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1.
Varela M. E. Bjerg E. A. Clocchiatti R. Labudia C. H. Kurat G. 《Mineralogy and Petrology》1997,60(3-4):145-164
Summary Three generations of fluid inclusions can be recognized in upper mantle xenoliths from alkali basalts of the Somoncura Massif, Northern Patagonia, Argentina. The first (early, primary) one consists of dense CO2 inclusions which were trapped in the mantle-crust boundary zone (22–36 km minimum trapping depth). Their co-genetic relationship with silicate melt inclusions enables us to constrain their minimum trapping temperature at 1200°C, indicating a high temperature event in a cooler environment. The late (pseudosecondary and secondary) generations of fluid inclusions were classified in accordance with their homogenization temperature to liquid CO2 (L1) and vapor CO2 (L2) phase. The minimum trapping depth for the first of the late inclusions (L1) is about 16 km. In spite of the uncertainties related to this value, L1 inclusions indicate that the upper mantle rocks, of which samples were delivered by the basalts, had some residence time in the middle crust where they experienced a metasomatic event. The fact that this event did not destroy the earlier inclusions, places severe constraints on its duration. The second late inclusions (L2) are low-pressure CO2 inclusions with a minimum trapping depth of only 2 km, presumably a shallow magma chamber of the host basalts. The succession of fluid inclusions strongly points toward a fairly fast uprising upper mantle underneath Northern Patagonia. The petrology and mineral chemistry of the peridotitic xenoliths support this view. Extensive partial melting and loss of these melts is indicated by the preponderance of harzburgites in the upper mantle underneath Northern Patagonia, a fairly unusual feature for a continental upper mantle. That depletion event as well as several metasomatic events — including those which left traces of fluid inclusions — are possibly related to a high-speed diapiric uprise of the upper mantle in this area. The path can be traced from the garnet peridotite stability field into the middle crust, a journey which must have been unusually fast. Differences in rock, mineral, and fluid inclusion properties between geographic locations suggest a diffuse and differential type of diapirism. Future studies will hopefully help to map the full extent and the highs and lows of this diapir and elucidate questions related to its origin and future.
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Fluid-Einschlüsse in Erdmantel-Xenolithen von Nord-Patagonien: Evidenz für einen Diapir im oberen Erdmantel
Zusammenfassung Erdmantel - Xenolithe in Alkali-Basalten des Somoncure Massivs, Nord-Patagonien, Argentinien, führen drei Generationen von Fluid-Einschlüssen. Die erste (frühe, primäre) Generation besteht aus dichten CO2-Einschlüssen, welche offenbar in der Mantel-Kruste Grenzzone (22–36 km Minimum-Tiefe) eingeschlossen wurden. CO2-Einschlüsse sind kogenetisch mit Silikat-Schmelzeinschlüssen. Dies erlaubt die Abschätzung der Einschließ-Temperatur mit minimal 1200°C, was auf ein Hochtemperatur-Ereignis in einer deutlich kühleren Umgebung hinweist. Die späten (pseudosekundäre und sekundäre) CO2- Fluid-Einschlüsse bilden zwei Generationen von denen die eine in die flüssige (L1), die andere in die Dampfphase (L2) homogenisieren. Die minimale Einschließ-Tiefe für die L1 Generation ist etwa 16 km. Dies bedeutet - auch bei Berücksichtigung der mit diesem Wert verbundenen Ungenauigkeit - daß diese Erdmantel-Gesteine einige Zeit in der mittleren Erdkruste verbrachten und ein metasomatisches Ereignis erlebten, bevor sie von den Basalten zur Erdoberfläche gebracht wurden. Die Tatsache, daß dieses Ereignis die frühen Einschlüsse nicht zerstörte, kann nur bedeuten, daß es von kurzer Dauer war. Die L2-Generation besteht aus Niedrigdruck CO2-Einschlüssen mit einer Minimum-Einschließtiefe von nur 2 km. Dies könnte in einer seichten Magmakammer des Wirt Basaltes geschehen sein.Die Abfolge von Fluid-Einschlüssen deutet auf einen relativ schnell aufsteigenden oberen Erdmantel unterhalb von Patagonien hin. Die Petrologie und Mineralchemie der peridotitischen Xenolithe unterstützen das. Die Vorherrschaft von Harzburgiten im Erdmantel unterhalb von Nord-Patagonien deutet auf umfangreiche Bildung partieller Schmelzen und deren Abfuhr hin — eine für einen kontinentalen Mantel ungewöhnliche Situation. Sowohl die Verarmungsereignisse, als auch die metasomatischen Veränderungen (einschließlich jene, welche Spuren in Form von Fluid Einschlüssen hinterließen) machen das Vorhandensein eines schnell aufsteigenden Daipirs im oberen Erdmantel dieser Gegend wahrscheinlich. Der Aufstieg kann vom Stabilitätsbereich der Granat-Peridotite bis in die mittlere Kruste verfolgt werden und muß daher relativ schnell erfolgt sein. Unterschiede in Gesteins-, Mineral und Fluid-Eigenschaften zwischen verschiedenen Lokalitäten legen einen diffusen und differenziellen Diapirismus nahe. Zukünftige Studien sollten es ermöglichen, das Gesamtausmaß und die unterschiedlichen Aufstiegshöhen des Diapirs zu kartieren und Hinweise auf seine Entstehung und zukünftige Entwicklung zu erhalten.
