Application of instantaneous amplitude gradient for ground penetrating radar signal analyses

Ground penetrating radar (GPR) is an effective geophysical method for environmental and engineering exploration. However, significant background interference occurs around most work sites, which increases the difficulty of analyzing and interpreting GPR profiles. For time-distance profile analyses, more accurate results can be obtained using the instantaneous parameters of the analytic signals. In this study, these instantaneous parameters are extracted and compared using 1D model waveform and 2D model strong interference profiles. The results show that the instantaneous amplitude gradient effectively reflects the model information, even under strong interference. The instantaneous amplitude gradient is applied to GPR survey data from a study site, and the results indicate that the technique reflects the underground structure information of the survey area. Drilling verification further confirms that the instantaneous amplitude gradient accurately reflects the underground structure information.     

嫩江科洛地区晚侏罗世深熔花岗岩对嫩江-黑河构造带的响应

通过对嫩江-黑河构造带内的岩石建造研究,在嫩江科洛地区识别出一套深熔花岗岩体,岩石宏观上为一套具非典型花岗岩结构的深熔型侵入岩,具交代结构、斑杂状构造和眼球状构造。对深熔花岗岩进行了锆石LA-ICP-MS U-Pb年龄测试,获得了3组不谐和的U-Pb年龄: 390 Ma、157~163 Ma和113 Ma。其中,113 Ma年龄代表了岩石遭受后期变质热事件年龄; 157~163 Ma的年龄代表了原岩结晶年龄。综合分析深熔花岗岩成因,认为其主要与嫩江-黑河断裂深部韧性剪切热效应作用下发生的深熔有关,深熔花岗岩的划分和厘定为深入研究嫩江-黑河断裂带在中生代的活动提供了新的素材。     

吉林永吉县头道沟地区镁铁—超镁铁质岩U-Pb年代学研究及地质意义

吉林省永吉县头道沟地区出露许多与头道沟岩组相伴产出的镁铁—超镁铁质岩,鉴于其处于长春-延吉构造带附近而受到业内关注,但由于缺少高精度年代学资料,制约了对区域大地构造的深入研究。本文采用锆石U-Pb(LA-ICP-MS)方法,对镁铁—超镁铁质岩进行了年代学研究。变质辉绿岩年龄为270±5 Ma,变质橄榄岩中捕获锆石最小年龄为297 Ma,考虑岩石组合及二者紧密相伴产出,认为二者均形成于中二叠世。镁铁—超镁铁质岩中捕获的锆石记录了华北克拉通及其北缘多次重要的构造热事件。其中,变辉绿岩中获得446±6 Ma的年龄与变质橄榄岩中获得的不一致线下交点434±240 Ma年龄共同对应了华北克拉通北缘早古生代的重要构造岩浆热事件;大量的1.8~2.4Ga年龄对应古元古代辽吉造山带热事件;1377 Ma、1542 Ma与蓟县系建造时代对应;869~997 Ma与青白口系建造时代对应;在变质辉绿岩中还存在众多3.0~3.2Ga锆石年龄。分析上述年龄结构及龙岗陆块北缘古生代地质体分布特征,推测研究区深部可能存在古老的变质基底,同时也表明研究区出露的镁铁—超镁铁质岩形成于陆内构造环境,而非蛇绿岩的组成成分,这对深化区域大地构造研究具有重要意义。     

Apatite-hosted melt inclusions from the Panzhihua gabbroic-layered intrusion associated with a giant Fe–Ti oxide deposit in SW China: insights for magma unmixing within a crystal mush

