大别山西部河南罗山熊店加里东期榴辉岩锆石特征及SHRIMP分析结果

熊店榴辉岩产于大别山西部苏家河构造混杂岩带内,是典型的高压一超高压中温榴辉岩。作者应用岩学结合阴极发光和扫描电镜方法,较系统地研究了榴辉岩中锆石在岩石中的赋存状态、内部结构及表面特征。锆石主要产于石榴子石等变质矿物内,与主晶界面清晰,具有多晶面等变质锆石特有形貌特征,内部均或发育变质生长结构,从而说明它们是变质作用的产物。ＳＨＲＩＭＰ分析表明,锆石＾２０６Ｐｂ／＾２３８Ｕ年龄为３３５～４２４Ｍａ,     

西秦岭北带大草滩群的解体及其地质意义——兼论北秦岭加里东运动的性质

分布于西秦岭北带的上泥盆统大草滩群 (D3dc) ,被众多研究秦岭的地质学家认为是典型的造山后的磨拉石建造 ,并将这套地层作为北秦岭加里东运动最直接、重要的证据之一。我们的工作发现 ,大草滩群是由两套不同时代、不同沉积建造的地层体经逆冲—推覆构造作用形成的地层叠置系统。因此 ,原大草滩群予以解体 ,建议取消。这一认识对探讨北秦岭加里东运动的性质以及整个北秦岭构造演化历史提供了重要资料     

广昌付坊花岗岩地质特征及侵位机制

付坊花岗岩出露在武夷山西坡中段。在１：５万广昌县幅区调工作中,通过对其岩性、化学万分、结构、构造等演化特征的研究,将其划分为洋背、高洲、胡竹、太和、石咀圩５个单元,归并为一个超单元;根据其Ｕ－Ｐb法同位素年龄确定其侵位时代为晚奥陶世,属加里东造山期岩浆活动的产物;侵位机制属早期底辟、晚期轻气球膨胀强力型主动就位。     

广西加里东运动构造古地理问题

广西历来被认为是我国加里东运动的典型地区,志留纪末的造山运动使早泥盆世莲花山组砾岩不整合于下伏地层之上。但是,实际上莲花山组只分布于广西中部的大明山－大瑶山地区和东北部扬子地块边缘,并且,它不具备同造山期磨拉石沉积特征,而是古陆剥蚀面上新海侵序列底部的滨海相沉积。广西西部的晚古生代台地相区,泥盆系底部为泥岩或粉砂岩,超覆于寒武系台地相沉积层之上。滇东南和越南北部邻区情况类似。推测在早古生代时它们属于一个地块,可称为“桂滇－北越地块”。早奥陶世云开地块和桂滇－北越地块、扬子地块的会聚和挤压,形成了大明山－大瑶山地体寒武系东西向的线形褶皱带。这是广西加里东运动的主幕。晚奥陶世-早志留世华夏地块和扬子地块的碰撞带在广西仅限于它的东北部,表现为震旦系-下志留统近南北向的线形褶皱带。志留纪末并无造山运动的证据。早泥盆世开始,可能由于地幔柱活动而使桂滇－北越地块裂解,形成北越地块、靖西台地和其他更小的块体。     

Two contrasting petrotectonic domains in the Kokchetav megamélange (north Kazakhstan): Difference in exhumation mechanisms of ultrahigh‐pressure crustal rocks,or a result of subsequent deformation?

Abstract In northern Kazakhstan the WNW striking Kokchetav megamélange includes different crustal sequences with high‐pressure/ultrahigh‐pressure (HP/UHP) remnants of their 540–520 Ma subduction metamorphism. Two domains separated by the north‐east trending Chaglinka fault are distinguished. The western domain exhibits NE–SW structures within a single Kumdy–Kol megaunit of diamond‐bearing UHP metasediments and high‐temperature (HT) eclogites. The eastern domain consists of the composite Kulet megaunit with the Kulet UHP unit (coesite‐bearing metasediments, whiteschists and eclogites), the Enbek–Berlyk medium‐pressure (MP) unit (kyanite‐bearing, high‐alumina rocks with interleaved coronitic metagabbro), and ortho‐ and paragneisses with eclogites and amphibolites included. All eclogites in the eastern domain are of the relatively low temperature (LT) type. Sillimanite is common and appears after kyanite in the sheared MP unit. A regional and moderately ESE plunging linear fabric coincides with the fold‐axis of the foliation poles from the eastern domain. Whether this also reflects a regional top to the WNW transport, as inferred from the dextral strike‐slip on steeply to SSW dipping foliation, needs further study. Top to the WNW shear is shown by weakly inclined low pressure (LP) cordierite rocks that flank the eastern domain in the south. Some new ³⁹Ar/⁴⁰Ar mica cooling ages (519, 521 Ma) from the Kulet UHP micaschists reflect the same early stage evolutionary event as was previously shown for the Kumdy–Kol UHP rocks (515, 517 Ma) in the west. Similar ³⁹Ar/⁴⁰Ar ages (500, 517 Ma) are recorded by micas and amphibole that outline a top to NNW shear fabric in the non‐subducted Proterozoic basement, north of the megamélange. A 447 Ma overprint of the MP sequences is considered to reflect the strike‐slip deformation with sillimanite and the reworking of an early kyanite‐bearing tectonite. Biotites from the LP cordierite rocks yielded approximately 400 Ma ³⁹Ar/⁴⁰Ar ages. In case they reflect the WNW shear deformation, the latter is considered to be associated with a regional granite magmatism (420–460 Ma) extending south of the eastern domain. In their present different structural domains the Kulet and Kumdy–Kol UHP units display a similar early stage event. Subsequent LP deformation, which is likely to be associated with regional granite magmatism (420–460 Ma), is assumed to have obliterated any common or uniform early exhumation structure for the whole megamélange. The north‐east structured Kumdy–Kol domain is assumed to have preserved the most information about the early stage exhumation. This domain is at an angle to the regional WNW strike of the megamélange.     

