不同降温速率约束下橄榄石晶体形态演变及其地质意义——五大连池老黑山钾质玄武质熔岩的动力结晶实验

基于控制降温速率的动力结晶实验,对五大连池老黑山钾质玄武质熔岩的冷却结晶过程中橄榄石晶体形态随降温速率变化动力学演变进行了研究。实验研究表明,老黑山钾质玄武岩的熔融温度发生在1 022℃～1 260℃之间,峰值为1 166.3℃～1 186.5℃;实验产物主要由橄榄石和玻璃质组成,新生的橄榄石晶体形态差异较大,有针状骸晶、铁轨状骸晶、羽毛状雏晶、细长条状和粒状微晶。橄榄石晶体的生长、尺寸和形态、分布和实验产物的结晶程度与降温速率之间存在着密切关联。随着降温速率的变慢,橄榄石从针状(0.075℃/min～0.5℃/min)、铁轨状(0.075℃/min～0.5℃/min)、放射状与羽毛状(0.046 8℃/min～0.075℃/min)、细长条状(0.062 5℃/min)等晶体演变为粒状微晶(0.03℃/min);同时,岩石的结晶程度逐渐增强,橄榄石晶体尺寸逐渐变大、自形程度逐渐变高,玻璃相和气孔逐渐减少。这种新生橄榄石形态的变化与降温速率的内在关联性,对认识老黑山熔岩流固结的动力结晶机制、熔岩流的运动机制有一定科学意义。     

马兰黄土沉积速率及其地质意义

马兰黄土平均沉积速率为0.078毫米/年.但又可分为三个沉积速率层段,即上部中等,中部最大,下部最小.沉积速率的变化与黄土颗粒粒径有关.粒度粗,分选好.沉积速率最小.反之.沉积速率则大.更重要的是,沉积速率受控于古气候的演化.气候愈旱干、寒冷.沉降黄土的次数增多.沉积速率就愈大.相反.暖湿气候则不利于黄土沉积.黄土-古土壤系列反映了这期间气候韵律和黄土沉积速率的关系.     

金川Ⅰ号岩体橄榄石Ni-MgO相互关系及其地质意义

金川超镁铁质岩体赋存着仅次于加拿大Sudbury和俄罗斯Noril'sk-Talnakh的世界第三大在采铜镍硫化物矿床,岩体以一系列的NE向断层为界分成四个小岩体,由西至东依次为:Ⅲ、Ⅰ、Ⅱ、Ⅳ岩体.Ⅰ号岩体主要由二辉橄榄岩、含辉橄榄岩和橄榄二辉岩构成,橄榄石在各岩相中均为保存较好的主要造岩矿物.本文研究得到金川Ⅰ号岩体上部二辉橄榄岩和含辉橄榄岩中橄榄石的镁橄榄石F_o值介于83.9～85.7,而其Ni含量为1396×10~(-6)～2043×10~(-6),大多低于从S不饱和玄武岩浆中结晶出来的橄榄石的Ni含量.模拟计算结果表明橄榄石较低的Ni含量是因为橄榄石结晶的同时,发生了强烈的硫化物熔离;橄榄石的Fo-Ni关系还因与晶间硅酸盐熔浆的物质交换而发生改变.模拟计算还证明大约有30%的晶间硅酸盐岩浆与橄榄石发生Fe-Mg物质交换反应,导致早结晶橄榄石的Fo值减少了1～1.5.同时,橄榄石较小的Fo值变化表明,在橄榄石结晶和硫化物熔离过程中,不断有新的岩浆贯入和补充.     

