0 ka B.P.时期的温度变化主要受到较强的太阳辐射量控制,属稳定高温期,对应全新世大暖期;约6.0 ka B.P.后,温度受到6.0~3.0 ka B.P.中低纬度冷事件以及上升温室气体辐射强迫共同影响,呈现先降后升的"V"型变化趋势。本研究表明长江下游地区自12.0 ka B.P.以来温度变化主要受全球温度变化控制,自晚全新世以来温室气体辐射强迫是影响其温度变化的主要因素。
The basement granite gneisses from the north-central Aravalli Craton in NW India were investigated for geochemistry and geochronology.In a peneplain terrain,the granite gneiss outcrops are scanty and samples were collected mainly from two small hills and several ground-level exposures in the Sakhun–Ladera region.Wellfoliated granite gneiss is the dominant lithology that also hosts dark,lenticular enclaves,and is in turn,intruded by mafic dykes.The granite gneiss has silica content ranging from 61.37 wt.% to 68.27 wt.% that marks a slight overlap with the enclaves(54.32 wt.% to 62.17 wt.%).Both groups have a high K_2O/Na_2O(~2 or higher) ratio.Geochemically,the granite gneiss classify as granite–granodiorite,and enclaves as granodiorite-diorite.The In-situ LA-ICP-MS zircon U–Pb geochronology of granite gneiss has yielded a statistically valid 1721 ± 9 Ma age that we interpret as the emplacement age for the granitic protolith.Geochemical characteristics of granite gneiss underline fractional crystallization of an I-type melt as the main process,and continuity of trends in enclaves underlines their mutual genetic link.The genetic association is further verified by a consistency in the trace element characteristics and REE patterns.The Nd-isotope signatures define a single grouping for both granite gneiss and enclaves,with εNd(t) values ranging from-6.38 to-6.61,further substantiating a common source.The geochemical tectonic discrimination schemes consistently point toward an extensional setting and A-type characteristics for granite gneiss and enclaves.These are analogous to the coeval(1.72–1.75 Ga),A-type granitoids from the Khetri and Alwar basin in the North Delhi Fold Belt,implying a much larger areal extent for the Paleoproterozoic anorogenic magmatism in the northern segment of the Aravalli Craton.The Paleoproterozoic age for the presumed ‘Archean' basement in this region offers tacit evidence that the BGC–II is a stratigraphically younger terrane as compared to the Archean age,BGC–I. 相似文献
As an important geothermal resource, hot dry rock(HDR) reserves have been studied in many countries. HDR resources in China have huge capacity and have become one of the most important resources for the potential replacement of fossil fuels. However, HDR resources are difficult to develop and utilise. Technologies for use with HDR, such as high–temperature drilling, reservoir characterisation, reservoir fracturing, microseismic monitoring and high–temperature power stations, originate from the field of oil and drilling. Addressing how to take advantage of these developed technologies is a key factor in the development of HDR reserves. Based on the thermal crustal structure in China, HDR resources can be divided into four types: high radioactive heat production, sedimentary basin, modern volcano and the inner–plate active tectonic belt. The prospective regions of HDR resources are located in South Tibet, West Yunnan, the southeast coast of China, Bohai Rim, Songliao Basin and Guanzhong Basin. The related essential technologies are relatively mature, and the prospect of HDR power generation is promising. Therefore, analysing the formation mechanisms of HDR resources and promoting the transformation of technological achievements, large–scale development and the utilisation of HDR resources can be achieved in China. 相似文献