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1.
The Tertiary volcanism of Eastern Macedonia and Western Thrace (Greece) developed in association with the sedimentary basin which formed, from Eocene to Oligocene, along the southern margin of the Rhodope Massif.The volcanic products, ranging in composition from basaltic andesites to rhyolites, show an overall calc-alkaline orogenic affinity, while chemical characteristics identify different groups of rocks, probably reflecting minor differences among parent magmas. The observed evolution within any group of rocks is compatible with fractional crystallization processes acting on relatively shallow magma bodies.The Sr isotopic composition of rhyolitic member shows an initial87Sr/86Sr ratio comparable with that of basaltic andesites, reinforcing the hypothesis of a crystal/liquid line of descent.Geochemical and petrographic evidence, on the whole, suggests that the investigated orogenic association developed on an active continental margin characterized by a relatively thick crust, acting as a density filter for the basic magmas and facilitating their storage and fractionation within the crust itself. Minor contamination by interaction with host materials may also have occurred.Stratigraphic and K/Ar geochronological data indicate that the volcanic activity started in Upper Eocene and reached its maximum development in Upper Oligocene. From Lower Miocene, the volcanism shifted southward in the Central Aegean area and in part of Western Anatolia, coming to an end by Middle Miocene.The southward migration of the volcanic front has been interpreted as a consequence of the increase in the dipping of the Benioff zone, due to the decrease of penetrative strength after the main phase of continental collision.  相似文献   

2.
The Ezine region is located in the northwestern part of Anatolia where young granitic and volcanic rocks are widespread and show close spatial and temporal association. In this region magmatism began with the Kestanbol granite, which intruded into metamorphic basement rocks, and formed contact metamorphic aureole. To the east and southeast the pluton is surrounded by hypabyssal rocks, which in turn, are surrounded by volcanic associations. The volcanic rocks may be divided into two main groups on the basis of their lithological properties. Lavas and lahar deposits dominate the northern sector while ignimbrites dominate the southern sector. The ignimbrite eruptions were formed partly coevally with the plutonic and the associated volcanic rocks during the early Miocene. They appear to have been associated in a caldera collapse environment. Geochemical properties of the plutonic and the associated volcanic assemblages indicate that the magmas are hybrid and co-genetic and, were formed from a similar mantle source, under a compressional regime prior to the opening of the present E–W-trending graben of the Aegean western Anatolian region.  相似文献   

3.
Twenty-four K-Ar radiometric ages are presented for late Cenozoic continental volcanic rocks of the Cordillera Occidental of southernmost Perú (lat. 16° 57′–17° 36′S). Rhyodacitic ignimbrite eruptions began in this transect during the Late Oligocene and continued episodically through the Miocene. The development of andesitic-dacitic strato volcanoes was initiated in the Pliocene and continues to the present.The earliest ignimbrite flows (25.3–22.7 Ma) are intercalated in the upper, coarsely-elastic member of the Moquegua Formation and demonstrate that this sedimentary unit accumulated in a trough, parallel to Andean tectonic trends, largely in the Oligocene. More voluminous ash-flow eruptions prevailed in the Early Miocene (22.8–17.6 Ma) and formed the extensively preserved Huaylillas Formation. This episode was coeval with a major phase of Andean uplift, and the pyroclastics overlie an erosional surface of regional extent incised into a Paleogene volcano-plutonic arc terrain. An age span of 14.2–8.9 Ma (mid-Late Miocene) is indicated for the younger Chuntacala Formation, which again comprises felsic ignimbrite flows, largely restricted to valleys incised into the pre-Huaylillas Formation lithologies, and, at lower altitudes, an extensive aggradational elastic facies. The youngest areally extensive ignimbrites, constituting the Sencca Formation, were extruded during the Late Miocene.In the earliest Pliocene, the ignimbrites were succeeded by more voluminous calcalkaline, intermediate flows which generated numerous large and small stratovolcanoes; these range in age from 5.3 to 1.6 Ma. Present-day, or Holocene, volcanism is restricted to several large stratovolcanoes which had begun their development during the Pleistocene (by 0.7 Ma).The late Oligocene/Early Miocene (ca. 22–23 Ma) reactivation of the volcanic arc coincided with a comparable increase in magmatic activity throughout much of the Cordilleras Occidental and Oriental of the Central Andes.  相似文献   

