Distribution of mineralization in time and space in Chihuahua,Mexico

Physiographically, Chihuahua includes Sierra Madre Occidental (western) and Mesa Central (eastern) provinces. Stratigraphically, coal occurs in Triassic-Jurassic strata and upper Cretaceous rocks, porphyry Cu-Mo deposits in stocks, fissure-vein Ag-Au lodes in andesite-rhyolite sequences and in Cretaceous sediments, Mn fissure-vein deposits in rhyolitic extrusives, U in fissures and contacts in rhyolites, gypsum in Late Jurassic and Early Cretaceous strata, manto Pb-Zn-Ag and stratiform Cu-Ba deposits separately in Lower Cretaceous strata, magmatic segregation and contact Fe deposits in trachyte and rhyolite and adjacent intrusives respectively, and fluorite as mantos and veins in Cretaceous sediments. Assemblages occur in zones that strike NW paralleling other mineral belts in adjacent northwestern Mexico. Temporal, spatial and genetic relationships link magmatic-hydrothermal origin deposits to magmatic suites that vary from calc-alkaline (west) to alkaline (east). Favorable localizing structures include doming by batholiths, normal faulting and contact metamorphism in the Sierra Madre Occidental Orogen and by folding, thrusting and stock emplacement in the eastern Chihuahua Tectonic Belt, all during Laramide time. Mineralization persisted through the Oligocene interval, although post-mineral volcanism continued until Late Cenozoic time. Contemporaneous events in the eastern Pacific basin suggest that tectonism, magmatism and metallogenesis are consistant with a convergent plate model along a continental margin.     

Records of Indosinian Orogenesis in Lhasa Terrane, Tibet

Based on the deformation characteristics of the ductile shear zones in Sumdo (松多) Group, the quartz fabric by EBSD (electron backscatter diffraction), the data of muscovite 40Ar-39Ar geochronology (220-230 Ma) from ductile shear zones and the zircon SHRIMP U-Pb chronology (190 Ma) of granites in Snmdo region, Lhasa (拉萨) terrane is thought to have experienced an important Indosinian orogenic event at 220-230 Ma, which caused the closure of the paleo-Tethys Ocean along the tectonic zone of eclogite and the collision between northern part and southern part of the Lhasa terrane. The zircon SHRIMP U-Pb chronology of 190 Ma for biotite adamellite, with the distributing characteristics of the granite massif intruding in Sumdo Group, indicates that the biotite adamellitc should be the late orogenic or post-orogenic granite resulting from the lndosinian orogenesis. The discovery of Indosinian orogenic belt in Lhasa terrane expansed the southern boundary of lndosinian orogenic belt in Qinghai (青海)-Tibet plateau to Lhasa terrane from Qiangtang (羌塘) terrane, which changed the understanding about the distribution of Indosinian orogenic belt in Qinghai-Tibet plateau and extended the "T" type lndosinian orogenic belt in China. The study is very important for the formation and distribution of paleo-Tethys Ocean in Tibet. The ancient terrane framework and evolution of Qinghai-Tibet plateau need further research.     

Comparative urbanization in Ghana and Kenya in time and space

There are few inter-African country urban analyses because of the continent’s enormous size and socioeconomic diversity, language barriers, and wide variations in national and regional urban research capacity. Nevertheless, comparative urban studies are critical in understanding contemporary African urbanization. In this comparative spatial and temporal analysis of Ghana and Kenya’s urbanization, we find that both countries are urbanizing rapidly and are faced with many common urban problems. Moreover, Ghana is more urbanized than Kenya and has a larger indigenous urban imprint and a more widely dispersed urban pattern. Besides their physiographic and population conditions, we trace these countries’ convergent and divergent urban trends to their shared but unique experiences of colonialism, nationalism and globalization.     

