敦煌地块南缘石炭纪埃达克岩的发现及其地质意义

侵位于敦煌杂岩中的青石沟黑云母石英闪长岩,锆石LA ICP-MS U-Pb同位素测年研究结果表明其形成年龄为335±2Ma。岩石地球化学分析显示其具有高SiO2、高Al2O3和低MgO的主量元素地球化学特征,强烈富集Sr、亏损Yb和Y,具有较高的Sr/Y比值等特征,与埃达克质岩石具有一致的地球化学特征。青石沟黑云母石英闪长岩的Nd和Hf同位素值(εNd(t)=-9.39~-11.03,εHf(t)=-7.6~-16.6)显示其具有明显的壳源特征;Nd及Hf模式年龄值(Nd模式年龄t DM=1.83~1.98Ga,Hf二阶段模式年龄t DM2=1.53~1.95Ga)均表明其源区可能与元古代敦煌杂岩相关;结合较高的Mg#,低Cr和Ni含量,无Eu异常等特征,暗示该岩体为加厚下地壳部分熔融的产物。综合区域地质特征,初步认为敦煌地区早石炭世处于由陆陆俯冲(地壳加厚)作用向陆内伸展体制转化的构造环境。     

塔里木北缘Rodinia超大陆聚合事件——来自新元古代早期花岗岩成因的证据

对塔里木板块拼入Rodinia超大陆聚合时限进行限定,报道塔里木板块北缘库鲁克塔格隆起奥依库如克岩体花岗闪长岩的年代学、岩石学、地球化学和锆石Hf同位素特征。花岗闪长岩的LA-ICP-MS锆石U-Pb年龄为(855±29)Ma,为新元古代早期岩浆作用产物。全岩化学组成上,该岩石为准铝质-弱过铝质、钙碱性系列"I"型花岗岩,轻重稀土元素分馏显著,基本无Eu异常,富集Rb,Ba,K,Sr等大离子亲石元素,亏损P,Ti,Nb,Ta等高场强元素。锆石Hf同位素分析结果显示:锆石εHf(t)值为-15.12～-11.52;二阶段模式年龄TDM2=2.46～2.66 Ga。研究表明,奥依库如克岩体形成于板块俯冲消减环境,指示Rodinia超大陆的汇聚。     

新疆谢米斯台地区乌兰萨拉岩体地球化学、年代学及全岩Sr-Nd和锆石Hf同位素研究

谢米斯台地区位于新疆西准噶尔北部,该地区中酸性岩浆活动强烈。本文对谢米斯台地区乌兰萨拉岩体进行了地质、地球化学、年代学及全岩Sr-Nd和锆石Hf同位素研究。结果表明,乌兰萨拉岩体是一个由碱长花岗岩和花岗闪长岩组成的复式岩体。碱长花岗岩形成时代为晚志留世(422.7±2.0Ma),岩石高硅、富碱,属于准铝质-弱过铝质高钾钙碱性花岗岩;球粒陨石标准化配分模式图显示"V"字型配分样式,Eu负异常强烈,相对富集Ga、K、Rb、Th、U和Pb,亏损Ba、Sr、P、Ti、Cr和Ni等;岩石具有低(~(87)Sr/~(86)Sr)i值(0.7017~0.7038),正的ε_(Nd)(t)值(+4.49~+6.58)和锆石ε_(Hf)(t)值(+10.0~+14.2),Hf同位素模式年龄(t_(DM2))为500~771Ma。花岗闪长岩形成时代为早泥盆世(411.7±1.7Ma),属于准铝质,高钾钙碱性-钾玄岩系列花岗岩;球粒陨石标准化配分模式图显示右倾型配分样式,无明显Eu异常,相对富集LREE、LILE(Rb、Ba、K)、Th、U和Pb,亏损Nb、Ta、P和Ti等;岩石具有低的(~(87)Sr/~(86)Sr)i值(0.7041~0.7046),正的ε_(Nd)(t)值(+1.66~+3.87)和锆石ε_(Hf)(t)值(+4.4~+13.9),Hf同位素模式年龄(t_(DM2))为516~1120Ma,岩石Nd同位素和锆石Hf同位素出现一定程度的解耦。综合研究认为,乌兰萨拉岩体碱长花岗岩属A_2型花岗岩,花岗闪长岩属I型花岗岩,两者都是由新生下地壳发生部分熔融而形成,前者经历了一定程度的分离结晶作用,后者受到亏损玄武质岩浆(俯冲板片脱水交代地幔楔产生的上涌岩浆)的底侵,它们均形成于陆缘弧环境。     

