Biostratigraphy of Dinantian limestones and associated volcanic rocks in the Limerick Syncline,Ireland

Rocks of Courceyan to Brigantian age are exposed in the Limerick Syncline. However, a complete Courceyan succession is known only from two boreholes which correlate closely, both faunally and lithologically, with a standard Limerick Province succession in the Pallaskenry Borehole on the Shannon estuary. This is followed by a thick Waulsortian sequence (the newly defined Limerick Limestone Formation) of late Courceyan to early Chadian age and overlying cherty micrites (the newly defined Lough Gur Formation) of early to late Chadian age, whose top is younger to the east. The Lough Gur Formation is succeeded by lavas and tuffs of the Knockroe Volcanic Formation whose upper part is interbedded with and overlain by shallow water oolites and algal-rich bioclastic limestones of the Herbertstown Limestone Formation. The higher part of the latter is in turn interbedded with lavas and tuffs of the Knockseefin Volcanic Formation. The Herbertstown Limestone has rich and diverse coral/brachiopod and foraminiferal assemblages of late Chadian to Asbian age. Its base is markedly diachronous: late Chadian in the west of the syncline and Holkerian in the east. Both the base and top of the Knockroe Volcanic Formation are thus shown to be markedly diachronous and volcanism extends from the Chadian to early Asbian. The Knockseefin Volcanic Formation is entirely of Asbian age. The highest limestones (Dromkeen Limestone Formation) have a diagnostic late Asbian–early Brigantian fauna and are overstepped by mid-Namurian shales.     

The stratigraphy of the arenig series in the Aberdaron to Sarn Area,Western Llŷcn,North Wales

A new interpretation of the Arenig succession in the Aberdaron area is presented based on biostratigraphical correlation. A lithostratigraphy based on section correlation is presented, and three subareas are identified, each with a different stratigraphy. The Sarn Formation comprises the basal ‘flaggy’ sandstone unit in all three areas but is diachronous: in the south it underlies a Moridunian fauna whilst north of the Bryncroes fault it comprises the majority of the Arenig succession and is probably Fennian in age. The Aberdaron Formation is restricted to the south and is dominated by laminated siltstone. The Wǐg Member, a mudstone unit at the base with a Mordunian fauna is found only to the east of the Wǐg–Nefyn fault, whilst the breccio-conglomerate Porth Meudway Member, at the top of the formation, is restricted to the west of the fault and is probably Fennian in age. The Arenig–Llanvirn boundary is approximately marked throughout the area by a tufaceous unit termed the Carw Formation. The new correlations require the repetition of the succession by a previously unrecognized NNE–SSW trending fault. The junction with the Mona Complex west of Aberdaron is considered to be predominantly faulted. The two subareas south of Bryncroes are sufficiently similar to suggest both belonged to the same deepening basin, probably initiated in the Moridunian. The absence of the Aberdaron Formation and the development of contemporary shallower water facies to the north is taken to indicate this area lay on the footwall of a normal fault bounding the basin to the northwest.     

Middle to early Late Ordovician hydrothermal veining in the Molong Volcanic Belt,northeastern Lachlan Fold Belt: Sedimentological evidence

