浙江中生代陆缘火山岩金矿成矿系统

浙江地处中国东南沿海大陆边缘火山岩成矿带，已发现众多金（银）矿床（点），它们在空间上往往不是孤立地出现，而是在数十至数百平方公里内围绕岩浆热中心相对集中，并与有色金属在矿田范围内伴生。研究证明，金（银）及有色金属矿床是同一火山—侵入旋回过程中形成的有成因联系的矿床。笔者将这种在同一火山—侵入旋回间，围绕同一个岩浆热中心，在不同深度和水平距离内形成的一系列具有成因联系的金（银）和有色金属矿床的总和称为火山岩金矿成矿系统。本文在此概念基础上，详细论述了浙江中生代陆线火山岩金矿成矿系统的类型。时空结构和物质来源。     

ENVIRONMENTAL CHANGE AND ITS IMPACTS ON HUMAN SETTLF, MENT IN THE CHANGJIANG RIVER DELTA IN NEOLITHIC AGE

Dating data, altitude of Neolithic sites, climatic changes from sedimentary records and previous research results were collected and analyzed to detect possible connections between climatic changes and human activities in the Changjiang River Delta in the Neolithic Age. The results indicated that hydrological changes greatly impacted the human activities in the study region. Low-lying geomorphology made the floods and sea level changes become the important factors affecting human activities, especially the altitude change of human settlements. People usually moved to higher places during the periods characterized by high sea level and frequent floods to escape the negative influences from water body expansion, which resulted in cultural hiatus in certain profiles. However, some higher-altitude settlements were not the results of climatic changes but the results of social factors, such as religious ceremony and social status. Therefore, further research will be necessary for the degree and types of impacts of climatic changes on human activities in the study area at that time.     

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Quantifying the effects of climate variability and human activities on runoff from the Laohahe basin in northern China using three different methods

Much attention has recently been focused on the effects that climate variability and human activities have had on runoff. In this study, these effects are quantified using three methods, namely, multi‐regression, hydrologic sensitivity analysis, and hydrologic model simulation. A conceptual framework is defined to separate the effects. As an example, the change in annual runoff from the semiarid Laohahe basin (18 112 km²) in northern China was investigated. Non‐parametric Mann‐Kendall test, Pettitt test, and precipitation‐runoff double cumulative curve method were adopted to identify the trends and change‐points in the annual runoff from 1964 to 2008 by first dividing the long‐term runoff series into a natural period (1964–1979) and a human‐induced period (1980–2008). Then the three quantifying methods were calibrated and calculated, and they provided consistent estimates of the percentage change in mean annual runoff for the human‐induced period. In 1980–2008, human activities were the main factors that reduced runoff with contributions of 89–93%, while the reduction percentages due to changes in precipitation and potential evapotranspiration only ranged from 7 to 11%. For the various effects at different durations, human activities were the main reasons runoff decreased during the two drier periods of 1980–1989 and 2000–2008. Increased runoff during the wetter period of 1990–1999 is mainly attributed to climate variability. This study quantitatively separates the effects of climate variability and human activities on runoff, which can serve as a reference for regional water resources assessment and management. Copyright © 2011 John Wiley & Sons, Ltd.     

小秦岭金矿田507脉成矿期内构造活动及矿体定位关系

根据构造控矿的观点，通过对成矿期内容矿断裂活动分析，阐述了构造活动与矿体定位的关系。     

Liquidus Equilibria in the System K2O-Na2O-Al2O3-SiO2-F2O-1-H2O to 100 MPa: II. Differentiation Paths of Fluorosilicic Magmas in Hydrous Systems

