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I. A. Sigurdsson Dr. V. S. Kamenetsky Dr. A. J. Crawford Dr. S. M. Eggins Dr. S. K. Zlobin 《Mineralogy and Petrology》1993,47(2-4):149-169
Summary At its southernmost end, the main spreading centre of the North Fiji Basin is propagating into arc crust of the poorly-known Hunter Ridge. We define nine magmatic groups from major element glass chemistry and olivine and spinel compositions in samples dredged from twenty six sites in this area by the R/V Academician A. Nesmeyanov in 1990. These include groups of boninites, island arc tholeiites (IAT), mid-ocean ridge basalts (MORB), enriched mid-ocean ridge basalts (E-MORB), olivine porphyritic andesites and basaltic andesite and Na-rhyolites. Primitive lavas containing highly forsteritic olivine phenocrysts are common in all the groups, except for the rhyolites.We report over 100 glass analyses for dredged rocks from this region, and about 300 olivine-spinel pairs for representatives of all the magmatic groups identified, except the Na-rhyolites.The MORB in this region are probably produced at the propagating spreading centre in the southern part of the North Fiji Basin. Juxtaposition of shallow, hot MORB-source diapirs supplying the MORB in this area, and the sub-arc damp, refractory upper mantle beneath the Hunter Ridge, provides suitable petrogenetic conditions to produce a range of magma types, from island arc tholeiites through to high-Ca boninites. The latter were recovered in eleven dredges.The E-MORB lavas recovered from the extreme southern margin of the North Fiji Basin are shown to be essentially identical to those dredged from adjacent older South Fiji Basin crust. It is hypothesized that the former were either scraped off the South Fiji Basin crust during an episode of oblique subduction that may have generated the Hunter Ridge during the last 5 Myr, or alternatively, that slices of the South Fiji Basin crust were trapped and incorporated into the North Fiji Basin as the subduction zones fronting the Vanuatu arc stepped or propagated southward.
Primitive Inselbogen- und ozeanische Laven von Hunter Rücken und der Hunter BruchZone: die Bedeutung der Zusammensetzung von Glas, Olivin und Spinell
Zusammenfassung Das spreading centre des Nord-Fidschi-Beckens setzt sich an seinem südlichsten Ende in die Inselbogen-Kruste des noch wenig bekannten Hunter-Rückens fort.Wir definieren 9 magmatische Gruppen auf der Basis der Hauptelement-Zusammensetzung von Gläsern und der Zusammensetzung von Olivin und Spinell in Proben die das Forschungsschiff R/V Akademiker A. Nesmeyanov von 26 Stellen im Jahr 1990 aufgesammelt hat. Zu diesen gehören Gruppen von Boniniten, Inselbogentholeiiten (IAT), Basalten zentralozeanischer Rücken (MORB), angereicherte zentralozeanische Rücken (E-MORB), Olivin-porphyritische Andesite und basaltische Andesite, sowie Na-Rhyolite. Primitive Laven mit Olivinkristallen, die reich an Forsterit-Komponenten sind, kommen in allen diesen Gruppen, mit Ausnahme der Rhyolite, vor.Wir legen über 100 Glas-Analysen von Gesteinen aus diesem Gebiet vor und über 300 Olivin-Spinell-Paare für Vertreter aller der hier identifizierten magmatischen Gruppen, mit Ausnahme der Natriumrhyolite.Die MORB in diesem Gebiet sind wahrscheinlich an dem aktiven Spreading Center im Südteil des Nord-Fidschi-Beckens entstanden. Das nebeneinander Vorkommen von seichten heißen MORB-Quellen Diapiren, die MORB in diesem Gebiet erzeugen, und der Sub-Inselbogen, wasserhaltige, refraktäre obere Mantel unter dem Hunter Rücken führen zu geeigneten petrogenetischen Bedingungen für die Entstehung einer Vielfalt von Magmatypen, von Inselbogentholeiiten bis zu sehr Kalziumreichen Boniniten. Die letzteren wurden in 11 Dredge-Proben gefunden.Die E-MORS Laven, die aus dem extremen Südteil des Nord-Fidschi-Beckens entnommen wurden, sind im wesentlichen mit jenen identisch, die aus der benachbarten älteren Kruste des Süd-Fidschi-Beckens stammen. Es wird vermutet, daß die letzteren entweder aus dem Süd-Fidschi-Becken während einer Episode obliger Subduktion, die in den letzten 5 Millionen Jahren zur Entstehung des Hunter Ridge geführt hat, abgeschert wurden, oder auch daß Teile der Kruste des Süd-Fidschi-Beckens in das Nord-Fidschi-Becken inkorporiert wurden als Subduktionszonen gegenüber dem Vanuato-Bogen sich nach Süden fortbewegten.相似文献