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2.
A study of melt inclusions at Vulcano (Aeolian Islands, Italy): insights on the primitive magmas and on the volcanic feeding system 总被引：5，自引：0，他引：5
A. Gioncada R. Clocchiatti A. Sbrana P. Bottazzi D. Massare L. Ottolini 《Bulletin of Volcanology》1998,60(4):286-306
This work presents the results of a microthermometric and EPMA-SIMS study of melt inclusions in phenocrysts of rocks of the
shoshonitic eruptive complex of Vulcano (Aeolian Islands, Italy). Different primitive magmas related to two different evolutionary
series, an older one (50–25 ka) and a younger one (15 ka to 1890 A.D.), were identified as melt inclusions in olivine Fo88–91 crystals. Both are characterized by high Ca/Al ratio and present very similar Rb/Sr, B/Be and patterns of trace elements,
with Nb and Ti anomalies typical of a subduction zone. The two basalts present the same temperature of crystallization (1180±20 °C)
and similar volatile abundances. The H2O, S and Cl contents are relatively high, whereas magmatic CO2 concentrations are very low, probably due to CO2 loss before low-pressure crystallization and entrapment of melt inclusions. The mineral chemistry of the basaltic assemblages
and the high Ca/Al ratio of melt inclusions indicate an origin from a depleted, metasomatized clinopyroxene-rich peridotitic
mantle. The younger primitive melt is characterized with respect to the older one by higher K2O and incompatible element abundances, by lower Zr/Nb and La/Nb, and by higher Ba/Rb and LREE enrichment. A different degree
of partial melting of the same source can explain the chemical differences between the two magmas. However, some anomalies
in Sr, Rb and K contents suggest either a slightly different source for the two magmas or differing extents of crustal contamination.
Low-pressure degassing and cooling of the basaltic magmas produce shoshonitic liquids. The melt inclusions indicate evolutionary
paths via fractional crystallization, leading to trachytic compositions during the older activity and to rhyolitic compositions
during the recent one. The bulk-rock compositions record a more complex history than do the melt inclusions, due to the syneruptive
mixing processes commonly affecting the magmas erupted at Vulcano. The composition and temperature data on melt inclusions
suggest that in the older period of activity several shallow magmatic reservoirs existed; in the younger one a relatively
homogeneous feeding system is active. The shallow magmatic reservoir feeding the recent eruptive activity probably has a vertical
configuration, with basaltic magma in the deeper zones and differentiated magmas in shallower, low-volume, dike-like reservoirs.
Received: 11 March 1998 / Accepted: 14 July 1998 相似文献
3.