Gondwana from top to base in space and time

Gondwana is reviewed from the unification of its several cratons in the Late Neoproterozoic, through its combination with Laurussia in the Carboniferous to form Pangea and up to its progressive fragmentation in the Mesozoic. For much of that time it was the largest continental unit on Earth, covering almost 100 million km², and its remnants constitute 64% of all land areas today. New palaeogeographical reconstructions are presented, ranging from the Early Cambrian (540 Ma) through to just before the final Pangea breakup at 200 Ma, which show the distributions of land, shallow and deep shelves, oceans, reefs and other features at nine selected Palaeozoic intervals. The South Pole was within Gondwana and the Gondwanan sector of Pangea for nearly all of the Palaeozoic, and thus the deposition of significant glaciogenic rocks in the brief Late Ordovician (Hirnantian) and the much longer Permo-Carboniferous ice ages help in determining where their ice caps lay, and plotting the evaporites in the superterrane area indicates the positions of the subtropics through time. Reefs are also plotted and selected faunal provinces shown, particularly at times such as the Early Devonian (Emsian), when high climatic gradients are reflected in the provincialisation of shallow-marine benthic faunas, such as brachiopods.In Late Palaeozoic and Early Mesozoic times, Gondwana (with Africa at its core) lay over the African large low shear-wave velocity province (LLSVP), one of two major thermochemical piles covering ca. 10% of the core–mantle boundary. The edges of the LLSVPs (Africa and its Pacific antipode) are the plume generation zones (PGZs) and the source regions of kimberlite intrusions and large igneous provinces (LIPs). Our palaeomagnetic reconstructions constrain the configuration of Gondwana and adjacent continents relative to the spin axis, but in order to relate deep mantle processes to surface processes in a palaeomagnetic reference frame, we have also rotated the PGZs to account for true polar wander. In this way, we visualize how the surface distribution of LIPs and kimberlites relate to Gondwana's passage over the PGZs. There are only two LIPs in the Palaeozoic (510 and 289 Ma) that directly affected Gondwanan continental crust, and kimberlites are rare (83 in total). This is because Gondwana was mostly located between the two LLSVPs. The majority of Palaeozoic kimberlites are Cambrian in age and most were derived from the African PGZ. Sixty-six Early Mesozoic kimberlites are also linked to the African LLSVP. All known LIPs (Kalkarindji, Panjal Traps, Central Atlantic Magmatic Province and Karoo) from 510 to 183 Ma (the lifetime of Gondwana) were derived from plumes associated with the African LLSVP, and three of them probably assisted the breakup of Gondwana and Pangea.     

Bunter quartzites: remarkable journeys in time and space

Quartzite pebbles and cobbles, commonly known as Bunter quartzites, are widely dispersed throughout southern Britain. They can be traced back to Early Triassic pebble beds outcropping in the Wessex Basin and the English Midlands. Derived fossils within the quartzites confirm that most, if not all, were derived from Ordovician and Devonian terrains, over what is now the general region of the Armorican peninsula of north‐west France. In Early Triassic times that area of ancient rocks formed part of a chain of young Variscan mountains which were subject to a monsoonal climate, and shed vast quantities of eroded quartzite. Ultimately, this debris was transported northwards into what is now southern Britain, by the Budleighensis river system.     

冈底斯复合造山带铜钼金多金属成矿作用与成矿系列

2001年以前西藏冈底斯斑岩铜钼多金属成矿带未列入国家重要成矿区带,而随后的成矿、找矿理论认识和方法创新,致使该带找矿取得历史性重大突破,新发现与评价了驱龙、甲玛、朱诺、雄村、努日、冲江、邦浦、蒙亚啊、洞中松多、查个勒等一系列大型-超大型矿床,仅探明的铜资源量就超过5 600万吨,形成了我国规模最大的世界级铜多金属勘查开发基地;新发现的矿床主要分布在南部拉萨地体及弧背断隆带,空间上的分布表现出东西成带、北东成行、交汇成矿、近等间距分布的规律性;同位素资料展示5期斑岩成矿作用(213 Ma、173～165 Ma、～45 Ma、～30 Ma、17～13 Ma)、5期矽卡岩成矿作用(～112 Ma、～77 Ma、67～55 Ma、～41～37 Ma、～23～16 Ma)及2期浅成低温热液成矿作用(～126 Ma、～65～55 Ma);伴随着新特提斯洋的形成、俯冲、消减及印-亚陆陆碰撞,冈底斯带经历了增生造山、碰撞造山、陆内造山及均衡造山四大造山作用过程,揭示了含矿岩浆来源于不同时期俯冲的玄武质洋壳——以幔源物质为主、或以古老地壳为主、或以新生下地壳为主的部分熔融,形成了与不同造山作用相关的斑...     

