构造动力体制与复合造山作用——兼论三江复合造山带时空演化

构造动力体制是研究区域大地构造演化和成矿地质环境的基础,而造山带作为全球金属矿产资源集中产出的地带,同时保留了地球地质构造演化最为丰富的记录,因而是用来解剖不同构造动力体制及相关成矿环境和成矿作用的主要对象.板块构造源于大洋,描述和解释的是以水平运动为主导的板块构造导致的大陆边缘增生和大洋板块消失及与其相关的地质现象,其动力学体制称为大洋动力体制;大陆构造描述和解释的主要是大陆内部而不是边缘发生的以垂直运动(壳幔相互作用)为主导的的大陆物质增生和消失及其相关的地质现象,其动力学体制称为大陆动力体制;而洋陆转换则是水平和垂直运动相互耦合、共同作用的动力学体制,描述和解释的是洋陆转换及其相关的地质现象,可以将其称为转换动力体制.不同构造动力体制在全球范围内具有同区转承和异区并存特点.每一种构造动力体制都可以激发造山作用,因此,地球上同时存在着不同类型的造山作用和造山带,可以归结为俯冲造山(带)、碰撞造山(带)、伸展造山(带)和陆内造山(带)等完整反映造山带演化过程的4种类型.复合造山概念科学地描述了全球不同造山带的复杂性.它具有三种涵义,一是不同时期相同或不同类型造山带在空间上的复合(叠置);二是同一造山带在不同地质历史阶段、不同构造动力体制下造山作用的时间复合(叠加);三是同时具有时空复合特征的复合造山带.对三江造山带时空结构的解析表明,它是具有时空复合特征的巨型复合造山带的典型代表.     

Environmental upheavals of the Ediacaran period and the Cambrian “explosion” of animal life

The second half of the Ediacaran period began with a large impact e the Acraman impact in South Australia, which was accompanied by a negative d13Ccarb anomaly and an extinction-radiation event involvi...     

The Origin of the Black Shale Series and Bentonites from the Wufeng Formation in the Southwestern Upper Yangtze: Implications for the Convergence of the Yangtze and Cathaysia Blocks in the Late Ordovician

Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary. However, the intimate relationship between their origins and the dynamic mechanisms are unclear, as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition (OST). In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks (i.e., the intracontinental Kwangsian Orogeny), two stratigraphic sections respectively in Zhaotong area (Northeast Yunnan) and Puyi area (Northwestern Guizhou) that were located in the semi-restricted inner Yangtze Sea during the OST were systematically studied, on the basis of whole-rock geochemical composition, pyrite δ34S (δ34Spy), total organic carbon (TOC), stable Sr isotope, pyrite framboid size distribution and zircon U-Pb age, trace elements. The evidence shows that the paleo-oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation. These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval. Based on previous research on the genetic relationship between black shale series and plate tectonic movement, a basin-mountain evolution model suitable for South China in the Late Ordovician is presented. The two bentonites in the Wufeng Formation with U-Pb ages of 445.5 ± 0.8 Ma and 441.9 ± 2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician, the provenance region probably being located in the Jiangnan orogenic belt. Thus, we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin-mountain transformation and the Kwangsian Orogeny in South China, which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician.     

Deformation history of the Hampden Synform in the Eastern Fold Belt of the Mt Isa terrane

The moderately metamorphosed and deformed rocks exposed in the Hampden Synform, Eastern Fold Belt, in the Mt Isa terrane, underwent complex multiple deformations during the early Mesoproterozoic Isan Orogeny (ca 1590–1500 Ma). The earliest deformation elements preserved in the Hampden Synform are first‐generation tight to isoclinal folds and an associated axial‐planar slaty cleavage. Preservation of recumbent first‐generation folds in the hinge zones of second‐generation folds, and the approximately northeast‐southwest orientation of restored L¹ ₀ intersection lineation suggest recumbent folding occurred during east‐west to northwest‐southeast shortening. First‐generation folds are refolded by north‐south‐oriented upright non‐cylindrical tight to isoclinal second‐generation folds. A differentiated axial‐planar cleavage to the second‐generation fold is the dominant fabric in the study area. This fabric crenulates an earlier fabric in the hinge zones of second‐generation folds, but forms a composite cleavage on the fold limbs. Two weakly developed steeply dipping crenulation cleavages overprint the dominant composite cleavage at a relatively high angle (>45°). These deformations appear to have had little regional effect. The composite cleavage is also overprinted by a subhorizontal crenulation cleavage inferred to have developed during vertical shortening associated with late‐orogenic pluton emplacement. We interpret the sequence of deformation events in the Hampden Synform to reflect the progression from thin‐skinned crustal shortening during the development of first‐generation structures to thick‐skinned crustal shortening during subsequent events. The Hampden Synform is interpreted to occur within a progressively deformed thrust slice located in the hangingwall of the Overhang Shear.     

