Possible effects of human impacts on epibenthic communities and coral rubble features in the marine Park of Bunaken (Indonesia)     

Federica Fava  Massimo Ponti  Alice Scinto  Barbara Calcinai  Carlo Cerrano 《Estuarine, Coastal and Shelf Science》2009

Indo-Pacific coral reefs are considered among the most complex and biodiversified ecosystems in the world. Their existence is threatened by both natural and anthropogenic factors. Therefore, the assessment of anthropogenic disturbances is necessary to protect and manage these marine natural resources. In Bunaken Marine Park (North Sulawesi, Indonesia) epibenthic assemblages and coral rubble features at four impacted sites (each of them located close to villages and frequently exploited as recreational diving spots), and four well preserved sites (far from villages and scarcely frequented by divers), were investigated at 6, 12 and 18 m depth, in order to identify possible reef modifications. The assemblages were sampled by way of photographs. Coral rubble cover was estimated both by way of photographs and along belt transects, while grain size and the living fraction of the coral rubble were assessed by direct samples. The data showed significant differences between the study sites and between depths with regard to human activity. The hard coral cover and the assemblage heterogeneity are higher in control sites than in the impacted site where, especially in shallow water, the mechanical damage can strongly affect the assemblage structure.  相似文献   

Crystal retention,fractionation and crustal assimilation in a convecting magma chamber,Nisyros Volcano,Greece   总被引：2，自引：0，他引：2  

L. Francalanci  J. C. Varekamp  G. Vougioukalakis  M. J. Delant  F. Innocenti  P. Manetti 《Bulletin of Volcanology》1995,56(8):601-620

Nisyros island is a calc-alkaline volcano, built up during the last 100 ka. The first cycle of its subaerial history includes the cone-building activity with three phases, each characterized by a similar sequence: (1) effusive and explosive activity fed by basaltic andesitic and andesitic magmas; and (2) effusive andextrusive activity fed by dacitic and rhyolitic magmas. The second eruptive cycle includes the caldera-forming explosive activity with two phases, each consisting of the sequence: (1) rhyolitic phreatomagmatic eruptions triggering a central caldera collapse; and (2) extrusion of dacitic-rhyolitic domes and lava flows. The rocks of this cycle are characteized by the presence of mafic enclaves with different petrographic and chemical features which testify to mixing-mingling processes between variously evolved magmas. Jumps in the degree of evolution are present in the stratigraphic series, accompanied by changes in the porphyritic index. This index ranges from 60% to about 5% and correlates with several teochemical parameters, including a negative correlation with Sr isotope ratios (0.703384–0.705120). The latter increase from basaltic andesites to intermediate rocks, but then slightly decrease in the most evolved volcanic rocks. The petrographic, geochemical and isotopic characteristics can be largely explained by processes occurring in a convecting, crystallizing and assimilating magma chamber, where crystal sorting, retention, resorption and accumulation take place. A group of crystal-rich basaltic andesites with high Sr and compatible element contents and low incompatible elements and Sr isotope ratios probably resulted from the accumulation of plagioclase and pyroxene in an andesitic liquid. Re-entrainment of plagioclase crystals in the crystallizing magma may have been responsible for the lower ⁸⁷Sr/⁸⁶Sr in the most evolved rocks. The gaps in the degree of evolution with time are interpreted as due to liquid segregation from a crystal mush once critical crystallinity was reached. At that stage convection halted, and a less dense, less porphyritic, more evolved magma separated from a denser crystal-rich magma portion. The differences in incompatible element enrichment of pre-and post-caldera dacites and the chemical variation in the post-caldera dome sequence are the result of hybridization of post-caldera dome magmas with more mafic magmas, as represented by the enclave compositions. The occurrence of the quenched, more mafic magmas in the two post-caldera units suggests that renewed intrusion of mafic magma took place after each collapse event.  相似文献   

Sr isotopic evidence for a multi-source origin of the potassic magmas in the neapolitan area (S. Italy)     

Massimo Cortini  O. Don Hermes 《Contributions to Mineralogy and Petrology》1981,77(1):47-55

New Sr isotopic data on lavas and xenoliths from Somma-Vesuvius and other nearby volcanic areas (Phlegrean Fields and Ischia) are presented. Chemical and isotopic evidences show that not all the Phlegrean Fields rocks belong to the low K series, but some of them may be interpreted as low pressure differentiates of Somma magmas, i.e. as a part of the high K series. Two rock groups are defined in the Ischia low K series, which are well identified both in time and in chemical and isotopic features, and cannot be derived from the same magma source. The low K series in the studied area generally has lower Sr isotopic values than the high K series.Historical Vesuvian lavas show two distinct linear trends with negative slopes when⁸⁷Sr/⁸⁶Sr ratios are plotted against their ages of eruption. Such trends are interpreted to result from mixing of magmas in two separate reservoirs. Evidence from the Vesuvian ejecta shows that Somma-Vesuvius magmas underwent high or low pressure fractionation, in connection with different events of the Vesuvian activity. Distinct magma reservoirs developed episodically at different depths. Isotopic and geochemical evidences do not favour large scale assimilation of crustal materials by Somma-Vesuvius magmas, but instead appear to reflect mantle characteristics.A minimum of three different (inhomogeneous) source regions is necessary to account for the isotopic features of the studied rocks.  相似文献   

Destructive effects of oxygen starvation and ash falls on benthic life: A pilot study     

Maria Bianca Cita  Massimo Podenzani 《Quaternary Research》1980,13(2):230-241

A quantitative study on faunal density and faunal diversity was carried out on benthic foraminifers from 15 samples of two eastern Mediterranean deep-sea cores. Samples were taken beneath, within, and above three distinctive levels well correlatable for over 1000 km: (a) Sapropel S-5, late Pleistocene in age, correlative with marine isotopic stage 5e and with the Tyrrhenian transgression, with an interpolated age of ～ 125,000 yr: (b) the “Ischia” tephra Y-5, the most widespread ash layer of the eastern Mediterranean, correlative with the transition from isotopic stages 3 to 2 and having an interpolated age of ～ 35,000 yr; and (c) Sapropel S-1, Holocene in age, correlative with the Flandrian transgression, radiometrically dated at ～8000 yr B.P. The most severe effects on benthic life were induced by stagnation (a). Deglaciation corresponding to Termination II was so rapid that the benthic assemblages could not adapt themselves to the too-rapidly decreasing oxygen levels and were entirely destroyed. More than 1000 yr after the termination of stagnant conditions no recolonization had yet started. The lesser disturbance was induced in the benthic community by the ash fall (b). The faunal destruction was ephemeral in duration and the colonizing population did not differ from that predating the ash fall. A progressive faunal change, with increasing abundance of taxa tolerant to low oxygen levels, was recorded beneath Sapropel S-1 (c). The recolonizing assemblage differs from the previously existing one, and is more similar to those recorded from the floor of the Mediterranean.  相似文献   

Acid and basic late neogene volcanism in central aegean sea: Its nature and geotectonic significance     

F. Innocenti  N. Kolios  P. Manetti  F. Rita  L. Villari  L. Villari 《Bulletin of Volcanology》1982,45(2):87-97

Local eruptions of acid volcanic rocks occurred in the Central Aegean region around the Miocene-Pliocene boundary. Rhyolites outcrop on the Island of Antiparos, located in the central part of the Attic-Cycladic Massif. The age of these volcanic rocks ranges from 4.0 to 5.4 m.y., and chemical and Sr isotopic data suggest they were generated by partial melting of the continental crust. At the same time, along the border of the Attic-Cycladic Massif,i.e. on the island of Patmos and Caloyeri, local eruptions of Naalkaline basalts occurred. The whole of the eruptive activity is interpreted as an expression of the marked tensional tectonic phase which has affected the Central Aegean area since Middle Miocene. The contrasting nature of the erupted volcanic rocks (crustal and sub-crustal) is attributed to the different thermal state of the lithosphere beneath the two areas, as emphasized also by the presence of a wide granitic belt, of mainly Miocene age, which developed in the median sector of the Attic-Cycladic Massif.  相似文献   

The campanian ignimbrite: a major prehistoric eruption in the Neapolitan area (Italy)     

F. Barberi  F. Innocenti  L. Lirer  R. Munno  T. Pescatore  R. Santacroce 《Bulletin of Volcanology》1978,41(1):10-31

A geological, chemical and petrographical study of the Campanian ignimbrite, a pyroclastic flow deposit erupted about 30,000 years ago on the Neapolitan area (Italy), is reported. The ignimbrite covered an area of at least 7,000 km²; it consists of a single flow unit, and the lateral variations in both pumice and lithic fragments indicate that the source was located in the Phlegraean Fields area. Textural features, areal distribution and its morphological constraints suggests that the eruption was of the type of highly expanded low-temperature pyroclastic cloud. The original composition was strongly modified by post-depositional chemical changes involving most of the major and trace elements. No primary differences in the composition of the magma have been recognized. The Campanian ignimbrite is a nearly saturated potassic trachyte, similar to many other trachytes of the Quaternary volcanic province of Campania. Its chemistry indicates an affinity with the so-called «low-K association» of the Roman volcanic province.  相似文献   

Radiometric age evidences of a Triassic Thermal Event in the Southern Alps     

Prof. Giorgio Ferrara  F. Innocenti 《International Journal of Earth Sciences》1974,63(2):572-581

In the Southern Alps several K/Ar age determinations point out the existence of a thermal event of Upper-Triassic age. Radiometric evidences concern overprinting on K/Ar ages of biotites belonging to hercynian periadriatic massives, and of muscovites of pegmatites in which also a Sr isotopic re-equilibration has taken place. Some evidences are also recognizable in ancient metamorphic basement. In the same time an extensive extrusive and intensive magmatic activity of alkaline affinity occurred. These facts are interpreted as predrift events shortly preceeding the set up of lower Jurassic oceanic conditions of alpine area.  相似文献   

Compositional variations in the Campanian Ignimbrite,Italy: Hydrothermal modification or pre-eruptive fractionation? — A reply     

F. Barberi  F. Innocenti  L. Lirer  R. Munno  T. Pescatore  R. Santacroce 《Bulletin of Volcanology》1983,46(4):433-434

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The evolution of the mantle source beneath Mt. Etna (Sicily,Italy): from the 600 ka tholeiites to the recent trachybasaltic magmas     

Federico Casetta  Pier Paolo Giacomoni  Carmelo Ferlito  Costanza Bonadiman  Massimo Coltorti 《International Geology Review》2020,62(3):338-359

ABSTRACT

The spatial/temporal proximity of Mt. Etna to the Hyblean Plateau and the Aeolian slab makes the discussion on the nature of its mantle source/s extremely controversial. In this study, a detailed geochemical overview of the entire Mt. Etna evolutionary sequence and a comparison with the magmatism of the Hyblean Plateau was proposed to: (i) simulate the composition of Mt. Etna tholeiitic to alkaline primitive magmas in equilibrium with a fertile mantle source; (ii) model the nature, composition and evolution of the mantle source from the tholeiitic stage (600 ka) to present magmatism. According to our simulations, two amphibole + phlogopite-bearing spinel lherzolite sources are able to explain the wide range of Etnean primary magmas. The enrichment in LILE, ⁸⁷Sr/⁸⁶Sr, Rb and H₂O of the magmas emitted after 1971 (but also discontinuously generated in both historic and prehistoric times) are caused by different melting proportions of amphibole and phlogopite in a modally and compositionally homogeneous mantle domain, with melting degrees analogous to those required to produce magmas erupted prior to 1971. The behaviour of the hydrous phases during melting could be ascribed to a variable H₂O/CO₂ activity in the mantle source, in turn related to the heat/fluxes supply from the asthenospheric upwelling beneath Mt. Etna. All these considerations, strengthened by numerical models, are then merged to review the complex Pliocene/Lower Pleistocene to present day’s geodynamic evolution of eastern Sicily.  相似文献   

On the evolution of the cosmic supernova rates     

Piero Madau  Massimo Della Valle  & Nino Panagia 《Monthly notices of the Royal Astronomical Society》1998,297(1):L17-L22

The Galactic radio-emitting X-ray binary Cygnus X-3 is known to be a source of large-scale radio jets associated with periods of intense radio flaring. These jets have been found to have an expansion velocity of ∼0.3 c and are believed (on kinematic grounds) to lie close to the plane of the sky. We present new observations of Cygnus X-3 using the VLBA at 15 GHz. These observations, which included the detection of two small flares, show an additional kind of behaviour with apparent superluminal expansion along both major and minor axes. Evidence for superluminal activity has been found in a number of X-ray binary systems such as GRS 1915+105 and GRO J1655−40 with their superluminal radio jets. Apparently similar morphologies of the Galactic and extragalactic jet sources have led to the X-ray binaries being described as 'micro-quasars'. The superluminal expansion seen in our results appears to be different in nature from these other two sources, and a number of mechanisms are presented and discussed.  相似文献