阿尔泰山南缘晚古生代火山岩的地质地球化学特征及其对构造演化的启示

阿尔泰山南缘晚古生代火山岩十分发育,从早泥盆世到早二叠世均有发育。其中中泥盆世北塔山组为一套中基性火山岩,并且底部含有厚度超过100m的苦橄岩;中泥盆世蕴都喀拉组为一套浅海相细碎屑沉积岩夹中性、中基性火山岩;晚泥盆世江孜尔库都克组为火山碎屑岩夹中基性和中酸性火山岩组合;而晚石炭世巴塔玛依内山组以玄武岩和玄武安山岩为主,夹凝灰岩、粉砂岩和炭质页岩。对这4个组火山岩的主要元素、微量元素地球化学特征研究表明,北塔山组和蕴都喀拉组为拉斑和钙碱性系列,并且均具有大离子亲石元素(LILE)富集,而高场强元素与MORB相当,说明其为岛弧环境。江孜尔库都克组火山岩为钾玄岩系列,并且具有较高的LILE富集,表明其形成于岛弧演化的晚期阶段;巴塔玛依内山组火山岩为碱性系列,并且具有强烈富集LILE的特征,指示了其形成于大陆板内环境。因此,从火山岩的时间和空间演化来看,本区晚古生代火山岩与准噶尔洋板块向北的俯冲有关,西伯利亚板块和准噶尔板块的碰撞发生在早石炭-晚石炭世。     

内蒙古东乌旗地区格根敖包组火山岩锆石LA-MC-ICP-MSU-Pb年龄及其地质意义

内蒙古东乌珠穆沁旗地区格根敖包组为一套海陆交互相中酸性火山岩、火山碎屑岩以及陆源碎屑岩组合,含有动植物化石。其时代具有争议。本文获得了格根敖包组二段火山岩LA-MC-ICP-MS锆石U-Pb年龄(307.3±0.99)Ma和(311.6±1.3)Ma,表明其形成于晚石炭世。结合前人古生物化石资料,认为格根敖包组上部(三、四、五段)陆源碎屑沉积地层,时代为早二叠世,而火山岩及其以下地层(一段、二段)属于晚石炭世。从而将格根敖包组形成时代限定为晚石炭—早二叠世。格根敖包组下部(一段、二段)地层与邻区宝力高庙组时代一致,同属晚石炭世。     

东准噶尔卡拉麦里地区巴塔玛依内山组火山岩LA-ICP-MS锆石U-Pb年龄

巴塔玛依内山组是一套以火山岩为主的陆相火山-沉积地层,在东准噶尔地区广泛分布,规模巨大,且形成时代久存争议。通过对卡拉麦里地区巴塔玛依内山组层型剖面的重新实测,以及对该组中下部层位玄武岩进行LA-ICP-MS测年,获得锆石U-Pb年龄为(338.7±7.7) Ma(MSWD=0.24)。所测锆石的CL图像上可见明显的震荡环带结构,且锆石Th/U比值为0.11～0.95,均大于0.10,13颗锆石的Th/U平均值为0.56,Th/U呈正相关,说明属岩浆锆石,指示其代表了巴塔玛依内山组的形成时代。结合前人的年代学数据及化石资料,将巴塔玛依内山组时代确定为早石炭世中期—晚石炭世初期,认为其中下部层位时代不晚于338.7 Ma。该成果进一步约束了区内陆相火山地层的时代,并为研究东准噶尔构造带的火山岩浆作用及其构造演化提供了新的年代学依据。     

东准噶尔巴塔玛依内山组火成岩锆石U-Pb年龄及其地质意义

以东准噶尔双井子地区巴塔玛依内山组和石钱滩组剖面为研究对象,通过岩矿鉴定、地球化学分析、锆石U-Pb定年和牙形刺挑选等方法,对巴塔玛依内山组和石钱滩组的年代学特征进行了研究。结果表明,巴塔玛依内山组火山岩的形成时间始于348. 7±2. 9Ma,318. 7±4. 2Ma之后结束,侵入岩的形成时间为255. 9±3. 5Ma,这些样品中普遍含有捕获锆石,这些锆石具有岩浆锆石的特征,年龄介于早石炭世杜内期和前寒武纪之间(354. 7～971. 2Ma),与盆地周边发育的岛弧火成岩和蛇绿岩年龄相仿,此外在石钱滩组灰岩内得到4颗牙形刺化石,分属于2个属,分别为Idiognathodus和Streptognathodus。以此为基础,通过搜集整理前人数据,得到如下结论:(1)巴塔玛依内山组火山岩地层是穿时的,从早石炭世到晚石炭世连续发育,形成时间介于348. 7±2. 9Ma～300. 4±1. 3Ma之间;(2)巴塔玛依内山组上部的石钱滩组形成于318. 7±4. 2Ma之后的晚石炭世;(3)卡拉麦里蛇绿岩所代表的准噶尔洋盆闭合时间在晚泥盆世法门期和348. 7Ma之间;(4)准噶尔盆地基底可能由岛弧和洋壳组成,且存在前寒武纪基底。本研究旨在确定巴塔玛依内山组和石钱滩组地层时代,并为卡拉麦里洋闭合时限以及盆地基底性质等问题的解决提供依据。     