4.
The Salal Creek area, at the north end of the main group of vents for the Quaternary Garibaldi (Cascade) Volcanic Belt, southwestern British Columbia, was the site of several small eruptions of mafic lava during the past 1 Ma. In contrast to the calc-alkaline character of all other parts of the Garibaldi Belt and the geographically nearly coincident Miocene and older Pemberton Volcanic Belt, the Salal Creek area Quaternary lavas are predominantly alkaline basalt and hawaiite with typical alkaline volcanic petrography, chemistry, and fractionation trends. Trace elements Ti-Zr-Y show within-plate character for the suite. As for other Garibaldi Belt volcanic rocks, Rb is low, Rb/Sr very low, and 87Sr/86Sr ratio is low, averaging 0.7032. The oxygen isotopic composition average, 18O = 5.9, is normal for mantle-derived volcanic rocks.This distinct change in magma type at the end of a volcanic are may be the consequence of a smaller degree of melting, melting at a slightly greater depth than calc-alkaline magma production, or a descending-plate edge effect.Ponded flows and pillow-palagonite accumulations indicate that several Salal Creek area eruptions occurred in proximity to ice which filled major valleys during pre-Wisconsin glacial periods.  相似文献   

5.
Superimposed on a regional pattern of oroclinal bending in the Aegean and west Anatolian regions, the coastal region of western Anatolia, shows a complex and chaotic pattern of coexisting clockwise and counterclockwise rotations. Here, we report new palaeomagnetic data from the eastern Aegean island of Chios, to test whether this fits the regional palaeomagnetic pattern associated with the Aegean orocline, or should be included in the narrow zone of chaotic palaeomagnetic directions. Therefore, a combined palaeomagnetic study of Miocene sediments and volcanic rocks has been carried out. Thermal and AF demagnetization of a 130-m thick Middle Miocene succession from the Michalos claypit allowed a stable component of both polarities to be isolated while rock magnetic experiments showed that the main magnetic carrier is magnetite. When compared with the Eurasian reference, the mean declination of 348 ± 5.1° implies 15° of counterclockwise rotation since Middle Miocene times. The obtained shallow inclination of 38 ± 6.7° was corrected to 61.8 ± 3.9°, by applying the elongation/inclination correction method for inclination shallowing. This result is similar to the expected inclination of 58° for the latitude of Chios. The palaeomagnetic analysis (demagnetization treatment and corresponding rock magnetic measurements) of the volcanic rocks identify a stable, predominantly normal, ChRM with poorly constrained mean declination of about 290 ± 19.8° based on five successfully resolved components. The significantly different palaeomagnetic results obtained from an island as small as Chios (and a very short distance), and the relatively large rotation amounts do not fit the regional palaeomagnetic direction of Lesbos and basins in northwestern Turkey which show little or no significant rotation. We thus prefer to include Chios in the coastal zone of chaotic rotations, which may represent a previously inferred tectonic transfer zone that accommodates lateral differences in extensional strain within the Aegean back-arc.  相似文献   

6.
A joint palaeomagnetic and 40Ar/39Ar study has been performed on two olistolithic blocks from the Cabrières Wildflysch in the Montagne Noire region of the Massif Central in France. There, andesitic volcanic and volcaniclastic rocks of Llanvirn-Early Caradoc age (ca 470-458 Ma) occur. Despite extensive secondary alteration, destruction of the dominant magnetic mineral phase and 40Ar/39Ar whole rock experiments that demonstrate that the volcanic rocks suffered significant argon loss, a positive fold test and the presence of dual polarities suggest that a primary, Ordovician magnetisation has mostly survived. This is one of the few documented cases where the argon system was substantially reset whilst a subordinate set of small, relatively unaltered magnetite grains, probably hosted in silicates, still carry the original, in this case Ordovician, remanence.The new data show that the Montagne Noire region was located at high southerly latitudes (68° +17/-15) during the Mid-Ordovician. This latitude represents the location for NW Gondwana of which the Massif Central was a part. Palaeomagnetic data from all the Central European massifs and terranes demonstrate a close link to the Gondwana Margin during the Lower and Middle Ordovician.  相似文献   

