The Sudbury Structure (Ontario,Canada): a tectonically deformed multi-ring impact basin

The occurrence of shock metamorphic features substantiates an impact origin for the 1.85 Ga old Sudbury Structure, but this has not been universally accepted. Recent improvements in knowledge of large-scale impact processes, combined with new petrographic, geochemical, geophysical (LITHOPROBE) and structural data, allow the Sudbury Structure to be interpreted as a multi-ring impact structure. The structure consists of the following lithologies: Sudbury Breccia —dike breccias occurring up to 80 km from the Sudbury Igneous Complex (SIC); Footwall rocks and Footwall Breccia — brecciated, shocked crater floor materials, in part thermally metamorphosed by the overlying SIC; Sublayer and Offset Dikes, Main Mass of the SIC and Basal Member of the Onaping Formation (OF) — geochemically heterogeneous coherent impact melt complex ranging from inclusion-rich basal unit through a dominantly inclusion-free to a capping inclusion-rich impact melt rock; Grey Member of OF — melt-rich impact breccia (suevite); Green Member of OF — thin layer of fall back ejecta; Black Member of OF — reworked and redeposited breccia material; Onwatin and Chelmsford Formations — post-impact sediments. Observational and analytical data support an integrated step-by-step impact model for the genesis of these units. Analysis of the present spatial distribution of various impact-related lithologies and shock metamorphic effects result in an estimated original rim-to-rim diameter of the final crater of 200 or even 280 km for the Sudbury Structure, prior to tectonic thrusting and deformation during the Penokean orogeny.     

新疆构造运动期序及特征

新疆地域辽阔,地质构造运动复杂,特征各异。前人曾对新疆构造运动的划分及命名做了大量工作,但多有不一致,有些构造运动的划分或命名依据不足,因此失去了应有的代表性。现根据实际资料,对新疆地质构造运动重新归纳和认识,提出新疆境内构造运动可划分为11期32幕(次),其中前寒武纪6期、古生代2期17幕(次),中新生代3期9幕(次)     

东亚大陆边缘的构造格架及其中-新生代演化

燕山运动在亚洲大陆雏形东缘形成2条北东向的剪切带:郯庐断裂带和长乐-南澳-中央构造线断裂带,晚侏罗世—古近纪早期沿之发生地体/地块的拼贴。系统叙述了各移置地体/地块的主要岩石记录和拼贴时代,据起源分为3类:异地的(包括源自冈瓦纳的和源自盘古大洋的)、半异地的和准原地的;据拼贴位置分为2组:拼贴后基本位于原地的(日本海张开以前) 和发生过向北东错移的。新生代内东亚大陆边缘发生解体,可以台湾岛以北的菲律宾海盆断裂为界将东亚大陆边缘弧分为2段,北段仍处于剪切-拉张中,南段已进入剪切挤压-造山阶段。强调该地区中—新生代演化经历了2个里丁旋回, 形成早白垩世的北东向和新近纪的北东东向2期新生构造。     

Post-collisional volcanism in a sinking slab setting—crustal anatectic origin of pyroxene-andesite magma, Caldear Volcanic Group, Neogene Alborán volcanic province, southeastern Spain

Caldear Volcanic Group (CVG), a stratigraphically well defined, calc-alkaline rock complex within S^a de Gata in the eastern part of the Alpine Betic mountain chain, S Spain, consists of three distinct formations: Hernández pyroxene andesites, Bujo hornblende-bearing pyroxene andesites and Viuda hornblende-bearing pyroxene dacites–rhyolites. The letter rock formation may have developed through crystal fractionation of mainly plagioclase and pyroxenes, however there is no direct relation between two formations. CVG has a domainal structure with a northeastern domain where Hernández formation is overlain by Bujo formation while Viuda formation is absent, and a southwestern domain where Viuda formation forms the only fractionate after Hernández formation. Hernández parent magma is thought generated through crustal anatexis by dehydration melting of a predominantly amphibolitic source rock complex which was formed by metamorphism from c. 500 Ma volcano-sedimentary parent material. The domainal structure of CVG is explained by compositional variation within this protogenetic complex. Single crystal U–Pb ages of c. 500 Ma to 1800 Ma for inherited zircon support the presence of clastic material of Proterozoic derivation within the original volcano-sedimentary complex. Regional study of syn-collisional rock formations (Alpine nappe complexes) indicate that the collisional tectonic stage in the Betic-Rif orogenic belt took place rather early (25–30 Ma?) and was followed by a stage of rapid regional rock uplift, fast cooling (c. 500°C/my) and extensional tectonics in the period 22–17 Ma. This later tectonic stage was set into motion by slab break-off which set the stage for a high temperature regime in the overlying lithosphere, providing the framework for the crustal melting and magma production responsible for the calc-alkaline rocks of Alborán volcanic province. Miocene zircon with ages ranging from c. 17 to 11 Ma indicate a rather protracted magmatic development prior to eruption at c. 11 Ma. Post-collisional character of Caldear Volcanic Group thus seems well established.     

