Development of a Neolithic pine tree‐ring chronology for northern Scotland

The peatlands of northern Scotland (one of the largest and most intact areas of blanket bog in the world) contain a rare widespread horizon of subfossil pine in stratigraphic context. Eighteen bog pine from three new sites are incorporated into a mean Neolithic pine chronology now composed of subfossil pine from 12 sites, which is tree‐ring‐dated against Irish bog pine chronologies to span 3198–2757 BC. Germination and peaks of radial growth infer drier conditions between 3199 and 3130 BC. Dying‐off phases and depression of growth reflect a change to wetter conditions between 3023 and 3002 BC and a terminal decline of pine between 2809 and 2782 BC. The close synchronization of germination/die‐off phases and major ring‐width variations between sites across this region indicates that the environmental changes are probably triggered by climate change. Twenty‐four bog pine samples remain unmatched. Future multi‐discipline research into this important example of climatic change at the Neolithic/Bronze Age transition is recommended. Copyright © 2012 John Wiley & Sons, Ltd.     

Centennial-to-millennial fluctuations in July temperatures in North Finland as recorded by timberline tree rings of Scots pine

A tree-ring proxy of summer temperature anomalies for northern Finland for the past 7500 yr was analyzed using Fourier spectrum and wavelet approaches. Multicentennial (250-450 yr) variability is present in the proxy record during most of the time range. This variability is suggested to reflect low-frequency variability in the North Atlantic Oscillation. Century-scale (90-130 yr) variation is another important feature of the tree-ring proxy data during the Holocene and may be attributed to Glessberg solar activity variations. In addition, an approximately 2000-yr quasi-period is found in this temperature proxy data, similar to the millennial-scale variability, present in many climate records from the North Atlantic region. The results point to the importance of multiple forcings underlying significant Holocene climatic fluctuations.     

Mid‐ and late Holocene tree population density changes in northern Fennoscandia derived by a new method using megafossil pines and their tree‐ring series

Changes in tree density are estimated for the northern forest‐limit region of Finnish Lapland over the past seven and a half millennia. This is done using dendrochronologically dated Scots pine megafossils and their tree‐ring series. Direct and indirect estimates of past tree density are derived from chronology sample size (CSS) and growth trend modelling (GTM) respectively. The latter is a new method, where the past levels of growth competition (the influence of nearby trees) are extracted from the behaviour of growth trends in cross‐dated tree‐ring series, trends that are expected to be driven by tree‐density control. Two records constructed from the same original data set but by different means (independently) correlate significantly. Both records show a tree‐density maximum around 3000–1750 BC , indicating relative warmth during that time. Another positive tree‐density anomaly occurred in accordance with the ‘Medieval Warm Period’, preceding the thinning at the forest‐limit due to the ‘Little Ice Age’. Copyright © 2005 John Wiley & Sons, Ltd.     

Diffusion of Sm-Nd in Scheelite and its Significance to Isotopic Dating and Tracing