Detrital volcanic and vein quartz, accompanied by felsic volcanic debris, occur as minor constituents in the Ordovician subduction‐related mafic volcanics of the Molong Volcanic Belt. In the western province of the Molong Volcanic Belt, detrital quartz is present in the three episodes of the mafic Volcanics. Volcanic quartz occurs in allochthonous limestone blocks in the Bendigonian Hensleigh Siltstone overlying the Mitchell Formation. The second volcanic episode (the Fairbridge Volcanics) commenced after a hiatus of approximately 20 million years and lasted around 10 million years from Darriwilian to Gisbornian time. Locally derived vein quartz, volcanic quartz and felsic detritus are concentrated at the bases of autochthonous Wahringa and Yuranigh Limestone Members of the volcanics and are extensive and abundant in basal beds of the regional Eastonian limestone body that transgressed over an eroded volcanic centre at Cargo. This early Eastonian debris, deposited early in an 8 million‐year volcanic hiatus preceding the final Ordovician Bolindian volcanism, establishes a pre‐Eastonian age for mineralisation at Cargo. It is inferred that the pauses in volcanism were preceded by magmatic fractionation, intrusion and hydrothermal activity and followed by erosion, subsidence and deposition of autochthonous limestones. Minor occurrences of vein and volcanic quartz are found in Bolindian volcanogenic sediments of the third volcanic phase. It is concluded that hydrothermal vein formation (and mineralisation by inference) was associated with pauses in volcanic activity throughout the Middle to early Late Ordovician over a wide area in the western province, culminating in the mineralisation at Cargo and Copper Hill near Molong. Volcanism in the eastern province of the Molong Volcanic Belt was continuous from at least Darriwilian to latest Ordovician time. Here, detrital hydrothermal vein quartz and volcanic quartz and felsic detritus are distributed through late Middle and early Late Ordovician turbidites of the Weemalla Formation. The possible existence of cycles in the source area like those of the Fairbridge Volcanics is masked by the distal nature of these deposits. Vein formation occurred in both provinces from late Middle Ordovician to early Late Ordovician, long before the formation of the world‐class mineral deposit at Cadia associated with the latest Ordovician Cadia Monzonite.     

The stratigraphy and sedimentology of the Ordovician Partry Group,southeastern Murrisk,Ireland

The uppermost part of the Ordovician succession in southeastern Murrisk, western Ireland, consists of coarse-grained sedimentary rocks and tuffs, the Partry Group, hitherto subdivided into the Mweelrea Formation, unconformably overlain by the Maumtrasna Formation. The age of the lower part of the succession is late Llanvirn whilst that of the upper part is unknown. Evidence is presented to show that the two formations are lateral equivalents. Consequently the Mweelrea Formation is redefined and the Maumtrasna Formation becomes redundant. The revision of the stratigraphy enables a coherent sedimentological model for the group to be proposed. The sediments of the Mweelrea Formation were deposited on alluvial fans and distally-equivalent alluvial plains and delta fans. The direction of sediment transport was towards the north and northwest.     

抚顺—清原地区鞍山群块状硫化物矿床的区域地质特征

抚顺-清原地区位于辽宁省东北部,面积约2500Km~2.区内太古代变质岩系广泛发育,其下部为深变质的麻粒岩相地层,上部为中深变质的角闪岩相地层,后者产出红透山式铜锌矿床多处(属红透山地区),以及张胡子沟铜矿床和大荒沟硫铁矿床(属清原北部地区)等一系列块状硫化物矿床(图1).矿石中铅同位素年令为25～26亿年,在形成时代上可以和鞍本地区鞍山群对比.     

Petrography,provenance, diaganesis and depositional environment of Murree Formation in Jhelum Valley,Sub Himalayas,Azad Jammu and Kashmir,Pakistan

The clastic sediments of the Murree Formation of Miocene age are exposed in Jhelum valley areas of Azad Jammu and Kashmir Pakistan. Field observations revealed the cyclic deposition in the Murree Formation. The sandstone, siltstone, and shale constitute a single cycle within the formation. This single unit is divided into five different lithofacies which constitute the Bouma sequence in the Murree Formation. The Murree Formation shows faulted contacts with Panjal Formation and Nagri Formation in the study area. The modal mineralogy data obtained from the petrography of sandstone indicates that sandstone is litharenite and lithic greywacke. The mineralogical and textural data suggests that sandstone is compositionally mature and poorly to moderately sorted. The dominantly angular to sub angular quartz grains show nearness of the source area. Fractured and sutured quartz grain reveals tectonodiagentic changes that occurred in Murree Formation. The sandstone experienced diagenetic changes. The pressure solution and cementation reduced the primary porosity of sandstone. However, alteration of feldspar and fractures in grains have produced secondary porosity. The X-ray diffraction (XRD) of the shale samples indicates that shale of the Murree Formation is argillaceous and dominated by illite clay mineral. The illite crystallinity values indicate very low grade metamorphism of Murree Formation in core of Hazara Kashmir Syntaxis. The petrographic data suggests that the provenance of sandstone is recycled orogen. Quartz is of igneous and metamorphic origin. Feldspar (albite and microcline) composition suggests its derivation from acidic igneous rocks. The rock fragments of volcanics, slate, phyllite, and schist suggest igneous and metamorphic provenance. The petrographic data suggests that at the time of deposition of Murree Formation, igneous and low grade metamorphic rocks were exposed. However, presence of some clasts of carbonates indicates that sedimentary rocks were also exposed in the source region. The quartz content and clay minerals in the shale revealed that source region was igneous and metamorphic rocks. Cyclic deposition, lithofacies, and various sedimentary structures like cross bedding, ripple marks, and calcite concretions suggest that deposition of Murree Formation occurred in fluviatile environment by meandering river system having decreasing turbidity current.     

