西藏雅鲁藏布蛇绿岩形成构造环境的地球化学鉴别

本文对西藏雅鲁藏布蛇绿岩带中部日喀则地区夏鲁蛇绿岩中的基性岩石进行了元素地球化学研究。岩石为低钾亚碱性玄武质岩石,具有低TiO2(0.64%～1.5%)、低K2O(<0.69%)、富Na2O(2.5%～6.0%)、烧失量普遍较高(2.0%～7.5%)的特征,表明样品普遍遭受蚀变。岩石具有与N-MORB类似的稀土元素和总体一致的微量元素特征,但是岩石明显富集大离子亲石元素和亏损高场强元素,显示了洋脊玄武岩向着岛弧岩浆作用的过渡趋势。日喀则蛇绿岩不是典型的洋中脊成因,应为SSZ型蛇绿岩,可能形成于与洋内俯冲有关的SSZ型的弧后或者弧前盆地中。对东西延伸超过1500km的雅鲁藏布蛇绿岩246套基性岩石形成的构造环境进行的地球化学判别,表明至少存在大陆岛弧型、地幔柱-洋内热点型、洋中脊-大洋岛弧型和典型大洋岛弧型等四种类型洋壳,揭示了特提斯洋存在多种构造环境的特征,有利于恢复和还原一个长期演化的、丰富的特提斯洋。     

新疆西准噶尔巴尔努克早石炭世富Nb岛弧玄武岩的发现及其地质意义

黑山头组玄武岩-玄武安山岩组合是西准噶尔早石炭世海相火山-沉积建造的重要组成部分,其与高Mg安山岩及O型adakite共生。此次分析的所有样品均为玄武质岩石,Si O2含量为49.62%~55.68%,平均为52.70%;明显高Ti O2(1.16%~1.99%),平均为1.56%;显著富Na2O而贫K2O,Na2O为3.17%~6.35%,平均为4.90%,Na2O/K2O为1.19~26.08,绝大多数样品该比值4(平均8.93)。样品明显富集Nb、Sr、Zr等,Nb含量均7×10-6(7.29×10-6~12.32×10-6,平均为9.48×10-6);全部样品Sr均400×10-6(618×10-6~1107×10-6,平均为825×10-6);Zr158×10-6(159×10-6~217×10-6,平均为182.6×10-6);Zr/Y比值4(6.63~11.09,平均为8.62)。显著高于一般岛弧玄武质岩类。轻稀土明显富集而重稀土亏损显著,且有基本一致的弱正Eu异常。(La/Nb)PM比值0.7(1.23~2.26,平均1.94),(87Sr/86Sr)i=0.7035~0.7039;143Nd/144Nd=0.5128~0.5129;εNd(t)=5.49~7.13。这些地球化学特征与Sajona et al.(1993,1994,1996)确立的富Nb岛弧玄武岩基本一致,而与一般岛弧玄武岩有显著区别。这一发现,为确认西准噶尔早石炭世存在富Nb岛弧玄武岩提供了地球化学佐证,丰富了新疆乃至我国富Nb岛弧玄武岩的产地与层位,也为确认本区早石炭世岛弧构造环境提供了重要依据。     

Distribution of porphyry deposits in the Eurasian continent and their corresponding tectonic settings

In the Eurasian continent there are three huge metallogenic belts of Cu and Mo porphyry deposits, comprising the Paleozoic Central Asian Ore Belt in the north, the Tethyan Eurasian Ore Belt of Jurassic to Cenozoic age in the southwest, and the East Margin Ore Belt of the Eurasian Continent of Jurassic to Cretaceous age in the east. The latter is considered to be part of the vast Circum-Pacific ore belt. Some of the main features of the spatial–temporal distribution of Cu and Mo porphyry systems and related geodynamic processes of the three metallogenic belts are described. In particular, the key role of post-subduction – related porphyry ore systems is emphasized, comprising collisional and post-collisional Cu–Mo porphyry deposits during the geological history of the Eurasian continent. The recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs, and mixing with a variable amount of crustal material during magma ascent to shallower levels.     