We investigated phase equilibria in the six-component systemNa₂O–K₂O–Al₂O₃–SiO₂–F₂O_–1–H₂Oat 100 MPa to characterize differentiation paths of naturalfluorine-bearing granitic and rhyolitic magmas. Topaz and cryoliteare stable saturating solid phases in calcium-poor systems.At 100 MPa the maximum solidus depression and fluorine solubilityin evolving silicic melts are controlled by the eutectics haplogranite–cryolite–H₂Oat 640°C and 4 wt % F, and haplogranite–topaz–H₂Oat 640°C and 2 wt % F. Topaz and cryolite form a binaryperalkaline eutectic at 660°C, 100 MPa and fluid saturation.The low-temperature nature of this invariant point causes displacementof multiphase eutectics with quartz and alkali feldspar towardsthe topaz–cryolite join and enables the silicate liquidusand cotectic surfaces to extend to very high fluorine concentrations(more than 30 wt % F) for weakly peraluminous and subaluminouscompositions. The differentiation of fluorine-bearing magmasfollows two distinct paths of fluorine behavior, depending onwhether additional minerals buffer the alkali/alumina ratioin the melt. In systems with micas or aluminosilicates thatbuffer the activity of alumina, magmatic crystallization willreach either topaz or cryolite saturation and the system solidifiesat low fluorine concentration. In leucogranitic suites precipitatingquartz and feldspar only, the liquid line of descent will reachtopaz or cryolite but fluorine will continue to increase untilthe quaternary eutectic with two fluorine-bearing solid phasesis reached at 540°C, 100 MPa and aqueous-fluid saturation.The maximum water solubility in the haplogranitic melts increaseswith the fluorine content and reaches 12· 5 ±0· 5 wt % H₂O at the quartz–cryolite–topazeutectic composition. A continuous transition between hydrousfluorosilicate melts and solute-rich aqueous fluids is not documentedby this study. Our experimental results are applicable to leucocraticfluorosilicic magmas. In multicomponent systems, however, thepresence of calcium may severely limit enrichment of fluorineby crystallization of fluorite. KEY WORDS: granite; rhyolite; topaz; cryolite; magmatic differentiation     

The Upper Crustal Evolution of a Large Silicic Magma Body: Evidence from Crystal-scale Rb Sr Isotopic Heterogeneities in the Fish Canyon Magmatic System, Colorado

Batholith-sized bodies of crystal-rich magmatic ‘mush’are widely inferred to represent the hidden sources of manylarge-volume high-silica rhyolite eruptive units. Occasionallythese mush bodies are ejected along with their trapped interstitialliquid, forming the distinctive crystal-rich ignimbrites knownas ‘monotonous intermediates’. These ignimbritesare notable for their combination of high crystal contents (35–55%),dacitic bulk compositions with interstitial high-silica rhyoliticglass, and general lack of compositional zonation. The 5000km³ Fish Canyon Tuff is an archetypal eruption deposit of thistype, and is the largest known silicic eruption on Earth. Ejectafrom the Fish Canyon magmatic system are notable for the limitedcompositional variation that they define on the basis of whole-rockchemistry, whereas 45 vol. % crystals in a matrix of high-silicarhyolite glass together span a large range of mineral-scaleisotopic variability (microns to millimetres). Rb/Sr isotopicanalyses of single crystals (sanidine, plagioclase, biotite,hornblende, apatite, titanite) and sampling by micromillingof selected zones within glass plus sanidine and plagioclasecrystals document widespread isotopic disequilibrium at manyscales. High and variable ⁸⁷Sr/⁸⁶Sr_i values for euhedral biotitegrains cannot be explained by any model involving closed-systemradiogenic ingrowth, and they are difficult to rationalize unlessmuch of this radiogenic Sr has been introduced at a late stagevia assimilation of local Proterozoic crust. Hornblende is theonly phase that approaches isotopic equilibrium with the surroundingmelt, but the melt (glass) was isotopically heterogeneous atthe millimetre scale, and was therefore apparently contaminatedwith radiogenic Sr shortly prior to eruption. The other mineralphases (plagioclase, sanidine, titanite, and apatite) have significantlylower ⁸⁷Sr/⁸⁶Sr_i values than whole-rock values (as much as –0·0005).Such isotopic disequilibrium implies that feldspars, titaniteand apatite are antecrysts that crystallized from less radiogenicmelt compositions at earlier stages of magma evolution, whereashighly radiogenic biotite xenocrysts and the development ofisotopic heterogeneity in matrix melt glass appear to coincidewith the final stage of the evolution of the Fish Canyon magmabody in the upper crust. Integrated petrographic and geochemicalevidence is consistent with pre-eruptive thermal rejuvenationof a near-solidus mineral assemblage from 720 to 760°C (i.e.partial dissolution of feldspars + quartz while hornblende +titanite + biotite were crystallizing). Assimilation and blendingof phenocrysts, antecrysts and xenocrysts reflects chamber-wide,low Reynolds number convection that occurred within the last10 000 years before eruption. KEY WORDS: Fish Canyon Tuff; Rb–Sr isotopes; microsampling; magmatic processes; crystal mush     