鄂东南地区何锡铺岩体锆石U-Pb定年、岩浆源区及其地质意义

鄂东南地区存在大量中酸性小岩体,部分小岩体与斑岩型铜钼金矿床关系密切。对位于鄂东南东区南部的何锡铺花岗闪长斑岩体进行了锆石U-Pb定年和Hf同位素组成测定。定年结果显示:花岗闪长斑岩样品的岩浆结晶年龄为(142±1)Ma,属早白垩世。这与鄂东南地区和九江-瑞昌地区含矿小岩体形成年代基本一致。何锡铺岩体锆石176 Hf/177 Hf比值为0.282 372~0.282 656,在t=142 Ma时,对应的εHf(t)值为-11.1~-1.1,平均值为-6.3。锆石εHf(t)值具不均一性,类似于阮宜湾岩体,而不同于铜山口岩体和龙角山岩体。岩体具高Sr/Y比值,无明显Eu负异常。全岩初始锶同位素比值(87Sr/86Sr)i为0.705 88,εNd(t)值为-4.9。全岩地球化学、Sr-Nd同位素和锆石Hf同位素特征一致表明富集地幔是何锡铺岩体的重要源区,原始幔源岩浆可能存在古老地壳物质的混染。何锡铺岩体不仅具有与铜山口岩体类似的岩石学特征,还具有与其类似的地球化学特征。幔源物质的参与指示该岩体具有形成斑岩型铜钼金矿床的潜力。     

宁国竹溪岭地区花岗闪长岩锆石U-Pb年代学及地球化学及

本文对宁国竹溪岭地区的花岗闪长岩进行了系统的研究,包括岩相学观察、全岩地球化学分析、锆石U-Pb年龄测定以及Hf同位素分析等工作。全岩主微量元素分析结果表明,竹溪岭岩体具有高硅、低镁、富钾的主量元素特征,富集大离子亲石元素K、Rb、Ba、Sr等,Sr/Y比值低,亏损高场强元素Nb、Ta、Zr和Ti,显示明显的Pb正异常。岩体中存在Zr/Hf比值的异常,Zr/Hf为21.5~26.7,明显低于平均地壳的Zr/Hf值（35.5）。推测认为可能是锆石的分离结晶所造成。根据锆石的U-Pb和Hf同位素分析结果,竹溪岭花岗闪长岩的形成年龄为140Ma左右,属于中生代燕山期早白垩世的侵入岩;锆石的εHf（t）多为负值（2.3 ~ -4.76）。结合地质背景,竹溪岭花岗闪长岩形成于弧后的拉长环境,与太平洋板块俯冲之后的回撤作用有关。     

