From A to B,randomly: a point-to-point random trajectory generator for animal movement

For applications in animal movement, we propose a random trajectory generator (RTG) algorithm that combines the concepts of random walks, space-time prisms, and the Brownian bridge movement model and is capable of efficiently generating random trajectories between a given origin and a destination point, with the least directional bias possible. Since we provide both a planar and a spherical version of the algorithm, it is suitable for simulating trajectories ranging from the local scale up to the (inter-)continental scale, as exemplified by the movement of migrating birds. The algorithm accounts for physical limitations, including maximum speed and maximum movement time, and provides the user with either single or multiple trajectories as a result. Single trajectories generated by the RTG algorithm can be used as a null model to test hypotheses about movement stimuli, while the multiple trajectories can be used to create a probability density surface akin to Brownian bridges.     

三维地层的三棱柱剖分与土方计算

三维地层剖分算法是实现地层三维可视化与土方计算的重要基础。采用三棱柱体建模方法构造三维地层,分析任意平面切割三棱柱的不同情形,得出了针对三棱柱地层的剖分算法;提出了以切割面为分界面,将单个三棱柱剖分成多个小三棱柱的三角投影分割法--将三棱柱顶面、底面及切割截面按一定规则进行合理三角化划分,使划分后三角形在水平面上的投影相重合;将该3层三角形组合成以切割面为分界面的2层小三棱柱,从而完成剖分。土方计算中首先给出开挖体的边界控制方程,根据该控制方程所限定的内边界得到开挖区域,结合上述剖分算法,对该区域内所有小三棱柱体积求和,得到开挖土方量。将以上算法应用到广东省某重大水利工程中,实现了基坑模拟开挖及其土方计算。     

Tectonically-driven mud volcanism since the late Pliocene on the Calabrian accretionary prism,central Mediterranean Sea

Mud volcanoes recently discovered on the offshore Calabrian Arc are investigated at two sites 60 km apart, in water depths of 1650--2300 m, using swath bathymetry, 2D&3D multichannel seismic and cores. The seabed and subsurface data provide information on their formation and functioning in relation to tectonic activity during the rapid Plio-Quaternary advance of the accretionary prism. Fore-arc extension and thrust-belt compression are seen to have involved two main phases of activity, separated by a regional unconformity recording a mid-Pliocene (3.5–3.0 Ma) tectonic reorganization. The two sites of mud volcanism lie in contrasting tectonic settings (inner fore-arc basin vs central fold-and-thrust belt) and record differing forms of seabed extrusive activity (twin mud cones and a caldera vs a broad mud pie). At both sites, subsurface data show that mud volcanism took place throughout the second tectonic phase, since the late Pliocene; differing forms of mud extrusion were accompanied by subsidence to form depressions beneath and within extrusive edifices up to 1.5 km thick. The basal subsidence depressions point to sources within the succession of thrusts underlying the inner to central Arc, consistent with microfossils within cored mud breccias from both sites that are derived from strata as old as Late Cretaceous.     

Tectono-magmatic evolution from accretion to collision in the southern margin of the Central Asian Orogenic BeltSCIEI北大核心CSCD

造山带演化及增生到碰撞的转变是板块构造与大陆动力学研究中的前沿科学问题。中亚造山带被认为是古亚洲洋长期俯冲-增生演化形成的显生宙最大的增生造山带,以发育巨量的面状展布的俯冲-增生相关的弧岩浆岩为特征。并且,由于中亚增生型造山带在潘吉亚最后聚合过程中发生弧弧(陆)碰撞,因此缺乏大规模且跨构造单元的碰撞相关的构造和变质等物质标志。显然,能否识别出大洋闭合期间碰撞作用的岩浆标志成为确定增生造山带增生过程终止的关键之一。本文系统研究确定:中亚造山带东南缘二叠纪到三叠纪钙碱性-碱钙性岩浆在空间分布上显示出由北西向南东迁移演化的特征;在岩浆性质上具有从二叠纪新生地壳来源的弧岩浆向早-中三叠世碰撞挤压背景下古老陆壳组分逐渐增多的高Sr/Y岩浆以及晚三叠世后造山伸展相关的A型花岗岩演化的特征。这些特征提供了俯冲-增生向碰撞造山演变的关键岩浆岩证据。结合区域资料,厘定出增生造山带最后碰撞相关的标志性岩浆为沿缝合带呈零星线性展布的增厚下地壳源区的高Sr/Y花岗岩类,构建了中亚造山带南缘从双向俯冲-增生到增生楔-增生楔碰撞及后造山伸展的三阶段构造-岩浆演化模型。系统对比研究,揭示出增生-碰撞相关的岩浆记录沿横向展布在中亚造山带南缘甘肃北山到吉林中部一带,表明碰撞挤压相关的岩浆作用在中亚造山带南缘具有一定的普适性。中亚造山带南缘从增生到碰撞的岩浆演化记录的厘定,证实显生宙最大的巨型增生造山带演化末期经历了碰撞造山作用,对进一步深入探索增生造山演化末期碰撞相关的标志性岩浆具有重要意义。     