Contested claims over space and identity between fishers and the oil industry in Mexico

This essay examines neoliberal forms of resource governance and emerging struggles over control of sea space between coastal fishers, the para-statal oil industry and government authorities in the State of Tabasco, Mexico. The analysis focuses on the changing mechanisms of resource governance and networking related to contested claims over rights to offshore space. The study is based on material collected during ethnographic field research in Tabasco in 2011–2014. By linking a post-Foucauldian approach to governmentality with a Deleuzian perspective on networks, our research examines resource governance as a socio-political arena, constructed in negotiation between multiple governmental, private and civil society actors, including heterogeneous groups from local populations. The study demonstrates how hybrid techniques of resource governance lead to fishers’ socio-spatial displacement, marginalization in the fields of political representation and subjection to ideas of aquaculture entrepreneurship. The ensemble of private regulation and governmental control provides a venue for drawing fishers into clientelist practices of governing while it diffuses questions of responsibility. These modes of governance fragment the fishers’ efforts to mobilize politically, making them rely on less visible networks of contestation shaped by heterogeneous fishing groups, with varying access to resources and political representation. Recent transformations in environmental legislation and the fishers’ mobile tactics of networking may offer opportunities for them to reclaim their resource rights.     

Structure of earthquake occurrence in space,time and magnitude

Distributions of time between consecutive earthquakes verify an approximately universal scaling law for stationary seismicity. The shape of these distributions is shown to arise as a mixture of one distribution for short‐distance events and an exponential distribution for far‐off events, the distinction from short and long distances being relative to the size of the region studied. The distributions of consecutive distances show a double power law decay and verify an approximate scaling law which guarantees the simultaneous fulfillment of the scaling laws for time. The interplay between space and time can be seen as well by looking at the distribution of distances for a fixed time separation. These results suggest that seismicity can be understood as a series of intertwined independent continuous‐time random walks, with power law‐distributed waiting times and Lévy‐flight jumps. However, a simple model based on these ideas does not capture the invariance of seismicity under renormalization.     

Distribution of an arctic ostracod fauna in space and time

A fossil locality on the Pembina Upland, in southern Manitoba (L. D. Delorme, Geological Association of Canada, Special Paper9, 301–304, 1971), contains three ostracod species near the base of the deposit. Two of these ostracods, Candona rectangulata and Cyclocypris globosa, are found alive only in the northern parts of the Northwest and Yukon territories of Canada. Both species are indicative of subarctic forest tundra and alpine tundra. Their position in the lower 69 cm of the deposit indicates that, as the glacier ice thinned over the upland and retreated from the Lake Agassiz basin, an arctic-subarctic environment could have existed with the potential for tundra vegetation to develop. A reverse situation occurred in the Northwest Territories based on seven fossil ostracod species from a peaty marl deposit. As reported by L. D. Delorme, S. C. Zoltai, and L. L. Kalas. (Canadian Journal of Earth Science14, 2029–2046, 1977) for other similar sites, the striking element is the absence of true arctic ostracods. The majority of the species live very successfully further south in Manitoba and Saskatchewan at present. At both sites, the fossil assemblage is different than the modern assemblage. This indicates a dislocation in space and time which is the basis for the change in paleoenvironmental interpretation.     

International Workshop on ＂Central Asian Orogenesis and Metallogeny＂

An ＂International Workshop on Central Asian Orogenesis and Metallogeny＂, sup- ported by Department of Science and Tech- nology of Xinjiang Uygur Autonomous Region, the Geosciences Department of the Natural Science Foundation of China, the Bureau of Science and Technology for Resources and Environment, the Chinese Academy of Science, Xinjiang Petroleum Company, and China National Petroleum Corporation, was held in Urumqi, Xinjiang, from 18-24 September, 2007 （hosted by the National 305 Project Office）.     

Orogenesis and flysch sedimentation—Critical remarks on the alpine model

The concept of flysch as an orogenic facies cannot be applied to all flysch-type deposits without discrimination. The tectonic environment of the Alpine flysch does not represent a unique model. The definition of flysch must accentuate its concrete sedimentary characteristics, without genetic implications.     

