Accretionary processes and metallogenesis of the Central Asian Orogenic Belt: Advances and perspectives     

Xiao  Wenjiao  Song  Dongfang  Windley  Brian F.  Li  Jiliang  Han  Chunming  Wan  Bo  Zhang  Ji’en  Ao  Songjian  Zhang  Zhiyong 《中国科学:地球科学(英文版)》2020,63(3):329-361

As one of the largest Phanerozoic orogens in the world,the Central Asian Orogenic Belt (CAOB) is a natural laboratory for studies of continental dynamics and metallogenesis.This paper summarizes the research progresses of the accretionary processes and metallogenesis of the CAOB since the Peopled Republic of China was founded,and puts forward the prospect for future research.During the early period (1950s-1970s),several geological theories were applied to explain the geological evolution of Central Asia.In the early period of China's reform and opening-up,the plate tectonics theory was applied to explain the evolution of the northern Xinjiang and Xingmeng regions,and the opinion of subduction-collision between Siberian Kazakhstan and China-North Korea-Tarim plates was proposed.The idea of the Solonker-Yanbian suture zone was established.In the 1990s,the study of the CAOB entered a period of rapid development.One school of scholars including geologists from the former Soviet Union proposed a multi-block collision model for the assemblage of the CAOB.In contrast,another school of scholars,led by a Turkish geologist,Celal Sengor,proposed that the Altaids was formed through the growth and strike-slip duplicates of a single island arc,and pointed out that the Altaids is a special type of collisional orogen.During this period,Chinese geologists carried out a lot of pioneering researches on ophiolites and high-pressure metamorphic rocks in northern China,and confirmed the main suture zones accordingly.In 1999,the concept of"Central Asian metallogenic domain"was proposed,and it became one of the three major metallogenic domains in the world.Since the 21st century,given the importance for understanding continental accretion and metallogenic mechanism,the CAOB has become the international academic forefront.China has laid out a series of scientific research projects in Central Asia.A large number of important scientific research achievements have been spawned,including the tectonic attribution of micro-continents,timing and tectonic settings of ophiolites,magmatic arcs,identification and anatomy of accretionary wedges,regional metamorphism-deformation,(ultra)high-pressure metamorphism,ridge subduction plume-plate interaction archipelagic paleogeography and spatio-temporal framework of multiple accretionary orogeny,continental growth accretionary metallogenesis,structural superposition and transformation etc.These achievements have made important international influences.There still exist the following aspects that need further study:(1) Early evolution history and subduction initiation of the Paleo-Asian Ocean;(2) The accretionary mechanism of the extroversion Paleo-Asian Ocean;(3) The properties of the mantle of the Paleo-Asian Ocean and their spatiotemporal distribution;(4) The interaction between the Paleo-Asian Ocean and the Tethys Ocean;(5) Phanerozoic continental growth mechanism and its global comparison;(6) Accretionary metallogenic mechanism of the Central Asian metallogenic domain;and (7) Continental transformation mechanism.  相似文献   

Sedimentary processes at ice sheet grounding-zone wedges revealed by outcrops,Washington State (USA)     

Brian P. Demet  Jeffrey A. Nittrouer  John B. Anderson  Lauren M. Simkins 《地球表面变化过程与地形》2019,44(6):1209-1220

Grounding-zone wedges (GZWs) mark the grounding terminus of flowing marine-based ice streams and, in the presence of an ice shelf, the transition from grounded ice to floating ice. The morphology and stratigraphy of GZWs is predominantly constrained by seafloor bathymetry, seismic data, and sediment cores from deglaciated continental shelves; however, due to minimal constraints on GZW sedimentation processes, there remains a general lack of knowledge concerning the production of these landforms. Herein, outcrop observations are provided of GZWs from Whidbey Island in the Puget Lowlands (Washington State, USA). These features are characterized by prograded diamictons bounded by glacial unconformities, whereby the lower unconformity indicates glacial advance of the southern Cordilleran Ice Sheet and the upper unconformity indicates locally restricted ice advance during GZW growth; the consistent presence of an upper unconformity supports the hypothesis that GZWs facilitate ice advance during landform construction. Based on outcrop stratigraphy, GZW construction is dominated by sediment transport of deformation till and melt-out of entrained basal debris at the grounding line. This material may be subsequently remobilized by debris flows. Additionally, there is evidence for subglacial meltwater discharge at the grounding line, as well as rhythmically bedded silt and sand, indicating possible tidal pumping at the grounding line. A series of GZWs on Whidbey Island provides evidence of punctuated ice sheet movement during retreat, rather than a rapid ice sheet lift-off. The distance between adjacent GZWs of 10²–10³ m and the consistency in their size relative to modern ice stream grounding lines suggests that individual wedges formed over decades to centuries. © 2018 John Wiley & Sons, Ltd.  相似文献   