阵发性洪水条件下辫状河型冲积扇构型研究:以准噶尔盆地西北缘现代白杨河冲积扇为例*

白杨河冲积扇是由阵发性洪水期的碎屑流沉积物与间洪期辫状河沉积物组成的复合型冲积扇,其构型与碎屑流扇的构型和河流型扇的构型有很大的不同。本研究选取准噶尔盆地西北缘干旱气候下发育的现代白杨河冲积扇作为解剖实例,对103个天然剖面和9个人工大型探槽进行了详细测量,在沉积微相及不同级别的沉积构型的观测和分析的基础上,分析了阵发性洪水条件下间歇性辫状河型冲积扇体的地貌单元的演化过程和沉积构型特征,研究不同流态的阵发性洪水条件下各种建造和改造机制,明确受阵发性洪水控制的间歇性辫状河型冲积扇的沉积特征,建立了其沉积构型模式。认为: 在洪水期,阵发性洪流(碎屑流)形成席状化的片流(或片洪)沉积,在洪退期,随着洪水强度的减弱,又转变为辫流沉积,而在间洪期,仍有持续的辫状流体(牵引流)在限制性的水道中流动,并对洪水期的碎屑流沉积物进行改造,形成了限制性的(条带状的)辫状河道沉积,2个时期的沉积物在时空上频繁叠置,形成了一种更加复杂的沉积构型。该模式对油田地下冲积扇砂砾储集层的成因识别、预测及对比具有一定的参考价值。     

Holocene initiation and expansion of the southern margins of northern peatlands triggered by the East Asian summer monsoon recession

Northern peatlands represent one of the largest biospheric carbon reservoirs in the world. Their southern margins act as new carbon reservoirs, which can greatly influence the global carbon dynamics. However, the Holocene initiation, expansion and climate sensitivity of these peatlands remain intensely debated. Here we used a compilation of basal peat ages across six isolated peatlands at the southern margins of northern peatlands to address these issues. We found that the earliest initiation event of these peatlands occurred after the Younger Dryas (YD, 12,800–11,700 years ago) period. The second initiation event and rapid expansion occurred since 5 ka cal. BP. The recession of East Asian summer monsoon (EASM) during the YD period and at around 5 ka cal. BP likely played a major role in controlling the initiation and expansion of these peatlands. The rapid expansion of these peatlands possibly contributed to the significant increases in atmospheric methane concentrations during the late Holocene because of the minerotrophic fens status and rapid expansion of them. These ecological processes are different from northern peatlands, indicating the special carbon sink and source implications of these peatlands in the global carbon cycle.     

江西德兴斑岩铜矿石英闪长玢岩成因及成矿学意义

为探究石英闪长玢岩成因及幔源基性岩浆对斑岩铜矿的贡献,本文选取德兴矿床石英闪长玢岩开展了锆石U-Pb定年、Hf同位素和全岩地球化学研究。获得石英闪长玢岩LA-ICP-MS锆石U-Pb年龄为169 Ma,与成矿花岗闪长斑岩侵位时间一致,岩体为中侏罗世岩浆活动的产物。石英闪长玢岩具有低的SiO₂(58.41%~63.12%)和K₂O(1.68%~2.94%)含量及A/CNK值(0.85~1.04),富集大离子亲石元素和轻稀土元素,亏损高场强元素Nb、Ta、Ti和重稀土元素,属于钙碱性到高钾钙碱性系列岩石。具有相对亏损的锆石Hf同位素组成,εHf(t)=2.20~7.93(最大值7.93),指示其源区为岩石圈地幔。锆石稀土元素配分模式图显示出明显的正Ce异常,岩浆氧逸度(lg f_O2)为-20.05~-6.66,达到磁铁矿-赤铁矿氧逸度等级,指示石英闪长玢岩结晶自高氧逸度岩浆。全岩地球化学特征显示,德兴石英闪长玢岩与成矿花岗闪长斑岩及其暗色包体符合岩浆混合的演化趋势,说明成矿花岗闪长斑岩可能是中侏罗世幔源基性岩浆和地壳酸性岩浆大规模混合作用的产物,并且石英闪长玢岩代表了岩浆混合过程中的幔源基性端员。结合前人研究成果,认为在中侏罗世伸展构造背景下,软流圈物质上涌导致新元古代受交代的岩石圈地幔部分熔融形成幔源基性岩浆,基性岩浆的底侵作用诱发下地壳物质熔融并与之发生一定程度的岩浆混合作用,形成了花岗闪长斑岩的母岩浆。高氧逸度幔源岩浆的加入可抑制斑岩体系硫化物的过早饱和,同时为德兴矿床注入了成矿所需的部分挥发分和金属元素。