The ～?2-km-thick Panzhihua gabbroic-layered intrusion in SW China is unusual because it hosts a giant Fe–Ti oxide deposit in its lower zone. The deposit consists of laterally extensive net-textured and massive Fe–Ti oxide ore layers, the thickest of which is ～?60 m. To examine the magmatic processes that resulted in the Fe enrichment of parental high-Ti basaltic magma and the formation of thick, Fe–Ti oxide ore layers, we carried out a detailed study of melt inclusions in apatite from a ～?500-m-thick profile of apatite-bearing leucogabbro in the middle zone of the intrusion. The apatite-hosted melt inclusions are light to dark brown in color and appear as polygonal, rounded, oval and negative crystal shapes, which range from ～?5 to ～?50 µm in width and from ～?5 to ～?100 µm in length. They have highly variable compositions and show a large and continuous range of SiO₂ and FeO_t with contrasting end-members; one end-member being Fe-rich and Si-poor (40.2 wt% FeO_t and 17.7 wt% SiO₂) and the other being Si-rich and Fe-poor (74.0 wt% SiO₂ and 1.20 wt% FeO_t). This range in composition may be attributed to entrapment of the melt inclusions over a range of temperature and may reflect the presence of µm-scale and immiscible Fe-rich and Si-rich components in different proportions. Simulating results for the motion of Si-rich droplets within a crystal mush indicate that Si-rich droplets would be separated from Fe-rich melt and migrate upward due to density differences in the interstitial liquid when the magma unmixed. Migration of the Si-rich, immiscible liquid component from the interstitial liquid caused the remaining Fe-rich melt in the lower part to react with plagioclase primocrysts (An_59–60), as evidenced by fine-grained lamellar intergrowth of An-rich plagioclase (An_79–84)?+?clinopyroxene in the oxide gabbro of the lower zone. Therefore, magma unmixing within a crystal mush, combined with gravitationally driven loss of the Si-rich component, resulted in the formation of Fe-rich, melagabbro and major Fe–Ti oxide ores in the lower part and Si-rich, leucogabbro in the upper part of the intrusion.     

Zircon U–Pb–Hf isotopes and geochemistry analyses of the Huyu igneous rocks in northwestern Beijing,China: possible new evidence for the initial destruction of the North China Craton

The timing and extent of cratonic destruction are crucial to understanding the crustal evolution of the North China Craton (NCC). Zircon U–Pb–Hf isotope data and the whole-rock major and trace element characteristics of the Huyu igneous rocks in northwestern Beijing, China, provide possible new evidence for the initial destruction of the NCC. The igneous rocks occur as several sills and dikes, including lamprophyre, monzonite porphyry, and aplite. The lamprophyres have high Mg^# and K₂O contents. The monzonite porphyries have high Mg^#, high K₂O contents, and negative ε_Hf(t) values with zircon U–Pb ages of 225.5–227.7 Ma. These two types of rocks are both enriched in large ion lithosphere elements (LILEs) and light rare earth elements (LREEs) but are depleted in high field strength elements (HFSEs) and high rare earth elements (HREEs) and have almost no Eu anomalies and relatively high total rare earth element (ΣREE) contents. In contrast, the aplites exhibit high silica and K₂O contents, low MgO contents, and more negative ε_Hf(t) values with a zircon U–Pb age of 206.2 Ma. The aplites are also enriched in LILEs and LREEs but are depleted in HFSEs and HREEs, with strongly negative Eu, Ti, P, La, Ce, and Sr anomalies and relatively low ΣREE contents. These results indicate that the lamprophyres and monzonite porphyries represent a continuous cogenetic magma evolution series after melt derived from an enriched metasomatized lithospheric mantle experienced crust assimilation and fractional crystallization. The aplites were produced by the fractional crystallization of low-Mg parental magma derived from melting of the ancient Archaean crust. The occurrence of the Huyu intrusive rocks with many other plutons of similar ages on the northern margin of the NCC suggests that the northern NCC entered an intraplate extensional tectonic environment in the Late Triassic.     