7.
A conspicuous graben extends for 800 kilometers through El Salvador and western Nicaragua to the Caribbean Sea in northeastern Costa Rica. Like the smaller but structurally similar Semangko and Toba Depressions of northern Sumatra, the trough is clearly related to voluminous volcanic eruptions during Late Tertiary time. In the region around Lakes Managua and Nicaragua, where the depression is best defined and reaches its greatest dimension, a thick series of Tertiary sediments and volcanic rocks provides a means of interpreting the Cenozoic history of the region. Following a long period of intermittent volcanic activity and sedimentation, extensive sheets of andesitic and dacitic ignimbrites were erupted during Late Miocene time from fissure sources which appear to have been located near the now-subsided central portion of the graben. Near the coast, ignimbrites flowed across a flat lagunal shore overwhelming and burying the tropical vegetation and finally coming to rest in shallow water. Unusual textures and chaotic mixtures of pumice with sediments and silicified wood characterize the bases of many of the water-laid ignimbrites. Subsidence of the graben does not appear to have occurred concurrently with the ignimbrite eruptions but followed them closely near the end of the Miocene or the beginning of Pliocene time. Subsequent activity has been confined to relatively smaller eruptions from central vents near the boundary faults of the graben.  相似文献   

8.
The Fekete-hegy volcanic complex is located in the centre of the Bakony Balaton Highland Volcanic Field, in the Pannonian Basin, which formed from the late Miocene to Pliocene period. The eruption of at least four very closely clustered maar volcanoes into two clearly distinct types of prevolcanic rocks allows the observation and comparison of hard-substrate and soft-substrate maars in one volcanic complex. The analyses of bedding features, determination of the proportion of accidental lithic clasts, granulometry and age determination helped to identify and distinguish the two types of maar volcanoes. Ascending magma interacted with meteoric water in karst aquifers in Mesozoic carbonates, as well as in porous media aquifers in Neogene unconsolidated, wet, siliciclastic sediments. The divided basement setting is reflected by distinct bedding characteristics and morphological features of the individual volcanic edifices as well as a distinct composition of pyroclastic rocks. Country rocks in hard-substrate maars have a steep angle of repose, leading to the formation of steep sided cone-shaped diatremes. Enlargement and filling of these diatreme is mainly a result of shattering material by FCI related shock waves and wall-rock collapse during downward penetration of the explosion locus. Country rocks in soft-substrate maars have much shallower angles of repose, leading to the formation of broad, bowl shaped structures or irregular depressions. Enlargement and filling of these diatremes is mainly the result of substrate collapse, for example due to liquefaction of unconsolidated material by FCI-related shock waves, and its emplacement by gravity flows. The Fekete-hegy is an important example illustrating that the substrate of a volcanic edifice has to be taken into account as an important interface, which can have major control on phreatomagmatic eruptions and the resulting characteristics of the volcanic complex.  相似文献   

