共查询到20条相似文献，搜索用时 593 毫秒
1.
An isotope-geochronological study has been performed to examine the products of Late Cenozoic collision volcanism on the northern
coast of Lake Van, Turkey. We obtained 45 new K—Ar dates, based on which the principal time characteristics of volcanic activity
in the region have been determined. Volcanic activity in the northern coast of Lake Van has lasted ∼15 myr; it has had an
expressed discrete nature, when periods of intense volcanic activity alternated with long-lasting pose periods. Four stages
of Neogene—Quaternary volcanism have been identified: Middle Miocene (15.0—13.5 Ma), Late Miocene (10—9 Ma), Pliocene (5.8—3.7
Ma), and Quaternary (1.0—0.4 Ma). The average duration of the stages was 1—2 myr; the stages were separated from each other
with periods of inactivity of approximately equal lengths (∼3 myr). For each of the Pliocene and Quaternary stages, three
additional phases of volcanism have been identified, which were separated from each other with short time intervals (a few
hundred thousand years). The last burst of volcanic activity in the study area occurred ∼400 ka; similar to Quaternary volcanism
in general, it was not characterized by a high intensity. An important result of the studies performed was to confirm the
existence of a separate Middle Miocene stage of collision volcanism for the Caucasian—Anatolian Segment of the Alpine Fold
Belt. New geochronological data generated presented in this paper indicate that Neogene—Quaternary volcanism in this portion
of the belt started much earlier (∼15 Ma) than assumed by the majority of the previous researchers. 相似文献
2.
Results of the isotope-geochronological studies of the Late Cenozoic magmatism of Caucasus have been considered. The Neogene-Quaternary
volcanic activity is found to have evolved during the last 15 m. y. being most intensive in the Middle-Late Pliocene. Within
separate neovolcanic areas of the Caucasus region, magmatism was of a clearly discrete character when intense eruption periods
interchanged with prolonged (up to several million years) times of quiet conditions. Four stages of young magmatism of the
Caucasus are recognized: the Middle Miocene (15–13 Ma), the Late Miocene (9–5 Ma), the Pliocene (4.5–1.6 Ma), and the Quaternary
(less than 1.5 Ma). However, for certain areas the time limits of these stages were shifted relative to each other and overlap
the whole age range from the mid-Miocene to the end of the Quaternary period. Therefore, within the collision zone, the Neogene-Quaternary
magmatism evolved almost continuously during almost the last 9 m. y., but in the time interval of 13–9 Ma in the Caucasian
segment, volcanic activity was possibly low. No evidence of directed lateral migration of volcanic activity within the entire
Caucasus region was found. At the same time, in the Lesser Caucasus the young magmatism commenced earlier (∼15 Ma), compared
to the Greater Caucasus (∼8 Ma). 相似文献
3.
S. V. Rasskazov V. S. Prikhod’ko T. A. Yasnygina N. N. Fefelov E. V. Saranina I. P. Voinova S. B. Brandt 《Russian Journal of Pacific Geology》2010,4(5):441-459
The Middle Cenozoic lava sequence of the Lake Kizi region was studied. It characterizes the activity of sources in the Northern
zone of the eastern Sikhote Alin: a Middle Eocene pulse of slab-related magmatism and prolonged injection of magmas from the
sublithospheric convecting mantle in the Late Oligocene. Low contents of high field strength elements (Nb and Ta) with low
Nb/Ta, Ce/Pb, and Nb/La and high K/Nb ratios and a low (87Sr/86Sr)0 of 0.703399 were determined in a Middle Eocene dacite with an age of ∼43.5 Ma. Three phases of Late Oligocene volcanic eruptions
were distinguished: (1) basaltic andesites (29–27 Ma), (2) basaltic trachyandesites and trachyandesites (27–24 Ma), and (3)
andesites (∼23 Ma). The lavas of the first and third phases showed low Ce/Pb, Nb/La, and Ba/La and high K/Nb ratios, which
are also characteristic of supraslab processes. The lavas of the second phase are shifted with respect to these ratios toward
ocean island basalt compositions. The entire Late Oligocene volcanic sequence falls within a narrow range of the initial strontium
isotope ratios, (87Sr/86Sr)0, from 0.703661 to 0.703853. Such ratios are characteristic of volcanic and subvolcanic rocks with ages of ∼37, 31–23, and
∼16 Ma over the whole region of the Tatar Strait coast. 相似文献
4.