马尼拉俯冲带中段增生楔精细构造特征及微型圈闭盆地发育模式探讨

对马尼拉俯冲带中段高精度地形数据编辑后绘制成图,联合之前所获取的地震剖面数据,对俯冲带增生楔的精细构造地貌特征及发育模式进行了深入探讨.在增生楔下构造区发现了大量狭长的微型圈闭盆地,经过对其平面断裂特点与深部应力状态的分析,发现增生楔从俯冲前缘到脊顶区其构造特点的转变对应着微型圈闭盆地4个完整的发育阶段,即初期的加积断裂阶段、中期的圈闭成盆阶段、后期的挤压消亡阶段乃至最终的隆升推覆阶段,揭示出一种新型的俯冲带增生楔发育模式,并推断其本质是深部板片俯冲活动所产生的压应力在海底面的表现.     

造山带中增生楔识别与地质意义

增生楔主要由海沟复理石、远洋—半远洋沉积和洋岛/海山等大洋板块地层岩石及蛇绿岩共同构成,是汇聚板块边缘古俯冲带构造—沉积作用的综合产物,以发育叠瓦状逆冲断层、双冲断层和紧闭—倒转褶皱,以及片理、碎裂构造、小型褶皱、膝折等不同尺度的构造为特征。增生楔组成包括连续单元和混杂岩两部分,严格受滑脱面位置控制。增生楔是增生型造山带最基本大地构造相,它与弧前盆地、岛弧/大陆边缘弧的时空配置关系可直接指示大洋板块俯冲极性、揭示洋盆演化与造山作用方式。准确识别增生楔,详细解剖其结构特征与组成特征,综合判别并恢复大洋板块地层,可为古板块边界与古大洋盆地消亡位置确定、造山带结构精细划分及造山作用过程重建提供基本依据。大比例尺地质填图是研究增生楔结构和组成、以及大洋板块地层重建的有效手段。以南祁连拉脊山石灰窑增生楔为例,地质填图结果表明它是由中寒武世—早奥陶世洋壳物质构成,自北而南依次可分为海沟—大洋盆地—海山OPS和六道沟SSZ型蛇绿岩,被南倾逆冲断层分割成多个岩片。海沟—大洋盆地OPS岩片基本保留完整地层序列,海山OPS岩片包括连续单元和混杂岩两部分。顶帽山增生楔主要由海山OPS构成,内部结构层序相对完好,是南祁连构造带中保留最为完整、规模最大的海山OPS岩石组合序列。上述不同类型OPS片段和六道沟SSZ型蛇绿岩组成的增生楔与其南侧岛弧带同时代。增生楔—岩浆弧的时空配置暗示寒武纪—早奥陶世时期原特提斯洋自北向南俯冲极性。这些认识为南祁连早古生代火山—岩浆—沉积构造演化以及是否存在古洋盆与古洋盆演化重建提供基本佐证。     

Paleozoic tectonism on the East Gondwana margin: Evidence from SHRIMP U–Pb zircon geochronology of a migmatite–granite complex in West Antarctica

The Fosdick Mountains migmatite–granite complex in West Antarctica records episodes of crustal melting and plutonism in Devonian–Carboniferous time that acted to transform transitional crust, dominated by immature oceanic turbidites of the accretionary margin of East Gondwana, into stable continental crust. West Antarctica, New Zealand and Australia originated as contiguous parts of this margin, according to plate reconstructions, however, detailed correlations are uncertain due to a lack of isotopic and geochronological data. Our study of the mid-crustal exposures of the Fosdick range uses U–Pb SHRIMP zircon geochronology to examine the tectonic environment and timing for Paleozoic magmatism in West Antarctica, and to assess a correlation with the better known Lachlan Orogen of eastern Australia and Western Province of New Zealand.NNE–SSW to NE–SW contraction occurred in West Antarctica in early Paleozoic time, and is expressed by km-scale folds developed both in lower crustal metasedimentary migmatite gneisses of the Fosdick Mountains and in low greenschist-grade turbidite successions of the upper crust, present in neighboring ranges. The metasedimentary rocks and structures were intruded by calc-alkaline, I-type plutons attributed to arc magmatism along the convergent East Gondwana margin. Within the Fosdick Mountains, the intrusions form a layered plutonic complex at lower structural levels and discrete plutons at upper levels. Dilational structures that host anatectic granite overprint plutonic layering and migmatitic foliation. They exhibit systematic geometries indicative of NNE–SSW stretching, parallel to a first-generation mineral lineation. New U–Pb SHRIMP zircon ages for granodiorite and porphyritic monzogranite plutons, and for leucogranites that occupy shear bands and other mesoscopic-scale structural sites, define an interval of 370 to 355 Ma for plutonism and migmatization.Paleozoic plutonism in West Antarctica postdates magmatism in the western Lachlan Orogen of Australia, but it coincides with that in the central part of the Lachlan Orogen and with the rapid main phase of emplacement of the Karamea Batholith of the Western Province, New Zealand. Emplaced within a 15 to 20 million year interval, the Paleozoic granitoids of the Fosdick Mountains are a product of subduction-related plutonism associated with high temperature metamorphism and crustal melting. The presence of anatectic granites within extensional structures is a possible indication of alternating strain states (‘tectonic switching’) in a supra-subduction zone setting characterized by thin crust and high heat flow along the Devonian–Carboniferous accretionary margin of East Gondwana.     

