Contributions of slab fluid and sediment melt components to magmatism in the Mariana Arc–Trough system: Evidence from geochemical compositions and Sr,Nd, and noble gas isotope systematics          下载免费PDF全文

Yasuo Ikeda  Keisuke Nagao  Teruaki Ishii  Daisuke Matsumoto  Robert J. Stern  Hiroo Kagami  Makoto Arima  Sherman H. Bloomer 《Island Arc》2016,25(4):253-273

This study presents new major and trace element, mineral, and Sr, Nd, and noble gas isotope geochemical analyses of basalts, gabbro, and clinopyroxenite from the Mariana Arc (Central Islands and Southern Seamount provinces) including the forearc, and the Mariana Trough (Central Graben and Spreading Ridge). Mantle source compositions beneath the Mariana Arc and the Mariana Trough indicate a mantle source that is depleted in high field strength elements relative to MORB (mid‐oceanic ridge basalt). Samples from the Mariana Arc, characterized by high ratios of Ba/Th, U/Th, ⁸⁴Kr/⁴He and ¹³²Xe/⁴He, are explained by addition of fluid from the subducted slab to the mantle wedge. Correlations of noble gas data, as well as large ion lithophile elements, indicate that heavy noble gases (Ar, Kr, and Xe) provide evidence for fluid fluxing into the mantle wedge. On the other hand, major elements and Sr, Nd, He, and Ne isotopic data of basalts from the Mariana Trough are geochemically indistinguishable from MORB. Correlations of ³He/⁴He and ⁴⁰Ar/³⁶Ar in the Mariana Trough samples are explained by mixing between MORB and atmosphere. One sample from the Central Graben indicates extreme enrichment in ²⁰Ne/²²Ne and ²¹Ne/²²Ne, suggesting incorporation of solar‐type Ne in the magma source. Excess ¹²⁹Xe is also observed in this sample suggesting primordial noble gases in the mantle source. The Mariana Trough basalts indicate that both fluid and sediment components contributed to the basalts, with slab‐derived fluids dominating beneath the Spreading Ridge, and that sediment melts, characterized by high La/Sm and relatively low U/Th and Zr/Nb, dominate in the source region of basalts from the Central Graben.  相似文献   

Characterization of organic matter in surface sediments of the Mackenzie River Basin, Canada     

Jesse Carrie  Hamed Sanei  Fariborz Goodarzi  Gary Stern  Feiyue Wang   《International Journal of Coal Geology》2009,77(3-4):416-423

The particulate organic matter in < 63 µm surface sediments from the Mackenzie River and its main tributaries was studied using Rock-Eval pyrolysis and organic petrology. The organic matter in the sediments is dominated by refractory residual organic carbon (RC) of mainly terrigenous nature, as indicated by abundant inertinite, vitrinite, and type III kerogen. Sediments from the tributaries contained significantly more algal-derived organic matter than from the main channel of the river, highlighting the importance of low-energy system dynamics in the tributaries, which allows modest algal production, more accumulation, and better preservation of autochthonous organic matter. This is particularly true for tributaries fed by lacustrine systems, which showed the highest S1 and S2 fractions, and consequently higher total particulate organic carbon (POC) in the basin. Organic petrology of the sediment samples confirms abundant liptinitic materials (i.e., fat-rich structured algae, spores and pollen, cuticles, and resins). Forest fire and coal deposits are also confirmed to contribute to the basin. Assuming that suspended and fine surfacial sediments have a similar OC composition, the Mackenzie River is estimated to deliver a total POC flux of 1.1 Mt C/yr to its delta, of which 85% is residual carbon with liptinitic OC (S1 + S2) and S3 accounting for another 9% and 6%, respectively.  相似文献   

Age,geochemistry, and emplacement of the ~40-Ma Baneh granite–appinite complex in a transpressional tectonic regime,Zagros suture zone,northwest Iran     

Hossein Azizi  Sepideh Hadad  Robert J. Stern  Yoshihiro Asahara 《International Geology Review》2019,61(2):195-223