This paper is aimed at studying the chronological evolution of the Neogene–Quaternary volcanic activity within the Çald?ran plain and its mountainous framing (Eastern Turkey). It is shown that the last pulse of continental-margin magmatism related to the subduction and closure of Neotethys oceanic basin occurred in the Middle Miocene (13.5–12.5 Ma). The post-collision volcanism proceeding simultaneously with large-scale regional tectonic rearrangement and initiation of the long-term Çald?ran fault began in the Late Miocene (7–6 Ma), and reached maximum activity in the Middle Pliocene (4.7–3.6 Ma). The Quaternary period in the region evolution was marked by the abundant within-plate magmatic activity restricted to the regional SW–NE trending zone, and the formation of Eastern Turkey’s largest Tendürek shield volcano (Late Pleistocene–Holocene). Petrological-geochemical data indicate that magmas during the overall evolution of young volcanism of the Çald?ran plain was generated from a single mantle reservoir, whose composition gently one-way evolved with time. Calculations show that melting occurred in the upper part of the asthenosphere (immediately near the boundary with thinned lithospheric mantle), which was metasomatized by pre-existing long-continued subduction. The chemical variations of mantle source with time (from the Middle Miocene to Quaternary) were mainly determined by a decrease of subduction component and the presence of aqueous phases, with a general trend from E-MORB to OIB-type for generated magmas. The composition of Late Quaternary basic lavas of Tendürek Volcano in terms of most petrological-geochemical characteristics corresponds to within-plate alkaline basalts. The main trend of geochemical evolution of mantle source is correlated with a systematic change of the predominant serial affinity of igneous rocks from calcalkaline through moderately alkaline to Na-alkaline varieties. Discrete character of young magmatism within the Çald?ran plain, and its subsequent evolution (sulrasubduction → post-collision → within-plate) were mainly determined by periodical large-scale changes in geotectonic setting within the Eurasian–Arabian collision zone: (1) cessation of subduction, (2) break-up and deepening of oceanic slab with its subsequent break off, (3) inferred emergence of incipient rift setting under conditions of intense submeridional compression. 相似文献
5.
S. Tommasini P. Manetti F. Innocenti T. Abebe M. Sintoni S. Conticelli 《Mineralogy and Petrology》2005,84(3-4):259-281
Summary Since the Cenozoic, Ethiopia was affected by a widespread volcanic activity related to the geodynamic evolution of the Afar
triple junction. The plateau building phase was followed by the formation of the Main Ethiopian Rift (MER) accompanied by
a bimodal volcanic activity in both the inner parts of the rift and its shoulders. Outside the rift, a concurrent volcanic
activity occurred mainly along transversal tectonic lineaments, the most important of which is the Yerer-Tullu Wellel Volcano-Tectonic
Lineament (YTVL) developing for ∼500 km westward of Addis Abeba. Scattered Pliocene – Quaternary volcanoes are reported also
inside the plateau such as those out cropping nearby Lake Tana.
Here we present the result of a study on carefully screened mafic lavas outcropping in two sectors located off-axis the MER,
namely, the YTVL and the southern part of Lake Tana; and in one sector located in the southern tip of the MER close to Megado,
in the Sidamo region. The screened samples are petrographically fresh and have SiO2<52 wt.% and MgO>4 wt.%, to minimise crystal fractionation effects. Most of the samples belong to the Late Miocene – Quaternary
volcanic activity of the East African Rift System (EARS), although a number of samples along the YTVL are representative of
the Late Eocene – Early Miocene Ethiopian Volcanic Plateau flood basalts. The selected mafic lavas offer the opportunity to
assess the geochemical diversity, if any, of the subcontinental mantle domains along the MER (Megado and the easternmost part
of the YTVL) and in sectors far away from the MER (YTVL and Lake Tana). The samples have a wide compositional range: from
basanite to alkali basalt, hy-normative basalt, qz-normative basalt, basaltic andesite, hawaiite, trachybasalt, and trachyandesite.
The major and trace element characteristics of the mafic lavas demonstrate an origin from a relatively fertile and trace element
enriched lithospheric mantle at pressure variable from ∼2.0 to 3.5 GPa. Moreover, systematic variations in K/Nb, Ba/Nb, and
Ba/Rb demand for the contribution of trace amounts of phlogopite to melt production.
