From seamount to oceanic island, Porto Santo, central East-Atlantic     

Ralf Schmidt  Hans-Ulrich Schmincke 《International Journal of Earth Sciences》2002,91(4):594-614

The uplifted and deeply eroded volcanic succession of Porto Santo (central East-Atlantic) is the product of a wide spectrum of dynamic processes that are active in shoaling to emergent seamounts. Two superimposed lapilli cones marking the base of the exposed section are interpreted as having formed from numerous submarine to subaerial phreatomagmatic explosions, pyroclastic fragmentation being subordinate. The lower basaltic and the upper mugearitic to trachytic sections are dominated by redeposited tephra and are called 'lapilli cone aprons'. Vertical growth due to accumulation of tephra, voluminous intrusions, and minor pillowed lava flows produced ephemeral islands which were subsequently leveled by wave erosion, as shown by conglomerate beds. Periods of volcanic quiescence are represented by abundant biocalcarenite lenses at several stratigraphic levels. The loose tephra piles became stabilized by widespread syn-volcanic intrusions such as dikes and trachytic to rhyolitic domes welding the volcanic and volcaniclastic ensemble into a solid edifice. Shattering of a submarine extrusive trachytic dome by pyroclastic and phreatomagmatic explosions, accentuated by quench fragmentation, resulted in pumice- and crystal-rich deposits emplaced in a prominent submarine erosional channel. The dome must have produced an island as indicated by a collapse breccia comprising surf-rounded boulders of dome material. Subaerial explosive activity is represented by scoria cones and tuff cones. Basaltic lava flows built a resistant cap that protected the island from wave erosion. Some lava flows entered the sea and formed two distinct types of lava delta: 1. closely-packed pillow lava and massive tabular lava flows along the southwestern coast of Porto Santo, and 2. a steeply inclined pillow-hyaloclastite breccia prism composed of foreset-bedded hydroclastic breccia, variably-shaped pillows, and thin sheet flows capped by subhorizontal submarine to subaerial lava flows along the eastern coast of Porto Santo.The facies architectures indicate emplacement: 1. on a gently sloping platform in southwestern Porto Santo, and 2. on steep offshore slopes along high energy shorelines in eastern Porto Santo.Growth of the pillow-hyaloclastite breccia prism is dominated by the formation of foreset beds but various types of syn-volcanic intrusions contributed significantly. Submarine flank eruptions occurred in very shallow water on the flanks of the hyaloclastite prism in eastern Porto Santo. The island became consolidated by intrusion of numerous dikes and by emplacement of prominent intrusions that penetrate the entire volcanic succession. Volcanic sedimentation ended with the emplacement of a debris avalanche that postdates the last subaerial volcanic activity.  相似文献   

Cone sheet swarm,resurgence of tejeda caldera,and the early geologic history of gran Canaria     

H. U. Schmincke 《Bulletin of Volcanology》1967,31(1):153-162

The southwestern half of Gran Canaria probably represents the lower part of a large Tertiary volcano. The following stages in its development are recognized: alkali olivine basalt shield volcano; caldera collapse and emission of large quantities of alkali trachytic to soda rhyolitic ash flows; building of a central volcano inside the caldera, and high level intrusion and resurgent doming of the central volcano’s substructure by thick trachytic sills, a central syenite stock, and numerous trachytic cone sheets. The syenite stock and the younger cone sheet system inside the caldera suggest that two stages of doming followed caldera collapse.  相似文献   

Legends of the Earth: Their Geologic Origins: Dorothy B. Vitaliano. Indiana University Press, Bloomington, Ind., U.S.A., 1976, approx. 400 pp.; U.S.$12.50     

H.U. Schmincke 《Journal of Volcanology and Geothermal Research》1977,2(4):398-399

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Polybaric differentiation of alkali basaltic magmas: evidence from green-core clinopyroxenes (Eifel,FRG)   总被引：5，自引：0，他引：5  

Antje Duda  Hans -Ulrich Schmincke 《Contributions to Mineralogy and Petrology》1985,91(4):340-353

