Geochronology,Petrogenesis and Tectonic Setting of the Late Jurassic I-type Granites in the North Qinling Orogenic Belt,Central China

The North Qinling Orogenic Belt(NQOB) is a composite orogenic belt in central China. It started evolving during the Meso–Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic. The Meso–Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt, with the tectonic evolution of the middle part of the belt being particularly controversial. The granites...     

Weathering of sulfidic shale and copper mine waste: secondary minerals and metal cycling in Great Smoky Mountains National Park,Tennessee, and North Carolina,USA

Metal cycling via physical and chemical weathering of discrete sources (copper mines) and regional (non-point) sources (sulfide-rich shale) is evaluated by examining the mineralogy and chemistry of weathering products in Great Smoky Mountains National Park, Tennessee, and North Carolina, USA. The elements in copper mine waste, secondary minerals, stream sediments, and waters that are most likely to have negative impacts on aquatic ecosystems are aluminum, copper, zinc, and arsenic because these elements locally exceed toxicity guidelines for surface waters or for stream sediments. Acid-mine drainage has not developed in streams draining inactive copper mines. Acid-rock drainage and chemical weathering processes that accompany debris flows or human disturbances of sulfidic rocks are comparable to processes that develop acid-mine drainage elsewhere. Despite the high rainfall in the mountain range, sheltered areas and intermittent dry spells provide local venues for development of secondary weathering products that can impact aquatic ecosystems.Electronic Supplementary Material  Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.

Geology and Genesis of the Ta'ergou Skarn - Quartz Vein Tungsten Deposit in the North Qilian Caledonian Orogenic Belt, Northwest China

Abstract. The Ta'ergou tungsten deposit in Gansu province, northwestern China, is located in the western part of the North Qilian Caledonian orogen, and consists of scheelite skarn bodies and wolframite quartz veins. The tungsten‐bearing skarn developed by the replacement of carbonate layers intercalated in the Precambrian schist and amphibolite whereas wolframite‐quartz ore veins developed along a group of fractures that cut through horizontal skarns. The Ta'ergou tungsten deposit is genetically related to the Caledonian Yeniutan granodiorite intrusion and occurs ca. 500 m wide in the exo‐contact zone 300 ～ 500 m apart from the intrusion. The granodiorite displays a lower grade of differentiation, low content of SiO₂ and high contents of mafic components. There are three types of fluid inclusions in the wolframite‐quartz vein systems, i. e. aqueous, CO₂‐H₂O and CO₂‐rich. The homogenization temperature of aqueous inclusion ranges from 140 to 380d?C and their salinities from 6.4 to 17.4 equivalent wt% NaCl. Laser Raman spectroscopy shows that the inclusions contain a relatively high content of CO₂. The δ³⁴S values of skarn type sulfides range from +8.1 to +12.7 per mil and those of quartz vein sulfides from +9.3 to +14.9 per mil, similar to sulfides of the granodiorite with from +6.0 to +11.7 per mil. The δ¹⁸O values of quartz are between +10.5 and +13.3 per mil and those of wolframite between +3.4 and +5.1 per mil. The δ¹⁸O water values of ore forming fluids range from +0.6 to +6.4 per mil and suggest the mixture of magmatic fluids with meteoric water formed the ore‐forming fluids. It has been proved that Precambrian strata in the west sector of North Qilian region are enriched in tungsten. We propose the strata were remelted to be tungsten‐granitoid during subduction. The polymetallic tungsten was gradually accumulated into the roof pendants of the granite intrusion by fractional crystallization and then was deposited by hydrothermal fluids during metasomatism and infilling along fractures. On the other hand, the granite intrusion also acted as “heating machine” to make hydrothermal fluids leach out the metals from Precambrian strata and these metals joined the ore‐forming hydrothermal system.     