The geochemical signature coupled with the geographical distribution of the Late Miocene – Quaternary samples along the YTVL
(∼500 km) and the Lake Tana and Megado sectors set constraints on a relatively homogenous lateral continuity of the deeper
lithospheric mantle domains (∼2–3.5 GPa). On the other hand, the trace element characteristics of the Ethiopian Volcanic Plateau
samples along the YTVL, demand for a chromatographic process en route to the surface and indicate a shallower lithospheric mantle domain (<2 GPa) with a different geochemical signature. Overall,
the selected mafic lavas provide evidence for vertically zoned lithospheric mantle domains: the shallower domain (<2 GPa)
consists of an enriched mantle component with a geochemical signature similar to continental crust material (EM II), whilst
the deeper domain (∼2–3.5 GPa) consists of an enriched component similar to the average composition of the subcontinental
lithospheric mantle (SCLM).
Supplementary material to this paper is available in electronic form at
Appendix available as electronic supplementary material 相似文献
6.
New data on the geology, age, and composition of the Late Cenozoic volcanic rocks of the Vitim Depression, a satellite of the Vitim Lava Plateau (VLP), have been obtained. Two-stage volcanic activity has been revealed. In the Middle Miocene (14–13 Ma), a basalt and trachybasalt (hawaiite) lava covers were formed. In the Pleistocene (1.6–0.7 Ma), basanite erupted from scoria cones. Both stages of volcanism were coeval to similar pulses of volcanism within the VLP. However, unlike the latter, there were no Pliocene and Late Miocene eruptions within the Vitim Depression. Additionally, the Vitim Depression basalts have depleted geochemical characteristics comparative to those of the VLP. These features of the Vitim Depression volcanics imply their autonomous formation, whereas the synchroneity of the initial and final stages of volcanism in the depression and in the VLP reflects the existence of a common regulating mechanism of igneous activity. 相似文献
7.
S. V. Vysotskii S. Yu. Budnitskii S. V. Rasskazov A. V. Ignat’ev T. A. Velivetskaya A. A. Karabtsov 《Doklady Earth Sciences》2011,440(2):1423-1426
This article presents new data on isotopic (K/Ar) dating of a series of volcanic units of the Shavaryn-Tsaram Volcano based
on rocks and minerals and the chemical composition of deep seated micas. Four age intervals have been identified, one of which
is pertinent to the Middle Miocene (15.5–12.2 Ma) and the other three, to the Quaternary (1.87–1.82, 1.44–1.33, and 0.54–0.44
Ma). The age intervals correlate with the known volcanic events. The xenolites examined are most similar to fragments of a
deep seated alkalineultramafic rock complex whose formation proceeded during the last 15.5 myr and was accompanied by sporadic
effusion of alkali-basaltoid lavas onto the surface. The micas from the inclusions of the Shavaryn-Tsaram Volcano had a high
activation energy of migration of radiogenic argon, which ensured argon accumulation during the radioactive transformation
of 40K and preservation in situ. The high equilibrium temperature of garnet lherzolite (1050–1150°C) and the calculated pressure
(20–22 kbar) played the role of mutually compensating factors in argon diffusion; high temperatures enhanced diffusion, while
pressure suppressed it. 相似文献
8.
The New Hebrides archipelago is a complex reversed-arc system that can be divided into four major volcanic provinces. The Western Belt is an Early to Middle Miocene extinct volcanic arc that, as a result of polarity reversal, is now incorporated into the frontal arc of the present-day configuration. The Eastern Belt initially received detritus in the early Middle Miocene from a tholeiitic arc complex but in the Mio-Pliocene became the locus of a more calc-alkaline arc volcanism. Volcanic activity then ceased in the Eastern Belt but is well-represented as a third and largely submerged Marginal Province through the Pliocene into the Early Pleistocene. The present volcanic line, the Central Chain, is essentially a continuation of the Marginal Province volcanism into Recent times.Initial tectonic events in the New Hebrides arc were associated with the regional disruption in the Middle Miocene of an east-facing system, with consequent termination of Western Belt arc volcanism. The Western Belt remained as a landmass during the lowermost Late Miocene but subsided following a Late Miocene renewal of island arc volcanism to the east. This latest phase was coeval with initial expansion of the North Fiji Basin and marked the advent of the New Hebrides as a westwards-migrating reversed-arc system. During arc migration there were apparent hiatuses in island arc volcanism, the most notable being a Middle Pliocene to Late Pleistocene period of quiescence in the central sector.Tectonism in the Early Pleistocene-Recent raised the fore-arc, brought about rifting and extension to the rear and concentrated volcanism along the presently-active Central Chain. 相似文献
9.
