Major Regional Events Research Articles

Geology, mineralization, igneous geochemistry, and zircon U-Pb geochronology of the early Paleozoic shoshonite-related Julia skarn deposit, SW Siberia, Russia: Toward a diversity of Cu-Au-Mo skarn to porphyry mineralization in the Altai-Sayan orogenic system

The small but high-grade (average 1.29% to 2.04% Cu and 0.09–0.12% Mo for different orebodies, with also significant Au contents) Julia skarn Cu-Au-Mo deposit is situated some 30 km northeast from the Sorskoe porphyry Mo-Cu deposit in the Kuznetsk Alatau, a Paleozoic terrane in the northernmost part of the Altai-Sayan orogenic system, part of the Central Asian Orogenic Belt. The deposit comprises prograde calcic skarns and later retrograde skarn characterized by abundant andradite-rich garnet defining their oxidized type. These alteration assemblages bear abundant Cu sulfides (chalcopyrite and bornite), which are associated with magnetite and are partially overprinted by weak propylitic and stronger phyllic (carbonate-phyllic) alteration assemblages. Molybdenite is present in these assemblages, and various sulfides and sulfosalts, tellurides, and Bi minerals, as well as native Au are associated with phyllic alteration.The deposit is related to a magnetite-series, I-type, multiphase monzonite-syenite(-quartz syenite)-quartz monzonite-monzogranite igneous complex. Isotopic U-Pb zircon data indicate a Late Cambrian age (∼505 to 485 Ma) of the igneous rocks, whereas their geochemical signatures correspond to high-K calc-alkaline to shoshonitic intrusions emplaced in a post-collisional environment, with possible relationships to a subducted slab break-off. Magmatic evolution included a generation of shoshonitic magma by a low-degree partial melting of the metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal?) magma chamber and then by magma fractionation and emplacement at shallower crustal levels. Although the overall magmatic evolution of the parental intrusions was long-lasting (ca. 20 m.y.), the mineralization is associated with a relatively rapid (ca. 5 m.y.) emplacement of more differentiated granitoid intrusions as well as late mafic dikes.The deposit represents an early Paleozoic (Late Cambrian) Cu-Au(-Mo) mineralization in the Altai-Sayan orogenic system and the broader Central Asian Orogenic Belt, thus confirming the Late Cambrian (to Early Ordovician) Cu-Au-Mo metallogenic event in the region. This, together with the broad regional occurrence of the Cambrian-Early Ordovician igneous complexes and related porphyry/skarn Cu-Au(-Mo) mineralization, emphasizes the early Paleozoic porphyries/skarns as a major regional event prior to much better known late Paleozoic porphyries/skarns in the Central Asian Orogenic Belt. There is a potential of the early Paleozoic terranes to host much more significant Cu-Au(-Mo) mineralization including that of skarn, porphyry and associated types.

From Regional to National Clouds: TV Coverage in the Czech Republic.

Media, and particularly TV media, have a great impact on the general public. In recent years, spatial patterns of information and the relevance of intangible geographies have become increasingly important. Gatekeeping plays a critical role in the selection of information that is transformed into media. Therefore, gatekeeping, through national media, also co-forms the generation of mental maps. In this paper, correspondence analysis (a statistical method) combined with cloud lines (a new visual analytics technique) is used to analyze how individual major regional events in one of the post-communist countries, the Czech Republic, penetrate into the media on a national scale. Although national news should minimize distortions about regions, this assumption has not been verified by our research. Impressions presented by the media of selected regions that were markedly influenced by one or several events in those regions demonstrate that gatekeepers, especially news reporters, functioned as a filter by selecting only a few specific, and in many cases, unusual events for dissemination.

Relating unconformity-type uranium mineralization of the Alligator Rivers Uranium Field (Northern Territory, Australia) to the regional Proterozoic tectono-thermal activity: An illite K–Ar dating approach

Illite particles of <0.4, 1–2 and <2μm size were separated from Kombolgie sandstones and basement rocks of the Alligator Rivers Uranium Field (Northern Territory, Australia) at the Jabiluka and Nabarlek deposits and at nearby exploration sites, on the basis of a previous X-ray diffraction and scanning electron microscope study. Dated by the conventional K–Ar method to constrain the regional tectono-thermal evolution, illite crystallized during successive Proterozoic tectono-thermal episodes at 1774±40Ma for one separate of a basement rock, and at ∼1656, 1600, 1554, 1457, 1425, 1371, 1355 and 1318Ma (mean-age peaks). Most of the studied host-rocks underwent hydrothermal processes, mainly from ∼1650 to 1300Ma, that monitored large-scale basin-derived brine flows initiated by contemporary tectonic pulses.Comparison with ages obtained before by U–Pb, 207Pb/206Pb, Sm–Nd and Rb–Sr on UO2, and Rb–Sr and 40Ar/39Ar on illite and other silicates of deposits comparable to those studied here, suggests that illitization was not always linked to U precipitation. However, significant amounts of illite crystallized between ∼1680 and 1520Ma (K–Ar individual ages) at the time U was deposited. This indicates that the unconformity-type U deposits formed probably during three major regional events between 1680 and 1520Ma (at 1656, 1600 and 1554Ma). Only detected away from U concentrations between ∼1457 and 1318Ma, the younger illitization episodes resulted probably from U-devoid hydrothermal fluids, although probably of basinal origin, during minor tectono-thermal events. Further U–Pb ages from 1300 to 500Ma obtained previously on UO2 are also considered as isotopic resets. Not linked to illitization, they were probably not connected to tectono-thermal activity and large-scale brine circulations. These late events appear to have played only a minor role in the U endowment of the region.This study demonstrates also that only specific tectono-thermal events of the 1680–1520Ma period in the ARUF region induced regional mineralizing brine circulations and subsequent U deposition, while younger illitization episodes until ∼1300Ma caused restricted fluid circulations and illitization episodes without U supply, as records of the further history of this U deposition. At a broader scale, this study confirms also the critical importance of the geodynamic and subsequent tectono-thermal conditions during this 140-Ma long period during which a variety of world-class metal deposits (U, but also Cu, Pb and Zn) formed in the Paleo-Proterozoic sedimentary basins of the North-Australian Craton.