The Roles of Reconnected Flux and Overlying Fields in CME Speeds     

Minda Deng  Brian T. Welsch 《Solar physics》2017,292(1):17

Researchers have reported i) correlations of coronal mass ejection (CME) speeds and the total photospheric magnetic flux swept out by flare ribbons in flare-associated eruptive events, and, separately, ii) correlations of CME speeds and more rapid decay, with height, of magnetic fields in potential-field coronal models above eruption sites. Here, we compare the roles of both ribbon fluxes and the decay rates of overlying fields in a set of 16 eruptive events. We confirm previous results that higher CME speeds are associated with both higher ribbon fluxes and more rapidly decaying overlying fields. We find the association with ribbon fluxes to be weaker than a previous report, but stronger than the dependence on the decay rate of overlying fields. Since the photospheric ribbon flux is thought to approximate the amount of coronal magnetic flux reconnected during the event, the correlation of speeds with ribbon fluxes suggests that reconnection plays some role in accelerating CMEs. One possibility is that reconnected fields that wrap around the rising ejection produce an increased outward hoop force, thereby increasing CME acceleration. The correlation of CME speeds with more rapidly decaying overlying fields might be caused by greater downward magnetic tension in stronger overlying fields, which could act as a source of drag on rising ejections.  相似文献   

Temporal and spatial variability of sea level and volume flux in the Murderkill Estuary     

Kuo-Chuin Wong  Brian Dzwonkowski  William J. Ullman 《Estuarine, Coastal and Shelf Science》2009,84(4):440-446

The instantaneous sea level determined at two sites in the Murderkill Estuary, a tributary of Delaware Bay, results from the superposition of temporal variability operating over different time and spatial scales. Over the relatively short tidal time scales, the semidiurnal tides that represent the dominant tidal constituents in lower Delaware Bay show a modest increase in tidal amplitudes from the bay mouth (Lewes, Delaware), up to Bowers Beach (the mouth of the Murderkill Estuary). However, as the tides propagate into the Murderkill Estuary, the semidiurnal constituents undergo heavy attenuation, resulting in a 48% reduction in tidal amplitude from Bowers to Frederica (approximately the extent of saline intrusion). The diurnal tide, on the other hand, experiences only a 25% reduction in amplitude. The limited tidal asymmetry that is observed may be a result of interaction between flows in the tidal channel and the adjacent salt marsh. At longer time scales, the subtidal sea level experiences no attenuation. The Murderkill Estuary thus behaves like a low pass filter to preferentially damp out high frequency sea level forcing from lower Delaware Bay. The subtidal volume flux in the Murderkill is highly coherent with the time rate of change of sea level, indicating that the Murderkill basically co-oscillates with Delaware Bay in a standing wave fashion over the subtidal time scale. This remote coupling controls more than 90% of the variance in subtidal sea level in the estuary. The surface slopes in the lower bay and the Murderkill Estuary are closely correlated with winds along the orientation of the two waterways, consistent with the effect of local wind on subtidal sea level.  相似文献   

Ecological performance and possible origin of a ubiquitous but under-studied gastropod     

Mad S. Thomsen  Thomas Wernberg  Fernando Tuya  Brian R. Silliman 《Estuarine, Coastal and Shelf Science》2010