Relationships between deformation and partial melting in the Palmer migmatites,South Australia

The migmatites of the Palmer area, in the core of the Mt Lofty Ranges metamorphic belt, are considered to have formed by partial melting of quartzo‐feldspathic schists and gneisses, rather than by metamorphic segregation as formerly suggested. Large‐ and small‐scale tectonic structures indicate that the Cambrian Kanmantoo Group rocks in the Palmer area have undergone three deformations during the Delamerian Orogeny and that these are similar to those described elsewhere in the Mt Lofty Ranges. The relationships of the migmatitic veins to these structures indicate that some partial melt was present during a large part of the structural history: some veins formed before and after the first folding event, and some formed during or after the third folding event even though the metamorphic grade appears to have been waning in areas more distant from the highest grade ore. The early onset of partial melting is consistent with previously reported evidence that thermal activity in the belt began before penetrative deformation.     

Structural history of the Arthur Lineament,northwest Tasmania: An analysis of critical outcrops

The Arthur Lineament of northwestern Tasmania is a Cambrian (510 ± 10 Ma) high‐strain metamorphic belt. In the south it is composed of metasedimentary and mafic meta‐igneous lithologies of the ‘eastern’ Ahrberg Group, Bowry Formation and a high‐strain part of the Oonah Formation. Regionally, the lineament separates the Rocky Cape Group correlates and ‘western’ Ahrberg Group to its west from the relatively low‐strain parts of the Oonah Formation, and the correlated Burnie Formation, to its east. Early folding and thrusting caused emplacement of the allochthonous Bowry Formation, which is interpreted to occur as a fault‐bound slice, towards the eastern margin of the parautochthonous ‘eastern’ Ahrberg Group metasediments. The early stages of formation of the Arthur Lineament involved two folding events. The first deformation (CaD₁) produced a schistose axial‐planar fabric and isoclinal folds synchronous with thrusting. The second deformation (CaD₂) produced a coarser schistosity and tight to isoclinal folds. South‐plunging, north‐south stretching lineations, top to the south shear sense indicators, and south‐verging, downward‐facing folds in the Arthur Lineament suggest south‐directed transport. CaF₁ and CaF₂ were rotated to a north‐south trend in zones of high strain during the CaD₂ event. CaD₃, later in the Cambrian, folded the earlier foliations in the Arthur Lineament and produced west‐dipping steep thrusts, creating the linear expression of the structure.     

燕山早期花岗岩基印支期侵位的岩浆动力学证据及构造 意义:基于南岭8个岩体侵位年龄计算结果

根据各花岗岩体地质构造特征、有关的热物理参数及主体花岗岩的放射性元素含量,采用简化的立方体数学模型计 算得出:南岭地区8个花岗岩基侵位后,其初始温度降低至结晶温度所需的时间(Δtcol)为3.9(金鸡岭)~5.5 Ma(九峰); 由于结晶潜热释放而使结晶过程延长的时间(ΔtL) 为2.6~3.5 Ma ;花岗岩浆侵位后产生的放射成因热使结晶过程延长的 时间(Δt A)为 5.2(陂头)~45.1 Ma(姑婆山) 。南岭地区 8 个燕山早期花岗岩基的侵位-结晶时差(△t ECTD)为 12.1(陂头) ~52.2 Ma(姑婆山), 结合锆石U-Pb年龄通过反演计算得出其侵位年龄 (tE ) 为194.4 (陂头)~219.3 Ma(九峰)。这为 南岭燕山早期花岗岩基属于印支期侵位提供了重要的岩浆动力学佐证, 揭示出近东西向展布的南岭晚中生代造山带具有印 支期构造格架(以侵位年龄为代表)和燕山早期花岗岩(以锆石 U-Pb 年龄为代表) 的双重特征。     

Basement massifs in the Appalachians: their role in deformation during the Appalachian Orogenies

Basement is constituted of rocks which belong to a previous orogenic cycle which have been reactivated and incorporated into a younger cycle. Basement massifs may be classified according to their relative position in an orogen as external or internal massifs. They may also be categorized according to their role in deformation, as thrust-related, fold-related and composite massifs. All Appalachian external massifs were transported following their removal from the overridden edge of the ancient North American continental margin. Most of the internal massifs are also probably transported, but several (Pine Mountain and Sauratown Mountains) may be present as windows exposing parautochthonous basement beneath the main thrust sheet. The latter reside immediately west of the low (west) to high (east) gravity gradient which probably outlines the old edge of Grenvillian crust. Reactivated crustal material generated during early Palaeozoic orogeny plays the same mechanical role in reactivation as basement from the previous Grenville cycle. The domes of the Bronson Hill anticlinorium cored with Ordovician or older gneisses illustrate this behaviour. Basement (Grenville) massifs are distributed throughout the Appalachians as a belt of external massifs (Blue Ridge, Reading Prong, Hudson and Berkshire Highlands, Green Mountains, and Long Range Mountains) along the western edge of the crystalline metamorphic core. Additionally, internal massifs are also present (Pine Mountain belt, Tallulah Falls and Toxaway domes, Sauratown Mountains anticlinorium, State Farm gneiss dome, Baltimore Gneiss domes, Mine Ridge anticline, and Chain Lakes massif). Basement internal massifs probably served to localize thrusts by causing them to ramp over and around the massifs. Their antiformal shape may in part be as much related to thrust mechanics as to folding.