Comparing impacts to shallow-water habitas through time and space

Impacts to shallow-water estuarine habitats should be assessed in a holistic context reflecting both the interrelatedness of habitats that characterize these environments and the history of impacts, human and natural, that have shaped their present ecology. In a holistic context these habitats are considered to be dynamic associations of macrohabitats and micro-habitats, interacting through time to affect the quantity (Q₁), quality (Q₂), and timing (T) of material and energy transfer within the system. Where data are available, this holistic approach (Q₁, Q₂ and T or Q₂T) allows impacts to be evaluated in a multidimensional framework of time and space. Unfortunately, few data are available to evaluate the long-term implications of timing, the T factor. Recorded observations of most estuarine systems cover tens of years, periods not extensive enough to assess long-term changes to the environment or to distinguish man's impacts from those of nature. Sustained droughts, for example, can cause massive disruption in estuaries, altering habitats and species composition. When these changes occur over periods of 5–10 yr, the changes are difficult to identify and may be attributed to man's activities rather than nature's Using the Hudson River estuary as an example, we have knowledge of historical impacts extending back to the 1700s, ranging from dredging to major droughts. For the Hudson River, recorded observations of rainfall and river flow extend back about 70 yr; however, tree rings provide a more extensive record since tree growth increments are directly dependent upon rainfall. The Hudson River drought record was extended back to 1694 using tree rings. Using the reconstructed record, the relationship between today's conditions—flow and average location of the ocean-derived salt front—can be placed in a historical context. This historical perspective allows us to place present-day human impacts into the contex of long-term natural impacts and to discriminate among these effects. The drought example is particularly relevant to shallow-water habitats because these habitats provide an interface between fresh and marine waters. *** DIRECT SUPPORT *** A01BY074 00008     

Variation of interlayer slip in space and time during flexural folding

This paper describes the results of an experiment which was performed with a Plasticine model to investigate the progressive evolution of flexural-slip folds. The model analyses the relationship between bulk shortening and the amount of flexural slip on fold limbs and in hinge zones. In the light of the experimental results, the theoretical relationship between limb dip and angular shear strain proposed by Ramsay (1967, p. 393) needs modifying to take into account the effect of hinge dilation and limb thinning at large deformations.     

Evolution of pore space in the Poza Rica trend (Mid-Cretaceous), Mexico

ABSTRACT The Poza Rica trend of the Tampico embayment, Mexico, will ultimately produce more than 2.3 × 10⁹ barrels of oil from Mid-Cretaceous (Albian-Cenomanian) basin-margin deposits. Bioclastic grainstone, packstone, and wackestone are interbedded with polymictic lime breccia and dolomitized debris; all were deposited by sediment gravity flow. Indigenous sediment was pelagic lime mud. Typical reservoir porosities are about 10%; permeabilities average 2 md and rarely exceed 100 md. Porosity is largely the result of selective dissolution of rudist fragments, which were originally aragonite. Detailed petrographic study, with emphasis on the diagenetic products, allows quantitative assessment of porosity at various diagenetic stages from original sediment to reservoir rock. A relatively simple diagenetic history is reflected by about 90% of the samples studied: primary porosity was reduced through lithification of matrix mud and initial cementation by clear, equant to bladed, non-ferroan calcite. Later dissolution produced extensive skelmoldic and minor vuggy porosity. Subsequently, non-ferroan calcite cement reduced porosity before the emplacement of hydrocarbons. Reconstructed sediment porosities are comparable to, but lower than, modern counterparts. The initial phase of cementation and presumed lithification of mud greatly reduced porosity in all lithologies, but appreciably more porosity persisted in grainstone and packstone than in wackestone or mudstone. Dissolution produced a porosity resurrection, which exceeded that of the initial sediment in some grainstones. Calcite cementation and local multiphase quartz cementation and dolomitization reduced porosity to present average values of 8–12% in grain-supported rocks and 3% in mud-supported rocks. The greater persistence of primary porosity and, therefore, permeability in grain-supported rocks probably accounts for their greater secondary porosity development and ultimate reservoir quality. Geometrically averaged permeabilities range from only 0.17 md in wackestone to 3.85 md in dolomite, but differ significantly with rock type and grain size. Permeability increases with porosity in all lithologies; the rate of increase is greater at higher porosities and with coarser grain sizes. The agent for both early cementation and development of secondary porosity appears to have been meteoric water. Subaerial exposure appears to be ruled out, however, by a basin-margin depositional environment and continued burial beneath Upper Cretaceous pelagic sediments. Early exposure to meteoric water can be explained by a hydrologic head developed during penecontemporaenous exposure that produced cavernous porosity in the adjacent Golden Lane trend. Descending meteoric water likely emerged as submarine springs along the Tamabra trend. Deposition of pelagic limestone during the Turonian blanketed part of the Golden Lane escarpment to enhance development of a large freshwater lens; gaps in the blanket localized springs and influenced flow patterns within the Poza Rica field. Analogous freshwater circulation exists today in northern Florida.     