As the principal ore mineral in various tungsten (-gold) deposits, scheelite (CaWO4) plays an important role in directly dating the timing of ore formation, and in tracing associated material sources through the study of its Sm-Nd geochronology and Nd isotopic characteristics. Since the retention of Sm-Nd systematics within scheelite is presently unconstrained, equivocal interpretations for isotopic data resulting from this method have occurred quite often in previous studies that apply these isotopic data. In order to better elucidate the closure of Sm-Nd in scheelite, the kinetics of Sm and Nd within this mineral lattice were investigated through calculation of diffusion constants presented herein. The following Arrhenius relations were obtained:DNd = 4.00exp(?438 kJ·mol–1/RT) cm2/sDSm = 1.85exp(?427 kJ·mol–1/RT) cm2/sshowing diffusion rate of Nd is near identical to Sm in scheelite when at the same temperature. However, compared to other rare earth elements (REEs), which have markedly different atomic radii to either Nd or Sm, these are shown to exhibit a great variation in diffusivities. The observed trends in our data are in excellent agreement with the diffusion characteristics of REEs in other tetragonal ABO4 minerals, indicating that ionic radius is a key constraint to the diffusivity of REEs in the various crystal lattices. With this in mind, the same substitution mechanism and a very slight discrepancy in radii will allow us to infer that significant Sm/Nd diffusional fractionation in scheelite is unlikely to occur during most geological processes.Based upon the diffusion data determined herein, Sm and Nd closure temperatures and retention times in scheelite are discussed in terms of diffusion dynamics. Those results suggest that closure temperatures for Sm-Nd within this mineral are relatively high in contrast to the temperature ranges of ore-formation responsible for scheelite-related deposits, and any later thermal environments. It is likely, therefore, that relevant isotopic information could be easily retained under most geological conditions, since initial crystallization of the scheelite. In addition, comparison of this mineral-element pair over a range of temperatures with some other common minerals used as geochronometers (e.g., zircon and apatite) indicates that Sm-Nd system has a slower diffusive rate in scheelite than for Sr in apatite or Ar in quartz, and only a little faster than for Pb in zircon. It should be noted, within most hydrothermal deposits where zircon has crystallized, its size is typically no more than 100 μm, whereas scheelite commonly occurs as macroscopic grains. For this reason, the larger dimensions of scheelite would provide a robust Sm-Nd system more able to resist perturbations, relating to any later thermal process. As such Sm-Nd investigations of scheelite are akin to U-Pb within zircon samples used in isotopic dating. These observations indicate that Sm-Nd age and isotopic information can provide reliable data in all but the most extreme case, especially when data are extracted from macroscopic grains of scheelite that are chosen to be “pristine” (i.e., free of surface alteration and/or fractures).     

大兴安岭北段漠河前陆盆地早侏罗世火山岩时代的厘定

黑龙江省大兴安岭地区大面积分布的中基性火山岩的时代厘定对研究大兴安岭中生代火山岩带的构造演化及地层划分具有重要意义.本次基于开展的黑龙江省盘古林场幅、布鲁克里河幅1:5万区域地质矿产调查项目,对该区原划为中—晚侏罗世塔木兰沟组的中基性火山岩进行了系统的LA-ICP-MS锆石U-Pb年代学、岩石学、岩石地球化学等方面研究...     

电子探针化学测年在攀枝花大田晶质铀矿中的应用及其意义

晶质铀矿和沥青铀矿是热液铀矿床的主要工业铀矿物,在研究热液铀矿床成因及成矿规律方面具有重要的意义。攀枝花大田地区是我国混合岩型热液铀矿分布区,已发现粗粒特富铀矿滚石(铀含量10%)及较富基岩矿石(铀含量为0.1%~2%),主要铀矿物为晶质铀矿,对两种晶质铀矿成分及形成时代的研究对该区混合岩型热液铀矿成矿规律研究具有重要的价值。本文通过对大田地区滚石中的晶质铀矿和基岩矿石中的晶质铀矿进行矿物学及电子探针分析,研究了晶质铀矿的成分及形成时代。结果表明:(1)大田地区滚石和基岩矿石中的晶质铀矿除铅之外化学成分较为相似,两类矿石晶质铀矿中UO_2含量为77.36%~84.04%,ThO_2含量为0.98%~5.59%,PbO含量为1.79%~8.8%,其中滚石晶质铀矿中的铅含量低于基岩晶质铀矿,钍含量高于基岩晶质铀矿;(2)电子探针化学定年结果表明,基岩矿石晶质铀矿的形成时代为774.9~785.5 Ma,滚石晶质铀矿的形成时代为783.7 Ma,与传统同位素测年结果(775~777.6 Ma)非常一致,一方面说明滚石晶质铀矿和基岩晶质铀矿为同一时代的产物,另一方面说明电子探针原位测年方法是可靠的;(3)在后期的热液蚀变中,晶质铀矿先后发生了硅化、碳酸盐化及赤铁矿化,蚀变发生的时间分别为730.6Ma、699.8 Ma和664.0 Ma。此结论对研究攀枝花大田地区热液铀矿成矿时代及成矿作用过程提供了依据。     

