西藏纳木错晚更新世以来湖面变化和湖相沉积中粘土矿物显示的环境信息

通过对西藏海拔最高、面积最大湖泊-纳木错周缘湖相沉积、湖岸堤的野外调查和湖岸阶地的水准测量,发现在纳木错沿岸拔湖48m以下,发育有6级湖岸阶地,拔湖48~139.2m发育有高位湖相沉积。湖相沉积物的同位素测年结果表明,纳木错湖泊发育与藏北高原东南部古大湖演化可划分为3个阶段:①116~37kaB.P.间的古大湖期;②37~30kaB.P.间的外流湖期;③30kaB.P.以来的纳木错期。根据纳木错晚更新世以来湖相沉积中粘土矿物的X光衍射分析结果,以及采用比值法、高岭石法和衍射峰法的研究,探讨了粘土矿物所显示的环境变化信息。粘土矿物成分变化表明,该区已具备了寒温带干旱、半干旱区的气候环境特征。为研究青藏高原的湖泊演化、气候变化、古地理变迁及其隆升过程等提供了新资料。      

“三江”云龙锡(钨)成矿带晚白垩世二云母花岗岩LA-ICP-MS锆石U-Pb定年及其地质意义

云龙成矿带位于西南“三江”中段,是该区重要的锡(钨)矿集区.本文利用LA-ICP-MS锆石U-Pb定年方法,对带内与成矿相关的二云母花岗岩进行了年龄测试,获得成岩年龄为72.2±0.8 Ma(MSWD=1.9),属晚白垩世.这是在保山地块首次发现确凿的晚白垩世岩浆岩,表明保山地块经受了该时期构造-岩浆活动的影响.通过锆石微量元素和主微量地球化学特征分析,认为其应属S型花岗岩.结合区域地质背景,认为云龙成矿带该期花岗岩可能与腾冲地块晚白垩世S型花岗岩形成于一致的动力学背景,为新特提斯东向俯冲过程中内陆增厚地壳熔融的产物.本次报道的晚白垩世S型花岗岩与成矿带内一期重要成矿期次时代一致.结合前人研究资料认为,云龙成矿带内三期主要的成矿事件均有同期构造-岩浆事件对应,其中早、晚白垩世成矿活动与同期花岗岩体侵入紧密相关,而新生代成矿活动则与崇山剪切带走滑活动关系密切.这表明本区锡(钨)矿床经历了多期成矿过程,岩浆侵入活动和构造相关混合岩化对矿床形成均有贡献,单一的成因机制(花岗岩相关或混合岩化)可能无法合理解释本区矿床的成因.     

雪峰造山带南段靖州盆地成因性质及形成背景

靖州盆地是位于雪峰构造带南段的一个NE向晚三叠世一中侏罗世小型陆相盆地,前人研究提出其为NNE向溆浦-靖州大断裂左行走滑形成的拉分伸展盆地.本文对靖州盆地构造特征、T3-J2沉积和原型盆地特征等进行了系统研究,在此基础上提出该盆地实为挤压类前陆盆地,主要依据有:①沉积物高成熟度以及残留盆地边界与盆地周缘先期地质界线总体协调一致,说明盆地沉积时为挤压挠曲作用下形成的低缓洼地;②沉积物高成熟度和远源特征,指示盆地形成于相对稳定构造环境;③盆地北端T3-J1沉积空间由岩层弯曲下凹提供;沉积物产状变化指示J2盆地受到NW向挤压并产生持续褶皱变形;沉积物特征指示沉积环境西浅东深,进一步暗示J2盆地发展受控于NW向挤压与东缘逆冲块体的重力载荷;④盆缘伸展断裂少见,因挤压形成的小型走滑断裂、逆断裂、共轭剪节理等则多见;⑤从溆浦-靖州断裂走向偏转情况来看,该断裂左行走滑时靖州盆地所处部位应为挤压区而非拉张区.据盆地沉积和构造特征及区域大地构造演化背景,盆地的形成主要与晚三叠世-早侏罗世区域SN向挤压、中侏罗世区域NWW向挤压和NNE向左行走滑有关.     

The Late Triassic I–Type Granites from the Longmu Co–Shuanghu Suture Zone in the interior of Tibetan Plateau, China: Petrogenesis and Implication for Slab Break–Off

The Jiangaidarina granitic mass(JM) is an important part of the magmatic belt in Longmu CoShuanghu Suture Zone(LSSZ) in the central Tibetan Plateau. An integrated research involving wholerock geochemistry, zircon LA-ICP-MS U-Pb ages and Hf isotopic compositions was carried out to define the timing, genesis and tectonic setting of the JM. Zircon LA-ICP-MS U-Pb ages have been obtained ranging from 210 to 215 Ma, rather than the Early Jurassic as previously thought. Fifteen granite samples contain hornblendes and show a negative correlation between P_2 O_5 and SiO_2, indicating that the JM is an I-type granite. All the granites are enriched in LREE relative to HREE, with negative Eu anomalies(Eu/Eu*=0.56-0.81), and have similar trace elements patterns, with depletion of Ba, Nb, Sr and P. These suggest that the JM was fractionated, and this is also proved by the characteristic of negative correlations between oxide elements(TiO_2, MgO, FeOt, MnO, CaO) and SiO_2. Almost all ε_(Hf)(t) values of the granites are between-10.3 and-5.8, implying that the JM has a crustal source intimately related with the South Qiangtang Block(SQB), except for one(+10.2), showing a minor contribution from mantle source.Moreover, relatively low Na_2 O/K_2 O ratios(0.42-0.93) and high A/CNK values(0.91-1.50) reflect that the JM was predominately derived from the medium-high potassium basaltic crust, interacted with greywacke. Our new geochemical data and geochronological results imply that the Late Triassic magmas were generated in a post-collisional tectonic setting, probably caused by slab break-off of the Longmu Co-Shuanghu Tethyan Ocean(LSTO). This mechanism caused the asthenosphere upwelling, formed extension setting, offered an enormous amount of heat, and provided favorable conditions for emplacement of voluminous felsic magmas. Furthermore, the LSTO could be completely closed during the Middle Triassic, succeed by continental collision and later the slab broke off in the Late Triassic.     