Pierre Schiano Bernard Bourdon Robert Clocchiatti Dominique Massare Maria E. Varela Yan Bottinga 《Earth and Planetary Science Letters》1998,160(3-4):537-550
The study of glass inclusions inside mantle minerals provides direct information about the chemistry of naturally occurring mantle-derived melts and the fine-scale complexity of the melting process responsible for their genesis. Minerals in a spinel lherzolite nodule from Grande Comore island contain glass inclusions which, after homogenization by heating, exhibit a continuous suite of chemical compositions clearly distinct from that of the host basanitic lava. The compositions range from silicic, with nepheline–olivine normative, 64 wt% SiO2 and 11 wt% alkali oxides, to almost basaltic, with quartz normative, 50 wt% SiO2 and 1–2 wt% alkali oxides. Within a single mineral phase, olivine, the inferred primary melt composition varies from 54 to 64 wt% SiO2 for MgO content ranging from 8 to 0.8 wt%. An experimental study of the glass and fluid inclusions indicates that trapped melts represent liquids that are in equilibrium with their host phases at moderate temperature and pressure (T≈1230°C and P≈1.0 Gpa for melts trapped in olivine). Quantitative modelling of the compositional trends defined in the suite shows that all of the glasses are part of a cogenetic set of melts formed by fractional melting of spinel lherzolite, with F varying between 0.2 and 5%. The initial highly silicic, alkali-rich melts preserved in Mg-rich olivine become richer in FeO, MgO, CaO and Cr2O3 and poorer in SiO2, K2O, Na2O, Al2O3 and Cl with increasing melt fractions, evolving toward the basaltic melts found in clinopyroxene. These results confirm the connection between glass inclusions inside mantle minerals and partial mantle melts, and indicate that primary melts with SiO2 >60 wt%, alkali oxides >11%, FeO <1 wt% and MgO <1 wt% are generated during incipient melting of spinel peridotite. The composition of the primary melts is inferred to be dependent on pressure, and to reflect both the speciation of dissolved CO2 and the effect of alkali oxides on the silica activity coefficient in the melt. At pressures around 1 GPa, low-degree melts are characterized by alkali and silica-rich compositions, with a limited effect of dissolved CO2 and a decreased silica activity coefficient caused by the presence of alkali oxides, whereas at higher pressures alkali oxides form complexes with carbonates and, consequently, alkali-rich silica-poor melts will be generated. 相似文献
4.
5.
M. F. Grasso R. Clocchiatti F. Carrot C. Deschamps F. Vurro 《Environmental Geology》1999,37(3):207-217
The aim of this paper is to verify whether lichens have the capacity to accumulate atmospheric contaminators linked to volcanic
activity. About 100 lichens were collected in 1994 and 1995 from two active volcanic areas in Italy: Mount Etna and Vulcano
Island. Twenty-seven elements were analyzed for each individual lichen using Instrumental Neutronic Activation Analysis and
Inductively Coupled Plasma-Mass Spectrometry. Lichen composition reflects the contribution of the volcanic particulate material,
and the two areas investigated can be distinguished on the basis of the concentration of some lithophile elements. Moreover,
the distribution in lichens of the elements (As, Sb, Br, Pb) – derived from gas emissions (plume, fumaroles) – also shows
different geochemical trends on Mt. Etna and Vulcano.
Received: 20 April 1998 · Accepted: 4 July 1998 相似文献
6.
Differentiation Mechanism and Evolution of High-level Magma Chamber at Xiangshan,China 总被引：2，自引：0，他引：2
The calc-alkaline volcanic magmas,which formed the Mesozoic uraniferous volcanic complex of Xiangshan,resulted from partial melting of the mixture of lower crust and enriched mantle with a high mixing proportion in a specific tectonic setting such as active continental margin or ocean-continent collision zone.The preliminary concentrations of Uand Th occur in low-degree par-tial melts.Only small part of these melts was rapidly extracted and erupted and most intruded into the high-level magma chamber(depth:12-13 km) of the compressed upper lithosphere ,in which occurred a strong differentiation which would resulted in strong preconcentrations of the high-hygromagmaphile elements U and Th associated with strong depletion of the 3-d transition ele-ments Ti,Sc,Co,Zr,etc.At the final stage of subduction of the West-Pacific-Kula plate towards the Asian continental plate,the regional tectonic environment was transformed from a compressive in-to a tensional setting.The strongly differentiated,U(and Th) enriched silicic alkalic magmas in high level magma chamber extensively erupted,extruded and intruded.The hydrothermal fluids released as a result of late volcano-degassing and dewatering during crystallization-solidification of magmas,re-sulted in the remobilization,leaching,migration and reconcentration of uranium ,which had been preconcentrated in volcanic rocks.Therefore,specific regional petrogeochemical criteria are expected for the uraniferous volcanic series. 相似文献
7.