独居石电子探针定年及其在新疆东天山变质作用研究中的应用

以化学法独居石电子探针定年的原理以及前人改良过的年龄计算公式为基础,利用全微分和最大误差原理,确定了年龄误差计算新方法。并用Visual C语言在Windows平台下编制出了计算年龄和年龄误差的计算机程序。运用此程序对前人公开发表的分析资料和计算的年龄以及年龄误差数据进行了重新计算,验证了给出的误差公式的可靠性。同时,利用JXA—8100电子探针仪对新疆东天山变质沉积岩的两个样品(KM2127—5,DK2107—2)中的独居石进行了电子探针微区U—Th—Pb成分分析。结果表明,样品DK2107—2记录了两期变质作用,峰期年龄分别是341．0±3．9Ma和255．2±3．3Ma,其中最主要的变质峰期年龄为341．0±3．9Ma,该期的矿物组合为Ky+St+Bt+Pl+Q+／-Or;而255．2±3．3Ma和样品KM2127-5记录的变质峰期年龄262．3±4．4Ma为次要变质峰期年龄,该期矿物组合是Cord+Bt+Pl+Or+Q。分析结果与前人用^40Ar—^39Ar法得到的结果相吻合,表明独居石电子探针定年技术是一种可靠有效的测年方法。     

小兴安岭东北部金林岩体全岩-角闪石Rb-Sr年龄

中国东北地区小兴安岭北段分布的兴东群与佳木斯地区的麻山群一直被认为是早元古代形成的变质岩系。近年来麻山群500 Ma左右变质年龄的确定为兴东群的变质时代提出了疑问。研究表明,分布于小兴安岭北部金林林场的兴东群四子山组“混合岩”为一套片麻状石英二长岩-花岗岩侵入体,岩石全岩-矿物（角闪石）Rb-Sr等时线年龄为(482±19) Ma,这表明小兴安岭巨型花岗岩带中存在早古生代岩浆事件。兴东群变质作用可能也与早古生代构造-热事件有关。早古生代花岗岩的确认对该区地质构造演化研究具有重要意义。     

锶同位素地层学在奥陶系海相地层定年中的应用--以塔里木盆地塔中12井为例

根据锶同位素地层学的基本原理,从国际上已有的锶同位素演化曲线建立了奥陶系87Sr/ 86Sr比值 年龄数据库。利用塔里木盆地塔中 12井海相碳酸盐的锶同位素分析结果,确定了该井中、上奥陶统和中、下奥陶统的界线,两个界线分别位于井深 5 12 0m( 87Sr/ 86Sr≈ 0.70 88,年龄为 4 6 5Ma)和 4 880m处 ( 87Sr/ 86Sr≈ 0.70 82,年龄为 4 5 5Ma),中、上奥陶统的界线为本文首次确定,中、下奥陶统的界线与前人利用牙形石资料确定的界线一致。塔中 12井的锶同位素演化曲线说明,尽管构造运动造成的盆地抬升和近地表的大气水作用影响了上奥陶统顶部碳酸盐的锶同位素组成,但塔中 12井奥陶系与上覆地层的关系基本上是连续的,奥陶系顶界的井深在 4 6 5 0m附近 ( 87Sr/ 86Sr≈ 0.70 79,年龄为4 35Ma)。     

Comparison of soil organic carbon content,hydraulic conductivity,and particle size fractions between a grassland and a nearby black pine plantation of 40 years in two surface depths