贵州关岭生物群海百合Traumatocrinus的再研究

在前人的研究基础上,通过对大量新发掘的贵州关岭地区晚三叠世海百合化石标本的再研究,肯定了Trauma-tocrinus的有效性。根据目前的材料,认为该属只有1个有效种,即Traumatocrinus hsui;而根据化石的埋藏学特征,认为幼年体Traumatocrinus hsui营假浮游生活,成年体是否能够适应底栖生活环境尚需进一步证实。     

西藏拉萨地体南部晚白垩纪石榴石二辉麻粒岩的发现及其构造意义

拉萨地体位于青藏高原南部,其中-新生代构造演化过程与新特提斯洋的俯冲、消亡和印度与欧亚大陆的碰撞密切相关,是揭示青藏高原形成与演化历史的关键之一。本文报道了在拉萨地体东南部林芝岩群中发现的石榴石二辉麻粒岩。这种岩石的共生矿物为石榴石、单斜辉石、斜方辉石、拉长石、富钛角闪石和黑云母,其原岩相当于基性岩,变质作用的温压条件为T=747~834℃和P=0.90~1.35GPa,形成深度可达45km。与麻粒岩伴生的石榴石斜长角闪岩和大理岩中锆石的U-Pb定年研究表明,它们的变质作用发生在85~90Ma。结合在林芝岩群中广泛发育的同时代岩浆作用和区域变质作用,我们认为拉萨地体南部在晚中生代发生了强烈的安第斯型造山作用。     

Hamatophyton from the Late Devonian of Anhui Province, South China and Evolution of Sphenophyllales

Abstract: Well-preserved specimens of Hamatophyton verticillatum collected from the Upper Devonian (Famennian) Wutong Formation of Chaohu district, Anhui Province, South China, display more complete fertile axes in three orders and multiple divisions. Comparisons indicate that Hamatophyton possibly does not have palmate planate sterile leaves but hook-like linear ones with rare divisions. We propose seven definitive characters of Sphenophyllales: (1) completely whorled lateral organs; (2) sterile leaves; (3) strobili; (4) “sporangiophores” or stalks with reflexed tips bearing sporangia; (5) three- or four-ribbed primary xylem; (6) exarch maturation of primary xylem; and (7) secondary xylem. The Sphenophyllales probably originated from the Iridopteridales based on similarities in whorled lateral organs, ribbed primary xylem and peripheral protoxylem strands. In transition from Iridopteridales to Sphenophyllales, morphological changes involve partially whorled to completely whorled lateral organs, sterile ultimate appendages to leaves, and fertile ultimate appendages to “sporangiophores”/stalks with bracts; anatomical modifications include configuration and maturation of primary xylem, and presence of secondary xylem.     

Description and Phylogenetic Position of Dinosaur Eggshells from the Luanchuan Area of Western Henan Province, China

Here, we examine 145 dinosaur eggshells from a new fossil locality in the Qiupa Formation (Upper Cretaceous) of the Luanchuan area in western Henan Province, China. The eggshells display elongatoolithid macro- and microstructures, including ridges and nodes on the outer surface, two ultrastructural layers, and an undulatory boundary between the mammillary and continuous layers. A phylogenic analysis shows that the Luanchuan eggshells belong to the ooclade Elongatoolithidae. Within Elongatoolithidae, the thickness ratio of the mammillary layer to the entire eggshell, and the porosity of the Luanchuan eggshells are comparable to the oogenera Macroolithus and Elongatoolithus. There is no direct evidence for the taxonomic identity of the Luanchuan eggshells; however, they were likely laid by oviraptorids based on their phylogenetic position and their similarities with known oviraptorid eggs.     

北淮阳金寨—苏仙石地区中生代花岗岩类岩石学及地球化学特征

位于大别山北麓的北淮阳金寨—苏仙石地区广泛发育花岗岩类侵入岩，同位素年龄为１４０～９７Ｍａ，时代属Ｊ３—Ｋ１。根据侵入岩的地质、岩石学和岩石地球化学特征，将本区侵入岩划分为３个超单元（包括１０个单元）和３个独立单元，分属中性岩和酸性岩两大类，岩石类型有闪长岩、二长岩和花岗岩等。根据岩石化学的判别结果，侵入岩均属亚碱性系列中的钙碱性岩石，并属于普通型和钾质型     

晚更新世末期北方陆架区沙漠-黄土堆积群的初步研究

晚更新世末期,强劲古季风活动的结果,在中国西部形成沙漠-黄土堆积群(黄土高原及其以西或西北的沙漠区),当它到达陆架区以后,风蚀作用继续存在,会产生同样的地质效果,因而在中国东部陆架区,形成两个新的沙漠-黄土堆积群。其一为渤海沙漠-黄土堆积群,包括渤海海底、渤海海岸一带的古沙漠活动区和辽东半岛西岸、庙岛群岛以及山东蓬莱以西的含有孔虫的黄土沉积。其二为黄海沙漠-黄土堆积群,包括苏北浅滩和长江三角洲地区全新世以前的沙漠活动区和南京一带的下蜀黄土。