Taiwan is located in the axis of the Manila Trench. It results from an oblique collision between the northernmost part of the Luzon arc and the Chinese passive margin. This active collision follows the subduction of the Oligocene-Miocene oceanic crust of the South China Sea along the Manila Trench. The tectonized Chinese margin emerged in the Hengchun peninsula (South Taiwan). Gentle folds which are delineated by the Quaternary reefal limestones demonstrate Recent deformations. These folds deformed a thick detrital sequence of Miocene age (Ssuchung Chi series) which was previously strongly folded and thrust westward (axis NS-N20) upon the Renting mélange of Latest Miocene age. These main deformations, sealed by the Middle Pliocene, are the evidence for the onset of collision in this part of Taiwan at the end of the Miocene. Because of its obliquity, the collision started already in the northern part of Taiwan during the Late Miocene (6-7-8 Ma ?).The Ssuchung Chi series, a sequence of proximal turbidites, has contained, since the Middle Miocene (NN 6~13 Ma), fragments of an Oligocene to Lower Miocene oceanic crust. This ophiolitic material is very similar to the East Taiwan Ophiolite of the Coastal Range. It originated most probably from a slice of South China Sea crust obducted in Middle Miocene times (13–14 Ma) upon the Chinese margin (North of the Hengchun peninsula). This obduction occurred 7 to 8 Ma before the beginning of collision. These results make it possible to propose an evolutionary model for Taiwan from the Oligocene to the Recent, with the different phases of a collision between a volcanic arc and a passive margin. 相似文献
10.
I. V. Chernyshev S. N. Bubnov V. A. Lebedev Yu. V. Gol’tsman E. D. Bairova A. I. Yakushev 《Stratigraphy and Geological Correlation》2014,22(1):96-121
The chronology of evolution of the young explosive volcanism in the Elbrus area of the Greater Caucasus is revealed. The isotopic-geochronological data indicate that ignimbrites and associated volcanic rocks were formed during the Middle Pliocene (3.0–2.75 Ma) and Early Pleistocene (0.84–0.70 Ma) stages of magmatic activity of the Greater Caucasus. The presence of two groups of pyroclastic rocks significantly different in age and analysis of their location indicate two spatially combined volcanic centers different in age in this part of the Elbrus volcanic area: Pliocene Tyrnyauz center localized in the eastern and southern parts and Quaternary Elbrus volcanic center which is the only newest center of volcanic activity both in the Elbrus and in the entire neovolcanic area. The analysis of chronology of magmatic events and compositional peculiarities of the young igneous rocks of the Elbrus area for the period from 3 Ma to the Holocene shows that the caldera stage of the evolution of the Elbrus Volcano has not come yet and future catastrophic magmatism is highly possible. 相似文献
11.
大洋钻探工程” 1 2 5航次的 782 A钻孔位于西太平洋菲律宾海东北部 ,井深 4 76.8m。基底为安山岩 ,上覆盖层为中始新统—更新统的沉积层 ,其中保存有低丰度的有孔虫。自下而上可划分出 8个浮游有孔虫带。由于出现 Catapsydrax dissimilis,C.stainforthi为 N5 、N6 带的带化石 ,表明本钻孔存在早中新世的地层。同时由于缺失浮游有孔虫带 P1 5 — P1 6 下部 ,N3上部—N4,N7—N1 1 带的带化石 ,说明在中始新世与晚始新世之间、晚渐新世与早中新世之间、早中新世与中中新世之间存在 3个沉积间断。钻孔中的有孔虫标志本区当时处于温暖亚热带环境。根据不同时期温度的变化 ,可划分出 5个阶段 ,包括 3个偏暖时期和 2个温凉时期。 相似文献
12.
