大兴安岭北段龙江盆地光华组碱流岩LA-ICP-MS锆石U-Pb年龄及其地质意义

对大兴安岭北段龙江盆地光华组碱流岩进行了岩石地球化学及锆石U-Pb年龄研究,并对其岩石成因及构造意义进行了讨论。结果表明,龙江盆地碱流岩的锆石具有典型的岩浆振荡生长环带和较高的Th/U值(0.71~2.12),反映了岩浆成因特征,LAICP-MS锆石U-Pb年龄为122.4±1.7Ma(n=19,MSWD=0.77)。岩石富硅、富碱,贫Mg、Ca;稀土元素配分曲线呈现右倾"V"字形特征,显示强烈的负Eu异常;微量元素显示具有较低的Sr和Ba丰度,以及较高的Rb、Th、U、Zr等特点。以上特征表明,龙江盆地碱流岩类似于铝质A1型花岗岩,为长英质地壳部分熔融及其后斜长石和Ti、Fe氧化物分离结晶作用的产物,代表了伸展的构造环境。     

秘鲁西北部早白垩世Oyotún组火山岩层序、年代学及地球化学特征——对古Farallon板块俯冲作用细节的揭示

Oyotún组火山岩为中安第斯西北缘中生代出露范围最广的一套火山岩,对研究中安第斯早白垩世壳幔相互作用具有重要意义。研究区西部Oyotún组火山岩出露面积小,厚度薄,岩性单一,而东部出露范围大,厚度厚,岩性复杂。LA-ICP-MS锆石U-Pb定年表明,Oyotún组火山岩时代集中在139.7~131.0Ma之间。主量元素SiO_2含量介于54.44%~72.33%之间,中等富MgO(0.56%~1.55%),偏铝-强过铝,A/CNK=0.98~3.51,富集Cs、Rb、Th、U、Pb和轻稀土元素,无明显Eu异常,亏损Nb、Ta、Ti、P等,具明显的火山弧特征。Oyotún组火山岩εHf(t)值在3.37~8.42之间,且底部εHf(t)值显著低于顶部,指示其可能形成于活动陆缘弧后伸展背景下,由亏损地幔衍生的新生玄武质下地壳,经板片流体作用而产生的低程度部分熔融过程,并受到太古宙古老陆壳物质的混染,其混染程度随时代变新而逐渐减小。     

湘北华容地区小墨山花岗岩体SHRIMPU—Pb年龄及地球化学特征

小墨山岩体侵位于中元古代冷家溪群中,由两期侵人体组成,早期为粗中粒-中粒斑状黑云母二长花岗岩;末期为细粒黑（二）云母二长花岗岩。通过锆石SHRIMPU—Pb法测得岩体侵位年龄为122．5±2．1Ma（20）,MSWD=1．9,成岩时代为早白垩世。主元素中,SiO2变化于67．20％～75．16％,K20含量高,且K2O〉Na2O,K2O／Na2O为1．16～1．72;ASI值变化于0．96～1．10之间,平均1．02,属准铝质-微过铝质、高钾钙碱性系列。岩石明显富集大离子亲石元素,亏损高场强元素,Rb／Sr=0．27～15．13;Nb／Ta=15．9～17．1,为锶和铌亏损型。EREE总体较高,重稀土含量相对较高,轻重稀土分馏稍弱,∑Ce／∑Y为0．49～6．18,（La／Yb）。为0．66～15．54。有较高的εNd（t）,为-6．8～-8．7;T2DM相对较小（1．47～1．62Ga）。综合研究表明,小墨山花岗岩石为壳源型富黑云母过铝花岗岩类（CPG）,其成因应为下地壳物质和上地壳物质混合而成,与花岗岩底侵作用或注入地壳中的幔源岩浆有关,形成的构造背景为陆内挤压造山向非造山转换的后造山拉张环境,是在紧随侏罗纪挤压造山运动之后的构造松驰和拉张减薄条件下所形成。     

Linkage of deep sea rapid acidification process and extinction of benthic foraminifera in the deep sea at the Paleocene/Eocene transition

Ocean Drilling Program Leg 199 Site 1220 provides a continuous sedimentary section across the Paleocene/Eocene (P/E) transition in the carbonate‐bearing sediments on 56–57 Ma oceanic crust. The large negative δ¹³C shift in seawater is likely due to the disintegration of methane hydrate, which is expected to be rapidly changed to carbon dioxide in the atmosphere and well‐oxygenated seawater, leading to a reduction in deep‐sea pH. A pH decrease was very likely responsible for the emergence of agglutinated foraminiferal fauna as calcareous fauna was eliminated by acidification at the P/E transition at Site 1220. The absence of the more resistant calcareous benthic foraminifera and the presence of the planktonic foraminifera at Site 1220 is interesting and unique, which indicates that calcareous benthic foraminifera suffered greatly from living on the seafloor. Box model calculation demonstrates that, assuming the same mean alkalinity as today, pCO₂ must increase from 280 ppm to about 410 ppm for the calcite undersaturation in the deep ocean and for the oversaturation in the surface ocean during the P/E transition. The calculated increased pCO₂ coincides with paleo‐botanical evidence. The current global emission rate (～7.3 peta (10¹⁵) gC/y) of anthropogenic carbon input is approximately 30 times of the estimate at the P/E transition. The results at the P/E transition give an implication that the deep sea benthic fauna will be threatened in future in combination with ocean acidification, increased sea surface temperature and more stratified surface water.     