湖南常宁水口山Pb—Zn矿区花岗闪长岩元素 地球化学，LA-ICP-MS锆石U-Pb 年龄和Hf同位素特征

在野外地质工作的基础上,本文通过显微观察、岩石化学、锆石U-Pb定年、锆石原位Hf同位素分析研究,深入探讨水口山Pb—Zn矿区花岗闪长岩的岩石化学性质、形成时代和物质来源。研究表明:花岗闪长岩以高钾、富碱,富集轻稀土元素、大离子亲石元素(Rb、Th、U、La)和Pb,亏损重稀土元素、高场强元素(Nb、Ta、Ti)和Ba、Sr等元素为特征。锆石U-Pb加权平均年龄为156.0±1.0Ma(MSWD=0.33,2σ,N=20),属于燕山早期产物。锆石原位Hf同位素初始比值εHf(t)为-10.80~-8.71,平均-9.71;Hf同位素二阶段模式年龄TCDM为1.75~1.88Ga,平均1.82Ga,指示花岗闪长岩的岩浆源区主要来自古元古界下地壳物质。燕山早期湘南地区岩石圈处于全面的拉张—减薄期,导致地幔物质上涌,岩浆底侵,引发大规模的地壳熔融,熔融形成的岩浆沿深大断裂上侵,形成水口山Pb—Zn矿区花岗闪长岩。     

甘肃北山南带晚泥盆世岩浆事件:锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素体系约束SCIEI北大核心CSCD

北山造山带处于中亚造山带南缘,研究其岩浆事件对于推演中亚造山带地质构造演化具有重要意义。在甘肃北山南带的双鹰山-花牛山岛弧带中,分布有大量花岗质岩体。本文选取甘肃北山南带双峰山南复式岩体中的花岗闪长岩和二长花岗岩,开展LA-ICP-MS锆石年代学、Hf同位素、全岩地球化学和Sr-Nd同位素研究。研究结果表明该复式岩体成岩时代、地球化学与同位素特征基本一致,具体如下:(1)锆石年代学结果显示二长花岗岩年龄为367.5±1.7Ma、368.0±1.8Ma,花岗闪长岩年龄为366.3±2.2Ma,均为晚泥盆世;(2)复式岩体SiO_(2)含量为64.39%~74.95%、碱含量为5.01%~9.21%,属准铝质(A/CNK=0.88~1.00),P 2O 5含量低(0.02%~0.17%),且与SiO_(2)呈负相关,具有典型的I型花岗岩特征;(3)样品总体富集轻稀土元素((La/Yb)N=6.23~23.0),具有较强烈的Eu负异常(δEu=0.31~0.55),富集Rb、Th、U等大离子亲石元素,亏损Nb、Ti、P等高场强元素;(4)锆石εHf(t)值为-3.1~+6.0,t DM2为928~1327Ma,全岩(87 Sr/86 Sr)i在0.705607~0.708523之间,εNd(t)在-4.1~-1.9之间。结合区域构造环境,实验数据表明,双峰山南晚泥盆世复式岩体是在活动大陆边缘的环境下,由幔源岩浆底侵加热下地壳使之部分熔融,并与之混合形成的,代表了晚泥盆世柳园洋向北俯冲的构造事件。     

东北三江盆地始新世花岗闪长岩的发现及其地质意义:锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素证据

本文报道了三江盆地富锦地区临山花岗质岩体的锆石LA-ICP-MS U-Pb年龄、全岩地球化学和Sr-Nd同位素与锆石Hf同位素资料,以确定其形成时代、岩石成因、源区性质及其构造属性。花岗闪长岩中的锆石均呈半自形-自形晶,震荡环带发育,Th/U比值=0.31~1.92,指示其岩浆成因。对岩浆锆石的定年结果显示,临山花岗闪长岩形成于~54Ma,这是目前东北地区报道的最年轻的花岗质岩浆作用。该期花岗闪长岩的SiO_2含量主要在68.71%~72.42%之间,Na_2O=3.29%~4.41%,K_2O=2.79%~3.47%,Na_2O/K_2O=0.95~1.58,A/CNK=0.99~1.12;该区花岗闪长岩富集轻稀土元素(LREEs)和大离子亲石元素(LILEs),亏损重稀土元素(HREEs)和高场强元素(HFSEs),且轻重稀土元素分馏较强[(La/Yb)N=21.8~34.1]。样品无明显Eu异常(δEu=0.84~1.19)。它们的(87Sr/86Sr)i=0.7068~0.7071,εNd(t)介于-2.4~-2.3之间;锆石εHf(t)值介于+1.7~+5.7之间,二阶段Hf模式年龄(tDM2)介于765~1020Ma之间。上述特征表明,该期花岗闪长岩属于弱过铝质高钾钙碱性I型花岗岩,其原始岩浆起源于中元古代末-新元古代期间增生的陆壳物质的部分熔融。对三江盆地与佳木斯地块东缘已发表锆石Hf同位素资料进行总结和时空对比发现,佳木斯地块东缘和三江盆地具有相似的地壳增生历史,暗示三江盆地之下的基底物质可能仍归属于佳木斯地块范畴。另外,新生代临山岩体的识别,限制了富锦隆起的时限为始新世之后,并非前人认为的中生代。     

