Insights into the complexity of crustal differentiation: K2O‐poor leucosomes within metasedimentary migmatites from the Southern Marginal Zone of the Limpopo Belt,South Africa          下载免费PDF全文

G. Nicoli  G. Stevens  J‐F. Moyen  A. Vezinet  M. Mayne 《Journal of Metamorphic Geology》2017,35(9):999-1022

Differentiation of the continental crust is the result of complex interactions between a large number of processes, which govern partial melting of the deep crust, magma formation and segregation, and magma ascent to significantly higher crustal levels. The anatectic metasedimentary rocks exposed in the Southern Marginal Zone of the Limpopo Belt represent an unusually well‐exposed natural laboratory where the portion of these processes that operate in the deep crust can be directly investigated in the field. The formation of these migmatites occurred via absent incongruent melting reactions involving biotite, which produced cm‐ to m‐scale, K₂O‐poor garnet‐bearing stromatic leucosomes, with high Ca/Na ratios relative to their source rocks. Field investigation combined with geochemical analyses, and phase equilibrium modelling designed to investigate some aspects of disequilibrium partial melting show that the outcrop features and compositions of the leucosomes suggest several steps in their evolution: (1) Melting of a portion of the source, with restricted plagioclase availability due to kinetic controls, to produce a magma (melt + entrained peritectic minerals in variable proportions relative to melt); (2) Segregation of the magma at near peak metamorphic conditions into melt accumulation sites (MAS), also known as future leucosome; (3a) Re‐equilibration of the magma with a portion of the bounding mafic residuum via chemical diffusion (H₂O, K₂O), which triggers the co‐precipitation of quartz and plagioclase in the MAS; (3b) Extraction of melt‐dominated magma to higher crustal levels, leaving peritectic minerals entrained from the site of the melting reaction, and the minerals precipitated in the MASs to form the leucosome in the source. The key mechanism controlling this behaviour is the kinetically induced restriction of the amount of plagioclase available to the melting reaction. This results in elevated melt H₂O and K₂O and chemical potential gradient for these components across the leucosome/mafic residuum contact. The combination of all of these processes accurately explains the composition of the K₂O‐poor leucosomes. These findings have important implications for our understanding of melt segregation in the lower crust and minimum melt residency time which, according to the chemical modelling, is <5 years. We demonstrate that in some migmatitic granulites, the leucosomes constitute a type of felsic refractory residuum, rather than evidence of failed magma extraction. This provides a new insight into the ways that source heterogeneity may control anatexis.  相似文献   

国内外岩溶塌陷监测方法综述   总被引：3，自引：0，他引：3       下载免费PDF全文

吴亚楠  周绍智  王延岭  焦玉国  陈伟清  程凤  赵志伟 《山东国土资源》2018,34(12)

岩溶塌陷是全球广泛分布的地质灾害问题,严重影响和制约了岩溶地区社会、经济发展,因此,开展岩溶塌陷监测工作,对塌陷预测预报具有及其重要的作用。岩溶塌陷的监测技术与塌陷形成的机理关系密切。该文分析了岩溶塌陷的分布规律和形成的条件,系统总结了国内外岩溶塌陷的监测内容、技术方法、各自优缺点,如BOTDR监测、TDR监测、地质雷达监测、水动力条件监测及地-沉降等方法,为系统性地开展岩溶塌陷监测工作提供技术和方法参考,展望了未来的岩溶塌陷监测工作,认为岩溶塌陷监测需结合塌陷的形成机理、塌陷地区覆盖层特征及水动力条件,综合利用多种监测手段联合进行,并形成完善的监测网络。  相似文献   

Dating the onset of Lower Tagus River terrace formation using electron spin resonance          下载免费PDF全文

PIERLUIGI ROSINA  PIERRE VOINCHET  JEAN‐JACQUES BAHAIN  JORGE CRISTOVÃO  CHRISTOPHE FALGUÈRES 《第四纪科学杂志》2014,29(2):153-162

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Distribution of continental red paleosols and their forming mechanisms in the Late Cretaceous Yaojia Formation of the Songliao Basin, NE China     

Xuebin Du  Xinong Xie  Yongchao Lu  Jianye Ren  Shun ZhangPenglin Lang  Tao ChengMing Su  Cheng Zhang 《Cretaceous Research》2011,32(2):244-257