Dating results on sedimentary quartz,bones and teeth from the Middle Pleistocene archaeological site of Coudoulous I (Lot,SW France): A comparative study between TT-OSL and ESR/U-series methods

This study presents palaeodosimetric results from the Middle Pleistocene archaeological site of Coudoulous I (Lot, SW France). Nine sedimentary quartz samples (41–60 μm) have been analyzed using a multiple aliquot protocol based on the measurement of the TT-OSL signal. In addition, 7 teeth and 7 bones have been dated by combining the ESR method with U-series analyses. Both methods gave consistent age results allowing correlation of the Early Middle Paleolithic Human occupation of the site to MIS 6 and part of the Lower Paleolithic tools to MIS 7. Beyond the establishment of a radiometric chronology for the Coudoulous I sequence, this study focuses on the information extracted from the intercomparison of the methods. Our data suggest that 1) the TT-OSL signal is stable over at least the last 230 ka (considering the age range of the studied samples), 2) there are not significant problems of incomplete bleaching leading support to the applicability of the TT-OSL technique for sedimentary deposits associated with karstic contexts. This approach highlights the interest of combining luminescence and ESR/U-series methods to discuss the reliability of the dating results.     

辽东半岛早白垩世地壳运动性质——来自兰河峪岩体的证据

通过对辽东半岛兰河峪岩体锆石SHRIMP U-Pb年龄和地球化学特征进行研究,将兰河峪岩体高钾钙碱性系列岩石形成时代归入早白垩世.本溪县兰河峪岩体形成的压力环境为0.8~1.0 GPa,推测本区的花岗岩岩浆形成时源区物质来源于30~40 km的地壳深处,地壳较薄.在花岗岩Rb-（Y+Nb）图和Y-Rb图解中,所有的样品都落入板内花岗岩区内,判断当时辽东陆块处在后造山期,岩石圈减薄环境中,反映当时处于伸展构造环境中.兰河峪花岗岩为辽东陆块在早白垩世处于伸展环境中提供了又一有利的证据.     

吉林南部义和盆地早侏罗世几种苏铁类化石及其古气候意义

报道了吉林南部早侏罗世义和植物群中的苏铁类化石3属7种,即Pterophyllum baotoum Zhang,Pterophyllum exhibens Li,Pterophyllum cf. tietzei Schenk,Pterophyllum sp.,Nilssonia inouyei Yokyama,Nilssonia orientalis Heer,Cycadolepis corrugata Zeiller.同时,讨论了苏铁类化石的古气候意义,认为吉林南部早侏罗世时期位于濒古太平洋带,气候温暖潮湿,有利于苏铁类繁茂生长.     

Cambrian trace fossils and worm like impressions from the Tal Group, Gopi-Chand-Ka Mahal section, Mussoorie syncline, Lesser Himalaya

Cambrian trace fossils and worm like impressions are described herein from the three stratigraphic units of Tal Group of rocks exposed along the track from Maldeota to Dhaulagiri in Gopi-Chand-Ka Mahal sec-tion, Mussoorie syncline. The upper 10 m thick sand-stone succession (Arenaceous Member) of Deo-Ka- Tibba Formation (lower Tal Group) contains high den-sity and low diversity Skolithos pipe rock. The Sko-lithos pipe rock in sandstone succession of Arenaceous Member (Deo-Ka-Tibba Formation) indicates shallow marine condition under sand shifting environment of deposition. Higher in the succession, in calcareous Member (Deo-Ka-Tibba Formation), Cruziana ichno-facies occurs in association with Monomorphichnus, Planolites and Paleophycus.     

内蒙古东北部阿龙山地区早白垩世A型花岗岩特征及其意义

内蒙古东北部阿龙山地区的早白垩世花岗岩岩体就位于火山喷发形成的塌陷破火山口中央或火山断裂中,岩石类型有石英二长（斑）岩、晶洞正长花岗岩、文象碱长石英正长岩等。岩石普遍具文象结构、晶洞构造,但未见碱性暗色矿物;岩石化学上具高硅、富碱和富铝、低钛镁等特征,且岩石中富集高场强元素（HFSE）,在微量元素蛛网图中出现Sr、Ba相对亏损,稀土配分曲线呈轻稀土富集的不对称右倾“海鸥”型,δEu亏损中等,岩石具较低的εNd（t）值（-3．00）和低的86Sr／87Sr初始值（0．708734）。以上岩体的岩石学、主微量元素及同位素特征表明,岩体具有铝质A1型花岗岩的特征,其成因与陆内巨量火山喷发造成的伸展、崩塌机制有关,反映了非造山板内拉张的构造环境。     

塔里木盆地西南部早白垩世风成沙丘古风向测量与古风带恢复

本文通过对塔里木盆地西南部早白垩世风成沙丘的前积层产状的测量,恢复了当时的古风向和古风带.研究结果表明:当时盛行东北风,研究区属于东北信风带,正好位于北半球中低纬度沙漠带之中.