Environmental changes inferred from lacustrine sediments and historical literature: A record from Gaoyou Lake, eastern China

Gaoyou Lake is located in the lower reaches of the Huai River and west of the Jing-Hang Grand Canal in eastern China. Based on the temporal sequence of core sediments taken from Gaoyou Lake, multiple proxies of lacustrine sediments, such as particle size, magnetic susceptibility, TOC and C/N, were analyzed to reconstruct the environmental changes of Gaoyou Lake over the past 1100 years, along with verification from historical records. The study focused on the response of lake evolution to climate changes as well as to regional events and human activities. The results show that Gaoyou Lake experienced a stage of low water level during AD 900–1300 and then began to expand under the influence of frequent Yellow River floods after AD 1300. Subsequently, the water levels dropped because of the dry climate during AD 1600–1900. During the modern time after AD 1900, Gaoyou Lake was greatly influenced by warming climate as well as from anthropogenic forcing such as reclamation and deforestation in the catchment. Major regional events such as catastrophic floods and course changes of the Yellow River were interpreted to be related to abrupt changes of sediment characteristics. The human-induced factors, including levee construction and implementation of a river management strategy in order to guarantee the shipping on the Grand Canal, also have contributed greatly to the evolution process of Gaoyou Lake.

Implications of Deep-Marine Miocene Deposits on the Evolution of the North Patagonian Andes

The North Patagonian Andes (38°–43°30′S) present topographic and geologic characteristics distinct from those of the Central Andes to the north, including a lower altitude, a predominance of plutonic rocks, and the presence of a major N-S-trending, dextral strike-slip, intra-arc discontinuity known as the Liquiñe-Ofqui Fault Zone (LOFZ). The timing for the uplift of the North Patagonian Andes remains poorly constrained principally because high exhumation rates resulted in the erosion of most of its volcano-sedimentary cover during the late Cenozoic. The strongly deformed Cenozoic marine deposits ascribed to the Ayacara Formation, which crop out on the western flank of this range at ∼42°S, can provide for a better understanding of the recent geologic evolution of this range. To discern this formation’s age and sedimentary environment, we have integrated sedimentology, ichnology, foraminiferal paleontology, and geochronology. Our results indicate that this unit was deposited in a deep-marine environment during the Early-Middle Miocene. Correlation of the Ayacara Formation with coeval deep-marine deposits in the forearc to the west indicate that deposition was caused by a major regional event of tectonic subsidence probably related to subduction erosion. An Early-Middle Miocene age for the Ayacara Formation is a reliable maximum age for the deformation and uplift of the western flank of the North Patagonian Andes as well as for the commencement of transpressional deformation associated with the LOFZ.

Going for gold: Creating a Chinese heritage festival in Nundle, New South Wales

Cultural tourism has become one of Australian tourism's most lucrative sectors, and the regional location of many of its prime sites and events means that increasing numbers of visitors are travelling beyond the major cities for ‘authentic’ local experiences. This paper focuses on Nundle's ‘Go for Gold Festival’, which is held annually over the Easter weekend. For its first six years, the festival had no relationship with Chinese heritage but in 2004, the seventh festival was rebranded as the ‘Go for Gold Chinese Festival’ and the event experienced something of a revival. Its transformation into a festival celebrating Chinese history and heritage has helped it develop into a major regional event, second only to Tamworth's Country Music Festival. What, however, are the finer-grained circumstances and consequences of these initiatives for Nundle's identity? What might it mean for ‘Chinese heritage’ to be mobilized in this way, and for Chinese Australian representation in the region?

Advancing Our Profession Through Annual Meetings Department

Advancing Our Profession Through Annual Meetings Department

Stress transfer and seismic instabilities in the upper crust: example of the western Pyrenees

When the regional state of stress is close to the condition for earthquakes to occur, small stress and strain changes could trigger seismic instabilities. Stress diffusion ( Δσ = 1–2 MPa) has been suggested to explain, at lithospheric scale, space and time correlated earthquakes and surface deformations in subduction zones (100–200 km, 10–40 years). We test the possible regional mechanisms, at the upper crustal scale, in the western Pyrenees, where major regional events (M max = 5.7), locally induced events and subsurface fluid pressure fluctuations are temporally and spatially correlated. In a first phase, fluid withdrawal (decrease of pore pressure of the aquifer at the gas-water interface) affects the natural regional seismicity rate. The locked fault inhibits small events for a time, during which tectonic stresses accumulate. Major regional events then occur on the Pyrenean Fault, when the energy of deformation is large enough to allow seismic instabilities to occur. These major events (M 1 > 5) trigger seismic instabilities (M 1 = 4), in the vicinity of the gas extraction area, 30 km away. As a result of gas extraction, the Lacq field zone has local weakness characteristics similar to the neighbouring main active fault. The Pyrenean earthquakes lead the gas field events by 2 years. This correlation is consistent with a viscoelastic model, where salt rock acts as a viscoelastic channel, below an elastic bed. The possible connections proposed here may give a new insight worldwide in understanding the role of fluids in seismic instabilities and seismic risk assessment in the neighbouring of man-made fluid pressure fluctuations, when natural seismic activity is high.