西藏西北部浅变质石英砂岩岩石学特征及其构造意义

羌塘盆地中央隆起带主要由浅变质石英砂岩组成,由于化石匮乏、变形强烈,长期以来对这套浅变质石英砂岩成因的争议颇大,导致了对藏西北地区前中生代构造演化的认识长期模糊不清,其中,何处才是冈瓦纳大陆北界就是一个长期争论的议题。在西藏西北部,近东西走向的布尔嘎错断裂带将北部的查多岗日地块与南部的南羌塘地块分隔开,浅变质石英砂岩广泛出露于这两地块之内。沿近东西走向布尔嘎错断裂带断续产出的冈玛错蓝片岩、蛇绿岩等岩片大体呈南北向逆冲于浅变质石英砂岩之上,因此早期曾认为布尔嘎错断裂带是冈瓦纳大陆之北界。本文的调查与研究发现查多岗日和南羌塘地块内浅变质石英砂岩岩相学特征完全相同,均主要由石英组成,遭受了绿片岩相的变质作用,形成了钠长石+绿泥石+白云母组合,充填于早期石英颗粒之间,钠长石交代钾长石。这两地的浅变质石英砂岩均被未变质钙质胶结的钾长石石英砂岩平行不整合覆盖。碎屑锆石的阴极发光分析与U-Pb定年结果进一步证实了查多岗日与南羌塘地块内浅变质石英砂岩内的锆石来源完全相同。这些证据充分反映了查多岗日与南羌塘地块早期构造演化过程相似,源自同一大陆。碎屑锆石定年结果进一步表明浅变质石英砂岩的最大沉积年龄为520±8Ma,该岩石再被约480Ma的花岗岩脉侵入,因此其很可能形成于晚寒武世,而不整合面之上沉积岩的最大沉积年龄为460±8Ma,表明该不整合面上、下沉积岩之间存在明显的沉积间断,证实了该平行不整合面形成于奥陶纪。不整合面之下的浅变质石英砂岩因此与杨耀等(2014)报道的荣玛组相同,不整合面之上未变质长石石英砂岩则属于中上奥陶统塔石山组。查多岗日地块因此是西藏境内最北端的冈瓦纳大陆的碎块。在西藏西北部,冈瓦纳大陆北界为龙木错-帮达错-(83°40'E、35°N)-红脊山-荣玛乡。布尔嘎错断裂带不是冈瓦纳大陆之北界。     

Late Paleozoic tectonic evolution in northern Korean Peninsula

Since Late Proterozoic era, the Korean Peninsula has been evolved into a state with relatively stable regions and orogenic belts which were developed differently each other. The Late Paleozoie （Late Carboniferous-Early Triassic） sediments are well developed in the Korean Peninsula, and called the Pyongan System. The Pyongan System from Late Carboniferous to Lower Triassic is distributed in the Pyongnan and Hyesan-Riwon Basins, and Rangrim Massif, and divided into Hongjom （ C2 ）, Ripsok （ C2 ）, Sadong （ C2-P1 ）, Kobangsan and Rokam （Taezhawon） （P2-T1） sequences. The sediments of the Tumangang Orogenic Belt are called Tuman System which is composed of the Amgi Series, consisting of elastic formation with mafic effusive material, overlaid by the Kyeryongsan Series, consisting mainly of marie volcano sediments. The Songsang Series which rests on the Kyeryongsan Series mainly consists of elastic formation with minor felsic effusive material. In the Tumangang Orogenic Belt the tectonic movement, called Tumangang Tectonic Movement, occurred in the Lower Permian-Lower Triassic.     

胶东半岛温泉的地热特征

胶东半岛位于欧亚板块与太平洋板块边缘内侧,是地壳长期稳定缓慢隆起地段,区内地质构造发育,大部分温泉出露在背斜核部,ＮＥ、ＮＮＥ向与ＮＷ、ＮＮＷ向断裂交泯外,地热系统属中低温深循环对流型,略为偏高的大地热流是其主要热源,地表水是地下热水的补给水源,地下水通过发育在花岗岩和变质岩中的断层或断裂破碎带,下渗和深循环对流,在径流过程中不断吸取围岩热量成热水,沿断裂上升过程中,与地下浅部裂隙水混合而成为化学     

胶东西北部重熔型磁铁矿花岗岩与金矿

胶东西北部是我国最主要的金矿集中区,金矿的同源岩为滦家河花岗岩,属中深侵入体。根据它富含磁铁矿及副矿物组合,高铁低镁的黑云母,岩石化学成分,锶、氧、硫同位素组成,认为属磁铁矿花岗岩,相当于Ⅰ型花岗岩。用K、Rb、Sr、岩石化学成分,稀土元素和硫同位素判别,确认其为壳源(相当于胶东群变质岩的成分)重熔型。我国脉状金矿的容矿围岩时代老,成矿时代新,空间受构造—岩浆带制约,成矿过程脉岩活动频繁,对其原因,本文提出了一种解释。     

短波红外光谱、X射线荧光光谱、黄铁矿热电性分析在胶东新城金矿田深部找矿中的应用

胶东半岛是我国最重要的金矿集区之一,其矿床是典型受北东向断裂构造(焦家断裂带、三山岛断裂带和招平断裂带),以及次生断裂构造(如望儿山断裂和灵北断裂等)控制的矿床类型.前人在该区域做了大量研究,但主要集中在地表和浅层成矿段,对于深部成矿规律与预测的研究相对较少.新城金矿田是胶东半岛的特大型金矿之一,由新城矿床、曲家矿床和...     