拉萨地块西段典中组火山岩岩浆作用过程及其地质意义

拉萨地块西段分布有大面积的古近纪火山岩,蕴含着丰富的地质信息。文章对措勤地区典中组火山岩年代学、地球化学的研究表明,典中组火山岩岩浆活动在晚白垩世晚期已经开始,之后逐步向东迁移,时间上一直持续到古新世。印度板块与亚洲板块碰撞可能是从西段开始的,之后逐渐向东碰撞过渡。典中组火山岩岩浆形成的过程中发生了部分熔融作用,且在成岩过程中发生了混合作用;典中组火山岩是岛弧型俯冲向碰撞过渡过程中产生的具有岛弧或陆缘弧特点的火山岩。     

Structure and U–Pb zircon geochronology in the Variscan foreland of SW Sardinia,Italy

New field mapping, U–Pb zircon geochronology and structural analysis of the southernmost Sardinia metamorphic basement, considered a branch of the Variscan foreland, indicate that it is, in part, allochthonous and was structurally emplaced within the foreland area, rather than being older depositional basement beneath the foreland succession. The Bithia Formation, classically considered part of the ‘Southern Sulcis metamorphic Complex’ (and here termed the Bithia tectonic unit, or BTU), is a greenschist facies metamorphic unit commonly interpreted as Precambrian in age. New geochronology of felsic volcanic rocks in the BTU, however, yield a U–Pb zircon age of 457.01 ± 0.17 Ma (Upper Ordovician). Thus, the depositional age of the unit is younger than the weakly metamorphosed Lower Cambrian rocks of the adjacent foreland succession. New detailed mapping and analysis of the field relationships between the BTU and foreland succession indicates that their contact is a mylonitic shear zone. The metamorphic character, general lithology, and deformational history of the BTU are similar to those of units in the Variscan Nappe Zone located northeast of the foreland area. We reinterpret the BTU as a synformal klippe of material related tectonically to the Variscan Nappe Zone. We infer that it was thrust over and became infolded into the foreland during late stages of the Variscan contractional deformation. Copyright © 2012 John Wiley & Sons, Ltd.     

藏北羌塘菊花山那底岗日组火山岩锆石SHRIMP定年及其意义

那底岗日组主要为一套中酸性火山岩、火山碎屑岩,夹砂砾岩的岩石组合,主要分布在藏北羌塘中部地区,龙木错-双湖缝合带的北侧。对那底岗日组底部安山岩进行锆石SHRIMP测年,时代为219±4Ma,确定那底岗日组火山岩早期喷发时间为晚三叠世而不是早侏罗世,与龙木错-双湖一线的低温高压变质带的时代基本一致。结合区域地质资料,那底岗日组火山岩可能形成于板块消减的火山弧构造环境,为龙木错-双湖缝合带晚三叠世向北俯冲消减的产物。     

腾冲地区晚新生代火山活动浅析

腾冲火山喷发活动具有多期多次性,并且各期各次火山岩在空间上存在复杂的重叠关系。本文应用数学地质方法对火山岩地质年龄值和某些重要化学组分进行研究,结合火山岩岩石化学特征、野外产状、风化剥蚀程度等进行分期分类。在此基础上,将该区火山活动划分为５个喷发期。它们组成由基性喷发向中酸性喷发过渡的２个喷发旋回。最后,对该区未来火山喷活动进行了预测。     

The farnacht formation along the south side of the clew bay fault zone,Western Ireland: Its chemistry and age of metamorphism