The Baneh plutonic complex is situated in the Zagros suture zone of northwest Iran between the Arabian and Eurasian plates. This complex is divided into granite and appinite groups. Zircon U–Pb dating shows that granites crystallized 41–38 million years ago but appinites experience more protracted magmatic evolution, from at 52 to 38 Ma. Whole-rock chemical compositions show significant major and trace element variations between the two lithologies. Granitic rocks are more evolved, with high contents of SiO₂ (62.4–77.0 wt%), low contents of TiO₂ (0.25 wt%), MgO (0.05–1.57 wt%), and Fe₂O₃ (0.40–4.06 wt%) and high contents of Na₂O + K₂O (≈10 wt%). In contrast, appinites have low contents of SiO₂ (51.0–57.0 wt%) and K₂O (<2.1 wt%) and high Fe₂O₃ (6.4–9.35 wt%), MgO (2.0–9.9 wt%), and Mg number (Mg# = 35–76). The concentration of rare earth elements in the appinites is higher than in granitic rocks, making it difficult to form granites solely by fractionation of appinite magma. (⁸⁷Sr/⁸⁶Sr)_i and ε_Nd(40 Ma) in both groups are similar, from 0.7045 to 0.7061 and ?1.2 to +2.6, except for a primitive gabbroic dike with ε_Nd(40 Ma) = +9.9. Appinites show mainly typical I-type characteristics, but granites have some S-type characteristics. The sigmoidal shape of the Baneh pluton and its emplacement into deformed Cretaceous shales and limestone showing kink bands, asymmetric and recumbent folds in a broad contact zone, with pervasive ductile to brittle structures in both host rocks and intrusion, indicate that magma emplacement was controlled by a transpressional tectonic regime, perhaps developed during early stages in the collision of Arabia and Eurasian plates.  相似文献   

X-ray observations of stellar coronae and flares: The “SOLAR-A connection”     

Stern  Robert A. 《Solar physics》1987,113(1-2):291-294

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Trends and variability of sea ice in Baffin Bay and Davis Strait, 1953–2001     

Harry L. Stern  Mads Peter Heide-Jørgensen 《Polar research》2003,22(1):11-18

The extent and duration of sea ice in Baffin Bay and Davis Strait has a major impact on the timing and strength of the marine production along West Greenland. The advance and retreat of the sea ice follows a predictable pattern, with maximum extent typically in March. We examine the area of sea ice in March in three overlapping study regions centred on Disko Bay on the west coast of Greenland. Sea ice concentration estimates derived from satellite passive microwave data are available for the years 1979-2001. We extend the record back in time by digitizing ice charts from the Danish Meteorological Institute, 1953-1981. There is reasonable agreement between the chart data and the satellite data during the three years of overlap: 1979-1981. We find a significant increasing trend in sea ice for the 49-year period (1953-2001) for the study regions that extend into Davis Strait and Baffin Bay. The cyclical nature of the wintertime ice area is also evident, with a period of about 8 to 9 years. Correlation of the winter sea ice concentration with the winter North Atlantic Oscillation (NAO) index shows moderately high values in Baffin Bay. The correlation of ice concentration with the previous winter's NAO is high in Davis Strait and suggests that next winter's ice conditions can be predicted to some extent by this winter's NAO index.  相似文献   

Agrigan: An introduction to the geology of an active volcano in the Northern Mariana Island arc     

R. J. Stern 《Bulletin of Volcanology》1978,41(1):43-55

Agrigan is the tallest (965 m a.s.l.) and largest (44 km²) of the volcanoes of the northern Mariana Islands. Its slopes are asymmetric to the east; a small caldera (4 km²) dominates the interior. The volcanic edifice has been disrupted along three sets of faults: 1) exterior slump faults, 2) radial faults, and 3) interior faults related to caldera-collapse. The rocks of the volcano are characterized by porphyritic clinopyroxene-olivine-plagioclase basalts and subordinate andesites. Cumulate xenoliths composed of Fo₈₁, An₉₅ and diopside are common in the basalts. Development of the volcano began with 3–4 km of submarine growth. The earliest recognizable flows are the result of fissural Hawaiian- and Strombolian-type eruptions. These were followed by the eruption of more viscous lavas from above the present summit. Flank eruptions of basalt and andesite preceded voluminous outpourings of andesitic pyroclastics contemporaneous with caldera-collapse. Subsequent magmatic resurgence is localized along a N10E rift zone. Violent ejection of lapilli and ash occurred in 1917.  相似文献   

Field and geochemical data bearing on the development of a mesozoic volcano-tectonic rift zone and back-arc basin in southernmost South America     

Ronald L. Bruhn  Charles R. Stern  Maarten J. De Wit 《Earth and Planetary Science Letters》1978,41(1):32-46

A broad zone of dominantly subaerial silicic volcanism associated with regional extensional faulting developed in southern South America during the Middle Jurassic, contemporaneously with the initiation of plutonism along the present Pacific continental margin. Stratigraphic variations observed in cross sections through the silicic Jurassic volcanics along the Pacific margin of southernmost South America indicate that this region of the rift zone developed as volcanism continued during faulting, subsidence and marine innundation. A deep, fault-bounded submarine trough formed near the Pacific margin of the southern part of the volcano-tectonic rift zone during the Late Jurassic. Tholeiitic magma intruded within the trough formed the mafic portion of the floor of this down-faulted basin. During the Early Cretaceous this basin separated an active calc-alkaline volcanic arc, founded on a sliver of continental crust, from the then volcanically quiescent South American continent. Geochemical data suggest that the Jurassic silicic volcanics along the Pacific margin of the volcano-tectonic rift zone were derived by crustal anatexis. Mafic lavas and sills which occur within the silicic volcanics have geochemical affinities with both the tholeiitic basalts forming the ophiolitic lenses which are the remnants of the mafic part of the back-arc basin floor, and also the calc-alkaline rocks of the adjacent Patagonian batholith and their flanking lavas which represent the eroded late Mesozoic calc-alkaline volcanic arc. The source of these tholeiitic and calc-alkaline igneous rocks was partially melted upper mantle material. The igneous and tectonic processes responsible for the development of the volcano-tectonic rift zone and the subsequent back-arc basin are attributed to diapirism in the upper mantle beneath southern South America. The tectonic setting and sequence of igneous and tectonic events suggest that diapirism may have been initiated in response to subduction.  相似文献   