Petrographic and SHRIMP Studies of Zircons fromthe Caledonian Xiongdian Eclogite, NorthwesternDabie Mountains

The Xiongdian eclogite occurring in the Sujiahe tectonic melange zone at Luoshan County, Henan Province, in the western Dabie Mountains, is typical high-pressure (HP)-ultrahigh-pressure (UHP) and medium-temperature eclogite. The occurrence, internal texture and surface characteristics of zircons in eclogite were studied rather systematically petrographically combined with the cathodoluminescence (CL) and scanning electron microscope (SEM) methods. Zircons are mainly hosted in garnet and other metamorphic minerals with sharp boundaries, have a multifaceted morphology and are homogeneous or exhibit a metamorphic growth texture in the interior, thus indicating that they are the product of metamorphism. SHRIMP analyses give zircon 206Pb/238U ages of 335 to 424 Ma and show a certain degree of radiogenic Pb loss; therefore it may be inferred that the age of 424? Ma represents the minimum age of a HP-UHP metamorphic age. From the above analyses coupled with previous Sm-Nd, 40Ar-39Ar, U-Pb and 207Pb/206Pb age d     

华夏地块:一个由古老物质组成的年轻陆块

对华夏地块三个主要前寒武纪地质体出露区变质岩的详细锆石年代学的综合分析显示,华夏地块大致可以被分成武夷山区和南岭-云开区。武夷山区由古元古代核和新元古代（形成于730-820 Ma）的盖层组成,构成华夏地块最老的古陆,在其深部很可能还存在一个新太古代基底。新元古代的沉积物主要来自武夷微古陆本身。南岭与云开具有相似的前寒武纪地壳组成,它们主要是由新元古代形成的沉积物夹少量火山岩组成。这些沉积物质中包含了非常古老的中太古代和新太古代组分,甚至古太古代组成。Grenville期和中元古代组分是其中最丰富的。这些组分在华夏没有对应出露的岩石,说明它们主要来自另外一个曾经与华夏相邻的陆块。该陆块很可能是东印度－东南极大陆。南岭－云开区最初可能是Rodinia超大陆裂解时形成的一个裂谷盆地,加里东的造山运动使盆地中的沉积物挤压、褶皱和隆起,与武夷陆块共同构成了一个新的年轻的大陆     

Genesis of lithium pegmatites from the leinster granite margin,southeast ireland: Geochemical constraints

Extensive and economically-important lithium pegmatites have been described from the eastern flank of the large S-type peraluminous Leinster Granite batholith in southeast Ireland. This flank area is also the locus of a major dip-slip ductile shear zone which was active during emplacement of the Tullow Lowlands pluton of the batholith. All the known bedrock occurrences of lithium pegmatite are contained within this marginal deformation zone. Most previous studies have suggested derivation of the lithium pegmatites by fractionation from the Leinster Granite itself, though none are conclusive. More recently, an anatectic model has been proposed whereby the pegmatites were derived by melting of Li-rich sediments adjacent to the batholithic contact. Our investigation has been concerned with a detailed study of the Rb-Sr isotope systematics and trace element geochemistry of the pegmatites and their host granitoids in an attempt to resolve the problem of pegmatite genesis. The results suggest a strong geochemical and temporal coherence between the Leinster Granite and the lithium pegmatites. A model is proposed in which Li enrichment in residual magmas may be linked to the development of muscovite instead of biotite in the Leinster Granite itself. The Li excluded from entry to biotite then accumulates in highly mobile, low-viscosity pegmatitic fluids which migrate into the marginal shear zone of the Tullow Lowlands pluton where they crystallize at considerably lower temperatures.     

Zoning and layering in diorites of the scottish caledonian appinite suite

Dioritic plugs (< 1 km across) are common associates of the late Caledonian, post-tectonic granites of the Scottish Highlands. These contain a very wide range of rock types from ultramafic through mesocratic diorites to anorthositic and granitic. These rocks form steeply dipping, wall-parallel layers and zones within the plugs. Outer layers are shown to form first, inner layers later. Mafic zones are composed of the minerals seen as phenocrysts in chilled margins and have the chemical characteristics of cumulates. The inner margins of the mafic zones reflect the onset of plagioclase crystallization. Core zones also show inward variations in mineralogy and texture which define vertical, wall-parallel cylinders. These variations are ascribed to fractional crystallization accompanying accretion of rock onto the pipe walls. Cores in different intrusions may be mafic, mesocratic, or leucocratic, which indicates vertical zonation in the bodies. The mafic cores additionally show that recharge with less evolved magma occurred in some cases. The few larger (> 1 km diameter) intrusions show examples of layering and lamination dipping at low to moderate angles. These indicate the beginning of a change from wall-dominated to floor-dominated crystallization as intrusion diameter increases. A comparison is made with the nature and origin of layering in other intrusions.