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T. K. Zlobin 《Doklady Earth Sciences》2018,480(1):599-601
The peculiarities of catastrophic earthquakes that occurred in the Northwest Pacific region on January 13, 2007, and January 15, 2007, east of the Kuril Islands and the Tohoku megaearthquake of March 11, 2011, east of Japan are considered and analyzed. It is revealed that these earthquakes, apart from the fact that they occurred in the transition zone from the Pacific to island arcs and the Eurasian continent, have common features and similar characteristics. The seismotectonic slip in the source of the chronologically first event, the 2006 Kuril earthquake, was a gentle thrust, while that of the second event of January 13, 2007, was a downthrow beneath the Kuril deep trench. 相似文献
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The Kuril-Kamchatka seismofocal zone was thought to be a single plate approximately 90 km wide and dipping to a depth of 700 km at an angle of 40°–45°. This concept reflects primarily the physical differences (elastic wave velocities, density, temperature, etc.) between the seismofocal zone and the mantle hosting it. Detailed investigations show that the seismofocal zone proper is also heterogeneous with earthquake hypocenters variably concentrated and clustered within this zone, where both seismogenic and aseismic strata, as well as subvertical zones, can be identified. The latter are reflected in the structure and faults of the Earth’s crust and upper mantle. 相似文献
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The data on catastrophic earthquakes with magnitudes of 8.3 and 8.1 that occurred in the Simushir Island area on November 15, 2006, and January 13, 2007, respectively, were compared with the results of land-sea deep seismic studies by different methods (deep seismic sounding, the correlation method of refracted waves, the earthquake converted-wave method, the common mid-point) in the Central Kuril segment. The structure of the Earth’s crust and the hypocentral zones of these earthquakes were analyzed. It was established that the hypocenter of the main shock of the first earthquake was located at the bend of the seismofocal zone under the island slope of the trench on the outer side of the subsiding lithospheric plate in the rapidly rising granulite-basite (ìbasalticî) crustal layer, which, at depths of 7–15 km, replaced the granulite-gneiss layer. This was accompanied by an increase of the seismic wave velocity from 6.4 to 7.1 km/s. The focus of the second earthquake was located beneath the axis of the deep-sea trench. The aftershocks were concentrated in two bands 60–120 km wide that extend along the trench, as well as in the third zone orthogonal to the island arc. It was shown that the epicenters of the earthquakes are linked with regional faults. The main shock of the first earthquake (November 15, 2006) was interpreted as a thrust fault and the second one (January 13, 2007) was attributed to a normal fault. 相似文献
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The catastrophic Shikotan earthquake of October 4 (5), 1994, occurred in the Pacific Ocean. Its focus was located 80 km eastward of Shikotan Island. The stress state of the Earth’s crust in this area was estimated by the method of the cataclastic analysis of the whole range of the earthquake mechanisms. The performed reconstruction of the parameters of the current stress state of the Earth’s crust and the upper mantle in the area of the Southern Kuril Islands made it possible to establish that this area is characterized, on the one hand, by the presence of extensive areas of steady behavior of the stress tensor parameters and, on the other hand, by the presence of local sections of anomalously fast changes in these parameters. 相似文献
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Doklady Earth Sciences - 相似文献