安徽省凤阳江山金矿床赋矿地层和相关岩浆岩锆石年代学研究及其意义

安徽省北部蚌埠隆起区被认为是山东胶东招远金成矿带以西的延伸部分,但蚌埠隆起区内之前一直未发现成规模的金矿床。江山金矿床是最近新发现的中型金矿床,区内成矿作用的时代、赋矿地层的归属仍缺乏系统的年代学证据。文章对蚌埠隆起区内江山金矿床的赋矿地层和相关岩浆岩开展系统的年代学研究,明确了赋矿地层时代归属,并限定了成矿时代的上限和下限。矿床赋矿围岩浅粒岩的结晶年龄为(2496±19)Ma,变质年龄为(2452±47)Ma;斜长角闪岩的变质年龄为(1824±11)Ma,对比区域地层岩性和时代,确定矿床的赋矿围岩为新太古代五河群西堌堆组,而非过去认为的庄子里组。矿床中穿切矿体的脉岩花岗闪长斑岩的结晶年龄为(121.2±1.4)Ma,代表成矿时代的下限;赋矿岩体巨斑花岗斑岩的结晶年龄为(128.3±1.7)Ma,代表了成矿时代的上限。通过与胶东金成矿带的对比,认为蚌埠隆起区与胶东地区的前寒武纪变质基底演化历史相似,江山金矿床的成矿作用类型属于胶东焦家式金矿,在此基础上,推测蚌埠隆起区西芦山岩体和淮光岩体有较大的成矿潜力。     

基于主成分分析的青藏高原多年冻土区高寒草地土壤质量评价

土壤质量评价是提高对土壤质量理解的关键环节。为了了解青藏高原多年冻土区高寒草地土壤质量的基本情况,在青藏高原腹地西大滩至安多地区,根据不同海拔梯度和植被盖度共采集了154个土壤样品。通过主成分分析（PCA）法确定了影响青藏高原多年冻土区高寒草地土壤质量的最小数据集（MDS）：全氮、全磷、全钾。根据影响土壤质量的最小数据集对青藏高原多年冻土区高寒草地土壤质量进行评价,得出了不同海拔、不同植被盖度下的土壤质量指数（SQI）。通过对不同海拔、不同植被盖度的土壤质量指数进行对比研究表明：随着海拔的升高,SQI呈增加的趋势,即海拔4 300～4 600 m（0.270±0.043） < 海拔4 600～4 900 m（0.326±0.061） < 海拔4 900～5 200 m（0.410±0.075）;随着植被盖度的增加,SQI也呈现增加的变化趋势,即植被盖度小于50%（0.262～0.265） < 植被盖度大于50%（0.336～0.344）。在分别考虑了有机质、盐分、土壤水分对土壤质量的影响下得出的土壤质量指数值与基于最小数据集得到的土壤质量指数相一致,说明基于主成分分析的最小数据集可以对青藏高原多年冻土区高寒草地土壤质量做出较准确的评价。     

南岭东部定南大湖沉积物粒度敏感组分及末次冰消期环境记录

为进一步探究定南大湖湖沼晚冰期以来的水文特征及气候变化,对研究区K02钻孔的粒度特征进行了详细的分析,采用粒级-标准偏差法和主成分分析法对348个沉积样品提取了对环境变化比较敏感的三个粒级组分:0.6~7.1 μm（组分1）,20~44.8 μm（组分2）和89.3~447.7 μm（组分3）。结合湖泊沉积物粒度一般分布规律,并根据敏感组分2和14C测年数据探讨了该区域近16 ka B.P.以来的气候变化。结果表明在过去的16 000年里,大湖地区的水文及气候变化可以分为4个阶段:1）在16.0~11.5 ka B.P.期间,气候总体偏冷干,敏感组分含量增降比较明显,能较好的对应老、中、新仙女木事件和B/A暖期;2）11.5~6.0 ka B.P.期间,大湖地区进入了湿润的全新世适宜期,敏感组分总体含量偏低;3）6.0~3.8 ka B.P.期间,敏感粒度组分含量迅速升高且波动较大,大湖湖沼地区进入一个相对干冷的时期;4）3.8 ka B.P.至今为第四阶段,敏感粒度组分含量总体偏低,考虑到人为干扰因素,暂不做详细讨论。通过对大湖地区水文状况的研究发现,大湖湖沼地区自晚冰期以来气候变化很不稳定。与格陵兰GISP 2冰芯、董哥洞D4石笋及其K02钻孔其他指标的记录对比可以发现,敏感组分2对仙女木、9.5 ka、8.2 ka等冷事件的记录更加明显,也说明了大湖地区的气候变化具有全球性,这种气候变化可能与太阳活动有关。     