In highlands of semiarid Turkey, ecosystems have been significantly transformed through human actions, and today changes are taking place very rapidly, causing harmful consequences such as soil degradation. This paper examines two neighboring land use types in Indagi Mountain Pass, Cankiri, Turkey, to determine effects of the conversion of Blackpine (Pinus nigra Arn. subsp. pallasiana) plantation from grassland 40 years ago on soil organic carbon (SOC) and soil erodibility (USLE-K). For this purpose, a total of 302 disturbed and undisturbed soil samples were taken at irregular intervals from two sites and from two soil depths of 0–10 cm (D₁) and 10–20 cm (D₂). In terms of SOC, conversion did not make any statistical difference between grassland and plantation; however, there were statistically significant differences with soil depth within each land use, and SOC contents significantly decreased with the soil depth (P < 0.05) and mostly accumulated in D₁. SOC values were 2.4 and 1.8% for grassland and 2.8 and 1.6% for plantation, respectively, at D₁ and D₂. USLE-K values also statistically differed significantly with the land use, and in contrast to the statistics of SOC, there was no change in USLE-K with the soil depth. Since USLE-K was estimated using SOC, hydraulic conductivity (HC) and soil textural composition––sand (S), silt (Si), and clay (C) contents of soils––as well as SOC did not change with the land use, we ascribed the changes of USLE-K with the land uses to the differences in the HC as strongly affected by the interactions between SOC and contents of S, Si, and C. On an average, the soil of the grassland (USLE-K = 0.161 t ha h ha⁻¹ MJ⁻¹ mm⁻¹) was more erodible than those of the plantation (USLE-K = 0.126 t ha h ha⁻¹ MJ⁻¹ mm⁻¹). Additionally, topographic factors, such as aspect and slope, were statistically effective on spatial distribution of the USLE-K and SOC.     

鄂尔多斯盆地南缘赵老峪剖面奥陶系凝灰岩 锆石SHRIMP U-Pb定年及其地质意义

鄂尔多斯盆地南缘奥陶系赵老峪组的时代一直是依据古生物化石组合确定的,但基于笔石带其时代为晚奥陶世,而依据牙形石组合则为中奥陶世或者中奥陶世晚期,存在明显的差异,缺少高质量同位素年龄的约束。本文选择富平赵老峪剖面赵老峪组凝灰岩夹层进行精确的SHRIMP锆石U-Pb同位素测年,获得了453.2±6.9 Ma年龄结果,将此前认为的中、晚奥陶世沉积严格地确定为晚奥陶世。结合区域地质资料讨论,认为鄂尔多斯南缘上奥陶统凝灰岩层的形成与古秦岭洋壳向北的俯冲有关,可能记录了与这个过程伴生的火山喷发事件。该同位素年龄表明这里的奥陶纪地层在华北克拉通是最年轻的,故它不仅准确地确定了地层的形成时代,而且对华北克拉通早古生代地质演化史的认识有着重要的意义。     

赣南矽卡岩型钨矿成岩成矿年代学及地质意义——以焦里和宝山矿床为例

矽卡岩型钨矿是赣南地区的一种重要钨矿床类型。本文以焦里和宝山两个典型的矽卡岩型钨多金属矿床为例,开展了系统的成岩成矿年代学和岩石地球化学研究,结合区域钨锡矿床最新年代学研究成果,探讨了赣南地区钨矿的成岩成矿时代及形成构造环境。结果表明,焦里矽卡岩型钨多金属矿区斑状花岗闪长岩SHRIMP锆石U-Pb年龄为164.4±1.1Ma,辉钼矿Re-Os等时线年龄为170.6±4.6Ma;宝山矽卡岩型钨矿区花岗岩SHRIMP锆石U-Pb年龄为156.6±3.9Ma,辉钼矿Re-Os模式年龄加权平均值为161.0±1.9Ma,厘定了它们的成岩成矿年龄为中-晚侏罗世,同一矿区的成岩和成矿年龄在误差范围内基本一致。结合赣南崇(义)-(大)余-(上)犹钨锡矿集区已有的年代学资料,指出本区的成岩成矿年龄介于170～150Ma,集中在160～150Ma,认为赣南钨矿形成于华南中生代岩石圈伸展-减薄时期的侏罗纪板内拉张的地球动力学背景,系同一成岩成矿系统的产物。     