The Quaternary foidites and basanites of the West Eifel (Germany) contain optically and chemically heterogeneous clinopyroxenes, some of which occur as discrete zones within individual crystals: Most clinopyroxene phenocrysts are made up of a core and a normally zoned comagmatic titanaugite mantle. Most cores are greenish pleochroic and moderately resorbed (fassaitic augite). Some are pale green and strongly resorbed (acmitic augite). Cores of Al-augite composition and of Cr-diopside derived from peridotite xenoliths are rare. The fassaitic augites are similar in trace element distribution pattern to the titanaugites, but are more enriched in incompatible elements. The acmitic augites, in contrast, are clearly different in their trace element composition and are enriched in Na, Mn, Fe and depleted in Al, Ti, Sr, Zr. A model for polybaric magma evolution in the West Eifel is proposed: Primitive alkali basaltic magma rises through the upper mantle precipitating Al-augite en route. It stagnates and differentiates near the crust/mantle boundary crystallizing Fe-rich fassaitic augites. The magma differentiated at high pressure is subsequently mixed with new pulses of primitive magma from which the rims of pyroxene are crystallized. Sporadic alkali pyroxenite xenoliths are interpreted to represent cumulates of cognate phases formed within the crust and not metasomatized upper mantle material (Lloyd and Bailey 1975).  相似文献   

Eruption and emplacement of a basaltic welded ignimbrite during caldera formation on Gran Canaria     

A. Freundt  H. -U. Schmincke 《Bulletin of Volcanology》1995,56(8):640-659

The 14.1 Ma old composite ignimbrite cooling unit P1 (45 km³) on Gran Canaria comprises a lower mixed rhyolite-trachyte tuff, a central rhyolite-basalt mixed tuff, and a slightly rhyolite-contaminated basaltic tuff at the top. The basaltic tuff is compositionally zoned with (a) an upward change in basalt composition to higher MgO content (4.3–5.2 wt.%), (b) variably admixed rhyolite or trachyte (commonly <5 wt.%), and (c) an upward increasing abundance of basaltic and plutonic lithic fragments and cognate cumulate fragments. The basaltic tuff is divided into three structural units: (I) the welded basaltic ignimbrite, which forms the thickest part (c. 95 vol.%) and is the main subject of the present paper; (II) poorly consolidated massive, bomb- and block-rich beds interpreted as phreatomagmatic pyroclastic flow deposits; and (III) various facies of reworked basaltic tuff. Tuff unit I is a basaltic ignimbrite rather than a lava flow because of the absence of top and bottom breccias, radial sheet-like distribution around the central Tejeda caldera, thickening in valleys but also covering higher ground, and local erosion of the underlying P1 ash. A gradual transition from dense rock in the interior to ash at the top of the basaltic ignimbrite reflects a decrease in welding; the shape of the welding profile is typical for emplacement temperatures well above the minimum welding temperature. A similar transition occurs at the base where the ignimbrite was emplaced on cold ground in distal sections. In proximal sections the base is dense where it was emplaced on hot felsic P1 tuff. The intensity of welding, especially at the base, and the presence of spherical particles and of mantled and composite particles formed by accretion and coalescence in a viscous state imply that the flow was a suspension of hot magma droplets. The flow most likely had to be density stratified and highly turbulent to prevent massive coalescence and collapse. Model calculations suggest eruption through low pyroclastic fountains (<1000 m high) with limited cooling during eruption and turbulent flow from an initial temperature of 1160°C. The large volume of 26 km³ of erupted basalt compared with only 16 km³ of the evolved P1 magmas, and the extremely high discharge rates inferred from model calculations are unusual for a basaltic eruption. It is suggested that the basaltic magma was erupted and emplaced in a fashion commonly only attributed to felsic magmas because it utilized the felsic P1 magma chamber and its ring-fissure conduits. Evolution of the entire P1 eruption was controlled by withdrawal dynamics involving magmas differing in viscosity by more than four orders of magnitude. The basaltic eruption phase was initially driven by buoyancy of the basaltic magma at chamber depth and continued degassing of felsic magma, but most of the large volume of basalt magma was driven out of the reservoir by subsidence of a c. 10 km diameter roof block, which followed a decrease in magma chamber pressure during low viscosity basaltic outflow.  相似文献   

Pseudotachylite on impact marks of block surfaces in block-and-ash flows at Merapi volcano, Central Java, Indonesia     

L. Schwarzkopf  H.-U. Schmincke  V. Troll 《International Journal of Earth Sciences》2001,90(4):769-775

Surfaces of meter-sized blocks in the 1998 block-and-ash flow deposits of Merapi volcano are partially covered by centimeter-sized, randomly orientated impact marks, which consist of an outer, glassy pseudotachylite underlain by a cataclastic layer. Whole rock, pseudotachylite, melt inclusion in plagioclase and host rock groundmass compositions indicate that the pseudotachylite was generated by remelting of bulk rock on block impact. The occurrence and distribution of this new type of collision-related pseudotachylite on volcanic block surfaces demonstrate that blocks were transported by chaotic rotation, saltation and tumbling. The random orientation of impact marks suggests grain flow as the dominant process rather than any other currently discussed pyroclastic flow mechanism. In addition, the chaotic orientation of striations is interpreted as reflecting momentum transfer having been dominated by short-lived intergranular collisions. The blocks have apparently been transported in the collisional regime of grain flow.  相似文献   

The genesis and significance of N-MORB sub-types     

L. G. Viereck  M. F. J. Flower  J. Hertogen  H. -U. Schmincke  G. A. Jenner 《Contributions to Mineralogy and Petrology》1989,102(1):112-126

A global compositional dichotomy for N-MORB magma (N1/N2) is recognized on the basis of Na₂O, TiO₂, CaO, and Al₂O₃ contents, and their respective ratios. We have characterized the two magma sub-types by means of their trace element patterns, and attempted to explain the differences in major and trace element contents in terms of a partial melting model, using data from DSDP/IPOD Leg 82. Mass balance calculations for N-MORB glass and rock compositions indicate that differences between N1-and N2-MORB are consistent with simple differences (5%–10%) in the degree of partial melting of a plagioclase-(±spinel) lherzolite, at pressures <10 kbar, rather than their respective derivation from plagioclase- and spinel-lher-zolite sources. Based on published and calculated partition coefficients, and calculated source magmaphile trace element compositions, the calculations indicate that the overall range of N-MORB compositions may be derived by between approximately 8% and 20% partial melting of a fertile lherzolite source. Fluid dynamic and melt kinematic considerations will probably necessitate refinement of the model, but should also take account of its qualitative precepts.  相似文献   

Reflection Seismic Investigations In the Volcaniclastic Apron of Gran Canaria and Implications For Its Volcanic Evolution     

Thomas Funck  Thomas Dickmann  Roland Rihm  Sebastian Krastel  Holger Lykke-Andersen  Hans-Ulrich Schmincke 《Geophysical Journal International》1996,125(2):519-536

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IAVCEI: Who we are and what we do     

H-U Schmincke 《Bulletin of Volcanology》1993,55(6):457-466

IAVCEI: Who we are and what we do  相似文献   

Evolution of the Quaternary melitite-nephelinite Herchenberg volcano (East Eifel)     

Ulrich Bednarz  Hans-Ulrich Schmincke 《Bulletin of Volcanology》1990,52(6):426-444

The Quaternary Herchenberg composite tephra cone (East Eifel, FR Germany) with an original bulk volume of 1.17·10⁷ m³ (DRE of 8.2·10⁶ m³) and dimensions of ca. 900·600·90 m (length·width·height) erupted in three main stages: (a) Initial eruptions along a NW-trending, 500-m-long fissure were dominantly Vulcanian in the northwest and Strombolian in the southeast. Removal of the unstable, underlying 20-m-thick Tertiary clays resulted in major collapse and repeated lateral caving of the crater. The northwestern Lower Cone 1 (LC1) was constructed by alternating Vulcanian and Strombolian eruptions. (b) Cone-building, mainly Strombolian eruptions resulted in two major scoria cones beginning initially in the northwest (Cone 1) and terminating in the southeast (Cones 2 and 3) following a period of simultaneous activity of cones 1 and 2. Lapilli deposits are subdivided by thin phreatomagmatic marker beds rich in Tertiary clays in the early stages and Devonian clasts in the later stages. Three dikes intruded radially into the flanks of cone 1. (c) The eruption and deposition of fine-grained uppermost layers (phreatomagmatic tuffs, accretionary lapilli, and Strombolian fallout lapilli) presumably from the northwestern center (cone 1) terminated the activity of Herchenberg volcano. The Herchenberg volcano is distinguished from most Strombolian scoria cones in the Eifel by (1) small volume of agglutinates in central craters, (2) scarcity of scoria bomb breccias, (3) well-bedded tephra deposits even in the proximal facies, (4) moderate fragmentation of tephra (small proportions of both ash and coarse lapilli/bomb-size fraction), (5) abundance of dense ellipsoidal juvenile lapilli, and (6) characteristic depositional cycles in the early eruptive stages beginning with laterally emplaced, fine-grained, xenolith-rich tephra and ending with fallout scoria lapilli. Herchenberg tephra is distinguished from maar deposits by (1) paucity of xenoliths, (2) higher depositional temperatures, (3) coarser grain size and thicker bedding, (4) absence of glassy quenched clasts except in the initial stages and late phreatomagmatic marker beds, and (5) predominance of Strombolian, cone-building activity. The characteristics of Herchenberg deposits are interpreted as due to a high proportion of magmatic volatiles (dominantly CO₂) relative to low-viscosity magma during most of the eruptive activity.  相似文献