New perspectives on the Negev continental bridge     

Yehuda Gradus  Eliahu Stern 《Geoforum》1977,8(5-6)

In a paper written immediately after the reopening of the Suez Canal in 1975, a question was raised: is the Israeli Negev a viable alternative to the Suez Canal? (Geoforum, 8, 29–32, 1977). The answer posted then was pessimistic — the continental land bridge was seen as having failed to function as a real alternative.Now, two years after the reopening of the Canal, it appears that the land bridge seems to be a more economically viable venture than previously suggested. The amount of cargo in transit over the land bridge and its percentage of the total port of Eilat traffic is increasing despite competition from the Canal. This phenomenon and new perspectives on the Negev land bridge are discussed in this follow-up paper.  相似文献   

Open and closed system igneous fractionation within two chilean ophiolites and the tectonic implication     

Charles Stern 《Contributions to Mineralogy and Petrology》1979,68(3):243-258

The Sarmiento and Tortuga complexes are two mafic complexes located in southern Chile that represent the remnants of the mafic portion of the floor of an Early Cretaceous extensional back-arc basin. Basaltic dikes and lavas within each complex exhibit tholeiite differentiation trends whereby FeO*, FeO*/MgO, TiO₂, P₂O₅, Zr, and Y increase together without significant increases in SiO₂. In both complexes, as FeO*/MgO increases, REE abundance increases without significant change in Ce/Yb ratio, but with an increasing negative Eu anomaly. The Sarmiento complex contains intermediate icelandites and silicic dikes and lavas which are conspicuously absent in the Tortuga complex. These non-basaltic compositions have higher Zr, Y and REE contents than the associated basalts, but similar Ce/Yb ratios, suggesting co-genetic origin. Thick cumulate gabbro sequences in both complexes suggest shallow level crystal-liquid fractionation as a major cause of the observed wide range of chemical variations. Significantly, in basalts from the Tortuga complex, incompatible elements (Zr, Y, REE) increase in abundance more rapidly with increasing FeO*/ MgO than in the Sarmiento complex. The rapid increase of incompatible elements relative to FeO*/ MgO in the Tortuga complex is best modeled by fractionation within an open magma chamber steadily replenished with new batches of undifferentiated magma. The observed chemical variations within the Sarmiento complex are best modeled by a magma chamber replenished only a limited number of times by a continuously decreasing volume of undifferentiated magma, followed, subsequent to the last input of new parental magma, by closed system fractionation which results in the formation of ferro-basalts, icelandites and silicic differentiates. Ferro-gabbros (FeO* >20 wt °/00) found within the gabbro unit of the Sarmiento complex closely approximate in composition the calculated crystal extracts required to evolve ferro-basalts into icelandites and the more silicic differentiates. The difference between the nature of the postulated magma chambers within the spreading centers at which the Sarmiento and Tortuga complexes originated suggests that the zone of magma intrusion from the mantle may have been diffuse in the region where the Sarmiento complex formed and more localized in the region where the Tortuga complex formed. This is consistent with other geochemical and field evidence suggesting that the Sarmiento complex represents a less developed stage of evolution than the Tortuga complex of the mafic floor of the Mesozoic back-arc basin in southern Chile. The apparent decoupling of major and trace element variations in ocean floor basalts may be explained by shallow level igneous fractionation without involving large proportions of clinopyroxene if the magma chambers within spreading centers at midocean ridges behave as open systems periodically replenished with batches of undifferentiated parental magma as is inferred for the Tortuga complex in southern Chile.  相似文献   

The med-dead sea project — A vision or reality?     

Eliahu Stern  Yehuda Gradus 《Geoforum》1981,12(3):265-272

The dramatic proposal to link the Mediterranean Sea to the Dead Sea by a canal or tunnel, for the purpose of power generation, is currently being investigated in Israel. This paper examines the various route alignments which have been advocated and suggests that the two Southern routes present the potentially greatest advantages. These are then discussed at greater detail, and attention directed to outlining the range of possible economic advantages as well as potential ecological impacts.  相似文献