9.
Nisyros is a totally volcanic island located at the eastern limit of the quaternary calc-alkaline island arc system of the South Aegean Sea. Its age is rather young since K/Ar dating has given an age of 0.2 m.y. B.P. for one of the oldest outcropping products of this volcano. The volcanological evolution of Nisyros has tentatively been reconstructed as follows:
  1. after a period (from 3.0? to 0.2 m.y. B.P.) of submarine activity, evidenced by the presence of pillow-lavas and hyaloclastites, the volcano grew above sea level;
  2. effusive and explosive subaerial activity from different vents built up a complex stratovolcano, probably around 0.2 m.y. B. P.;
  3. at the end of an intense explosive activity (between 0.2 m.y. B.P. and Present) the top of the volcano collapsed forming a caldera which is still perfectly preserved. A post-caldera activity with eruptions of huge and viscous domes and lava flows of uniform composition, both inside and outside the caldera, concluded this stage of the volcano evolution;
  4. in historical times, spectacular phreatic explosion craters formed on the caldera floor;
  5. presently, a large area of the caldera floor is affected by a considerable hydrothermal activity. The hypothesis is formed that Nisyros volcano is not yet extinct.
Four small volcanic islets — Yali, Stronjili, Pakia and Perigusa — located a few miles on the North and West of Nisyros, although volcanologically independent of one another, are composed of products which are attributable, from the petrologic point of view, to the Nisyros magma. The volcanic rocks of Nisyros and of its neighbouring minor islands as well as the volcanics of the coeval volcanoes of the South Aegean Sea arc (Aegina, Milos, Santorini, etc.) belong to a typical orogenic calc-alkaline series (from basic andesites through andesites-dacites-rhyodacites to strongly silicic rhyolites) with normal K2O contents. The potassium contents of these rocks are compatible with the depth of 150 km (as inferred from geophysical data) for the inclined seismic zone underneath the active volcanic arc. The existence of a top-caldera as well as the occurrence of a huge amount of xenoliths (hornblende-rich cumulates and contact-metamorphic calcareous rock derivatives) suggest the presence of a magma chamber at a relatively shallow depth beneath the volcano. The rhyolitic obsidians of Yali can be considered as residual liquids from the Nisyros rhyodacites, thus representing the end-members of a fractionation process. Volcanological and petrological arguments are in favour of fractional crystallization as the most probable genetic process for the calc-alkaline differentiation series of Nisyros and of its neighbouring minor islands. However, the lack of any rock with a high alumina basalt composition makes it difficult to define exactly the nature of the parent magma. According to recent geophysical data, continental collision is already in progress at the Hellenic trench. Therefore, Nisyros and the other active volcanoes of the South Aegean Sea arc are approaching the senile stage. What would follow could be a transition to shoshonitic magmatism as a consequence of the deepening of the lithospheric slab under the Aegean microplate. The limited extension and the relatively short-lived calc-alkaline activity of the South Aegean Sea arc could be related to the particular geodynamic pattern of the Mediterranean area which is characterized by a microplates mosaic between the two converging African and Eurasian major plates.  相似文献   

10.
This petrologic analysis of the Negra Muerta Volcanic Complex (NMVC) contributes to understanding the magmatic evolution of eruptive centres associated with prominent NW-striking fault zones in the southern Central Andes. Specifically, the geochemical characteristics and magmatic evolution of the two eruptive episodes of this Complex are analysed. The first one occurred as an explosive eruption at 9 Ma and is represented by a strongly welded, fiamme-rich, andesitic to dacitic ignimbrite deposit. The second commenced with an eruption of a rhyolitic ignimbrite at 7.6 Ma followed by effusive discharge of hybrid lavas at 7.3 Ma and by emplacement of andesitic to rhyodacitic dykes and domes. Both explosive and effusive eruptions of the second episode occurred within a short time span, but geochemical interpretations permit consideration of the existence of different magmas interacting in the same magma chamber. Our model involves an andesitic recharge into a partially cooled rhyolitic magma chamber, pressurising the magmatic system and triggering explosive eruption of rhyolitic magma. Chemical or mechanical evidence for interaction between the rhyolitic and andesitic magma in the initial stages are not obvious because of their difference in composition, which could have been strong enough to inhibit the interaction between the two magmas. After the initial explosive stages of the eruption at 7.6 Ma, the magma chamber become more depressurised and the most mafic magma settled in compositional layers by fractional crystallisation. Restricted hybridisation occurred and was effective between adjacent and thermally equivalent layers close to the top of the magma chamber. At 7.3 Ma, increments of caldera formation were accompanied by effusive discharge of hybrid lavas through radially disposed dykes whereby andesitic magma gained in importance toward the end of this effusive episode in the central portion of the caldera. Assimilation during turbulent ascent (ATA) is invoked to explain a conspicuous reversed isotopic signature (87Sr/86Sr and 143Nd/144Nd) in the entire volcanic series. Therefore, the 7.6 to 7.3 Ma volcanic rocks of the NMVC resulted from synchronous and mutually interacting petrological processes such as recharge, fractional crystallization, hybridisation, and Assimilation during Turbulent Ascent (ATA).Geochemical characteristics of both volcanic episodes show diverse type and/or depth in the sources and variable influence of upper crustal processes, and indicate a recurrence in the magma-forming conditions. Similarly, other minor volcanic centres in the transversal volcanic belts of the Central Andes repeated their geochemical signatures throughout the Miocene.  相似文献   