硫酸盐渍土在不同降温速率下的盐胀规律

降温速率对硫酸盐渍土的盐胀率有显著影响。随降温速率的减小，各种含盐量、密实度的硫酸渍土的盐胀率以幂函数增长，其通式为ｙ＝ＡＶＴ＾－Ｂ，但其增长规律彼此又有显著差别，主要表现在Ａ、Ｂ参数的变化上，在试验范围内，Ａ、Ｂ值随含盐量的增加而增加，随密度的增大而减小。     

橄榄石标型特征及其找矿意义

通过国内２０个含铬铁矿、铜镍矿和饥钛磁铁矿的基性、超基性岩体中６８个橄榄石化学成分、产出状态、地球化学特征、有序度和岩浆包裹体橄榄石子矿物、温度、压力等标型特征研究显示，产于不同矿化基性、超基性岩中橄榄石的标型特征明显不同，为找寻铬铁矿、铜镍矿和钒钛磁铁矿矿产提供重要标志。     

降温速率对硫酸钠溶液晶体析出影响的试验研究

为探讨硫酸钠盐渍土盐胀机理,研究了十水硫酸钠晶体在硫酸钠溶液中的析出规律.针对不同浓度的硫酸钠溶液,在1℃·min^-1、0.1℃·min^-1和0.02℃·min^-13种降温速率下,通过降温试验对晶体初始析出温度进行观测.试验表明：十水硫酸钠晶体的析出受降温速率的影响,随着降温速率的减小,晶体初始析出温度升高;降温速率的大小对晶体析出后溶液浓度变化几乎没有影响,但其会影响晶体形态,降温速率越小,晶体形态更为稳定;晶体析出受到相变驱动力作用,相变驱动力与降温速率大小呈正比,降温速率越大,晶体初始析出结晶力越大.     

中国末前寒武纪生物群演变及其地质意义

<正> “末前寒武纪(系)”(Terminal Precambrian)一词是本文作者之一邢裕盛于1980年在巴黎召开的第26届国际地质大会期间,在国际前寒武系—寒武系界线工作组召开的一次学术讨论会上提出的,目的是为了在国际上还没有建立一个前寒武纪最上部的、国际统一的系级年代地层单位之前,暂时用这个名词代表这一段地质历史时期。这个名词最先在国际前寒武系—寒武系界线工作组主席J.W.考依1980年度工作报告中使用,以后又在27届国际地质大会上作为一个分组会议的名称使用,1987年在宜昌召开的国际末前寒武系及     

太行山中段羊角玄武岩形态特征及其地质意义

太行山中段左权羊角镇发育新生代玄武岩,记录了太行山新生代以来的构造隆升事件.在详细的野外调查和研究的基础上,通过与玄武岩发育相关的地貌面及其上的地层特征分析,初步确定该玄武岩是上新世末期到早更新世初期的喷发产物,初步揭示了太行山中段区域上晚上新世以来地貌发育历史,主要存在6次构造隆升与剥蚀期:在唐县期宽谷面形成的基础上,于上新世晚期存在一次隆升和一次稳定侵蚀期,并侵蚀形成U形谷;早更新世初,玄武岩开始间歇性喷发,同时发生以西武家坪为中心的地区上拱,U形谷为玄武岩充填,之后经剥蚀堆积形成第四级阶地面;早更新世末,该区再次发生隆升,并形成第四级阶地:中更新世末,该区发生隆升,形成第三级阶地;晚更新世以来,太行山中段又连续发生两次抬升,从而在玄武岩体上形成了4级阶地,形成太行山现今地貌.研究同时表明,太行山中段上新世晚期以来的隆升主要发生于上新世末到早更新世时期.这一认识为探讨太行山中段晚上新世以来的构造隆升提供了具体证据.     

下侏罗日当组中黄铁矿形态研究学及其地质意义

下侏罗统日当组地层是扎西康Pb-Zn-Ag-Sb多金属矿集区内重要的赋矿层和矿源层之一。为查明日当组中成矿元素的初始富集机理,开展了该地层中草莓状黄铁矿的形态学研究。结果表明日当组沉积时的底层海水是氧化-次氧化的;地层中草莓状黄铁矿在剖面上的粒径分布表明:日当组沉积过程中,其底层海水曾发生过短暂的充氧过程。该结果日当组沉积时的底层海水是含氧的,地层中所赋存的成矿元素,并非是在缺氧硫化的底层水体条件下,由矿物自生富集形成的。     

山东蒙阴金伯利岩中蛇纹石化橄榄石的微组构特征及其地质意义

为探究山东蒙阴金伯利岩中蛇纹石化橄榄石的微组构特征、蚀变环境、元素迁移规律及其对金伯利岩表生演化的指示意义,对该区金伯利岩中部分蛇纹石化的橄榄石和完全蚀变的橄榄石进行了 XRD、EPMA和LA-ICP-MS分析测试.结果表明,蛇纹石中少部分Mg被Fe、Al、Ca、Ni、Mn取代,其中Fe含量仅次于Mg;从蚀变橄榄石的中...     