Andrea Brogi 《International Journal of Earth Sciences》2008,97(4):677-703
The tectonic evolution of the Mt Amiata volcano-geothermal area is under discussion. Some authors state that this region,
as well as the hinterland of the Northern Apennines, were affected by compression from the Cretaceous to the Quaternary. In
contrast, most authors believe that extension drove the tectonic evolution of the Northern Apennines from the Early Miocene
to the Quaternary. Field data, seismic analyses and borehole logs have been integrated in order to better define the structural
features of the continental crust in the Mt Amiata geothermal area. In this paper I propose the hypothesis that the structure
of the crust in the Mt Amiata volcano-geothermal area derives from two main geological processes: (1) contractional tectonics
related to the stacking of the Northern Apennines (Cretaceous–Early Miocene), (2) subsequent extensional collapse of the hinterland
of the mountain chain, and related opening of the Northern Tyrrhenian Sea (Early Miocene–Quaternary). Compressional and extensional
structures characterise the Mt Amiata region, although extensional structures dominate its geological framework. In particular
the extension produced: (a) Middle-Late Miocene boudinage of the previously stacked tectonic units; (b) Pliocene–Quaternary
normal faulting which favoured the emplacement of a magmatic body in the middle-upper crust; and (c) the eruption of the Mt
Amiata volcano, which gave rise to an acid and intermediate volcanic complex (0.3–0.19 Ma). The extension produced the space
necessary to accommodate the Middle-Late Miocene marine and continental sediments. Pliocene and Quaternary normal and transtensional
faults dissected the previous structures and influenced the Early Middle Pliocene marine sedimentation within the structural
depressions neighbouring the Mt Amiata volcano. The magmatic body was emplaced at depth (about 6–7 km) during the Pliocene
extension, and produced the eruption of the Mt Amiata volcano during the Late Pleistocene. This gave rise to local uplift,
presently reaching about 3,000 m, as well as a negative Bouguer anomaly (−16 mgal), both centred on the Mt Amiata area. The
crustal dome shows a good correspondence with the convex shape of the regional seismic marker known as the K-horizon, which
corresponds to the 450°C isotherm, and the areas with greatest heat flow. This is probably a consequence of the above-cited
magmatic body presently in the process of solidification. A Late Pleistocene eruption occurred along a crustal fissure striking
N50° (Mt Amiata Fault), which crosscuts the crustal dome. Hydrothermal circulation, proven by the occurrence of thermal springs
and gas vents (mainly CO2 and H2S), mainly occurs along the Mt Amiata Fault both in the northeastern ans southwestern sides of the volcano. 相似文献
13.
Cenozoic volcanic rocks widespread in eastern China constitute an important part of the circum-Pacific volcanic belt.This paper presents more than 150K-Ar dates and a great deal of petrochemical analysis data from the Cenozoic volcanic rocks distributed in Tengchong,China‘s southeast coast,Shandong,Hebei,Nei Monggol and Northeast China.An integrated study shows that ubiquitous but uneven volcanic activities prevailed from the Eogene to the Holocene,characterized as being multi-eqisodic and multicycled.For example,in the Paleocene(67-58Ma),Eocene(57-37.5Ma),Miocene(22-18,16-19Ma),Pliocene(8-3Ma),and Early Pleistocene-Middle Pleistocene(1.2-0.5Ma) there were upsurges of volcanism,while in the Oligocene there was a repose period.In space,the older Eogene volcanic rocks are distributed within the region or in the central part of the NE-NNE-striking fault depression,while the younger Neogene and Quaternary volcanic rocks are distributed in the eastern and western parts.Petrologically,they belong essentially to tholeiite-series and alkali-series basalts,with alkalinity in the rocks increasing from old to youg.The above regularities are controlled by both global plate movement and regional inherent tectonic pattern. 相似文献
14.
15.
Hiroyuki MAEDA 《Resource Geology》1998,48(3):197-208
Abstract: Neogene magmatism in the Muka mine area in the Kitami metallogenic province was characterized on the basis of K-Ar age data by felsic–to–mafic terrestrial extrusive and intrusive volcanism from Late Miocene to Early Pliocene. The geology of the Muka mine area comprises the Upper Cretaceous-Paleocene Yubetsu Group, consisting primarily of sandstone and shale; Upper Miocene Ikutahara Formation, consisting of clastic and felsic volcaniclastic rocks and Kane-hana Lava (rhyolite) of 7. 5 Ma; Upper Miocene Yahagi Formation, consisting of clastics, felsic volcaniclastics and rhyolite lavas; Late Miocene andesite and rhyolite dikes (Chidanosawa Rhyolite of 7. 2 Ma and Hon-Mukagawa Andesite of 6. 6 Ma); Lower Pliocene Hakugindai Lava (basalt: 4. 