The tectonically isolated Farnacht Formation consists of calc-alkaline dacitic-andesitic lavas of volcanic arc affinity. It is situated immediately to the south of the Clew Bay Fault Zone (western continuation of the Highland Boundary Fault Zone of Scotland) in the northeast corner of the Lower Palaeozoic South Mayo Trough in northwest Ireland. It has been metamorphosed to biotite grade greenschist facies following the development of a pervasive, c-s composite muscovite, quartz, and feldspar schistosity. The Farnacht Formation may comprise a terrane that is directly unrelated to nearby Ordovician and Silurian rocks; its present position was fixed largely by Wenlock times. The age of the Farnacht Formation and the deformational event(s) that produced the schistosity are not known. ⁴⁰Ar/³⁹ Ar step heating from four specimens have dated the crystallization of biotite at from 422 ± 2 to 405 ± 14 Ma with a mean age of 413 Ma. These ages date either the post-D2, pre-D3 metamorphic peak, or a hornfelsing of the same structural age related to an unseen thermal source, and provide a minimum age for the end Silurian - early Devonian Caledonian tectonothermal activity in the northeast part of the South Mayo Trough.     

五台山区七图金矿的物源特征及矿床成因浅析

矿区成矿元素地球化学以及成矿流休的初步研究表明，五台山七图金矿的成矿物质（金，银）主要来源于围岩的滹沱群四集庄组粗碎屑岩组合，变质基性火山岩的去硫作用提供了金矿化的硫源，韧－脆性剪切事宾发育及活动是金矿化的动力学机制，成矿流体具有变质流体的性质，在变质基性火山岩中形成的蚀变岩与金矿化密切相关，矿床成因类型为沉积变质热液叠加型金矿床。     

辽宁宽甸地区辽河群里尔峪组基性火山岩锆石U-Pb年代学及其地质意义

辽东古元古代构造带内辽河群的形成时代及其演化一直是学者研究的热点.本文对宽甸地区里尔峪组变沉积岩夹层的基性火山岩进行锆石LA-ICP-MS U-Pb年代学研究.7件基性火山岩样品的锆石分为岩浆锆石和变质锆石.测年结果显示代表岩石成岩年龄的岩浆活动有2期:2 150~2 130 Ma、2 050~2 020 Ma,结合本区出露的酸性火山岩,表明宽甸地区辽河群形成时代至少处于2.17~2.03 Ga.获得的5件斜长角闪岩变质年龄显示变质作用发生在1 900 Ma以后,持续时间比较长为1 870~1 780 Ma;进一步可分为3个阶段1 870~1 861 Ma、1 845~1 842 Ma、1 790~1 780 Ma,变质作用峰期为~1 850 Ma,属于本区古元古代第2个强烈的变质峰期,第3阶段与~1 800 Ma左右的变质事件一致.变质闪长岩（D015）脉体形成时代为1 314±24 Ma,斜长角闪岩（D1465-1）变质年龄为1 290±21 Ma,这是首次在辽东地区识别出中元古代岩浆和变质事件,结合辽西和冀北地区1 320~1 380 Ma岩浆活动,认为这些事件是华北板块对Columbia超大陆的裂解过程的响应.      

吉林安图海沟岩群的解体：地质与锆石年代学证据

对吉林安图地区原划为中元古代构造地层的海沟岩群进行的野外地质工作和锆石 SHRIMP U-Pb 年代学工作表明, 海沟岩群不同岩组的变质程度和形成时代都存在明显差异。 以条带状含铁建造为特征的四岔子岩组受到高级变质作用改造, 变质程度为高角闪岩相并伴有深熔。 侵入 BIF 铁矿的奥长花岗质片麻岩给出的形成时代为 2 554 ± 3 Ma 或更老, 变质时代为 2 528 ± 11 Ma, 表明四岔子岩组应当老于 2 554 Ma。 结合区域对比, 推测其为新太古代变质表壳岩。 而东方红岩组虽然变形作用强烈, 但仅为绿片岩相变质。 该岩组中的变流纹岩形成年龄为 178 ± 2 Ma, 表明其为早侏罗世火山岩, 受到后期韧性变形作用的改造。 新资料表 明原划的海沟岩群需要解体, 其中既包括太古宙变质基底, 也包括受到变形影响的中生代地层。 太古宙地质体在古生代末-中生代初古亚洲洋闭合及造山后构造作用下, 呈岩片出露在年轻地质体之间。 本文的奥长花岗质片麻岩变质增生边和变质新生锆石具有异常高的 Th/U 比 值, 推测其和变质过程中高 U 矿物的形成有关。 高 Th/U 比变质锆石和低 Th/U 比岩浆锆石的实例表明：对锆石成因进行判别时, Th/U 比值只能作为一个辅助手段谨慎使用。     

