论中国陆相侏罗系——白垩系界线

介绍了中国学者近几年在陆相侏罗系-白垩系界线研究领域的最新成果,讨论了陆相侏罗系-白垩系界线研究的原则和方法,指出了目前工作中存在的问题,初步认为在建立中国陆相中生界区域年代系统时要特别注意系、统的界线必须与国际接轨,时间上应与国际系、统界线相一致.如果国际地质科学联合会和国际地层委员会最终采用135Ma作为国际侏罗系-白垩系界线的年龄值,那么冀北-辽西地区陆相侏罗系-白垩系界线推测应在张家口组底部,与区域不整合面相一致,表明热河生物群的时代肯定为早白垩世.如果国际侏罗系-白垩系界线的年龄值将来确定为145Ma,那么冀北-辽西地区陆相侏罗系-白垩系界线推测位于土城子组的上部,意味着冀北地区缺失凡兰吟阶的地层,辽西地区可能缺失凡兰吟阶和欧特里沃阶的地层.     

青海南部金沙江缝合带二叠纪硅质岩地球化学特征及沉积环境

青海省南部扎河地区金沙江缝合带中出露的通天河蛇绿混杂岩由不同时代、不同岩性的地层断片组成.对其中的二叠纪硅质岩进行地球化学研究后发现,该地区的硅质岩SiO2含量在71.56%～88.24%之间,Al/(Al Fe Mn)平均值为0.64,MnO/TiO2平均值为0.74,ΣREE平均为138.51×10-6,稀土元素配分曲线呈平坦型,δCe为0.97～1.49,平均为1.14,无明显异常;(La/Yb)N平均值为1.85,(La/Ce)N平均值为1.08,与已知大地构造背景的硅质岩地球化学特征对比,表明其形成环境为陆间洋盆环境.因此,金沙江带不能作为古特提斯域的主缝合带.     

布卡拉曼加拉贝氏牙形石动物群在西藏日土地区的发现及其意义

布卡拉曼加拉贝氏牙形石动物群首次在西藏阿里日土县多玛区脱塔拉剖面的吞龙共巴组底部发现,主要由Rabeignathusbucaramangus,Sweetognathuswhitei,Sweetognathusironatus和Mesogondolellacf.bissilli组成,指示的地层时代为Artinskian中晚期—Kungurian早期。此前,该动物群仅发现于美国犹他州、堪萨斯州、哥伦比亚的布卡拉曼加、帕米尔东南部和中国滇西保山地区。该牙形石动物群的产出地点位于班公湖以北、龙木错以南的喀喇昆仑地层分区,跨越了班公湖-怒江断裂带北界,而这一动物群被认为是冈瓦纳北缘浅海区特有的浅水相类型,因此推测班公湖-怒江缝合带可能不是冈瓦纳大陆的北界。     

A cost–benefit appraisal of coastal managed realignment policy

European coasts are coming under increasing threat as a result of climate change from erosion and flooding. While coastal defences such as sea walls have been constructed since Roman times to protect human settlements from the sea, it is now increasingly recognised that these defences are unsustainable. The security provided by ‘hard’ engineered defences has encouraged development on the coast, and the defences themselves have led to the loss of intertidal habitat and the natural protection it provides.An alternative to maintaining ‘hard’ defences (hold-the-line) to protect land from increasing sea levels is managed realignment, where the engineered defences are deliberately breached. By allowing the coastline to recede to a new line of defence further inland, intertidal habitat is created providing natural protection from flooding and erosion.The study evaluates the economic efficiency—using cost–benefit analysis—of various managed realignment scenarios compared to a strategy of holding-the-line within the Humber estuary in North-east England. The results of this analysis show that managed realignment can be more economically efficient than holding-the-line over a sufficiently long time period—generally greater than 25 years. Sensitivity analysis demonstrates that results are more sensitive to the amount and value of intertidal habitat generated than they are to the amount and value of carbon stored by this habitat. Cost–benefit analysis is viewed as one component of a wider policy appraisal process within integrated coastal management.     

地下洞室超欠挖问题非线性有限元分析

运用数值分析的方法,采用ANSYS10.0版有限元分析程序对洞室超欠挖进行三维模拟计算,分析了不同超挖位置、超挖深度、超挖数量等对洞室围岩稳定性的影响,得出了超欠挖部位应力集中数值解及塑性区产生的影响范围,为地下工程掘进施工和初期支护设计提供重要的参考依据。     

Cenozoic volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, China： Petrochemical evidence for partial melting of the mantle-crust transition zone