青藏铁路对西藏各经济部门发展影响的定量评估

青藏铁路对西藏经济发展影响重大,定量评估其对各经济部门发展的影响程度,是全面评价铁路交通基础设施效益、分析未来冰冻圈变化对线性工程及经济社会重大影响的基础。将灰色关联分析法与投入产出法相结合,既填补了关联度分析的黑箱式缺陷,又弥补了西藏投入产出调查缺乏长时间序列数据的问题,以此来认识青藏铁路对西藏经济发展的影响机理与路径。以2006-2016年统计数据为基础,采用灰色关联度模型计算青藏铁路与西藏各经济部门发展的灰色关联度值,表明铁路运输水平与西藏地区生产总值（GDP）、第三产业高度相关,其中与货运邮电业、住宿餐饮业两个部门关联度达到了0.9以上。在灰色关联度结果的基础上,运用西藏2012年投入产出表及投入产出模型计算铁路的直接作用,以及对各经济部门的间接波及作用,研究发现：青藏铁路建设及运营的劳动密集程度高,且通过灰色关联度较高行业的产品及服务影响其他行业,以直接作用、后向和前向波及作用、消费波及作用三种路径对区域经济的发展产生重要影响,扣除消费波及作用的总体贡献达到41.7亿元,相当于2012年西藏GDP的5.95%。由于铁路交通基础设施重要的直接作用及间接波及作用,建议在工程条件适宜地区加快铁路运输网络建设,同时,将工程设施的社会经济效益纳入冰冻圈服务功能核算中。     

渤海湾盆地济阳坳陷碎屑锆石裂变径迹年龄记录的构造抬升事件

对采自渤海湾盆地东南部济阳坳陷的碎屑岩进行测年研究,目的是通过碎屑锆石裂变径迹年龄揭示源区及其抬升剥露史和构造热事件,为华北克拉通构造演化特别是元古宙构造演化提供新的热年代学约束。14件上白垩统-上新统砂岩/粉砂岩岩心样品测年结果显示,锆石裂变径迹年龄分布在308±35Ma~145±19Ma之间,且所有单颗粒锆石径迹年龄均大于其沉积年龄,表明这些锆石为碎屑锆石。除1件样品外,其余13件样品的单颗粒年龄的,可以用来识别源区及其构造抬升。未通过χ2检验的锆石二项式最佳拟合峰值年龄集中分为9组:P1(1187Ma)、P2(720~548Ma)、P3(526Ma)、P4(330~319Ma)、P5(296~274Ma)、P6(213~201Ma)、P7(195~177Ma、162Ma)、P8(134~102Ma)和P9(94Ma),加上通过χ2检验的三叠纪(230Ma),指示源区中元古代-晚白垩世经历的9期构造抬升/岩浆活动。它们分别是发生在中元古代的芹峪运动、新元古代的构造抬升(约720~575Ma)、~548Ma的蓟县运动;古生代~526Ma早寒武世末构造运动、海西期构造抬升;晚三叠世印支期挤压构造抬升、早-中侏罗世印支期弱挤压抬升、早白垩世燕山期强烈岩浆活动及晚白垩世燕山晚期的抬升。华北克拉通北缘、克拉通内部古陆和盆地内部是渤海湾盆地上白垩统-上新统的主要物源区,古生代以来剥露速率逐渐增大,古生代、三叠纪、早-中侏罗世和白垩纪分别为0.020~0.033mm/y,0.033~0.042mm/y,0.034~0.049mm/y和0.041~0.097mm/y,反映源区白垩纪构造/岩浆活动最强烈。锆石裂变径迹年龄记录的中元古代-晚白垩世构造运动对探讨华北克拉通的构造演化特别是元古宙的演化提供了年代学证据,综合分析推断华北克拉通可能参与了Rodinia超大陆的形成与裂解。