延边金谷山地区早二叠世"柯岛岩组"火山喷发-沉积构造划分及构造环境

延边金谷山地区二叠纪"柯岛岩组"为一套低绿片岩相变质岩系,其原岩为一套酸性-中酸性火山碎屑沉积岩系.通过剖面详细测量和岩石学研究,建立了该地区"柯岛岩组"层序,划分了6个火山喷发-沉积旋回,并依据各旋回序列岩相组合特征,恢复了该地区在陆表海裂陷(槽)构造条件水下火山喷发-沉积作用及演化环境.     

Crustal structure of the Ordovician Macquarie Arc,Eastern Lachlan Orogen,based on seismic‐reflection profiling

In the Eastern Lachlan Orogen, the mineralised Molong and Junee‐Narromine Volcanic Belts are two structural belts that once formed part of the Ordovician Macquarie Arc, but are now separated by younger Silurian‐Devonian strata as well as by Ordovician quartz‐rich turbidites. Interpretation of deep seismic reflection and refraction data across and along these belts provides answers to some of the key questions in understanding the evolution of the Eastern Lachlan Orogen—the relationship between coeval Ordovician volcanics and quartz‐rich turbidites, and the relationship between separate belts of Ordovician volcanics and the intervening strata. In particular, the data provide evidence for major thrust juxtaposition of the arc rocks and Ordovician quartz‐rich turbidites, with Wagga Belt rocks thrust eastward over the arc rocks of the Junee‐Narromine Volcanic Belt, and the Adaminaby Group thrust north over arc rocks in the southern part of the Molong Volcanic Belt. The seismic data also provide evidence for regional contraction, especially for crustal‐scale deformation in the western part of the Junee‐Narromine Volcanic Belt. The data further suggest that this belt and the Ordovician quartz‐rich turbidites to the east (Kirribilli Formation) were together thrust over ?Cambrian‐Ordovician rocks of the Jindalee Group and associated rocks along west‐dipping inferred faults that belong to a set that characterises the middle crust of the Eastern Lachlan Orogen. The Macquarie Arc was subsequently rifted apart in the Silurian‐Devonian, with Ordovician volcanics preserved under the younger troughs and shelves (e.g. Hill End Trough). The Molong Volcanic Belt, in particular, was reworked by major down‐to‐the‐east normal faults that were thrust‐reactivated with younger‐on‐older geometries in the late Early ‐ Middle Devonian and again in the Carboniferous.     

东昆仑诺木洪地区白沙河岩组岩石学、地球化学及年代学特征

金水口岩群上部的白沙河岩组作为东昆仑的基底变质岩系之一,对研究东昆仑造山带的形成与演化具有重要的地质意义.选择青海省诺木洪地区出露的白沙河岩组作为研究对象,对其开展野外地质调查、岩石学、岩石地球化学、锆石U-Pb同位素年代学等相关研究.通过调查将该地区白沙河岩组划分为上中下3个岩性段,从中识别出矽线石、石榴子石、单斜辉石、白云石等特征变质矿物组合,表明该岩组经历了高角闪岩相-低麻粒岩相变质作用.对识别出的泥质变质岩利用石榴子石-黑云母温度计和石榴子石-黑云母-斜长石-石英压力计所恢复的视峰期变质温度为660~683℃,压力为3.9~4.2 kbar;对基性变质岩使用角闪石-斜长石温度计与角闪石-斜长石-石英压力计,恢复其变质温度为723~772℃,压力为3.4~4.9 kbar.对其中的长英质副变质岩进行碎屑锆石年代学研究,频数峰值集中在1 300 Ma,其原岩沉积年龄应晚于中元古代.白沙河岩组中变质基性岩原岩为形成于板内伸展环境的拉斑玄武岩;长英质变质岩原岩为泥质-砂质陆缘碎屑岩.白沙河岩组原岩建造为陆缘碎屑岩夹基性火山岩系列,上部为碳酸盐岩沉积,其可能形成于由伸展向挤压转换的构造条件下的大陆裂谷晚期.      