A statistical approach to evaluating distance metrics and analog assignments for pollen records

The modern analog technique typically uses a distance metric to determine the dissimilarity between fossil and modern biological assemblages. Despite this quantitative approach, interpretation of distance metrics is usually qualitative and rules for selection of analogs tend to be ad hoc. We present a statistical tool, the receiver operating characteristic (ROC) curve, which provides a framework for identifying analogs from distance metrics. If modern assemblages are placed into groups (e.g., biomes), this method can (1) evaluate the ability of different distance metrics to distinguish among groups, (2) objectively identify thresholds of the distance metric for determining analogs, and (3) compute a likelihood ratio and a Bayesian probability that a modern group is an analog for an unknown (fossil) assemblage. Applied to a set of 1689 modern pollen assemblages from eastern North America classified into eight biomes, ROC analysis confirmed that the squared-chord distance (SCD) outperforms most other distance metrics. The optimal threshold increased when more dissimilar biomes were compared. The probability of an analog vs no-analog result (a likelihood ratio) increased sharply when SCD decreased below the optimal threshold, indicating a nonlinear relationship between SCD and the probability of analog. Probabilities of analog computed for a postglacial pollen record at Tannersville Bog (Pennsylvania, USA) identified transitions between biomes and periods of no analog.     

Recent Precipitation Trends in Hungary in the Context of Larger Scale Climatic Changes

The time series of monthly precipitation totals from 14 Hungarian observing stations (1901–1998) were analysed to reveal the long term changes in precipitation characteristics occurred in the 20th century. A particular attention was given to the changes in the recent decades and their links with the larger scale climatic and circulation changes over Europe and the Atlantic.The statistical significancesof systematic changes are controlled by linear trend analysis and the Mann–Kendall test. The long term fluctuations are illustrated applying a 15-point Gaussian filter on the time series. The Standardised Precipitation Index is used to evaluate the changes in the drought event frequency. The relationships with larger scale changes are mostly discussed relying on contemporary papers, and the Grosswetterlagen Catalogue is used as well.The annual precipitation total decreased by 15–20% in Hungary during the 20th century. The decline is substantial in both halves of the century, but the precipitation sums in the transition seasons declined in the first 50 years, and the winter precipitation decreased in the latest decades. The precipitation total of the period November–February declined significantly in the last 50 years. In the same time the mean winter value of the North Atlantic Oscillation Index (NAOI) increased, the positions of the main pressure patterns over the Atlantic are shifted northeastward, and lot of other coherent changes detected in the winter climate of the European–Atlantic region. The mean summer precipitation total has hardly changed, but the frequency of summer drought events increased. There are some signs of a shift of the Hungarian summer climate towards a Mediterranean like climate.     

青海南部杂多地区新建扎青组的地层层序及地质意义

在青藏高原北羌塘盆地青海南部,青海省杂多县扎青乡地区的然者涌一带,发现以基性火山熔岩为主夹有中基性火山碎屑岩,具大陆板内裂谷拉斑玄武岩喷发特点的一套火山地层。该地层底部角度不整合接触覆盖在早中二叠世开心岭群诺日巴尕日保组、九十道班组之上,其上被晚三叠世结扎群甲丕拉组角度不整合覆盖。主要岩性为灰绿—灰紫色橄榄玄武岩、粗面玄武岩、玄武粗安岩及流纹岩、中基性火山角砾岩、角砾凝灰岩夹少量流纹岩和紫红色岩屑砂岩及细砾岩,其特征与峨眉山低钛玄武岩相似,具陆相喷发-沉积特征。区域对比在北羌塘地区具有独特地层特征,可与四川峨眉山玄武岩地层进行对比。而区域上该地区晚二叠世主要为一套海陆交互相含煤碎屑岩建造,未发现陆相火山岩出露,本文建立正式地层单位扎青组,以供参考,其时代暂归晚二叠—早三叠世。     

Chronology, Geochemistry and Tectonic Settings of the Hadamiao Granodiorite on the Northern Margin of the North China Platform

<正>The Hadamiao granodiorite,located on the northern margin of the North China platform and acting as the country rock of gold deposits in the Hadamiao region,was formed in the same age and similar tectonic settings with the Hadamiao gold deposit and the large-scale Bilihe gold deposit in the same area.By using the LA-ICP-MS method,the U-Pb age obtained is 267±1.3 Ma,which represents the crystallized age of the granodiorite,and that of the xenolithic zircon is 442.8±5 Ma. Base on the main elements,it exhibits the features of calc-alkaline to high-potassium calc-alkaline series,low silicon,and quasi-aluminous I-type granites,and with high magnesium(Mg~#=0.45-0.57) and high sodium contents(Na_2O/K_2O=0.98-2.29).The SREE values(81.6-110.15 ppm) are relatively low,the fractionations between LREE and HREE are obvious,showing a right-inclined dispersion in the REE distribution diagram.Compared with the primitive mantle,the rock is relatively rich in LREE(La and Ce),LILE(K,Sr,and Th),and intensively depleted in HFSE(Ti,P,Nb and Ta).The ratios of Sr/Y and(La/Yb)_N and the contents of Rb,Nb and Y are relatively low,the Sr values are high (436.35-567.26 ppm),and the Yb contents of most samples are low(1.25-1.8),which indicate the features of typical continental margin arc and adakitic rocks.According to the values ofε_(Nd)(t)(-2.4 to +0.2) and I_(Sr)(0.7028-0.7083),and variations of the La/Sm ratios,the Hadamiao granodiorite was formed from mixing of the thickened molten lower crust and the mantle wedge substances.The rock was related to the southward subduction and accretion of the Paleo-Asia Ocean in the Late Paleozoic, being Late Paleozoic magma of the continental margin arc formed on the basement of the Early Paleozoic accretion complexes,and showing a trend of turning into adakitic rocks,which indicates their great metallogenic(Au) potential.     