卡拉麦里地区黑山头组火山岩地球化学特征及构造环境分析

黑山头组火山岩位于新疆东准噶尔卡拉麦里蛇绿岩带东北缘,主要为玄武岩、玄武质安山岩和安山岩,属钙碱性-高钾钙碱性系列.火山岩Mg#介于8.62～43.90,全碱含量较高(Na2O+K2O为4.19%～9.33%),且Na2O(2.20%～4.93%)>K2O(0.54%～4.40%),TiO2和P2O5含量较高(分别为0.68%～1.28%和0.10%～0.28%),轻稀土元素(LREE)相对重稀土元素(HREE)富集((La/Yb)N=1.06～3.56),无明显重稀土分馏((Gd/Yb)N=0.73～1.54),弱铕异常(δEu=0.60～1.17)和铈异常(δCe=0.89～0.95),强烈富集LILE(如Rb,Th),适度富集Ba,K等,强烈亏损HFSE(如Nb,Ta),弱亏损Zr,Hf和Ti,显示较明显TNT负异常,较高Ba/La(13.30～124.43)、Ba/Nb(11.48～161.29)和La/Nb(0.86～2.37)比值,较低的Nb/Y(0.2～0.4)、Nb/Ta(7～16)和Zr/Hf(17～37)比值.同位素年代学、地球化学特征及构造环境判别图解综合研究表明,卡拉麦里地区早石炭世岩浆活动显示板内岩浆演化特征,具弧火山岩地球化学痕迹,形成于后碰撞期伸展背景下,是软流圈物质上涌并发生部分熔融,形成岩浆在上升和侵位过程中受早石炭世弧组分混染的产物.     

江西卧龙谷花岗岩和铜厂花岗闪长斑岩的地球 化学特征及成因 ——对赣东北地区铜矿成矿地质背景的制约

赣东北地区是江南造山带东北段重要的多金属成矿区。卧龙谷花岗岩体是典型的非铜矿成矿花岗岩体,由二长花岗岩组成,其LA-ICP-MS锆石U-Pb同位素分析揭示其岩浆结晶年龄为133 Ma±1Ma,形成于早白垩世。这些岩石表现出高的初始87Sr/86Sr比值（0.716079~ 0.719392）和较低的εNd(t)（-6.51~-5.14）值,指示其岩浆起源于壳源变质沉积岩部分熔融。铜厂花岗闪长斑岩体是典型的铜矿成矿花岗岩体,主要由花岗闪长斑岩组成,形成于中侏罗世（171Ma±3Ma）,表现出很低的初始87Sr/86Sr比值（0.704403~0.704475）、较高的εNd(t)（-1.14~+1.80）和高的Mg#值（28~53）,指示铜厂花岗闪长斑岩体可能为俯冲板片和俯冲沉积物部分熔融的产物,并受到幔源物质污染。通过非铜矿成矿卧龙谷花岗岩和成矿的铜厂花岗闪长斑岩的对比,分析中生代花岗质岩浆作用对成矿地质背景的制约,为区域斑岩型铜矿找矿提供找矿标志和基础地质背景资料。     

Geologic settings of the potassium formations in the Lanping-Simao Basin,Yunnan provinceEI北大核心CSCD

The Lanping-Simao Basin is an important potash basin in western Yunnan province. In this paper, we study the potash deposit potential of the basin by systemic analysis of the tectonic evolution, paleogeography, paleoclimate, distribution of salt deposition and geochemical characteristics. The geochemical characteristics of Br and 87Sr/86Sr reflect that the salts maybe originated from sea water. Based on geological setting analysis, we suggest that the Late Triassic and Jurassic are important salt-forming eras of the Lanping-Simao Basin, and there may be a thick layer of source salt at the depth of the basin, with huge potash potential. With analysis of 87Sr/86Sr ratio, we argue that the potassium deposits in the Mengyejing area were sourced from the deep buried Mesozoic evaporate strata. We suggest that attention should be paid to the deep buried Mesozoic evaporate strata in the future potash exploration in Southwestern Yunnan.     

鄂尔多斯盆地陇东地区延长组物源区构造属性研究

鄂尔多斯盆地延长组物源区的构造属性和物源方向一直是研究热点,但存在不确定性。为加深对这一问题的理解, 文中选择陇东地区三叠系延长组长8-长6沉积期的砂岩,通过对岩矿特征以及稀土元素地球化学特征及配分模式分析,研 究了物源区的母岩构造属性及不同地区的母岩差异性。结果表明陇东地区延长组长8-长6沉积期母岩主要来自火山弧物源 区及与褶皱逆冲相关的过渡大陆物源区,但是研究区西部环县、演武地区长7-长6沉积期的部分物源还有来自稳定克拉通 的陆块物源区,展示出差异性。砂岩稀土元素丰度分析发现,轻稀土元素相对富集,重稀土元素相对亏损,Eu元素负异 常,反映源区主要与花岗质地壳物质有关,以含较多的长英质岩性为特征。将陇东地区东北部、西北部、西南部、南部的 样品与盆地周缘古陆各类岩石的稀土元素配分模式进行了对比,发现稀土元素配分模式既普遍具有右倾的特征,又具有一 定的差异性,各地区样品稀土元素配分模式均能与盆地周缘古陆匹配良好,反映了母岩来源与构造属性的差异性。     