五大连池老黑山火山钾质玄武岩结晶动力学研究

本文模拟了五大连池地区老黑山火山钾质响质碱玄岩熔岩在不同降温速率下从1150℃冷却到700℃橄榄石的结晶动力学过程,并从晶体粒度、晶体数量和晶体形态三方面研究了晶体结晶特征与降温速率之间的关系。结果表明:(1)晶体粒度分布(CSD)显示七组不同降温速率下的晶体粒度与布居密度均呈现较好的幂率关系,且幂律指数相近,斜率范围在3.69～4.42之间,这说明了晶体粒度分布对降温速率的依赖性并不显著。(2)随着降温速率由快变慢,晶体数量总体增长。当降温速率为0.0468℃/min时,晶体数量达到峰值。随后,结晶进入以退火合并为主的晶体粗化过程,直至结晶动力学达到平衡。(3)各降温速率下晶体形态呈现出分形特征,分形维数界于1.39～1.62之间,反映了新生晶体生长的自组织临界性。不同降温速率下的晶体边界复杂程度出现较大无规波动,显示出晶体形态对降温速率的高度敏感性。当降温速率为0.1℃/min时,晶体边界形态最复杂,当降温速率变慢到0.0468℃/min后,晶体边界形态的复杂程度趋于稳定。本项动力结晶实验对于深入了解五大连池新期火山熔岩流的运动机制以及动力结晶过程有重要的科学意义。     

Dependence of clinopyroxene composition on cooling rate in basaltic magmas: Implications for thermobarometry

The compositional variation of clinopyroxene and the partitioning of major elements between clinopyroxene and melt are estimated as a function of the cooling rate. Clinopyroxenes were crystallized under variable cooling regimes (15, 9.4, 3, 2.1, and 0.5 °C/min from 1250 down to 1000 °C) and at isothermal conditions of 1000 °C from a basaltic composition at a pressure of 500 MPa under anhydrous and hydrous (H₂O = 1.3 wt.%) conditions. The clinopyroxene chemistry shows that, as the cooling rate increases, crystals are progressively depleted in Ca, Mg, Fe²⁺ and Si and enriched in Na, Fe³⁺, Al (mainly Al^IV), and Ti. Di and Hd versus CaTs and CaFeTs form a continuous binary solid solution characterized by higher amounts of tschermakitic components with increasing cooling rate. Two parameters (DH = Di + Hd and TE = CaTs + CaFeTs + En) are calculated to describe the effect of cooling rate on the clinopyroxene composition. The variation of DH/TE with increasing cooling rate evidences the kinetic process induced by rapid cooling in basic rocks under hydrous and anhydrous conditions.Dynamic crystallization conditions affect the partitioning of major elements between clinopyroxene and melt; with increasing cooling rate, the value of crystal–melt partition coefficient departs from that obtained at the isothermal condition. However, in spite of these variations, the values of ^cpx–meltKd_Fe–Mg remain almost constant. Therefore, the Fe²–Mg exchange between clinopyroxene and melt is not suitable to prove the (dis)equilibrium conditions in basaltic cooling magmas, giving rise to possible mismatches in the application of thermobarometers. The results of our study are consistent with that observed at the margin of dikes or in the exterior portions of lavas, where the cooling rate is maximized and disequilibrium compositions of clinopyroxene have been found.     