东准噶尔纸房地区晚石炭世巴塔玛依内山组陆相火山-沉积体系特征

东准噶尔巴塔玛依内山组是典型陆相火山．沉积体系(盆地)，主体由基性及中酸性火山熔岩组成，火山碎屑岩及火山碎屑沉积岩较少，通过对纸房地区晚石炭世巴塔玛依内山组陆相火山岩的岩石化学、地球化学特征进行系统研究，认为它属于造山期后固结初期，新陆壳裂谷向高原火山岩演化的同岩浆源、同沉积盆地、同火山作用的钙碱系列双峰式火山岩．     

东准噶尔奥依托浪格地区原三塘湖组陆相火山岩地层的重新厘定与解体

笔者通过岩性组合与岩相组合对比研究、SHRIMP锆石U-Pb测年与化石年代学研究等手段,认为东准噶尔奥依托浪格地区原三塘湖组陆相火山岩应重新厘定为巴塔玛依内山组,并建议将这套准噶尔盆地东北缘广泛分布的陆相火山岩根据地质时代解体为巴塔玛依内山组与三塘湖组,三塘湖组仅代表早二叠纪陆相火山岩。年代学研究表明:奥依托浪格地区巴塔玛依内山组年龄具有穿时性,下段年龄为(335.6±6.5)Ma,上段年龄为(320.5±7.1)Ma,属早石炭世晚期到晚石炭世,解决了巴塔玛依内山组长久以来的下、上石炭统之争。综合研究认为:这套陆相火山岩属于东准噶尔构造带自西向东链式缝合背景下的构造-岩浆活动,残余洋盆消失至陆相火山活动开启,同时受到西侧拉张环境与东侧岛弧环境的影响。奥依托浪格地区巴塔玛依内山组火山机构、构造、喷发间歇期发育,具有石油地质意义。     

东天山大南湖岛弧带石炭纪岩石地层与构造演化

详细的地质解剖工作表明,东天山地区大南湖岛弧带石炭纪出露4套岩石地层组合,即早石炭世小热泉子组火山岩、晚石炭世底坎儿组碎屑岩和碳酸盐岩、晚石炭世企鹅山组火山岩、晚石炭世脐山组碎屑岩夹碳酸盐岩。根据其岩石组合、岩石地球化学、生物化石、同位素资料以及彼此的产出关系,认为这4套岩石地层组合的沉积环境分别为岛弧、残余海盆、岛弧和弧后盆地。结合区域资料重塑了大南湖岛弧带晚古生代的构造格架及演化模式。早、晚石炭世的4套岩石地层组合并置体现了东天山的复杂增生过程。     

藏北北羌塘盆地那底岗日组时代归属的新证据

藏北北羌塘盆地那底岗日组是一套角度不整合于三叠系肖茶卡组灰岩之上、假整合伏于侏罗系雀莫错组陆源碎屑岩之下的一套陆相火山岩夹火山碎屑岩及陆源碎屑岩地层,现有的资料都将其时代归属于早侏罗世。取自北羌塘盆地不同地区的2个那底岗日组流纹质晶屑凝灰岩和1个流纹质英安岩样品的SHRIMP锆石U-Pb定年结果分别为205Ma±4Ma、208Ma±4Ma和210Ma±4Ma,它们代表了那底岗日火山岩的形成时代,即那底岗日组的时代应为晚三叠世中期(诺利期)。那底岗日组形成时代的重新确定,对于重新认识羌塘盆地中生代火山喷发事件、羌塘盆地的性质与沉积构造演化具有重要意义。     