Neogene volcanic rocks in the Belog Co area, Qiangtang, northern Tibet, are represented by a typical intermediate-basic and intermediate alkaline rock association, with latite-trachyte as the main rock type. The results of chemical analysis are: SiO2=52%–62%, Al2O3>15%, Na2O/K2O>1 and MgO<3.30%. In addition, the volcanic rocks are LREE-enriched with LREE/HREE=10–13, (La/Yb)N=15–19, and show a weak negative Eu anomaly with δEu=0.71–0.89. The close relationship between Mg# and SiO2 and the co-variation of the magmatophile elements and ultra-magmatophile elements such as La/Sm-La and Cr-Tb indicate that this association of volcanic rocks is the product of comagmatic fractional crystallization. The rock association type and lower Sm/Yb values (Sm/Yb=3.23–3.97) imply that this association of volcanic rocks should have originated from partial melting of spinel lherzolite in the lithospheric mantle. On the other hand, the weak negative Eu anomaly and relative depletion in Nb, Ta and Ti reflect the features of terrigenous magma. So the Neogene Belog Co alkaline volcanic rocks should be the result of partial melting of the special crust-mantle transition zone on the Qinghai-Tibet Plateau.     

龙永聚煤盆地构造演化与富煤带展布的相关性分析

通过龙永聚煤盆地构造演化及富煤带赋存层段机理分析,发现聚煤盆地构造演化与富煤带展布有一定的相关性,主要表现在一定时期、一定空间、一定样式的构造与一定层段的富煤带在走向、倾向上,具有一定的相关性,即一定的富煤带产生在一定的滑覆、推覆构造及其组合中。龙永煤田西部主要产生印支期的滑覆断层,应寻找走向上的富煤带;龙永煤田东部主要产生燕山期的推覆断层,应寻找倾向上的富煤带;龙永煤田中部主要产生印支期及燕山期的组合滑脱断层,应寻找上推下留型、上滑下留型、滑褶集中型的走向、倾向的富煤带。此项研究为龙永煤田进一步寻找富煤带指明了方向,同类型的勘探区可以参考。     

辽西朝阳地区晚侏罗世逆冲断裂及同构造沉积盆地系统

位于晚侏罗世燕山冲断带前缘拗陷盆地群东段的辽西金岭寺羊山盆地和北票盆地，形成于同沉积期的板内挤压变形。两个盆地横断面均显示出北西翼岩层陡立或倒转而南东翼平缓、以及同期碎屑堆积北西翼厚而南西翼薄的特点，具有典型的不对称结构。分别位于两个盆地北西侧的雷家营子和风凰山逆冲断裂带控制了它们的形成和演化。砾石成分统计分析显示，晚侏罗世土城子时期碎屑物质主要来源于辽西的西北部，即“内蒙地轴”上，是响应逆冲推覆活动的产物。两条断裂带及其所控制的盆地，构成了背驮式盆地构造系统，清楚地反映出这一时期的逆冲推覆扩展总体上指向SE方向。辽西地区土城子期盆地的形成和沉积充填是区域地壳缩短或增厚的重要方式之一。     

内蒙古东部重力场特征以及寻找内生矿床的意义

依据岩石密度特征，应用布格重力异常资料，在内蒙古东部地区推断7个大型岩浆岩活动区（带）。这些岩浆岩活动区（带）控制着内蒙古自治区东部地区大部分内生矿床，也就是说每一个大型岩浆岩活动区（带）实际上是一个成矿系统。因此，应用布格重力异常资料可以推断岩浆岩活动区（带），预测内生矿床，筛选化探异常。     

Bulk-rock geochemistry and plagioclase zoning in lavas exposed along the northern flank of the Western Blanco Depression (Northeast Pacific): Insight into open-system magma chamber processes

The present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the Blanco Transform Fault, Northeast Pacific. The studied area consists of a small basin, the Western Blanco Depression (WBD), extending from the southern end of the Juan de Fuca ridge to a pseudofault trace 60 km eastward. The Northern Scarp of the WBD comprises a volcanic unit overlying a sheeted-dike complex. Major and trace element data, coupled with Sr–Nd isotope ratios, reveal a two-component mantle source, composed by an isotopically depleted matrix variably veined by more enriched material. One chemical group (NS2), indistinguishable from the other Northern Scarp samples on the basis of trace element data, has an unusually depleted isotopic composition typical of a nearly pure mantle end-member. Some cogenetic samples of the Northern Scarp have been used to constrain the differentiation modalities. Anorthite and MgO content profiles in plagioclase xenocrysts and phenocrysts reveal (i) the existence of H₂O-bearing evolved melts in the mushy zones and (ii) the occurrence of mixing process between these melts and anhydrous mafic liquids. The hydration is supported by other petrographic features such as high magmatic fO₂ values, calculated from Fe–Ti oxide pairs, and the presence of pyroxene inclusions in plagioclase phenocrysts. Mixing, consistent with the existence of Ni-rich ferrobasalts, is interpreted to be the consequence of the reservoir refilling by mafic liquids (Mg# = 70). These petrological and geochemical evidences are combined with the evolution of Mg# with depth to suggest a periodic open-system magma chamber evolution beneath the southern end of the Juan de Fuca ridge.