Invasions by non-indigenous species (NIS) have been suggested to alter local, regional and global biota on unprecedented scales. To manage NIS, it is pivotal to identify whether a species is introduced or native, but even today the geographical origin of thousands of species worldwide remain uncertain. Most of these ‘cryptogenic species’ are inconspicuous and rare, but in a few instances, they can also be abundant and conspicuous species, with large impacts on community structure. The identification of cryptogenic species, and summarizing information on their most likely origin, is an important task in invasion biology, and can highlight the need for research and management. Here, we document that the gastropod Batillaria australis in the Swan River estuary (Perth, Western Australia) is a conspicuous species of uncertain origin. A literature review combined with new survey data revealed that all evidence point to a recent human-mediated transfer; for example, it is absent from the fossil record, was first collected in 1954, has a low parasite diversity, has increased its population size dramatically in recent times, is separated by >3000 km from conspecifics, has no long-distance dispersal mechanisms, and existing ocean currents run against a natural range extension. Surprisingly, despite political and scientific focus on NIS hardly any ecological data have been published on this species from Western Australia. We show that B. australis is highly abundant in both seagrass beds (424 ± 29 ind m⁻²) and on unvegetated sand flats (92 ± 22 ind m⁻²) being orders of magnitudes more abundant than any native gastropod in the Swan River. Experiments showed that high resistance to predation and environmental stress potentially explains its success. From our survey data, we calculated that >3.6 billion invasive snails today occupy the Swan River. This large snail populations support other organisms; for example, almost 1 billion macroalgae are found attached to living B. australis and >100 million hermit crabs occupy its empty shells. Given Battilaria’s high abundance, wide distribution, large size, persistent shells that support other organisms and bioturbating behavior, it seems inescapable that this potential invader has impacted the ecosystem functioning of the Swan River. We argue that the search for abundant species of uncertain origin should continue, and that these species generally should be treated with the same interest as high status invaders to mitigate impacts in already invaded systems and to avoid secondary spread into neighboring ecosystems.  相似文献   

An unusual occurrence of coesite at the Lonar crater,India          下载免费PDF全文

Steven J. Jaret  Brian L. Phillips  David T. King Jr  Tim D. Glotch  Zia Rahman  Shawn P. Wright 《Meteoritics & planetary science》2017,52(1):147-163

Coesite has been identified within ejected blocks of shocked basalt at Lonar crater, India. This is the first report of coesite from the Lonar crater. Coesite occurs within SiO₂ glass as distinct ~30 μm spherical aggregates of “granular coesite” identifiable both with optical petrography and with micro‐Raman spectroscopy. The coesite+glass occurs only within former silica amygdules, which is also the first report of high‐pressure polymorphs forming from a shocked secondary mineral. Detailed petrography and NMR spectroscopy suggest that the coesite crystallized directly from a localized SiO₂ melt, as the result of complex interactions between the shock wave and these vesicle fillings.  相似文献   

Use of voltammetric solid-state (micro)electrodes for studying biogeochemical processes: Laboratory measurements to real time measurements with an in situ electrochemical analyzer (ISEA)     

George W. Luther III  Brian T. Glazer  Shufen Ma  Robert E. Trouwborst  Tommy S. Moore  Edouard Metzger  Chareonkwan Kraiya  Tim J. Waite  Gregory Druschel  Bjrn Sundby  Martial Taillefert  Donald B. Nuzzio  Timothy M. Shank  Brent L. Lewis  Paul J. Brendel 《Marine Chemistry》2008,108(3-4):221-235