西准噶尔石炭系哈拉阿拉特组新知

哈拉阿拉特组是西准噶尔地区重要的石炭纪海相地层,岩性组合二分性明显:灰绿色为主的火山岩、火山碎屑岩夹灰岩透镜体与灰黑色为主的正常碎屑岩、火山碎屑岩夹少量生物碎屑灰岩。长期以来均认为前者在上,后者在下。根据该组层型剖面中的地层产状、层劈关系、冲刷构造和粒序层理,认为该剖面并未发生倒转,应是火山岩、火山碎屑岩夹灰岩透镜体在下,正常碎屑岩、火山碎屑岩夹生物碎屑灰岩整合覆在其上。根据`哈拉阿拉特组内所发现的化石材料,认为该组是西准噶尔地区一跨早—晚石炭世的岩石地层单位,下石炭统-上石炭统的界线位于该组下段上部。在克拉玛依西北部达尔布特蛇绿混杂岩带与达尔布特断裂之间新识别出的哈拉阿拉特组地层,其中含有早石炭世晚期至晚石炭世的化石,前人用这些材料来确定包古图组和太勒古拉组的时代是错误的,目前包古图组和太勒古拉组尚无可延续到晚石炭世的古生物依据。     

东准卡拉麦里地区苏吉泉一带黑山头组的厘定

分布于卡拉麦里大断裂之北苏吉泉一带的一套以陆源碎屑岩为主,夹有少量火山碎屑岩和火山熔岩的地层,前人将其划归中泥盆世平顶山组(蕴都喀拉组),作者等新获得该地层中火山岩夹层的全岩Rb-Sr等时年龄(339±4)Ma,依据岩石组合并与区内同时代地层对比分析,将其厘定为早石炭世黑山头组.黑山头组的厘定为确立卡拉麦里大断裂之北地层总体为一单斜构造提供了重要佐证,也为东准噶尔地区的地层正确划分与对比,建立区域地层格架和重建中亚地区晚古生代地质历史有重要意义.     

Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA

Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N₂ in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.     

Isotopic systematics of He,Ar, S,Cu, Ni,Re, Os,Pb, U,Sm, Nd,Rb, Sr,Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.     

深港西部通道填海区地下水铜、钒、铊、镉、钨迁移的实验研究

填海工程使滨海地区的地下水物理化学条件改变,导致该区域地下水中重金属浓度升高。本文以深港西部通道填海区为例,采用实验室模拟填海条件的办法,初步探讨了影响填海区地下水重金属迁移的关键因素。模拟实验结果表明,填海区地下水中钨元素含量升高与地下水淡化、淤泥氧化过程以及填料风化有关;铜元素含量升高则与淤泥氧化过程以及填料风化有关;钒元素含量升高与地下水淡化和淤泥氧化过程有关,而其他元素含量升高则主要与填料风化释放有关。     

贵州岑巩羊桥罗家塘杷榔动物群的发现及其后生动物早期演化的意义

岑巩县羊桥乡罗家塘杷榔组仅出露中-上部地层,岩性单一,均为青灰、灰绿色粉砂质泥、页岩.在其上部层位发现了俞氏贵州始海百合(Guizhoueocrinus yui Zhao,Parsley et Peng,2007),计有棘皮动物始海百合、腕足动物、软体动物-软舌螺、节肢动物-三叶虫等8属9种,包括了2个未定名的新种和1...     

扬子北缘马元铅锌矿床闪锌矿微量元素及S-Pb-He-Ar-C同位素地球化学研究

马元铅锌矿床是近年扬子陆块北缘铅锌找矿的新突破。矿体呈层状、似层状产于碑坝隆起翼部震旦系灯影组角砾状白云岩层间构造带中,围岩蚀变很弱。矿石中硫化物以闪锌矿、方铅矿为主,中粗粒晶质结构,充填于白云岩角砾间。闪锌矿富集Cd、Ge、Ag,贫In、Tl、Se,Ga/In为6~132,Ge/In多1000,成矿温度以中-低温为主。金属硫化物ε~(34)S值相对集中,为12.9‰~19.4‰,平均为17.4‰,来自于海相硫酸盐的还原。铅同位素组成稳定,~(206)Pb/~(204)Pb为17.858~17.918:~(207)Pb/~(204)Pb为15.603~15.694;~(208)Pb/~(204)Pb为37.756~38.046,具有造山带和上地壳铅的特征,震旦系可能提供了金属成矿物质。闪锌矿中流体包裹体的~3He/~4He为0.03Ra~1.05Ra,~(40)Ar/~(36)Ar为326.1~765.1,~(38)Ar/~(36)Ar为0.183~0.204,表明成矿流体主要为地壳流体和饱和大气水(大气降水或海水)的混合。闪锌矿内流体包裹体挥发分δ~(13)C_(CH_4)值为-36.01‰~-28.80‰,δ~(13)C_(C_2H_6)值为-27.72‰~-22.44‰,δ~(13)C_(CO_2)值为-23.24‰~-9.68‰,表明有机流体参与了成矿作用。石英、方解石的H-O同位素结果表明具有海水和有机水混合的特征。可见,成矿流体具有两种流体混合的特征,一为蒸发海水与围岩反应所形成的盆地卤水,二为有机流体。推测矿区可能存在一个古油气藏,由于TSR生成一高硫气藏,为区内还原性有机流体的主要来源。当富含Pb、Zn等成矿物质的成矿流体运移至富含CH_4和H_2S的还原性流体的矿区角砾岩带时,两种流体混合,Pb、Zn等遇到H_2S发生反应而沉淀成矿,并伴生热液白云石等,形成了马元铅锌矿床。综上所述,我们认为马元矿床属MVT型铅锌矿床。     