浙西北淳安银山地区银铅锌矿床矿石结构构造、矿石成分及成矿机制

浙西北与同处钦杭成矿带东段的赣东北和皖南相比,由于其地质研究程度较低,在该区尚未能找到大型多金属矿床。近年来,随着地质勘查程度的不断提高,淳安地区银山一带发现中型以上银铅锌矿床。本文选取银山矿区钻井岩芯中富含银、铅、锌矿石样品,利用显微镜观察和电子探针分析等方法,对其中的银等多金属的矿石结构构造、矿石成分及成矿机制等进行了较深入的研究。研究表明,银山地区多金属(银、铅、锌)矿体主要分布在蓝田组上段与上覆皮园村组之间的接触带中,另有部分处于蓝田组层内岩性变化的界面以及蓝田组底部白云质灰岩和下伏南沱组含砾泥岩之间,均呈似层状展布。矿石呈自形-半自形粒状结构、他形粒状结构和交代残余结构以及块状构造、浸染状构造和网脉状构造。金属矿物组合主要分为黄铁矿-黄铜矿-方铅矿-闪锌矿和磁黄铁矿-毒砂-闪锌矿两组,其中前者位于蓝田组顶部和皮园村组之间,属于中低温热液型的矿物组合,后者位于蓝田组下部和南沱组之间,属于中温热液型的矿物组合。通过对不同金属矿物中银含量的对比分析,得出银山地区银元素主要赋存在方铅矿中。脉石矿物有石英、方解石、白云母、绿泥石、单斜辉石等,尤其在矿石中多见的细粒单斜辉石按其成分上的差异分为透辉石和钙铁辉石两类,指示了热液作用对成矿的显著影响。综上所述,笔者认为浙西北银山多金属矿床成因很可能为早期层控-后期中低温热液改造的叠生型矿床。其形成机制是:震旦纪时期海相火山喷流沉积使得部分多金属成层聚集,蓝田组地层为银山多金属矿床的形成提供了部分的物质来源,加里东期的变质变形作用及其发育的断裂构造也具有一定的控制作用;随后,大规模的燕山期花岗质岩浆及其流体组分沿断裂带上侵,不仅使得原有地层中的多金属元素进一步富集,而且其本身也可能带入部分多金属流体,从而使得富含多金属元素热液流体在具有地球化学障的岩性界面上富集成矿。此项研究对该地区及邻区进一步找矿勘探具有重要的科学意义和应用价值。     

Evidence of two-stage extensional tectonics from the northern edge of the Edremit Graben,NW Turkey

Western Turkey is a place of active continental extension, characterized by the occurrence of several WNW-ESE-trending major grabens. The central part of the northern edge of the Edremit Graben is delineated by various geological units, namely the metamorphic Kazda? Massif, the Mid-Cretaceous Çetmi mélange, the sedimentary Küçükkuyu formation, and loose Plio-Quaternary deposits. Detailed structural and sedimentological study suggests a two-stage extensional evolution of the area, separated by a short break in the tectonic regime. The first stage, possibly related to back-arc extension and/or orogenic collapse, is marked by the activity of a newly described low-angle detachment fault, the ?elale detachment fault, from the latest Oligocene onward. The fault plane, separating the mylonitized rocks of the Kazda? Massif in the footwall from the unmetamorphosed Çetmi mélange and Küçükkuyu formation in the hanging wall, must have played a significant role in the initial exhumation processes of the Kazda? Massif at that time. The Lower Miocene syntectonic Küçükkuyu formation has recorded the initiation and filling up of a small basin, which has developed in a typical supra-detachment basin, above the detachment fault. After a short phase of possible compression and erosion, the second stage—which marks the onset of neotectonic activity—is marked by the development of Plio-Quaternary step-like normal faults, which cut through all the previous units. Coarse, loose sediments were deposited following the fault activity. These local results are extrapolated to apply to the entire Edremit Graben. In that case, its evolution is seen as the succession of two extensional stages, characterized by distinct structural and sedimentological patterns, and possibly separated by a short compressional phase.     