Exceptionally preserved fossil assemblages through geologic time and space

Geologic deposits containing fossils with remains of non-biomineralized tissues (i.e. Konservat-Lagerstätten) provide key insights into ancient organisms and ecosystems. Such deposits are not evenly distributed through geologic time or space, suggesting that global phenomena play a key role in exceptional fossil preservation. Nonetheless, establishing the influence of global phenomena requires documenting temporal and spatial trends in occurrences of exceptionally preserved fossil assemblages. To this end, we compiled and analyzed a dataset of 694 globally distributed exceptional fossil assemblages spanning the history of complex eukaryotic life (~ 610 to 3 Ma). Our analyses demonstrate that assemblages with similar ages and depositional settings commonly occur in clusters, each signifying an ancient geographic region (up to hundreds of kilometers in scale), which repeatedly developed conditions conducive to soft tissue preservation. Using a novel hierarchical clustering approach, we show that these clusters decrease in number and shift from open marine to transitional and non-marine settings across the Cambrian-Ordovician interval. Conditions conducive to exceptional preservation declined worldwide during the early Paleozoic in response to transformations of near-surface environments that promoted degradation of tissues and curbed authigenic mineralization potential. We propose a holistic explanation relating these environmental transitions to ocean oxygenation and bioturbation, which affected virtually all taphonomic pathways, in addition to changes in seawater chemistry that disproportionately affected processes of soft tissue conservation. After these transitions, exceptional preservation rarely occurred in open marine settings, excepting times of widespread oceanic anoxia, when low oxygen levels set the stage. With these patterns, non-marine cluster count is correlated with non-marine rock quantity, and generally decreases with age. This result suggests that geologic processes, which progressively destroy terrestrial rocks over time, limit sampling of non-marine deposits on a global scale. Future efforts should aim to assess the impacts of such phenomena on evolutionary and ecological patterns in the fossil record.     

Triassic Orogenesis in Southwest China: the Structural Origins of the Northeast Tibetan Plateau

TRIASSIC OROGENESIS IN SOUTHWEST CHINA: THE STRUCTURAL ORIGINS OF THE NORTHEAST TIBETAN PLATEAU     

保山地块西缘早古生代增生造山作用

在保山地块西缘泸水-潞西构造带内, 出露一套构造混杂岩.主体为强变形的震旦系-古生界蒲满哨群、公养河群浅变质碎屑岩夹碳酸盐岩及火山岩等复理石浊积岩系等构成, 另有硅质岩、杂砂岩、灰岩、砾岩、玄武岩及花岗岩等弱变形的构造块体.岩石时代从震旦纪至古生代, 跨度大, 高度混杂, 并有从东向西变新的逐势, 表现为后退式增生.构造样式早期为同斜倒转冲断作用的叠瓦构造, 后期表现为近N-S向剪切.玄武安山岩、流纹岩类具弧火山岩特征, 而玄武岩类则为板内火山岩, 2种火山岩分别对应岛弧与弧后拉张洋盆产物.寒武纪、奥陶纪侵位的花岗岩也分为东西2个带, 西晚东早, 代表了保山陆块西缘岩浆弧的一部分.这样就记录了洋壳俯冲消亡、增生楔形成过程的沉积、火山-岩浆、变质和构造变形的地质事件群, 也记录了保山地块西缘早古生代增生造山形成过程的地质事件, 并证明了泸水-潞西构造带在震旦纪-古生代存在一洋盆.      

天山造山带东段构造变形对增生造山末期的响应

天山造山带位于中亚造山带最南端,是研究和认识中亚造山带晚古生代增生造山过程的关键地区。本文聚焦于天山造山带东段发育的最晚一期脆韧性构造变形,通过对阿其克库都克断裂带、康古尔断裂带和哈尔里克构造带等变形带内的构造几何学和运动学特征解析,认为阿其克库都克断裂带表现为由南向北逆冲兼右行剪切变形特征,康古尔断裂带表现为南北向挤压兼右行剪切变形特征,哈尔里克构造带表现为由北向南的逆冲叠加稍晚期的左行走滑剪切变形特征。结合大量已有的构造热年代学数据分析,指出各构造单元内最晚一期脆韧性变形时间为二叠纪晚期-中三叠世,指示该时间段内近东西走向的天山造山带东段和北西-南东走向的东准噶尔造山带与西侧哈萨克斯坦弧形造山系呈现为三向汇聚的动力学特征,代表中亚造山带增生造山末期的演化特征。