黑龙江三矿沟铁铜矿床花岗闪长岩锆石U-Pb定年、岩石成因及构造意义

黑龙江三矿沟Fe-Cu矿床是中亚造山带东段大兴安岭北部裸河-多宝山-三矿沟NW向成矿带中矽卡岩型矿床的典型代表。LA-ICP-MS锆石U-Pb年代学表明,与成矿密切相关的黑云母花岗闪长岩的锆石谐和年龄和238U/206Pb加权平均年岭分别为175.9±1.6Ma和175.9±1.1Ma,二者在误差范围内具有良好的一致性,表明多宝山成矿区在早侏罗世晚期存在一期重要的岩浆-热液成矿事件。三矿沟花岗闪长岩的元素地球化学特征具有岛弧岩浆岩的地球化学亲缘性:岩石富钠(Na2O/K2O=1.39～1.59),准铝质(A/CNK=0.87～0.91),富集轻稀土元素(LREE),(La/Yb)N=8.02～10.45,Eu显示弱负异常(δEu=0.82～0.98),富集大离子亲石元素(LILE,如Rb、Ba、K)和元素地球化学性质活泼的不相容元素(U、Th、Pb),相对亏损高场强元素(HFSE,如Nb、Ta、Zr、Hf、Ti)。Sr-Nd-Pb同位素分析结果表明:三矿沟花岗闪长岩具有低的Sr同位素初始比值((87Sr/86Sr)i=0.7041～0.7045)、高的Nd同位素初始比值((143Nd/144Nd)i=0.512556～0.512576)、正的εNd(t)值(2.8～3.9)、年轻的二阶段亏损地幔模式年龄(tDM2=647～733Ma)和幔源铅同位素组成特征((206Pb/204Pb)t=18.121～18.418;(207Pb/204Pb)t=15.480～15.511;(208Pb/204Pb)t=37.628～37.713),上述同位素地球化学特征均显示花岗闪长质岩浆主要源于亏损地幔源区。结合东北地区区域构造演化和岩体微量元素及同位素组成特征反映该矿床形成于岛弧的构造背景,其形成可能与侏罗纪古太平洋板块的俯冲作用密切相关。     

西藏拉萨地体西北部革吉地区两期早白垩世岩浆作用——锆石U-Pb年龄、Hf同位素和地球化学特征

邦巴岩体位于拉萨地块西部革吉地区,由主体花岗岩、花岗闪长岩、闪长质包体及一系列近平行、南北向展布的花岗斑岩脉体组成。野外地质调查和LA-MC-ICP-MS锆石U-Pb定年表明,革吉地区白垩纪的两期岩浆活动分别发生在131~132Ma和127Ma。早期岩浆作用形成主体花岗岩、花岗闪长岩及闪长质包体,具有以下特征:(1)明显富集K、Cs等大离子亲石元素,亏损Nb、Ti、Zr等高场强元素;(2)具有明显的负Eu异常(Eu/Eu*=0.49~0.61)及负Ce异常;(3)具负εHf(t)值(-3.2~-0.3)及古老的地壳模式年龄(1.210~1.399Ga);(4)初始Sr同位素比值为0.70424~0.71472,εHf(t)值为-5.70~-5.54。晚期岩浆作用形成花岗斑岩脉体,具有以下特征:(1)富集K、Cs等大离子亲石元素,强烈亏损Nb、Ta、Ti等高场强元素;(2)基本不具有负Eu异常或具有轻微的负Eu异常(Eu/Eu*=0.74~0.87);(3)具有更老的Hf同位素地壳模式年龄(1.226~1.576Ga)及更负的大范围变化的εHf(t)值(-6.1~-0.7)。晚期岩浆作用锆饱和温度(777~796℃)及轻稀土元素不饱和温度(794~812℃)均高于早期岩浆的锆饱和温度(661~762℃)及轻稀土元素不饱和温度(750~769℃)。上述特征表明,两期岩浆作用均为中拉萨地块古老基底部分与地幔物质混染部分熔融的产物,随着岩浆作用的持续进行,岩浆中的古老地壳组分增加,熔体温度也增加,可能与南向俯冲的班公-怒江洋壳回转驱动的地幔岩浆活动向北迁移有关。     