Crustal structure of the continental margin of Korea in the East Sea (Japan Sea) from deep seismic sounding data: evidence for rifting affected by the hotter than normal mantle

Despite the various opening models of the southwestern part of the East Sea (Japan Sea) between the Korean Peninsula and the Japan Arc, the continental margin of the Korean Peninsula remains unknown in crustal structure. As a result, continental rifting and subsequent seafloor spreading processes to explain the opening of the East Sea have not been adequately addressed. We investigated crustal and sedimentary velocity structures across the Korean margin into the adjacent Ulleung Basin from multichannel seismic (MCS) reflection and ocean bottom seismometer (OBS) data. The Ulleung Basin shows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal. The continental margin documents rapid transition from continental to oceanic crust, exhibiting a remarkable decrease in crustal thickness accompanied by shallowing of Moho over a distance of about 50 km. The crustal model of the margin is characterized by a high-velocity (up to 7.4 km/s) lower crustal (HVLC) layer that is thicker than 10 km under the slope base and pinches out seawards. The HVLC layer is interpreted as magmatic underplating emplaced during continental rifting in response to high upper mantle temperature. The acoustic basement of the slope base shows an igneous stratigraphy developed by massive volcanic eruption. These features suggest that the evolution of the Korean margin can be explained by the processes occurring at volcanic rifted margins. Global earthquake tomography supports our interpretation by defining the abnormally hot upper mantle across the Korean margin and in the Ulleung Basin.     

雷州半岛中西部第四纪火山岩的40Ar/39Ar年龄及地质意义

雷州半岛地区第四纪火山岩广泛分布,但对火山岩形成的时代还存在争议。文章利用高精度的激光阶段加热40Ar/39Ar法对雷州半岛中西部火山岩的年龄进行了测定,并结合与相邻地层的接触关系,划分了2个火山活动旋回。第Ⅰ旋回火山岩呈夹层产于湛江组内部,仅见于钻孔ZKC12中,岩性为橄榄拉斑玄武岩;第Ⅱ旋回火山岩在区内分布最广,覆盖在湛江组之上,40Ar/39Ar年龄为2.02～0.88 Ma,时代为早更新世早期至早更新世晚期,结合与周围地层的接触关系,进一步划分为4个喷发期。第1喷发期（Ⅱ1）规模最大,出露面积最广,形成2个喷发中心,40Ar/39Ar年龄为2.02±0.03 Ma;第2喷发期（Ⅱ2）主要分布于锅盖岭和北插一带,40Ar/39Ar年龄分别为1.77±0.03 Ma、1.70±0.03 Ma;第3喷发期（Ⅱ3）喷发中心位于火炬农场,40Ar/39Ar年龄为1.51±0.07 Ma;第4喷发期（Ⅱ4）岩性以沿裂隙喷发形成的溢流相的玄武质熔岩为主, 40Ar/39Ar年龄为0.88±0.14 Ma。火山活动明显受北东向和北西向基底断裂的控制。研究成果为雷州半岛地区火山活动时代、期次和活动规律研究提供了重要年龄证据。     

Small sized charophyte gyrogonites in the Maastrichtian of Coll de Nargó, Eastern Pyrenees: An adaptation to temporary floodplain ponds

Charophytes bearing small sized fructifications dominated in fluviatile floodplain facies (red beds) from the Maastrichtian of Coll de Nargó and neighbouring basins in the southern Pyrenees (Catalonia, Spain). These charophytes mainly belong to the genus Microchara and are often disregarded in biostratigraphic studies, which focus their attention instead on facies from permanent lakes that are richer in species which usually bear fructifications with a larger size range. However, small sized gyrogonites are also significant for biostratigraphic purposes and even include some of the index species for Maastrichtian biozones in Europe. Indeed, the charophyte assemblages from the Maastrichtian of Coll de Nargó belong to the Microchara punctata biozone, recently calibrated to the middle-upper Maastrichtian.Floodplain ponds from the Maastrichtian red beds of Coll de Nargó (Lower Red Unit) were extremely shallow, received considerable terrigenous influx and were frequently exposed, probably resulting in turbid, warm waters with high light availability. These conditions could explain the almost exclusive occurrence of charophytes with small fructifications in the Lower Red Unit. The available data, mainly based on oospores from extant species, indicate that the small size observed in gyrogonites from temporary ponds may represent an adaptation to environmental stress. Fossil species with small gyrogonites of Microchara cristata, M. punctata and Microchara nana would thus develop massively in stressed shallow ponds on fluvial floodplains. To contrast these hypotheses, we compared our results to those of four well-known case studies with similar sedimentological contexts, ranging from the Lower Cretaceous to the upper Eocene–lower Oligocene. Gyrogonite size patterns were similar in all cases, possibly suggesting that characeans display a long history of adaptation to shallow, temporary and turbid floodplain ponds by means of producing a high number of small gyrogonites, probably representing short life cycles and opportunistic strategies.