赣东北地区构造演化的新认识

根据近几年来赣东北地区的区域地质调查及科研工作所获的地质资料、化石资料和实测数据,论述了该区晋宁期以来的构造演化,提出了以下看法：①该区是一个多期造山作用的复合体,它经历了褶皱基底形成、洋陆转化和陆内发展三大阶段和晋宁期、加里东期、印支期、燕山期四个构造旋回;②早古生代该区存在一小洋盆;③加里东期构造旋回在赣东北地区是明显的,其造山作用是存在的,并由此奠定了该区构造分区的总体格局。     

青藏高原南部晚新生代板内造山与动力成矿

青藏高原晚新生代构造隆升是板块碰撞成因还是板内造山过程 ,关系到高原形成机制、演化过程以及岩石圈动力学与大陆动力学的关系等一系列重大科学问题。近年来在冈底斯发现多个以斑岩铜矿为主的大型和超大型矿床 ,其成矿时代为 2 0～ 12Ma ,与青藏高原构造隆升时代一致 ,也与笔者10年前以大陆动力学和成矿动力学为理论指导的预测结果吻合。青藏高原南部晚新生代大量的地质、地球物理、矿床等方面的证据根本不支持碰撞造山理论 ,如青藏高原内部伸展边缘逆冲、碰撞与隆升之间时差明显 ,壳内低速层和低阻层发育 ,造山与成盆关系密切 ,板内隆升环境下发生大规模构造变形、岩浆活动和动力成矿等。青藏高原南部晚新生代构造隆升作用是在新特提斯开合转换、碰撞造陆之后 ,在下地壳层流作用的驱动下 ,发生板内造山、地壳增厚、热隆伸展和改造成矿的构造成矿过程 ,大规模的板内金属成矿在 3～ 4Ma以来的均衡隆升、成山过程中进一步改造。     

青藏高原南部与东南部重要成矿带的大地构造定格与找矿前景

印度/亚洲汇聚-碰撞过程经历了新特提斯洋盆滋生、消减和俯冲、亚洲南缘增生造山以及印度/亚洲碰撞造山和青藏高原的隆升,在青藏高原南部和东南部造就了"冈底斯火山岩浆带"、"雅鲁藏布江缝合带"、"喜马拉雅碰撞造山带"和大量物质向南东逃逸的"三江侧向挤出地体群",以及相应形成具有重大找矿突破战略前景的"冈底斯成矿带"、"雅鲁藏布江成矿带"、"特提斯喜马拉雅成矿带"和"三江成矿带"。本文通过对四大成矿带的大地构造定格讨论了与资源前景相关的科学问题,提出"冈底斯成矿带"中的岛弧型斑岩铜金矿具有找矿的重大潜力、重视藏东—滇西地区的俯冲-碰撞型岩浆成矿专属性研究;提出扩大西藏罗布莎铬铁矿矿集区的开发规模,以及在西部阿里地区的大型超基性岩体中寻找新的铬铁矿远景地的思路;在三江多阶段成矿作用的叠合型矿床中,集中古特提斯和新特提斯成矿类型,关注与斜向碰撞有关的走滑剪切带对成矿作用的制约机制;需进一步确定特提斯喜马拉雅矿化带与藏南拆离系关系和重视始—中新世高Sr/Y花岗(斑)岩的成矿专属性及找矿前景。     

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。     

Arc magmatism in eastern Kumaun Himalaya,India: A study based on geochemistry of granitoid rocks

Petrochemical studies of granitoid rocks from the eastern part of Kumaun region suggest that the leading edge of India represents an active arc during Late Paleoproterozoic times. It has been observed that melt generation for granodiorite rocks from the eastern Almora Nappe and Chhiplakot klippe along with the Askot klippe was caused through a subduction‐related process involving hydrous partial melting of a Paleoproterozoic amphibole‐ and/or garnet‐bearing mafic source with the involvement of sediments from the subduction zone. The medium‐ to high‐K basic rocks, common in subduction‐related magmatic arcs, can also explain the generation of the high‐K granodiorites of the Chhiplakot klippe. The augen gneisses from the eastern Almora nappe and Chhiplakot klippe along with the Askot klippe further show geochemical similarity with the associated granodiorites, suggesting there is a genetic linkage with one another.