东海陆架盆地西湖凹陷新生代反转构造样式及其形成机制初探

通过对东海陆架盆地西湖凹陷十多条地震剖面的精细解释,发现西湖凹陷自晚白垩世以来,经历了早期的拉张和晚期的断续挤压两个构造演化阶段.晚期的断续挤压在凹陷内产生构造反转的样式复杂多样,可划分为上下均正型、下正上逆型、下凹上凸型、上下均凸型、下正上隆型和下隆上逆型等6种单个的反转构造样式及y形、帚状、"似花状"等7种反转构造组合样式.对反转断层生长指数（G_i）并结合平衡剖面的研究,表明西湖凹陷新生代经历了多期构造反转.通过计算反转率（R_i）,发现凹陷内反转程度存在明显的不均一性,具有中带强和东、西弱的特征.结合晚白垩世以来东亚大陆边缘的区域构造演化及新生代以来太平洋板块相对欧亚板块的俯冲速度讨论了西湖凹陷构造反转的机制,并探讨了它对油气勘探的意义.     

Lipid Biomarkers and Their Stable Carbon Isotopes inAncient Seep Carbonates from SW Taiwan,China

Four massive brecciated, chimney-like, and slender pipe network carbonate samples(JA-4, JA-5, JX-8 and BG-12) were collected from southwestern Taiwan, which were suggested to have formed as a result of anaerobic oxidization of methane(AOM). Considering that the environmental conditions of the carbonates precipitation and the sources of carbon and organic matter need to be further declared, molecular fossils and compound-specific carbon isotopic investigations of the carbonates were conducted in this study. According to lipid biomarkers of 2,6,10,15,19-pentamethyleicosane(PMI) and squalane diagnostic to methanotrophic archaea, as well as the extremely low δ¹³C values(as low as -1¹³.4‰) detected in samples JA-4, JA-5 and JX-8, these carbonates were revealed to be a result of AOM. Based on the varied δ¹³C values of characteristic archaea biomarkers in specific samples, biogenic methane was proposed to be responsible for the formation of samples JA-4 and JA-5, whereas a mixed carbon source of ¹³C-depleted methane and ¹³C-enriched residual CO_2 from methanogenesis was suggested for the carbonate of JX-8 due to the co-occurrence of a highly positive δ¹³ C_carb value(+8‰) and a moderate ¹³C depletion of PMI. The low content of AOM-related biomarkers and the absence of indicators for ANME-2 suggested that these carbonates were formed in weak seep settings. By comparison, no typical lipid biomarkers for methanotrophic archaea was detected in carbonate BG-12. The short-chain and long-chain n-alkanes accounted for 30% and 45% of all hydrocarbons, respectively, with a CPI value of 1.2, suggesting that the n-alkanes were derived from both marine organisms and terrestrial inputs. A low thermal maturity could be revealed by the incomplete equilibrium value of the C³¹αβ 22S/(22S+22R) ratio(0.5), and the carbonate BG-12 was probably deposited in a suboxic condition indicated by a value of Pr/Ph ratio(2.5).     

花岗岩大地构造研究的若干重要问题

宇宙星球中只有地球发育花岗质岩石及广义的花岗岩,它是大陆最主要的组成。因此,花岗岩在固体地球科学研究中具有举足轻重的意义。对此,作者提出花岗岩大地构造,其基本研究内容可概括为物理特性（构造）、物质组成（岩石地化）和年代学三大方面。文章在已有的初步论述基础上,进一步阐述了以下若干研究方面的进展、问题和发展方向:花岗岩岩石组合及其构造背景与环境厘定;花岗岩演化及其构造环境与演化（构造过程）;花岗岩变形、壳内流变及构造动力学意义;花岗岩深部物源填图与造山带及地壳生长。花岗岩大地构造是从花岗岩角度,探索解决大地构造问题,丰富大地构造研究内容,是当今地球科学学科交叉、融合发展的必要。