The geometry of space-time prisms with uncertain anchors

Space-time prisms envelop all spatio-temporal locations that moving objects may have visited between two of their known spatio-temporal locations, given a bound on their travel speed. In this context, the known locations are often the result of observations or measurements, and they are called ‘anchor points’. The classic space-time prism, in isotropic two-dimensional space, as well as in transportation networks, assumes that the measurements of these anchor points are exact. Whereas, in many applications, we can assume that time can be measured fairly precisely, this assumption is unrealistic for the spatial components of measured locations (we think of Global Positioning System (GPS) errors, for instance). In this paper, we extend the classical prism from anchor points to circular ‘anchor regions’ that capture the uncertainty or error on their measurement. We define the notion of a space-time prism with uncertain anchor points, called uncertain prism, for short. We study the geometry of uncertain prisms in an arbitrary metric space to make this concept as widely applicable as possible. We also focus on the rims of uncertain space-time prisms, which demarcate the area that a moving object can have visited between two anchor regions (given some local speed limitations).     

Rhyacian and Neoproterozoic magmatic associations of the Gurupi Belt,Brazil: Implications for the tectonic evolution,and regional correlations

The Gurupi Belt, in north-northeastern Brazil, is a mobile belt developed in the south-southwestern margin of the São Luís cratonic fragment and crops out as a tectonic and erosional window within the Phanerozoic cover. Field, petrographic, geochemical, geochronological, and Nd isotopic information (new and published) constrain the timing and types of magmatic associations present in the belt and the tectonic settings in which they formed. The Rhyacian was the main period of magmatic activity, which can be grouped into two main stages. (1) ~2185–2130 ​Ma: pre-collisional, juvenile, calc-alkaline magnesian and calcic ferroan granitoid suites, and minor calc-alkaline and tholeiitic mafic plutonism (now amphibolites), formed in intra-oceanic to transitional/continental arcs; and intra- or back-arc volcano-sedimentary basin. (2) ~2125–2070 ​Ma: syn- (two-mica granites) to late-collisional (potassic to shoshonitic granites and quartz-syenite) plutonic suites produced after crustal thickening and melting, with localized migmatization, that intruded during the compressive D₁ deformational phase and concomitantly with greenschist to amphibolite metamorphism. There is a zonation of the Rhyacian episodes, with intra-oceanic stages occurring to the northeast, and the continental arc and collisional phases occurring to the southwest, indicating the presence of an active continental margin to the southwest, and subduction from NE to SW (present-day configuration). This magmatic framework is a continuation to the south of what is described for the São Luís cratonic fragment to the north, and the orogenic scenario is identical to what is observed for the same period in the West African Craton (Eburnean/Birrimian orogen), which additionally supports previous geological correlations. In the Neoproterozoic, a few magmatic occurrences are recognized. An extensional event allowed the intrusion of an anorogenic, nepheline syenite at ca. 730 Ma, which was followed by the intrusion of a crustal, calc-alkaline microtonalite, of uncertain tectonic setting, at 624 ​Ma. Both intrusions underwent greenschist to amphibolite facies metamorphism between 580 Ma and 529 ​Ma. This metamorphic event is probably related to crustal thickening, which produced crustal melting and intrusion of two-mica granites between 595 Ma and 549 ​Ma. The absence of oceanic and arc-related assemblages, along with geophysical information about the basement of the Phanerozoic cover indicates an intracontinental setting for the Neoproterozoic–Early Cambrian evolution of the Gurupi Belt, with rifting and posterior closure of the basin, without oceanization. Rifting and closure correlate in time with the onset of Rodinia breakup and West Gondwana assembly, respectively, but we interpret the events in the Gurupi Belt as having no direct role in these two global supercontinent-related events, but, instead, as being related to orogenic events occurring in the periphery of the West African and Amazonian cratons at that time.     

敦煌北部岩浆-变质杂岩构造环境初步探讨:对中亚造山带南缘扩展方式的启示

中亚造山带南缘如何向南扩展,对深入理解增生型造山作用和大陆地壳生长机制以及中亚构造域与特提斯构造域的衔接具有重要科学意义.作为中亚造山带南缘的关键构造单元,敦煌构造带大地构造属性长期备受关注且颇有争议.传统观点认为敦煌构造带是古亚洲洋南侧的前寒武纪稳定大陆地块,以刚性块体的形式参与了中亚造山带南缘的最终拼贴过程.然而,...