山西五台山区滹沱群变质玄武岩岩石学、地球化学特征及其成因意义

在野外地质调查的基础上,选取滹沱群豆村亚群底部四集庄组玄武岩、顶部青石村组玄武岩和东冶亚群中下部河边村组玄武岩,进行岩石学和地球化学研究。分析结果表明：玄武岩主量元素高TiO2、TFeO,低MgO,具有演化的基性岩浆的特征。稀土元素含量相对较高,具有弱—中等程度的轻稀土元素富集,中等程度的轻重稀土元素分异,轻微的Eu异常;玄武岩中Cr、Ni含量变化较大,但与Mg#具有很好的正相关性。微量元素配分图解中具有明显的Sr负异常,部分样品具有Nb、Ta和Ti负异常,无Zr、Hf负异常,与岛弧火山岩不同;同时Nb、Ta无分异,Zr/Hf值较高,具有板内玄武岩浆的特征。综合分析认为,滹沱群玄武岩可能形成于板内裂谷环境。在岩浆上升过程中发生橄榄石与尖晶石的分离结晶作用,同时不同程度地受到地壳的混染。     

Pressure Increases, the Formation of Chromite Seams, and the Development of the Ultramafic Series in the Stillwater Complex, Montana

This paper explores the hypothesis that chromite seams in theStillwater Complex formed in response to periodic increasesin total pressure in the chamber. Total pressure increased becauseof the positive V of nucleation of CO₂ bubbles in the melt andtheir subsequent rise through the magma chamber, during whichthe bubbles increased in volume by a factor of 4–6. Byanalogy with the pressure changes in the summit chambers ofKilauea and Krafla volcanoes, the maximum variation was 0•2–0•25kbar, or 5–10% of the total pressure in the Stillwaterchamber. An evaluation of the likelihood of fountaining andmixing of a new, primitive liquid that entered the chamber withthe somewhat more evolved liquid already in the chamber is basedupon calculations using observed and inferred velocities andflow rates of basaltic magmas moving through volcanic fissures.The calculations indicate that hot, dense magma would have oozed,rather than fountained into the chamber, and early mixing ofthe new and residual magmas that could have resulted in chromitecrystallizing alone did not take place. Mixing was an important process in the Stillwater magma chamber,however. After the new magma in the chamber underwent {smalltilde}5% fractional crystallization, its composition, temperature,and density approached those of the overlying liquid in thechamber and the liquids then mixed. If this process occurredmany times over the course of the development of the Ultramaficseries, a thick column of magma with orthopyroxene on its liquiduswould have been the result. Thus, the sequence of multiple injections,fractionation, and mixing with previously fractionated magmacould have been the mechanism that produced the thick bronzitecumulate layer (the Bronzitite zone) above the cyclic units.     

西藏南木林县秦马弄地区二长花岗岩体岩石成因

以出露在西藏南木林县秦马弄地区二长花岗岩体为研究对象,从野外地质调查、岩石学、LA-ICP-MS锆石U-Pb定年、元素和Lu-Hf同位素地球化学等方面对其进行了分析研究。结果显示：秦马弄地区二长花岗岩体类似于A型花岗岩,形成于古近纪(E1),其LA-ICP-MS锆石U-Pb年龄为(62.0±0.5)~(63.0±0.5) Ma;岩体形成的温度较高(锆石饱和温度为745~805 ℃,平均766 ℃);岩石富SiO2(72.6%~75.0%)、Na2O(2.86%~3.59%)和K2O(4.12%~5.25%),贫CaO(0.72%~1.39%)和MgO(0.26%~0.36%),高FeOT/MgO值(7.26~10.3),属高钾钙碱性系列,弱过铝质;岩石具明显的负Eu异常(Eu/Eu*=0.40~0.70),普遍表现出Ba、Sr、P、Ti元素的亏损和Rb、Th、K、Zr、Hf元素的富集。εHf(t)值为-4.7~-1.8,其两阶段地壳Hf模式年龄tDM2为(1.1~1.3) Ga。秦马弄A型花岗岩体是冈底斯基底地壳物质部分熔融的岩浆产物,形成于古近纪印度板块与欧亚板块俯冲碰撞引起的总体为岛弧背景下的局部拉张构造环境。