Solid-state voltammetric (micro)electrodes have been used in a variety of environments to study biogeochemical processes. Here we show the wealth of information that has been obtained in the study of sediments, microbial mats, cultures and the water column including hydrothermal vents. Voltammetric analyzers have been developed to function with operator guidance and in unattended mode for temporal studies with an in situ electrochemical analyzer (ISEA). The electrodes can detect the presence (or absence) of a host of redox species and trace metals simultaneously. The multi-species capacity of the voltammetric electrode can be used to examine complex heterogeneous environments such as the root zone of salt marsh sediments. The data obtained with these systems clearly show that O₂ and Mn²⁺ profiles in marine sedimentary porewaters and in microbial biofilms on metal surfaces rarely overlap indicating that O₂ is not a direct oxidant for Mn²⁺. This lack of overlap was suggested originally by Joris Gieskes' group. In waters emanating from hydrothermal vents, Fe²⁺, H₂S and soluble molecular FeS clusters (FeS_aq) are detected indicating that the reactants for the pyrite formation reaction are H₂S and soluble molecular FeS clusters. Using the ISEA with electrodes at fixed positions, data collected continuously over three days near a Riftia pachyptila tubeworm field generally show that O₂ and H₂S anti-correlate and that H₂S and temperature generally correlate. Unlike sedimentary environments, the data clearly show that Riftia live in areas where both O₂ and H₂S co-exist so that its endosymbiont bacteria can perform chemosynthesis. However, physical mixing of diffuse flow vent waters with oceanic bottom waters above or to the side of the tubeworm field can dampen these correlations or even reverse them. Voltammetry is a powerful technique because it provides chemical speciation data (e.g.; oxidation state and different elemental compounds/ions) as well as quantitative data. Because (micro)organisms occupy environmental niches due to the system's chemistry, it is necessary to know chemical speciation. Voltammetric methods allow us to study how chemistry drives biology and how biology can affect chemistry for its own benefit.  相似文献   

Simulation of Synthetic Exploration and Geometallurgical Database of Porphyry Copper Deposits for Educational Purposes     

Garrido  Mauricio  Sepúlveda  Exequiel  Ortiz  Julián  Townley  Brian 《Natural Resources Research》2020,29(6):3527-3545

Natural Resources Research - The access to real geometallurgical data is very limited in practice, making it difficult for practitioners, researchers and students to test methods, models and...  相似文献   

太阳活动驱动气候变化空间天气机制研究进展     

周立旻  郑祥民  王世杰 《地球科学进展》2007,22(11):1099-1109

大量研究表明,从数小时到十年、百年时间尺度上的天气、气候变化受太阳活动影响显著。近年来,全球云量、北大西洋冬季气旋等气候、气象要素与银河宇宙射线通量变化、太阳能量粒子事件等空间天气事件显著的统计相关被陆续发现。在此基础上,提出太阳活动驱动气候变化空间天气机制,其基本观点是：空间天气事件通过改变云物理特性影响气象、气候,其核心是：太阳活动造成的空间天气事件与云微物理过程的联系,目前空间天气理论分化为离子诱导成核机制和全球大气电路—静电云微物理机制（简称Tinsley机制）。主要回顾和总结了近年来空间天气机制研究的发展,包括观测与理论,取得的成果,并对其未来的发展提出展望。   相似文献   

Implications for groundwater recharge from stable isotopic composition of precipitation in Hawai'i during the 2017–2018 La Niña     

Daniel Dores  Craig R. Glenn  Giuseppe Torri  Robert B. Whittier  Brian N. Popp 《水文研究》2020,34(24):4675-4696

The project captured a subset of the hydrological cycle for the tropical island of O'ahu, linking precipitation to groundwater recharge and aquifer storage. We determined seasonal storm events contributed more to aquifer recharge than year-round baseline orographic trade wind rainfall. Hydrogen and oxygen isotope values from an island-wide rain collector network with 20 locations deployed for 16 months and sampled at 3-month intervals were used to create the first local meteoric water line for O'ahu. Isotopic measurements were influenced by the amount effect, seasonality, storm type, and La Niña, though little elevation control was noted. Certain groundwater compositions from legacy data showed a strong similarity with collected precipitation from our stations. The majority of these significant relationships were between wet season precipitation and groundwater. A high number of moderate and heavy rainfall days during the dry season, large percentage of event-based rainfall, and wind directions outside of the typical NE trade wind direction were characteristics of the 2017–2018 wet season. This indicates that the majority of wet season precipitation is from event-based storms rather than typical trade wind weather. The deuterium-excess values provided the strongest evidence of a relationship between groundwater and different precipitation sources, indicating that this may be a useful metric for determining the extent of recharge from different rain events and systems.  相似文献