南岭东段淋洋岩体的锆石铀-铅定年及其构造和成矿意义

南岭东段淋洋岩体研究程度低,成岩时代众说纷纭,其主要由中细-中粗粒斑状黑云(二云)花岗岩组成。本研究运用激光剥蚀-多接收器电感耦合等离子体质谱(LA-MC-ICPMS)对岩体进行锆石U-Pb精确测年。定年结果表明,淋洋岩体某一断层附近花岗岩的成岩年龄为(233.1±1.3)Ma(MSWD=1.11),下村矿点附近岩体的成岩年龄为(243.3±2.1)Ma(MSWD=2.3),二者均属于印支期,说明淋洋岩体形成于印支期陆陆碰撞和地壳抬升和增厚的构造环境,暗示淋洋岩体可能存在印支期或燕山期的成矿作用,具有进一步研究的价值。     

北大巴山凤凰山岩体锆石U Pb LA ICP MS年龄及其构造意义

北大巴山凤凰山岩体是扬子陆块北缘典型的新元古代侵入岩群,对采自岩体的6个花岗岩(闪长岩)样品进行了LA-ICP-MS锆石U-Pb同位素定年分析。定年数据显示,岩浆活动可分为早期(797±6Ma)、中期(770±6Ma、774±5Ma)、晚期(755±6Ma、750±13Ma和743±6Ma)三个阶段,证实凤凰山岩体为多期岩浆侵入形成。这几期岩浆活动在扬子陆块具同步性和普遍性,广泛被记录在黄陵、汉南等其它新元古代杂岩中。凤凰山花岗岩完整记录了扬子陆块北缘南华纪初期的区域拉张—裂陷事件,其形成可能与导致Rodinia超大陆裂解作用的幕式地幔柱活动有关。本次研究对认识扬子陆块新元古代地壳生长与再造过程及Rodinia超大陆裂解机制具有重要意义。     

太原西山上二叠统—下三叠统地层最大沉积年龄的碎屑锆石U Pb定年约束

二叠纪—三叠纪之交是古生界向中生界过渡的重要地质历史转折时期,发生了地史时期规模最大的生物灭绝事件。石千峰组作为华北地台二叠系—三叠系过渡阶段沉积,其时代归属对二叠系—三叠系界线的准确划分至关重要。本文应用LA-MC-ICPMS对华北中部太原西山晚二叠世—早三叠世上石盒子组、石千峰组、刘家沟组中4件砂岩样品进行碎屑锆石U-Pb定年,4件砂岩样品(SNF、XM、K8、LJG)分别给出了最年轻锆石峰值年龄270Ma、296Ma、250Ma、262Ma,表明太原西山上石盒子组师脑峰砂岩(SNF)的沉积时间不早于270Ma,石千峰组底部K8砂岩(K8)沉积时间不早于250Ma。因此,太原西山地区石千峰组应归属于早三叠世,二叠系—三叠系的界线应位于石千峰组K8砂岩之下。     

锶、碳同位素演化在新元古代地层定年中的应用——以胶辽徐淮地层分区为例

根据Sr、C同位素地层学原理，利用胶辽徐淮地区晚前寒武纪地层Sr、C同位素数据，与国际上已有的Sr、C同位素演化曲线对比，结果表明，胶辽徐淮地区晚前寒武纪地层是同一时期的沉积物，沉积主体之间Sr、C同位素比值的对比性很好，沉积时限约在750-860Ma之间，并延续到震旦纪，为北方青白口纪及其后的沉积。同时也表明，Sr、C同位素演化相结合是解决缺乏大化石的晚前寒武纪地层对比的有效方法。     

柴达木盆地一里坪石膏~(230)Th定年及成盐期与第四纪冰期和构造运动的关系

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