滇西"三江"地区高镁钾质火山岩地球化学特征及其地质意义

本文报导了位于金沙江-哀牢山断裂带中段6个暗色超基性-基性火山岩的岩石学特征与稀土微量及Sr-Nd-Pb同位素地球化学数据,并对其成因和起源条件等进行了讨论。研究表明这6个暗色超基性-基性火山岩属于钾质碱性-钙碱性系列,依SiO₂含量包括超基性、基性(或中基性)岩类。岩石的Mg^#值较高(54.53~79.81),属于高镁火山岩。所有岩石样品具有富集轻稀土和大离子亲石元素,亏损高场强元素的特征。Sr-Nd-Pb同位素显示,源区具有具有较明显的Dupal异常和EMⅡ型富集地幔端元的特征。火山岩的岩石学与地球化学一致表明,本区多数暗色基性火山岩具有原生岩浆性质,其成因与富集地幔的部分熔融有关。源区显著的EMII富集地幔端元可能是扬子古陆和古特提斯洋的双向俯冲及俯冲的下地壳物质和古特提斯洋壳沉积物的再循环的物质记录。这套岩石形成于印度-欧亚大陆碰撞后的剪切和拉张构造环境,软流层地幔的上涌与俯冲的古特提斯洋壳沉积物和扬子古陆壳物质的混合,是诱发源区发生部分熔融的主要原因。金沙江-哀牢山断裂带强烈的剪切和拉张,使这些岩浆直接快速喷发至地表,因此形成具有原生岩浆性质的火山岩。     

新疆阿舍勒铜锌矿区潜玄武安山岩的岩石地球化学特征及其地质意义

对新疆阿舍勒铜锌矿区潜玄武安山岩进行了岩石学、岩石地球化学和同位素地球化学研究,结果表明:岩石具有中等的SiO_2(51.90%~52.85%)、MgO(4.44%~5.08%)、Al_2O_3(14.94%~16.11%)、TiO_2(0.99%~1.03%)含量,较低的K_2O(0.01%~0.27%)含量,属于低钾拉斑玄武岩系列;岩石具有较低的稀土元素总量,ΣREE=38.07×10~(-6)~41.70×10~(-6),亏损轻稀土元素,LREE/HREE=0.57~0.61,(La/Yb)N=0.84~0.91,具有明显Eu正异常(δEu=1.13~1.23);富集Sr、Ba、Th等大离子亲石元素,亏损Nb、Ta、Zr、Hf等高场强元素,具有洋中脊玄武岩(MORB)和岛弧拉斑玄武岩(IAB)的特征,形成于岛弧(或弧前)环境;具有相对高的εNd(t)值(+6.9~+7.6),表明其原始岩浆来源于俯冲流体交代地幔楔的部分熔融,没有明显深海沉积物加入。结合阿尔泰造山带南缘的区域地质资料及潜玄武安山岩的地球化学特征,认为阿尔泰南缘在晚古生代处于活动大陆边缘,阿舍勒盆地处于岛弧(或弧前)背景。     

The origin and evolution of the parental magmas of frontal volcanoes in Kamchatka: Evidence from magmatic inclusions in olivine from Zhupanovsky volcano

The paper presents data on naturally quenched melt inclusions in olivine (Fo 69–84) from Late Pleistocene pyroclastic rocks of Zhupanovsky volcano in the frontal zone of the Eastern Volcanic Belt of Kamchatka. The composition of the melt inclusions provides insight into the latest crystallization stages (∼70% crystallization) of the parental melt (∼46.4 wt % SiO₂, ∼2.5 wt % H₂O, ∼0.3 wt % S), which proceeded at decompression and started at a depth of approximately 10 km from the surface. The crystallization temperature was estimated at 1100 ± 20°C at an oxygen fugacity of ΔFMQ = 0.9–1.7. The melts evolved due to the simultaneous crystallization of olivine, plagioclase, pyroxene, chromite, and magnetite (Ol: Pl: Cpx: (Crt-Mt) ∼ 13: 54: 24: 4) along the tholeiite evolutionary trend and became progressively enriched in FeO, SiO₂, Na₂O, and K₂O and depleted in MgO, CaO, and Al₂O₃. Melt crystallization was associated with the segregation of fluid rich in S-bearing compounds and, to a lesser extent, in H₂O and Cl. The primary melt of Zhupanovsky volcano (whose composition was estimated from data on the most primitive melt inclusions) had a composition of low-Si (∼45 wt % SiO₂) picrobasalt (∼14 wt % MgO), as is typical of parental melts in Kamchatka and other island arcs, and was different from MORB. This primary melt could be derived by ∼8% melting of mantle peridotite of composition close to the MORB source, under pressures of 1.5 ± 0.2 GPa and temperatures 20–30°C lower than the solidus temperature of “dry” peridotite (1230–1240°C). Melting was induced by the interaction of the hot peridotite with a hydrous component that was brought to the mantle from the subducted slab and was also responsible for the enrichment of the Zhupanovsky magmas in LREE, LILE, B, Cl, Th, U, and Pb. The hydrous component in the magma source of Zhupanovsky volcano was produced by the partial slab melting under water-saturated conditions at temperatures of 760–810°C and pressures of ∼3.5 GPa. As the depth of the subducted slab beneath Kamchatkan volcanoes varies from 100 to 125 km, the composition of the hydrous component drastically changes from relatively low-temperature H₂O-rich fluid to higher temperature H₂O-bearing melt. The geothermal gradient at the surface of the slab within the depth range of 100–125 km beneath Kamchatka was estimated at 4°C/km.     