11.
New geochemical and 40Ar/39Ar age data are presented from the Neogene volcanic units of the Karaburun Peninsula, the westernmost part of Western Anatolia. The volcanic rocks in the region are associated with Neogene lacustrine deposition and are characterized by (1) olivine-bearing basaltic-andesites to shoshonites (Karaburun volcanics), high-K calc-alkaline andesites, dacites and latites (Yaylaköy, Arma?anda? and Kocada? volcanics) of ~ 16–18 Ma, and (2) mildly-alkaline basalts (Ovac?k basalt) and rhyolites (Urla volcanics) of ~ 11–12 Ma. The first group of rocks is enriched in LILE and LREE with respect to the HREE and HFSE on N-MORB-normalised REE and multi-element spider diagrams. They are comparable geochemically with volcanic rocks in the surrounding regions such as Chios Island and other localities in Western Anatolia. The Ovac?k basalt is geochemically similar to the first stage early–middle Miocene volcanic rocks but differs from NW Anatolian late Miocene alkali basalts.  相似文献   

12.
Costa Rica is located geographically in the southern part of the Central American Volcanic Front, a zone where interaction between the Mesoamerican and South American cultures occurred in pre-Columbian times. Several volcanoes violently erupted during the Holocene, when the first nomadic human hunters and later settlers were present. Volcanic rocks were the most important geo-resource in making artifacts and as construction materials for pre-Columbian inhabitants. Some pottery products are believed to resemble smoking volcanoes, and the settlements around volcanoes would seem to indicate their influence on daily life. Undoubtedly, volcanic eruptions disrupted the life of early settlers, particularly in the vicinity of Arenal and Irazú volcanoes, where archaeological remains show transient effects and displacement caused by periodical eruptions, but later resilient occupations around the volcanoes. Most native languages are extinct, with the exception of those presently spoken in areas far away from active volcanoes, where no words are related to volcanic phenomena or structures. The preserved legends are ambiguous, suggesting that they were either produced during the early Spanish conquest or were altered following the pre-Columbian period.  相似文献   

13.
This paper reports the analysis on cores and rock slices,data on seismic and logging activities,characteristics of core samples,and the paleogeographic background of the Yingcheng Formation of the Xujiaweizi faulted depression in the Songliao Basin.The results show that some of the volcanic rocks were formed during subaquatic eruptions.These subaqueous volcanic rocks are further characterized by the interbedded black mudstone and tuffite,the presence of double-layer perlite enclosing aphyric or sparsely phyric rhyolite,the presence of a bentonite layer,and the coefficient of oxidation(Fe2O3/FeO).The types of rocks are volcanic breccia,lava breccias,perlite,rhyolite,tuff and sedimentary tuff.The subaquatic eruptions are distributed mainly in Wangjiatun,Shengping,Xuxi,Xuzhong,and Xudong.The XS-1 area is the most typical.The organic abundance of overburden mud rocks within the volcanic rocks of the Yingcheng Formation indicates that these rocks represent high-quality source rocks.The analysis also shows that continental subaquatic volcanic eruptions provide a rich supply of minerals and energies for the lake basin and increase the organic matter content in the water.Moreover,the water differentiation provides a good reducing environment for the conservation of organic matter,and is beneficial for the formation of high-quality source rocks.Finally,we propose a hypothesis to describe the mode of subaquatic eruptions and the formation of high-quality source rocks.  相似文献   

14.
We provide a new scheme to classify Late Cenozoic volcanic rocks in the Udokan lava plateau based on isotope datings of rocks derived during the last 15 years. The scheme distinguishes five structural-material complexes (SMCs): Middle Miocene, Late Miocene, Early/Middle Pliocene, Late Pliocene, and Quaternary. Each SMC has its ejecta of central-type eruptions and subvolcanic emplacement episodes that classify themselves into individual rock complexes, while the ejecta of mass fissure effusions from three SMCs (the Late Miocene, the Early/Middle Pliocene, and the Late Pliocene) can be lumped into three stratigraphic series. Each series includes three suites, with the middle position (in the series section) being occupied by suites composed of basaltic melt differentiates.  相似文献   