Lower and Middle Ordovician conodonts of Laurentian affinity from blocks of limestone in the Rosroe Formation,South Mayo Trough,western Ireland and their palaeogeographic implication

The Middle Ordovician Rosroe Formation consists of some 1350 m of coarse, mainly siliciclastic to volcaniclastic sedimentary rocks, deposited in a submarine fan environment, and is restricted to the southern limb of the South Mayo Trough, western Ireland. Discrete allochthonous blocks, reaching 5 m in size, are present in the formation at several localities. Conodonts recovered from these blocks, collected from two separate locations, are of late Early and mid Mid Ordovician age. The conodonts have high conodont‐alteration indices (CAI 5) indicative of temperatures as high as 300^o to max. 480 °C; some found in the Lough Nafooey area have abnormally high indices (CAI 6), which correspond to temperatures of about 360^o to max. 550 °C. The oldest fauna is dominated by Periodon aff. aculeatus and characterized by Oepikodus evae typical of the Oepikodus evae Zone (Floian Stage; Stage Slices Fl2–3, Lower Ordovician). The younger conodont assemblage, characterized by Periodon macrodentatus associated with Oistodella pulchra, is referred to the P. macrodentatus conodont Biozone (lower Darriwilian; Stage Slices Dw1–2). The Rosroe conodont assemblages are of Laurentian affinity; comparable faunas are well known from several locations along the east to south‐eastern platform margin of Laurentia and the Notre Dame subzone of central Newfoundland, Canada. The faunal composition from the limestone blocks suggests a shelf edge to slope (or fringing carbonate) setting. The faunal assemblages are coeval with, respectively, the Tourmakeady Formation (Floian–Dapingian) and Srah Formation (Darriwilian) in the Tourmakeady Volcanic Group in the eastern part of the South Mayo Trough and probably are derived from the same or similar laterally equivalent short‐lived carbonate successions that accumulated at offshore ‘peri‐Laurentian’ islands, close to and along the Laurentian margin. During collapse of the carbonate system in the late Mid Ordovician, the blocks were transported down a steep slope and into deep‐water by debris flows, mixing with other rock types now found in the coarse polymict clastics of the Rosroe Formation. The faunas fill the stratigraphical ‘gap’ between the Lower Ordovician Lough Nafooey Volcanic Group and the upper Middle Ordovician Rosroe Formation in the South Mayo Trough and represent a brief interval conducive to carbonate accumulation in an otherwise siliciclastic‐ and volcaniclastic‐dominated sedimentary environment. Copyright © 2015 John Wiley & Sons, Ltd.     

Age of the Mt Boggola volcanic succession and further geochronological constraint on the Ashburton Basin,Western Australia

The age of strata in the Palaeoproterozoic Ashburton Basin is not well constrained, particularly the generally homogeneous, turbiditic and thick Ashburton Formation containing only a small fraction of volcanics suitable for geochronological examination. The Mt Boggola volcanic succession is one of these rare occurrences, consisting of mafic pillow lavas and breccia overlain by BIF, chert, ferruginous pelite, mafic volcaniclastics and possible felsic tuffs identified in the course of mineral exploration. A locality proximal to the volcanic succession is interpreted as a fragmental volcaniclastic unit derived with minimal reworking from a tuff. Zircon extracted from this unit has yielded a SHRIMP ²⁰⁷Pb/²⁰⁶Pb weighted‐mean age of 1829 ± 5 Ma (95% conf.: χ² 1.0). This age is significantly older than that of the June Hill Volcanics in the northwest of the Ashburton Basin that had previously been surmised to be potentially coeval, and provides a further constraint on the evolution and diachroneity of the Ashburton Formation.