辽宁花坤头营子旋卷构造中侵入岩特征与构造演化的关系

花坤头营子侵入岩是花坤头营子旋卷构造的重要组成部分,共分出4个侵入体,分别为早石炭世辉绿岩、早三叠世闪长岩、中侏罗世二长花岗岩、早白垩世花岗斑岩,最晚还有一期流纹斑岩脉侵入.岩浆来源除早石炭世辉绿岩来自上地幔,余下几个序次来源于下地壳,并熔融了部分陆壳物质.以被动就位机制为特征.     

扬子西北缘碧口微地块南华系碎屑锆石物源示踪及其地质意义

扬子板块西北缘碧口微地块华严寺地区碧口群之上发育一套含砾沉积地层,其确切沉积时限对研究该区域的沉积—构造演化具有重要意义。本文对该套地层中的2件砂岩样品进行了碎屑锆石LA-ICP-MS U-Pb测年分析,结果显示,锆石晶型较好,无色透明,磨圆度较差,具典型岩浆生长振荡环带和韵律结构,Th/U比值为0.28~3.6,锆石U-Pb年龄介于706~2489 Ma之间。存在3个主要的年龄组：新元古代年龄组（706~951 Ma）,占92.9%,显著峰值为850 Ma和843 Ma;中元古代年龄组（1017~1080 Ma）,占2.6%;古元古代年龄组（1628~2489 Ma）,占4.5%。最小年龄组为706~715 Ma（峰值为711 Ma）,结合区域地质和研究资料,华严寺地区沉积地层时代应属于南华纪,沉积时限约为720~635 Ma,物源区主要包括扬子板块西北缘碧口微地块以及南东侧的后龙门山构造带和汉南—米仓山微地块。新元古代晚期碧口微地块及扬子板块西北缘后碰撞—裂解阶段,华严寺地区南华纪沉积为碧口微地块及邻区新元古代岩浆岩在边缘裂谷环境中快速堆积形成。

     

辽宁北部早古生代弧－陆碰撞作用的发现及其构造意义

自然资源部中国地质调查局沈阳地质调查中心基础地质室构造研究团队在辽宁北部法库地区地质调查过程中,初步识别出了一次弧－陆碰撞作用.根据地质年代学研究,其主要发生在早古生代.该发现为华北板块北缘东段松辽盆地覆盖区的早古生代的构造演化史研究提供重要依据.     

华北板块北缘勃隆克A型花岗岩锆石U-Pb定年及其地质意义

内蒙古翁牛特旗勃隆克岩体位于华北板块北缘,侵位于上侏罗系火山岩地层中。详细的岩相学研究显示,勃隆克花岗岩具有粒状结构、蠕虫结构和文像结构,块状构造,部分斜长石已绢云母化、泥化。对勃隆克花岗岩进行了LA-ICP-MS锆石U-Pb定年,获得134.0±1.8Ma和134.9±4.1Ma的侵位年龄,表明其形成于早白垩世。地球化学特征显示,花岗岩属于高钾钙碱性系列,有较高的SO2（74.1%~75.6%）、Na2O+K2O（8.98%~9.2%）、Rb（210×10-6~225×10-6）含量和10000×Ga/Al（2.69~2.80）、Rb/Sr（5.8~18.9）值,具有较低的CaO、MgO、Ba和Sr含量。铝饱和指数A/CNK=0.99~1.03,属于偏铝质或过铝质A型花岗岩。稀土元素球粒陨石标准化图解显示,轻稀土元素相对富集,负Eu异常明显;在原始地幔标准化图解上,Ba、Sr、Nb、Ta、P、T强烈亏损,富集Rb、Th、K、Hf等元素,与华北板块北缘早白垩世A型花岗岩类似。结合区域构造演化,认为勃隆克花岗岩形成于伸展构造背景。晚中生代,华北板块北缘构造体制经历了重大的转变,地壳从挤压体制转为岩石圈减薄和地壳伸展体制,软流圈物质上涌导致上覆地壳长英质物质的部分熔融形成勃隆克A型花岗岩。     

内蒙古盘羊山逆冲推覆构造系统的组合特征

通过1/25万四子王旗幅的野外地质填图,在蒙古寺-盘羊山-乌兰合雅一线存在古生代末大型逆冲推覆构造系统,新太古代色尔腾山岩群和新太古代花岗岩自北向南被逆冲推覆于震旦系什那干组灰岩和古生代碎屑岩之上,并形成大小规模的飞来峰和构造窗.整个推覆系统由顶板逆冲断层与底板逆冲断层及夹于其中的一套叠瓦式逆冲断层和断层夹块组合而成,构成典型的双重逆冲推覆构造系统(Duplex).该逆冲推覆构造总体逆冲方向指向南南西向,形成时代为二叠纪末,估算推覆距离应大于7.1 km.此逆冲推覆构造与华北板块与西伯利亚板块在二叠纪末陆内碰撞造山有关,是华北板块北缘造山带的重要组成部分.     