15.
Many volcanic forms resulting from phreatomagmatic eruptions of differentiated magmas have been studied in the Massif Central (France), in the Phlegrean Fields (Italy), and on Saõ Miguel island (Azores). They show a continuous series between explosion crater maar type — and the hyaoloclastic tuff-cone. An essential feature of this morphological series is the preponderance of tuff-rings resulting from subaerial eruptions. Subaerial tuff-rings of basic compositions are less common than maars. A thermodynamic approach shows that the quantity of heat supplied by the different kinds of magmas and the water / magma ratio are the essential parameters controlling the activity, and the resulting morohology of these volcanoes.  相似文献   

16.
A buried, old volcanic body (pre‐Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre‐Komitake Volcano is characterized by hornblende‐bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine‐bearing basaltic rocks of Fuji Volcano. K‐Ar age determinations and geological analysis of drilling cores suggest that the pre‐Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre‐Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long‐term eruption rate of about 3 km3/ka or more for Fuji Volcano is much higher than that estimated for pre‐Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO2, differs from that within pre‐Komitake and other volcanoes in the northern Izu‐Bonin arc, where incompatible elements increase with increasing SiO2. These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven.  相似文献   

17.
Results of a paleomagnetic study carried out on the exposed volcanic rocks on the western side of the South Kenya Rift Valley are presented. Nine stratigraphic groups ranging in age from Miocene to Pleistocene were sampled. The rocks consist of basalts, trachytes, nephelinites, melanephelinites, olivine melanephelinites and ignimbrites. Paleomagnetic poles obtained for different age ranges are as follows: Period I (0.64–0.72 Ma), 116°E, 85°N (A95 = 6°); Period II (1.6–6.9 Ma), 297°E, 84°N (A95 = 4°); Period III (12.0–15.0 Ma), 34°E, 80°N (A95 = 9°). The results for Period II show large secular variations which are in disagreement with the model predictions for near-equatorial sites.  相似文献   

18.
The volcanic rocks along the south-eastern and eastern Tyrrhenian border of Italy have been classified as converging plate margin magma types by using discriminant functions based on major element patterns. These rocks belong to calc-alkaline and shoshonitic associations (shoshonites, and predominant leucitic rocks) ranging in age from Upper Miocene to, mostly, Quaternary. According to the same method of classification, the remaining Italian volcanic rocks — alkali-sodic and subordinate tholeiitic basalts — around the Tyrrhenian border are found to be rocks of the tensional type of Mesozoic to prevailingly Quaternary age. The volcanic materials of the 650 km long SE and E Tyrrhenian border can be related to the convergence of the African-Adriatic and Tyrrhenian plates.  相似文献   

19.
This paper emphasizes the fact that tsunamis can occur in continental lakes and focuses on tsunami triggering by processes related to volcanic eruptions and instability of volcanic edifices. The two large lakes of Nicaragua, Lake Managua and Lake Nicaragua, host a section of the Central American Volcanic Arc including several active volcanoes. One case of a tsunami in Lake Managua triggered by an explosive volcanic eruption is documented in the geologic record. However, a number of events occurred in the past at both lakes which were probably tsunamigenic. These include massive intrusion of pyroclastic flows from Apoyo volcano as well as of flank-collapse avalanches from Mombacho volcano into Lake Nicaragua. Maar-forming phreatomagmatic eruptions, which repeatedly occurred in Lake Managua, are highly explosive phenomena able to create hugh water waves as was observed elsewhere. The shallow water depth of the Nicaraguan lakes is discussed as the major limiting factor of tsunami amplitude and propagation speed. The very low-profile shores facilitate substantial in-land flooding even of relatively small waves. Implications for conceiving a possible warning system are also discussed.  相似文献   

20.
We have determined K, Rb and Sr concentrations and87Sr/86Sr ratios in fresh surface waters, a rain water sample and five geothermal waters from the Cantal volcanic area in the Massif Central, France. A comparison with appropriate rock types of the region showed no apparent chemical and isotopic fractionation occurring in the fresh water-surface rock system. The thermo-mineral water results suggest that all springs discharge dissolved Sr from the following contributors: Hercynian granito-metamorphic basement, lacustrian sediments underlying the volcano, Miocene-Pliocene volcanic rocks of basaltic to rhyolitic composition.  相似文献   

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