Group IVA irons: New constraints on the crystallization and cooling history of an asteroidal core with a complex history

We report analyses of 14 group IVA iron meteorites, and the ungrouped but possibly related, Elephant Moraine (EET) 83230, for siderophile elements by laser ablation ICP-MS and isotope dilution. EET was also analyzed for oxygen isotopic composition and metallographic structure, and Fuzzy Creek, currently the IVA with the highest Ni concentration, was analyzed for metallographic structure. Highly siderophile elements (HSE) Re, Os and Ir concentrations vary by nearly three orders of magnitude over the entire range of IVA irons, while Ru, Pt and Pd vary by less than factors of five. Chondrite normalized abundances of HSE form nested patterns consistent with progressive crystal-liquid fractionation. Attempts to collectively model the HSE abundances resulting from fractional crystallization achieved best results for 3 wt.% S, compared to 0.5 or 9 wt.% S. Consistent with prior studies, concentrations of HSE and other refractory siderophile elements estimated for the bulk IVA core and its parent body are in generally chondritic proportions. Projected abundances of Pd and Au, relative to more refractory HSE, are slightly elevated and modestly differ from L/LL chondrites, which some have linked with group IVA, based on oxygen isotope similarities.Abundance trends for the moderately volatile and siderophile element Ga cannot be adequately modeled for any S concentration, the cause of which remains enigmatic. Further, concentrations of some moderately volatile and siderophile elements indicate marked, progressive depletions in the IVA system. However, if the IVA core began crystallization with ∼3 wt.% S, depletions of more volatile elements cannot be explained as a result of prior volatilization/condensation processes. The initial IVA core had an approximately chondritic Ni/Co ratio, but a fractionated Fe/Ni ratio of ∼10, indicates an Fe-depleted core. This composition is most easily accounted for by assuming that the surrounding silicate shell was enriched in iron, consistent with an oxidized parent body. The depletions in Ga may reflect decreased siderophilic behavior in a relatively oxidized body, and more favorable partitioning into the silicate portion of the parent body.Phosphate inclusions in EET show Δ¹⁷O values within the range measured for silicates in IVA iron meteorites. EET has a typical ataxitic microstructure with precipitates of kamacite within a matrix of plessite. Chemical and isotopic evidence for a genetic relation between EET and group IVA is strong, but the high Ni content and the newly determined, rapid cooling rate of this meteorite show that it should continue to be classified as ungrouped. Previously reported metallographic cooling rates for IVA iron meteorites have been interpreted to indicate an inwardly crystallizing, ∼150 km radius metallic body with little or no silicate mantle. Hence, the IVA group was likely formed as a mass of molten metal separated from a much larger parent body that was broken apart by a large impact. Given the apparent genetic relation with IVA, EET was most likely generated via crystal-liquid fractionation in another, smaller body spawned from the same initial liquid during the impact event that generated the IVA body.     