双地震带的影响因素探讨

讨论了全球39个俯冲带内的双地震带层间距、应力类型与俯冲参数的相互关系,这些俯冲参数包括动力学参数(板块年龄、热参数、板片拉力)、运动学参数(俯冲板块速度、上覆板块运动速度、海沟迁移速度、弧后形变特征)、几何形态参数(浅俯冲角、深俯冲角、俯冲深度、长度)及上覆板块性质等. 结果表明:(1)I型双地震带易形成于年龄较古老(>60 Ma)的俯冲板块,其层间距主要与动力学参数有关;(2)II型双地震带出现在较年轻(<60 Ma)的板块,其层间距及应力状态更容易受局部应力场的影响;(3)当热参数大于5000 km时仅能形成I型双地震带,而当热参数小于5000 km时,两类双地震带都能形成;(4)上覆板块的性质似乎决定着双地震带层间距的上下限,其中大陆型上覆板块所对应的双地震带层间距小于20 km;而海洋型对应DSZ层间距则大于15 km. 限于现有的观测条件,本文基于有限样本的统计结果仍需要进一步验证.     

大地震的18.6年周期

将全球分为15个研究区,用1900~2009年MW≥7.0地震目录,统计分析了各区大地震与月球交点运动周期的关系,得出15个研究区中有10个区,大地震存在统计意义上的18.6 a周期:活跃段为12.4 a,平静段为6.2 a;环太平洋地震带北、南、西、东4大区的大地震,不仅有这样的周期,而且其地震活跃段的时间存在一定规律.用第6个18.6 a(1991~2009年)期间的大地震,检验据前5个18.6 a(1900~1990年)地震目录所得18.6 a 周期的稳定性和实用性,发现有这种周期的地区多数的周期性是稳定的.大地震18.6 a周期的可能成因有: (1)18.6 a潮波通过调制日潮和半日潮调制大地震; (2)上地幔内流体的潮汐(地内潮)作用; (3)18.6 a潮波通过影响地球自转变化调制大地震.     

利用海洋重力场变化分析洋底板块运动

洋底板块运动是地球动力学和全球变化研究的重要内容.本文根据质量迁移与地球外部重力场变化的对应关系,利用不同时期测高资料推算的1995—2019全球海洋重力场变化结果,反演分析全球洋底板块运动特征.研究表明,板块汇聚边界、板块内无震海岭、海山群、断裂带等区域重力异常变化显著,而在板块离散边界无明显变化趋势;西南印度洋中脊、大西洋中脊、中印度洋中脊等地区重力异常垂直梯度变化显著,且在西太平洋俯冲带、部分海岭区域也存在明显变化,其空间分布与地形基本吻合.海洋重力场变化整体上准确反映了全球洋底板块构造运动.相较于重力异常变化反演结果,重力垂直梯度的变化能够更为准确地反映洋底板块运动特征,特别是在洋中脊区域,扩张速率越小,垂直重力梯度变化越显著.此外,详细讨论了测高海洋重力场不确定因素对洋底板块运动分析结果的影响,海面坡度改正是主要因素之一.

     

Fairtrade bananas in the Caribbean: Towards a moral economy of recognition

Working through a Caribbean case study, this paper examines the networks and associations of Fair Trade bananas as they move both materially and morally from farms in St Vincent and the Grenadines to supermarkets and households in the United Kingdom. In doing so, the paper provides grounded empirical evidence of Fair Trade’s moral economy as experienced by banana producers in the Caribbean. The paper follows Nancy Fraser’s distinction between ways of framing justice to argue that, in order to transcend its complex postcolonial positionalities, the Fair Trade Foundation needs to include recognition in its moral economy as well as representation and redistribution. The paper compares the moral framework of Fair Trade as an ideology and social movement with the lived experience of certified Fairtrade banana farmers in the Windward Islands who work mostly for, rather than within, an idealized moral economy. The paper also contributes to several recent debates in the agri-food literature exploring the interconnections between production and consumption, the role of materiality in contemporary food networks, the historical and (post)colonial nature of food moralities, and links between political and moral economies of food. Following an outline of recent debates about the moral economies of food and its relation to Fair Trade as a movement, the paper dissects the moral economy of the Fairtrade Foundation, highlighting the historical and geographical, material and symbolic, gendered and generational ways that food producers in the Global South (in this case, banana farmers in St Vincent and the Grenadines) may be counterposed to ‘responsible’ consumers in the Global North. Despite the good intentions of those who promote the Fair Trade movement through the Fairtrade Foundation and the Fairtrade Labelling Organisation (FLO), our case study reveals a moral economy of non- (or partial) recognition, which has a range of unintended consequences and paradoxical effects.     

Geochemistry and Petrogenesis of Intracontinental Basaltic Volcanism on the Northwest Arabian Plate,Gaziantep Basin,Southeast Anatolia,Turkey

Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel–peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightly contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their ~(87) Sr/~(86) Sr and ~(143) Nd/~(144) Nd isotopic compositions in addition to their classifications based on their chemical compositions(alkaline and calc-alkaline). These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone.