湘西沅麻盆地早白垩世红层古地磁学研究及其对川东褶皱带新生代构造变形的指示

川东褶皱带作为华南板块中部的"侏罗山式"褶皱,开始形成于晚古生代.自白垩纪晚期开始,受太平洋板块和印度板块对欧亚大陆挤压的影响,这一构造带乃至华南板块中部又叠加了新的构造变形.但是,目前对于川东褶皱带白垩纪以来的构造演化缺乏足够的认识.位于川东褶皱带东侧、雪峰造山带西麓的沅麻盆地形成于早白垩世.晚白垩世以来,沅麻盆地与川东褶皱带处于同一构造应力场中,因此对盆地内早白垩世红层的古地磁研究对于解释川东褶皱带中生代晚期以来的构造演化有着重要的意义.该研究在沅麻盆地早白垩世红层中开展的古地磁学研究获得了可靠的原生剩磁分量：Ds=15.6°,Is=42.9°,k=118.6,α95=2.6°,表明沅麻盆地自早白垩世以来发生了4.1°±3.0°的顺时针构造转动.对川东褶皱带周缘白垩纪古地磁数据所揭示的地壳旋转变形,与断裂和褶皱轴组成的构造线迹变化之间的线性相关性分析,表明川东褶皱带位于齐岳山断裂带东南侧的部分,受印度板块-欧亚大陆、太平洋板块-华南板块间的挤压作用,自晚白垩世以来累积了约50~93 km的右旋错断量.     

The Pindos Fold-and-thrust belt (Greece): inversion kinematics of a passive continental margin

Continuous exposure in the Pindos mountain chain (Greece) and the detailed stratigraphic measurements in the area enable us to construct eight balanced cross sections across the Pindos Fold-and-thrust belt (PFTB) and to approach quantitatively some parameters which controlled foreland evolution. The 160-km-wide passive continental margin of the Apulian continent in Greece was progressively shortened from east to west at rates of 6 mm/year between the Early Oligocene and Late Eocene. From the rear to the frontal part of the wedge, fault-bend folds, duplexes and imbricates were formed, while strain was partitioned into faulting (~34%), layer parallel shortening (~23%) and buckling (~9%). Foreland subsidence and internal deformation of the orogenic wedge are strongly affected by two parameters of equal importance: the thrust load of the overthrusted microcontinents and the rigidity of the underthrusted Apulian passive margin. Changes in the thickness of the pre-orogenic sediments and reactivated transform faults induced salients. During the Lower Miocene, the orogenic wedge in the Peloponnese suffered additional uplift and westward gravitational gliding induced by the intracontinental subduction of the Palaeozoic rift zone of the Phyllite-Quartzite Series, which was reactivated and returned to the earths surface during the Hellenic orogeny.     

长江中下游成矿带陆内斑岩型矿床的成岩成矿作用

陆内环境斑岩型矿床的发现对斑岩成矿理论的完善具有重要意义。长江中下游成矿带作为中国东部重要的陆内成矿带之一,成矿带内发育多个重要的斑岩型矿床,如铜山口Cu-Mo矿床、鸡冠嘴Cu-Au矿床、白云山Cu矿、城门山Cu-Mo矿床、武山Cu-Mo矿床、丰山洞Cu-Au矿床、丁家山Cu矿、洋鸡山Au矿、沙溪Cu-Au矿床、冬瓜山Cu-Au矿床、舒家店Cu矿床和安基山Cu矿床等。本文选取成矿带内典型的、具有代表性的斑岩型矿床,对其地质特征(地层、构造、含矿斑岩、脉体特征和围岩蚀变)、成岩成矿年代、成矿岩体的岩石化学和成岩成矿地球化学等方面的研究资料和成果进行了系统总结,讨论和试图阐明长江中下游成矿带陆内斑岩型矿床的成岩成矿作用与成矿模式。研究显示,长江中下游成矿带形成于燕山期陆内造山过程,成矿斑岩岩浆活动和成矿作用主要发生于149~105Ma之间,进一步可以分为早、中、晚三阶段:149~135Ma、133~125Ma和123~105Ma,三阶段岩浆活动和成矿作用主要发生于成矿带中的断隆区,早阶段(149~135Ma)和晚阶段(123~105Ma)多为斑岩-矽卡岩型矿化,中阶段(133~125Ma)矿化为典型的斑岩型矿化。长江中下游成矿带内斑岩型矿床的含矿斑岩为高钾钙碱性-钙碱性系列岩石,大部分具有埃达克岩的地球化学特征,可能为源自富集地幔的岩浆和加厚下地壳部分熔融的岩浆混合的产物,源自富集地幔的基性岩浆对成矿具有至关重要的作用,它的混入使得混合岩浆富水、硫和金属(Cu、Au)等。进一步通过与岩浆弧环境的斑岩型矿床对比研究发现,长江中下游成矿带斑岩型矿床一般不发育高级泥化岩帽(advanced argillic liithocaps)以及浅部的高-中硫矿化蚀变系统,含矿岩浆源区性质和成矿物质来源等与岩浆弧环境的斑岩型矿床明显不同。     

Trace elements contamination of agricultural soils affected by sulphide exploitation (Iberian Pyrite Belt,Sw Spain)

Agricultural soils of the Riotinto mining area (Iberian Pyrite Belt) have been studied to assess the degree of pollution by trace elements as a consequence of the extraction and treatment of sulphides. Fifteen soil samples were collected and analysed by ICP-OES and INAA for 51 elements. Chemical analyses showed an As–Cu–Pb–Zn association related with the mineralisation of the Iberian Pyrite Belt. Concentrations were 19–994 mg kg⁻¹ for As, 41–4,890 mg kg⁻¹ for Pb, 95–897 mg kg⁻¹ for Zn and of 27–1,160 mg kg⁻¹ for Cu. Most of the samples displayed concentrations of these elements higher than the 90th percentile of the corresponding geological dominium, which suggests an anthropogenic input besides the bedrock influence. Samples collected from sediments were more contaminated than leptosols because they were polluted by leachates or by mining spills coming from the waste rock piles. The weathering of the bedrock is responsible for high concentrations in Co, Cr and Ni, but an anthropogenic input, such as wind-blown dust, seems to be indicative of the high content of As, Cu, Pb and Zn in leptosols. The metal partitioning patterns show that most trace elements are associated with Fe amorphous oxy-hydroxides, or take part of the residual fraction. According to the results obtained, the following mobility sequence is proposed for major and minor elements: Mn, Pb, Cd, > Zn, Cu > Ni > As > Fe > Cr. The high mobility of Pb, Cu and Zn involve an environmental risk in this area, even in soils where the concentrations are not so high.     

Amphibole Ar/Ar Geochronology from the Okcheon Metamorphic Belt, South Korea and its Tectonic Implications

An understanding of the Okcheon Metamorphic Belt (OMB) in South Korea is central to unraveling the tectono-metamorphic evolution of East Asia. Amphibole-bearing rocks in the OMB occur as calcsilicate layers and lenses in psammitic rocks, in the psammitic rocks themselves, and in the mafic volcanic layers and intrusives. Most amphiboles fail to show ⁴⁰Ar/³⁹Ar plateau ages; those that do have ages ranging from 132 to 975 Ma. The disturbed age pattern and wide variation in ⁴⁰Ar/³⁹Ar ages can be related to metamorphic grade, retrograde chemical reactions, excess Ar and amphibole composition. The oldest age (975 Ma) can be interpreted either as an old igneous or metamorphic age predating sedimentation or a false age caused by excess Ar. The youngest age of 132 Ma and the disturbed age pattern found in amphiboles from rocks located close to Jurassic granitoids are the result of retrograde thermal metamorphic effects accompanying intrusion of the granitoids. Some medium- or coarse-grained amphiboles in the calcsilicates are aggregates of fine-grained crystals. As a result, they are heterogeneous and prove to be readily affected by excess Ar. A disturbed age pattern in amphiboles from the calcsilicates occurring in the high-grade metamorphic zone may also be the product of excess Ar. On the other hand, the disturbed pattern of amphiboles present in the calcsilicates from the low-grade metamorphic zone could arise from both excess Ar and mixed ages. However, amphiboles from psammitic rocks and some calcsilicates in the high-grade metamorphic zone and in intrusive metabasites display real plateau ages of 237 to 261 Ma. The temperature conditions in the high-grade metamorphic zone were higher than the argon closing temperature for amphibole, and the amphiboles in this zone give plateau ages only when they are homogeneous in composition, lack excess Ar, and have not been thermally affected by intrusion of the granitoids. The unmodified ⁴⁰Ar/³⁹Ar ages prove rather younger than the age of the Late Paleozoic metamorphic event of 280 to 300 Ma, but they are close to muscovite K-Ar ages of 263 to 277 Ma. These ⁴⁰Ar/³⁹Ar amphibole ages are interpreted as the time of cooling that followed the main regional, intermediate-P/T metamorphic climax. The results demonstrate that interpretation of ⁴⁰Ar/³⁹Ar amphibole ages in an area subjected to several metamorphic events can be accomplished only by undertaking a thorough tectono-metamorphic study, accompanied by detailed chemical analysis of the amphiboles.     

内蒙古东乌旗北部早古生代火山岩年代学、地球化学特征及地质意义

内蒙古北部二连-东乌旗地区出露早古生代火山岩,为兴蒙造山带北缘构造-岩浆岩带的组成部分,对研究造山带早古生代构造格局及演化具有重要作用。本文对东乌旗北部早古生代中基性及酸性火山岩进行了锆石U-Pb年代学、岩石学、全岩地球化学及Sr-Nd-Hf同位素分析。定年结果显示,中基性火山岩成岩年龄为452±2Ma,酸性火山岩为430±20Ma,表明早古生代岩浆活动可延续至中志留世。地球化学组成上,中基性火山岩稀土总量中等,Eu异常不明显,富集Rb、Sr、Th、U等大离子亲石元素,亏损Nb、Ta等高场强元素,特征类似岛弧岩浆岩;酸性火山岩富集Th、U,Eu负异常显著,但Rb、Ba等大离子亲石元素富集程度不高,Nb、Ta等高场强元素亏损不明显,表现出板内岩浆特点。中基性和酸性火山岩均具有亏损的同位素组成:中基性火山岩ε_(Nd)(t)=+203～+267,ε_(Hf)(t)值介于+79～+145之间;酸性火山岩ε_(Nd)(t)=+494,ε_(Hf)(t)值为+99～+153。岩石学及地球化学分析表明,中基性火山岩为岛弧环境下遭受俯冲流体交代的地幔楔部分熔融产物,酸性火山岩则来源于新生基性下地壳熔融并具有板内岩浆特征,可能指示了俯冲的结束。结合前人资料,二连-东乌旗地区早古生代岩浆活动介于晚寒武-中志留世之间,形成时间及阶段性演化特征近似于苏尼特左旗-锡林浩特早古生代岩浆岩带,暗示两者可能具有成因联系,均为早古生代古亚洲洋向北俯冲的产物。     

微陆块属性厘定的依据——以中亚造山带南缘中段为例

造山带中残存有许多前寒武纪地质体,其中一些被当作前寒武纪基底用于探讨所在微陆块的大地构造属性。由于微陆块属性对于造山带结构和演化具有重要意义,以及所讨论的前寒武纪地质体蕴含地球早期历史演化信息,对微陆块属性的厘定成为造山带研究的重点和难点问题之一。笔者等以中亚造山带南缘中段的微陆块为例,总结梳理了微陆块厘定的相关依据：岩石组合和变质变形特征,碎屑锆石谱峰显示的源区时代特征,地质事件序列,前寒武纪地壳演化信息,继承锆石、捕获锆石和古生代侵入体同位素显示的深源地壳信息,以及地球物理等方面的特征。由于不同学者采用的厘定依据不同,对微陆块属性认识争论不断,即使相同依据也有一定的差异,从而影响对造山带结构和演化的认识。基于以上原因,笔者等认为前寒武纪基底的亲缘性探讨不仅要注重岩石组合和形成时代,还要在精细野外解剖和高精度年代学工作基础上,注意其变质—变形特征、接触关系、源区时代特征、岩石成因和构造环境、地壳增生信息和深源地壳信息等的综合对比分析,以得到较全面依据,探讨其构造属性。当获得一组前寒武纪地质体信息时,可先进行同构造单元内对比,再与其他构造单元对比。当特征相异时则需进行构造单元拆分或考虑构造就位的可能（包括但不限于推覆体、走滑外来体、俯冲刮削的构造岩片）;当特征相似时,可能指示了相同微陆块的裂解或破坏或者不同的微陆块共同经历了相似的前寒武纪演化历程。     

Revised stratigraphy and eruption rates of Ceboruco stratovolcano and surrounding monogenetic vents (Nayarit,Mexico) from historical documents and new radiocarbon dates

More than a dozen new radiocarbon dates reconstruct the eruptive history of Ceboruco volcano. Six of these further constrain previous results for the important plinian Jala eruption, which occurred near 1060 ± 55 yr BP. A calibrated radiocarbon age of AD 990–1020 was obtained as best overlap range for all samples. Pottery fragments found directly underneath the pumice deposit indicate that this area was inhabited by human populations that witnessed the eruption. This age therefore represents an important time marker in the prehistory of this region, because an area of > 560 km2 was devastated and covered by a thickness of > 50 cm of pumice and ash fallout.     

“一带一路”背景下中国国际航空网络的空间格局及演变

2013年“一带一路”倡议提出将设施联通作为合作战略重点之一,航空网络作为设施联通的重要组成部分,其地位提升到新的高度。为评估“一带一路”倡议的提出对中国国际航空网络的影响,论文选取了2013年和2018年数据,从国际航线、国际航班以及通航城市3个方面分析“一带一路”倡议提出以来中国国际航空网络的空间格局及其演变特征。研究结果表明：① 整体上来看,“一带一路”倡议并未从根本上改变中国国际航空网络的空间格局,仍以东亚、东南亚、美国以及俄罗斯等地区和国家为主,5 a来其变化主要集中在进一步加深与已有城市的联系;② 从沿线国家来看,一带一路”倡议增加了与中国直接通航的沿线国家数量,并提升了沿线国家在中国国际航空网络中的地位;③ 越来越多的境内城市参与到中国对外开放格局中,且航线和航班在北京、上海、广州的聚集程度下降,而其他城市的航线和航班占比逐渐增加。     

新疆西准噶尔发现早泥盆世埃达克岩:大地构造及成矿意义

新疆西准噶尔博什库尔-成吉斯(Boshchekul-Chingiz)岩浆弧南缘,额敏县东南约100km的阿克乔克含铜花岗闪长岩和花岗闪长斑岩,其锆石U-Pb年龄为410.5±2.9Ma,形成于泥盆世早期.岩石具有埃达克岩的地球化学特征,表现为高钾钙碱性-钙碱性,SiO2含量在61％～66％之间,具高Al(Al2O3=15.67％ ～ 16.87％)、Sr(475×10-6 ～ 879×10-6)及高Sr/Y比值(36 ～77),低Y(9.87×10-6～14.46×10-6)、Yb(0.96×10-6～ 1.49×10-6),富钠贫钾(Na2O =4.25％ ～5.58％,K2O=2.26％ ～3.27％,Na2O/K2O=1.40～ 2.47),MgO=1.51％ ～2.58％,Mg#=41～48,并显示富集强不相容元素(Ba、Rb、Sr、Th、U)和LREE,(La/Yb)N=6.0～10.2,强烈亏损高场强元素(Nb-Ta、Ti),Y/Yb=10,无Eu异常(Eu/Eu*≈1.0)和HREE呈平坦型的配分特点,以及与环太平洋新生代埃达克岩相当的Rb/Sr(0.04 ～0.07)和La/Ce(0.42 ～0.51)比值,但偏低的Nb/U比值可能与俯冲沉积物加入有关.阿克乔克花岗闪长岩及花岗闪长斑岩是早泥盆世早期库吉拜-和布克赛尔(Kujibai-Hebukesaier)及洪古勒楞蛇绿岩带所代表的古大洋向南俯冲的玄武质洋壳部分熔融的产物,源区残留相主要为角闪石+辉石+石榴石,源岩应为石榴角闪岩;阿克乔克早泥盆世埃达克岩及谢米斯台-赛尔山晚志留世-早泥盆世A-型花岗岩(422～405 Ma,Chen et al.,2010)构造岩浆岩带可东延至扎河坝-阿尔曼太蛇绿岩带之北的岛弧带,构成一条贯穿东、西准噶尔北部的巨型构造带;阿克乔克埃达克岩伴有斑岩型Cu成矿作用,因此,在东、西准噶尔博什库尔-成吉斯-达拉特-巴依塔格巨型岩浆弧带有可能存在与埃达克岩有关的Cu-Au矿带.