Dr. M. E. Varela Dr. R. Clocchiatti D. Massare Dr. P. Schiano 《Mineralogy and Petrology》1998,62(1-2):103-121
Summary In an attempt to investigate metasomatic processes in the subcontinental upper mantle beneath Northern Patagonia, melt and fluid inclusions trapped in spinel lherzolite and harzburgite xenoliths have been studied. The xenoliths contain three types of genetically related inclusions hosted by olivine, orthopyroxene, clinopyroxene and spinel: silicate glass inclusions, multiphase silicate melt inclusions and C02 fluid inclusions. CO2 densities of early fluid inclusions (0.93–1.02 g/cm3) and homogenization temperatures of melt inclusions (1220 °C) indicate that they were trapped at uppermantle depths.Silicate melt inclusions occur as isolated inclusions as trails along fractures and decorating lamellae deformation. They are composed of glass, or of glass with daughter crystals of clinopyroxene, amphibole, apatite and ilmenite. Glass inclusions are characterized by high contents of silica, alumina and alkali elements. The nature and chemistry of the daughter minerals indicate that melt inclusions can be considered as trapped metasomatic melts. Moreover, glass inclusions show chemical variations from high silica (68 wt%) melts trapped as isolated inclusions in olivine Fog, towards less siliceous (60 wt%) melts trapped as secondary inclusions in olivine FO89-90, orthopyroxene and spinel. This chemical evolution cannot be reconciled with magmatic processes, like fractional crystallization or different degrees of partial melting. The existence of two stages in their evolution, could reflect the heterogenous nature of the mantle source of the melts and the presence of a deep-seated fluid phase during melting.
Les inclusions vitreuses riches en silice: témoignages du métasomatisme du manteau subcontinental de la province de Rio Negro (Patagonie septentrionale, Argentine)
Résumé Les inclusions fluides et vitreuses piégées dans les minéraux des xénolithes de lherzolite á spinelle et de harzburgite ont fait l'objet d'études thermométriques et barochimiques afin de mieux cerner les processus métasomatiques qui ont affecté le manteau supérieur subcontinental du nord de la Patagonie. Les xénolithes contiennent trois types d'inclusions génétiquement reliées entre elles et piégées dans l'olivine, l'orthopyroxène, le clinopyroxène et les spinelles: 1) inclusions vitreuses, 2) inclusions vitreuses multiphasées, 3) inclusions fluides á CO2. La densité des inclusions fluides précoces (0.93 á 1.02g/c3) et la température d'homogénéisation des inclusions vitreuses (Th = 1220°C) indiquent que les inclusions ont été piégées dans le manteau supérieur.Les inclusions vitreuses sont soit en individus isolés, soit en alignements disposés selon des fractures et des lamelles de déformation (inclusions secondaires). Elles sont formées par du verre et par une bulle pouvant contenir du CO2 auxquels peuvent s'associer des minéraux fils (clinopyroxènes, amphiboles, apatites et ilménites). La phase vitreuse, caractérisée par une composition riche en silice, alumine, alcalins et volatils élevés et la nature des minéraux fils indiquent que les inclusions vitreuses résultent du piégeage de liquides métasomatiques.La composition des inclusions vitreuses varie. La teneur en SiO2 atteint 68% en poids dans les inclusions isolées des Fo 91, elle est par contre proche de 60% dans les inclusions secondaires des Fo 89-90, de l'orthopyroxène et du spinelle. La composition chimique des différents types d'inclusions ne peut être expliquée par les processus classiques de différenciation magmatique tels que la cristallisation fractionnée ou la fusion partielle. L'existence d'une bimodalité dans les compositions chimiques et dans les niveaux de piégeage plaident en faveur d'une source mantellique hétérogène et de l'intervention de fluides profonds lors du processus de fusion ayant généré les liquides métasomatiques.相似文献
8.
Crystallization paths of basaltic (1763 eruption) and hawaiitic (1865 and 1329 eruptions) scoria from Etna were deduced from mineralogy and melt inclusion chemistry. The volatile behaviour was investigated through the study of melt inclusions trapped in the phenocrysts and those of the whole rocks and the matrix glasses. The results from the 1763 eruption point to the early crystallization of olivine Fo 81.7 from a water-rich alkaline basalt, with high Cl (1750–2000 ppm) and S (2100–2400 ppm) concentrations. The hawaiitic melt inclusions trapped in olivine Fo 74, salite and plagioclase are characterized by a decrease in Cl/K2O and S/K2O ratios. In each investigated system there is good correlation between K2O and P2O5. In the whole rocks, Cl ranges from 980 to 1680 ppm, from basaltic to hawaiitic lavas, whereas S (110–136 ppm) remains low. Cl and S behaviour in the 1763 magma suggests an early degassing stage of Cl and S, with CO2 and a water-rich gaseous phase for a pressure close to 100 MPa, consistent with a permanent outgassing at the summit craters of Etna. During the eruption, the sulphur remaining in the hawaiitic liquid is lost, and the degassing of chlorine is limited. Such a degassing model can be extended to the 1865 and 1329a.d. eruptions. 相似文献
9.
Resume Les différentes étapes de la cristallisation des pyroclastes des Monti Rossi et Silvestri ont été reconstituées par l'étude des inclusions vitreuses intraminérales.L'olivine magnésienne (Fo 82) et le diopside cristallisent à partir d'un liquide basaltique de nature alcaline au cours de l'ascension, sous une forte pression de fluides liée à la quantité importante de gaz dissous (4 à 5% dont 2800–3500 ppm de S).L'« ouverture » du système s'accompagne de la démixtion d'environ 50% de la phase volatile dissoute.Les oxydes Fe-Ti, les olivines (Fo 74-75) et les salites cristallisent alors, à partir d'un liquide partiellement dégazé (2 à 2,5% d'éléments volatils, dont 1200 ppm de S), de composition hawaïtique, dans un domaine de température compris entre 1160 et 1140°C.Le plagioclase (An 82) se sépare tardivement dans un liquide dont la composition se rapproche de celle du liquide résiduel. Ce stade d'évolution qui s'accompagne d'une accumulation de gaz démixé, témoigne de conditions pré-éruptives de subsurface.Les teneurs anormalement élevées en fluides des basaltes alcalins etnéens comparées à celles de basaltes de même composition (par exemple dans les inclusions des Fo 82 du Piton de la Fournaise, des volatils 2%, S=1200 ppm et Cl=200 à 400 ppm) nous ont conduit à envisager la contribution de l'encaissant sédimentaire.La présence dans les produits des Silvestri de nombreuses enclaves carbonatées (fassaïte, wollastonite, anorthite), argilo-schisteuses (plagioclase, hercynite, sulfures) et gréseuses (quartz, verres rhyolitiques), l'abondance des inclusions fluides (CO2, SO2) dans les minéraux néoformés, les témoignages de phénomènes locaux d'assimilation (verres riches en Ca, Si...) viennent renforcer l'idée du rôle de la contamination (au moins en ce qui concerne les fluides) par l'encaissant sédimentaire, négligée jusqu'ici dans le cas des laves de l'Etna.
The melt inclusions trapped inside crystals have allowed the determination of the different crystallization steps, for the M. Rossi and M. Silvestri pyroclastic products.Magnesian olivine (Fo 82) and diopside crystallize from an alkali basaltic liquid, during ascent. The high concentration (4–5% with S=2800–3500 ppm) of volatiles in glass inclusions involves a strong fluid pressure.The release of about 50% of dissolved gases reflects the « opening » of the magmatic system. Therefore, olivine (Fo 74-70), salite and Fe-Ti oxydes, crystallize from an hawaiitic melt, with lower volatile content (2 to 2,5% with S=1200 ppm). The temperatures range from 1160°C to 1140°C.Plagioclase phenocrysts (An 82) grow later from a more evolved liquid. Equivalences of gas accumulation infer a pre-eruption crystallization.The unusual content of volatiles in the alkali basalts compared to equivalent oceanic basalts (2% with S=1200 ppm and Cl= 200 to 400 ppm in olivine melt inclusions from Piton de la Fournaise volcano) suggests a wall rock contribution.Numerous xenoliths of carbonates (with fassaite, wollastonite, anorthite assemblages), shale (with plagioclase, hercynite and sulfide) or sandstone (with quartz and rhyolitic glasses) have been found among the M. Silvestri products.Fluid inclusions in the minerals as well as local SiO2, CaO, FeO enrichments of the magmatic liquid infer partial assimilation of sedimentary rocks.All these observations support a contamination hypothesis, at least for the volatile phase.相似文献
10.
Denis Vincent Roberto Clocchiatti Yves Langevin 《Earth and Planetary Science Letters》1984,71(2):340-348
We have extended fission-track dating techniques to volcanic pyroclastic rocks, using quartz-bearing uranium-rich glass inclusions. We use both the glass itself and the surrounding quartz as track detectors, the latter having a much higher resetting temperature. We can thus derive the age of the last low-temperature thermal event, as well as that of the most recent deposition of quartz on the walls of the inclusions. This method has been applied to a Sardinian sample and to a Moroccan Precambrian sample. 相似文献