Experimental constraints on the low-pressure evolution of transitional and mildly alkalic basalts: the effect of Fe-Ti oxide minerals and the origin of basaltic andesites

One-atmosphere, melting experiments, controlled at the fayalite-magnetite-quartz oxygen buffer, on mildly alkalic and transitional basalts from Iceland show that these begin to crystallize Fe-Ti oxide minerals (magnetite and/or ilmenite) at 1105±5°C, apparently independently of bulk composition and the order of silicate and oxide mineral crystallization. Most samples crystalline plagioclase and olivine as the first two crystalline phases, augite as the third phase, and an Fe-Ti oxide mineral as the fourth phase. The main effects of Fe-Ti oxide crystallization are a marked decrease in FeO and TiO₂ in the liquid, and a notable increase in SiO₂ and Al₂O₃, and the minor oxides K₂O and P₂O₅, with decreasing temperature. The most silicic glasses are compositionally mugearitic and shoshonitic basaltic andesites. Because the smallest amount of glass that could be analyzed with the microprobe represents 20–55 percent liquid remaining, it can be expected that more silicic liquids will occur at lower temperatures. On normative, pseudoternary projections, the general effect of Fe-Ti oxide crystallization for mildly alkalic and transitional basalts is a marked increase in normative quartz. This is caused by a strong systematic convergence, with the appearance of Fe-Ti oxides, of the bulk solid precipitates toward the liquid compositions, as projected on the triangle plagioclase-diopside-olivine. For alkalic basalts, the bulk solid precipitate shows an increase in normative diopside with falling temperature and Fe-Ti oxide crystallization. This causes the liquids to move toward decreasing normative diopside and relatively little variation in nepheline. The experimental observations imply that mildly alkalic and transitional magmas, without stabilizing a Fe-Ti oxide mineral, will not evolve toward early silica saturation.     

Global significance of the carbon cycle in the karst dynamic system: evidence from geological and ecological processes

On the basis of proposing the existence of a karst carbon cycle and carbon sink at a watershed scale, this paper provides four pieces of evidence for the integration of geology and ecology during the carbon cycle processes in the karst dynamic system, and estimated the karst carbon sink effect using the methods of comparative monitoring of paired watersheds and the carbon stable isotope tracer technique. The results of the soil carbon cycle in Maocun, Guilin, showed that the soil carbon cycle in the karst area, the weathering and dissolution of carbonate rocks under the soil, resulted in a lower soil respiration of 25% in the karst area than in a non-karst area (sandstone and shale), and the carbon isotope results indicated that 13.46% of the heavy carbon of the limestone is involved in the soil carbon cycle. The comparative monitoring results in paired watersheds, suggesting that the HCO₃^- concentration in a karst spring is 10 times that of a rivulet in a non-karst area, while the concentration of inorganic carbon flux is 23.8 times. With both chemical stoichiometry and carbon stable isotopes, the proportion of carbon in karst springs derived from carbonate rocks was found to be 58.52% and 37.65% respectively. The comparison on carbon exchange and isotopes at the water-gas interface between the granite and carbonate rock basins in the Li River showed that the CO₂ emission of the karst water is 10.92 times that of the allogenic water from the non-karst area, while the carbon isotope of HCO₃^- in karst water is lighter by 8.62‰. However, this does not mean that the karst water body has a larger carbon source effect. On the contrary, it means the karst water body has a greater karst carbon sink effect. When the karst subterranean stream in Zhaidi, Guilin, is exposed at the surface, carbon-rich karst water stimulated the growth of aquatic plants. The values of carbon stable isotopes in the same species of submerged plants gradually becomes heavier and heavier, and the 512 m flow process has a maximum range of 15.46‰. The calculation results showed that 12.52% of inorganic carbon is converted into organic carbon. According to the data that has been published, the global karst carbon sink flux was estimated to be 0.53-0.58 PgC/a, equivalent to 31.18%-34.41% of the global forest carbon sink flux. In the meanwhile, the karst carbon sink flux in China was calculated to be 0.051 PgC/a, accounting for 68% of its forest carbon sink flux.