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川中地区上三叠统须家河组气田异常高压演化研究   总被引：1，自引：0，他引：1  

马德文  邱楠生  谢增业  许威 《沉积学报》2011,29(5):953-961

根据川中地区上三叠统须家河组典型气田的现今实测地层压力分析了异常高压发育的特征。以现今实测压力为约束,利用流体压实耦合方法恢复了须家河组气田主要储层的压力演化史。研究结果表明：上三叠统须家河组储层超压的发育在总体上是逐渐增大的,其地层压力演化可划分为三个阶段：（1）150 Ma之前为常压阶段,地层压力等于静水压力;（2...  相似文献   

聚油古地貌成因类型及其有利成藏条件分析——以鄂尔多斯盆地上里塬地区前侏罗纪古地貌为例   总被引：1，自引：0，他引：1  

李树同  张海峰  王多云  陶辉飞  楚美娟  陈丹丹 《沉积学报》2011,29(5):962-969

运用地层厚度印模法（延9＋延10＋富县组地层厚度）恢复出了陇东上里塬地区前侏罗纪古地貌形态,其形态为一级甘陕古河呈近东西向分布,二级庆西古河位于研究区南部向北注入甘陕古河,研究区的北部和南部分别发育姬塬和演武高地,在高地和河谷的过度带分别发育姬塬南斜坡和演武北斜坡,此外,在一级河谷中央还发育有河间丘,在斜坡上发育残丘、...  相似文献   

河南桐柏吴城碱矿定向水平对接采卤井堵漏工艺可行性分析          下载免费PDF全文

唐孟龙  崔桂平  邹柒庚 《探矿工程》2011,38(11):27-31

河南桐柏吴城碱矿采卤生产井堵漏问题一直困扰着该地区采卤井钻井速度,多年来未取得突破性进展。经过在SP08井现场进行水泥注浆堵漏试验,得出该地层漏失特性为遇水可溶的裂缝性漏失。根据这个特性,结合室内试验,从堵漏材料选择、工艺两方面较为系统地总结出该地区堵漏技术,制定出以高失水材料为主,配合桥堵材料综合技术措施及承压工艺方法。为今后该矿区快速、高效堵漏提供了有效的技术支持。  相似文献   

地层温度对科学超深井井壁稳定的影响          下载免费PDF全文

张培丰 《探矿工程》2011,38(10):1-5

井壁稳定问题包括井壁坍塌和地层破裂2种基本类型,科学超深井钻探的目的层是处于高地应力、高地温和高地层压力的深部岩层,井壁稳定问题更加突出。以12000 m科学超深井为例,从地层温度入手,分析钻井液循环温度变化所引起的当量静态钻井液密度和环空压力当量密度的变化,以及温梯应力、温差应力对井壁稳定的影响。  相似文献   

破碎地层孔壁稳定技术的探讨与实践          下载免费PDF全文

胡继良  陶士先  纪卫军 《探矿工程》2011,38(9):30-32,64

在破碎地层钻探施工中,提高破碎带地层破碎岩块之间的胶结力、快速封堵地层裂缝形成完整孔壁及适当的冲洗液密度是破碎地层孔壁稳定的关键。防塌型随钻堵漏剂、改性沥青的加入能有效封堵地层裂缝,提高孔壁承压能力。LBM冲洗液体系和接枝淀粉冲洗液体系具有良好的造壁性能和流变性能,在破碎地层施工中取得良好的使用效果。  相似文献   

栾川县多金属矿复杂地层岩心钻探技术          下载免费PDF全文

李振学  邓敏 《探矿工程》2011,38(9):56-59,95

栾川县多金属成矿区处于马超营大断裂带中,区内4条大断裂横贯全区,主、次级构造极为发育。因碎裂蚀变带、泥质砂砾岩等松散破碎地层而引发的孔内坍塌、取心困难等钻进难题此起彼伏,软硬互层变化频繁,对钻头要求高、选择性强。而且钻孔结构复杂,生产效率难提高,多数钻孔施工中均出现程度不同的夹钻、埋钻、断钻、烧钻等孔内事故,给钻探施工带来很大困难。通过改善冲洗液性能、采用JS122绳索取心钻具,并进行钻头与地层适应性研究,取得了较好成效。  相似文献