Police, politics, and the right to the city

Space and spatiality have recently been at the core of debates concerning the political possibilities of the city. The arguments advanced in this paper might be seen as an attempt to contribute to these debates through a reflection on the spatiality of (in) justice, politics, and the right to the city. The case of French urban policy, with its focus on distressed urban areas, and the `suburban problem' in France are used as examples to make arguments more concrete.     

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.     

Delivery of Trace Metals (Al,Fe, Mn,V, Co,Ni, Cu,Cd, Ag,Pb) from the Trinity River Watershed Towards the Ocean

The Trinity River (Texas, USA) contains in its watershed 23 different reservoir lakes, the largest one being Lake Livingston situated in the lower Trinity River watershed and two potentially polluting metroplexes, Dallas and Houston. In order to determine fluxes of nutrients and trace metals to Galveston Bay, a survey that included 24 discreet samples collected over a year and at various stages of discharge was carried out during 2000–2001. Geochemical (i.e., sorption by Fe oxyhydroxides), biological (i.e., seasonal uptake by sinking algae in Lake Livingston), and hydrological (i.e., dilution effects by increasing flow rates) controls were found to be mainly responsible for variations in dissolved trace metal concentrations rather than pollution sources. The Trinity River loads of suspended sediments and pollutant trace metals entering Galveston Bay at Anahuac were <20% of those reaching Lake Livingston, and only a few percent of the total upstream trace metal load is entering the Gulf of Mexico. Thus, during the transit through the 23 man-made lakes and an estuary, >96% of the pollutant trace metal load is lost to sediments.     

Composition,formation conditions,and genesis of the Talatui gold deposit,the Eastern Transbaikal Region,Russia

The mineral composition of the Talatui gold deposit has been studied with modern methods. Previously unknown minerals (ilmenite, siegenite, glaucodot, wittichenite, matildite, hessite, pilsenite, zircon, tremolite, cummingtonite, hercynite, and goethite) have been identified in the ore. A high Re content has been detected in molybdenite. The spatiotemporal separation of Au and Ag is caused by different mineral species of these elements and their diachronous precipitation during the ore-forming process. Gold crystallized along with early mineral assemblages, beginning from virtually pure gold (the fineness is 996). Silver precipitated largely at the end of the process as hessite (Ag₂Te) and matildite (AgBiS₂). The temperature of ore deposition varied from 610 to 145°C, the pressure was 3370–110 bar, and the salt concentration ranged from 56.3 to 0.4 wt % NaCl equiv. The heterogeneous state (boiling) of fluid at the early stages has been documented. The chemical and isotopic compositions of the fluid testify to its magmatic nature and the participation of meteoric water at late stages in the ore-forming process. Thermodynamic modeling reproduces the main specific features of ore formation, including separation of Au and Ag. A physicochemical model of the gold mineralization in the Darasun ore district has been proposed. On the basis of several attributes, the Talatui deposit has been referred to the prophyry gold-copper economic type.     

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.     

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。     

Rb-Sr, K-Ar, H-and O-Isotope systematics of the Middle Riphean shales from the Debengda Formation, the Olenek Uplift, North Sibera

Clay subfractions (SFs) of <0.1, 0.1–0.2, 0.2–0.3, 0.3–0.6, 0.6–2 and 2–5 μm separated from Middle Riphean shales of the Debengda Formation are studied using the TEM, XRD, K-Ar and Rb-Sr isotopic methods. The oxygen and hydrogen isotope compositions in the SFs are studied as well. The low-temperature illite-smectite is dominant mineral in all the SFs except for the coarsest ones. The XRD, chemical and isotopic data imply that two generations of authigenic illite-smectite different in age are mixed in the SFs. The illite crystallinity index decreases in parallel with size diminishing of clay particles. As compared to coarser SFs, illite of fine-grained subfractions is enriched in Al relative to Fe and Mg, contains more K, and reveals higher K/Rb and Rb/Sr ratios. The Rb-Sr age calculated by means of the leachochron (“inner isochron”) method declines gradually from 1254-1272 Ma in the coarsest SFs to 1038-1044 Ma in finest ones, while the K-Ar age decreases simultaneously from 1225–1240 to 1080 Ma. The established positive correlation of δ¹⁸O and δD values with dimensions of clay particles in the SFs seems to be also consistent with the mixing systematics. The isotopic systematics along with data on mineral composition and morphology lead to the conclusion that mixedlayer illite-smectite was formed in the Debengda shales during two periods 1211–1272 and 1038–1080 Ma ago. The first period is likely close to the deposition time of sediments and corresponds to events of burial catagenesis, whereas the second one is correlative with the regional uplift and changes in hydrological regime during the pre-Khaipakh break in sedimentation.     

Breakthroughs in the biodiversity, biogeography, biostratigraphy, and basin analysis of the Beaufort group

Over the past decade researchers working on the rocks of the Beaufort Group in the main Karoo Basin of South Africa have vastly increased our understanding of this important Permo-Triassic sequence. Many new fossil forms have been discovered, allowing for breakthroughs into the biodiversity, biogeography and biostratigraphy of the group. Taxonomic and phylogenetic advances are many and varied, and cover most of the vertebrate taxa, but with emphasis placed on the temnospondyl amphibians, archosauriforms and non-mammalian synapsids, in particular the anomodontia. Biostratigraphic breakthroughs have centered on the Middle Permian Eodicynodon and Tapinocephalus assemblage zones, the Late Permian Dicynodon Assemblage Zone, and the Triassic Lystrosaurus and Cynognathus assemblage zones. Correlation of these biozones with better dated sequences in Europe, Russia and China has allowed for many chronostratigraphic refinements, which are in turn vital for sequence stratigraphical analysis of the basin fill. Based on fossil data, both the lower (Ecca–Beaufort) and upper (Beaufort–Molteno) contacts of the group have been proved to be highly diachronous. The refined chronostratigraphic framework has also allowed for a better analysis of the basin evolution through time, particularly in terms of the correlation of external stimuli that affect basin sedimentation patterns.     

藏北羌塘丁固—加措地区康托组的时代

自西藏区域地质调查大队创建康托组以来,康托组岩石地层单位广泛应用于羌塘地区,普遍认为其时代为新近纪.笔者于丁固-加措地区的康托组地层中采获古近纪轮藻化石Obtusocharat sp.,O.lanpingenis,Gyrogona qinajiangica和部分孢粉化石,并在康托组底部安山岩中获K-Ar年龄65.1～66.5Ma.上述轮藻组合与同位素年龄指示的地层时代为古新世-始新世,据此将测区康托组的时代确定为古近纪.由于测区康托组之上被唢纳湖组或鱼鳞山组角度不整合覆盖,因此康托组时代的确定不仅进一步完善了测区新生代地层系统,还指示测区在康托组与唢纳湖组或鱼鳞山组之间发生了一次强烈的构造运动.