华北板块南缘安徽青白口纪-早奥陶世层序地层与格架

华北地台南缘,主要出露青白口纪—早古生代地层,属被动大陆稳定克拉通盆地发育过程,以台地碳酸盐沉积为主。通过对十余条实测剖面及主干、辅助路线的观察研究,青白口纪—早古生代奥陶纪早期,测区可区分出二个巨层序、十二个三级层序。本文通过三级层序的划分,建立了华北地台南缘青白口纪—早古生代奥陶纪早期层序地层格架、探讨了各岩石地层单位的变化规律。     

辽宁北票地区江沟山岩体锆石U-Pb年代学和地球化学

辽宁北票地区江沟山岩体主要岩性为二长花岗岩,属高钾钙碱性岩系.SiO2含量高（71.4%~73.78%）,富碱并相对富Na2O（Na2O/K2O平均为1.17）,Mg#较低（平均为0.18）.岩石的铝饱和指数（A/CNK）较高（1.09~1.24）,为过铝质岩石.标准矿物中普遍出现刚玉分子（1.36~3.01）,应属S型花岗岩特点.稀土总量较低（平均为96.99×10-6）,轻、重稀土分馏明显（（La/Yb）N=6.27~32.88）,有中等程度的负铕异常（0.77~0.87）.在微量元素蜘蛛网图上,强烈富集大离子亲石元素（如Rb、Ba）,高场强元素（如Ti）强烈亏损.在R1-R2图解中,江沟山岩体投影在同碰撞环境.该岩体锆石U-Pb年龄加权平均分别为239±2 Ma和233±4 Ma,表明该岩体为三叠纪侵位.前人研究发现,本区西部有中三叠世（229.2~237.5 Ma）侵入的S型花岗岩体,认为是西伯利亚板块与华北板块碰撞的产物.本文结论与之完全一致,从而为两大板块边缘大陆岩石圈演化提供了新的依据.     

贺兰山高压泥质麻粒岩——华北克拉通西部陆块拼合的岩石学证据

贺兰山孔兹岩系作为华北克拉通西部孔兹岩带的重要组成部分,其成因问题一直存在争议。近来,在对贺兰山富铝岩系研究过程中,发现了具有"蓝晶石+条纹长石+石榴石"特征组合的高压泥质麻粒岩。通过岩相观测与相平衡定量模拟,确定其曾经历四个阶段的变质演化过程,即早期进变质阶段(M1)、变质峰期阶段(M2)、峰期后降压阶段(M3)和晚期退变阶段(M4)。早期进变质阶段,以石榴石中包裹黑云母和白云母为特征。变质峰期阶段,以出现"蓝晶石+条纹长石+石榴石"组合为特征,变质温、压条件为850～870℃、1.4～1.5GPa。峰期后降压阶段以峰期石榴石和蓝晶石转变为堇青石和夕线石为特征,温压条件大致为840～860℃、0.6～0.8GPa。晚期退变阶段以出现新生黑云母为标志,温、压条件为780～810℃、0.45～0.55GPa。PT轨迹具有顺时针演化样式,峰期后表现为先发生近等温降压(ITD)、后发生近等压冷却(IBC)的退变过程,反映陆-陆碰撞发生高压麻粒岩相变质作用,后又快速折返到正常地壳深度的变质动力学过程,进而从岩石学角度证明华北克拉通西部孔兹岩带是由北部的阴山陆块与南部的鄂尔多斯陆块发生碰撞所致。