0 Ma); and Quaternary System. The volcanism consists of earlier Late Miocene felsic extrusive activity during the sedimentation of the Ikutahara Formation, later Late Miocene felsic extrusive and intrusive activities during the sedimentation of the Yahagi Formation and intermediate intrusive activity after the sedimentation of the Yahagi Formation and Early Pliocene mafic extrusive activity. The Muka gold-silver ore deposit occurs primarily in the felsic volcaniclastic rocks and Kanehana Lava of the Ikutahara Formation and in Hon-Mukagawa Andesite. These wall–rocks, the clastic rocks of the Ikutahara Formation and the clastic and felsic volcaniclastic rocks of the Yahagi Formation were affected to various extents by hydrothermal alteration. The hydrother-mal alteration can be divided into two stages (early and late) based on the modes of occurrence and mineral assemblages. Early hydrothermal alteration is characterized by regional and vein-related alterations associated with epithermal gold-silver mineralization in a near-neutral hydrothermal system. Regional alteration can be subdivided into a zeolite zone (mordenite+adularia±heulandite–clinoptilolite series mineral±smectite±quartz°Cristobalite±opal–CT) and a smectite zone (smec–tite±quartz±opal–CT). Vein-related alteration can be subdivided into a K-feldspar zone (quartz+adularia±illite±interstratified illite/smectite±pyrite), an illite zone (quartz+illite°Chlorite±interstratified illite/smectite±smectite±pyrite) and an interstratified illite/smectite zone (quartz+interstratified illite/smectite±smectite±pyrite). The adularization age of 6. 8 Ma in the K-feldspar zone that developed in Kanehana Lava hosting ore veins coincides well with the epithermal gold-silver mineralization age of 6. 6 Ma. Late hydrothermal alteration is characterized by a kaolinite zone (kaolinite±dickite±alunite±quartz°Cristobalite± tridymite±pyrite) in an acid hydrothermal system, and cuts early alteration zones such as the K-feldspar zone. Other modes of occurrence of acid alteration are a 7Å halloysite-kaolinite vein in the hydrothermal explosion breccia dike and smectite–kaoli–nite veins along joint planes of Kanehana Lava. The style of the gold-silver deposit associated with early near-neutral hydrothermal alteration is a low-sulfidation epithermal type. The low-sulfidation epithermal gold-silver mineralization of 6. 6 Ma in the vicinity of the Muka ore deposit was essentially accompanied by felsic volcanic activity during the sedimentation of the Yahagi Formation, and was closely related both temporally and spatially to the felsic intrusive activity of Chidanosawa Rhyolite of 7. 2 Ma. The related hydrother-mal activity of the gold-silver mineralization took place at intervals of approximately 0. 4–0. 6 Ma after the volcanic activity related to the mineralization. 相似文献
16.
Quaternary Volcanic Activities in Shandong Peninsula and Northern Parts of Jiangsu and Anhui Provinces 总被引：1，自引：0，他引：1
Quaternary volcanic rocks often coexist with loess,as observed in the same geologic sections in the Shandong Peninsula and northern parts of Jiangsu and Anhui provinces.The development age of Shandong loess in close to that in the middle reaches of the Yellow River.Loess strata are of synchronous implication in the loess belt of North China.So the ages of volcanic activities can be es-timated approximately from the stratigraphic relations between loess layers and volcanic rocks.The re-sults of dating of the Quaternary volcanic rocks,baked layers and the TL dates of loess samples sug-gest that the Quaternary volcanic activity can be divided into 4 stages in the region studied,with the ages being 1.15-1.03,0.86-0.72,0.55-0.33 and 0.02 Ma B.P.respectively .The occurrence of tephra in the Shandong loess sections is possible due to multiple episodes of volcanism during the Quaternary time. 相似文献
17.
《Journal of Asian Earth Sciences》2010,39(6):233-254
The Bone Mountains, located in Southwest Sulawesi along the SE margin of Sundaland, are composed of Oligocene to possibly lower Miocene marginal basin successions (Bone Group) that are juxtaposed against continental margin assemblages of Eocene–Miocene age (Salokalupang Group). Three distinct units make up the latter: (i) Middle–Upper Eocene volcaniclastic sediments with volcanic and limestone intercalations in the upper part (Matajang Formation), reflecting a period of arc volcanism and carbonate development along the Sundaland margin; (ii) a well-bedded series of Oligocene calc-arenites (Karopa Formation), deposited in a passive margin environment following cessation of volcanic activity, and (iii) a series of Lower–Middle Miocene sedimentary rocks, in part turbiditic, which interfinger in the upper part with volcaniclastic and volcanic rocks of potassic affinity (Baco Formation), formed in an extensional regime without subduction.The Bone Group consists of MORB-like volcanics, showing weak to moderate subduction signatures (Kalamiseng Formation), and a series of interbedded hemipelagic mudstones and volcanics (Deko Formation). The Deko volcanics are in part subduction-related and in part formed from melting of a basaltic precursor in the overriding crust. We postulate that the Bone Group rocks formed in a transtensional marginal basin bordered by a transform passive margin to the west (Sundaland) and by a newly initiated westerly-dipping subduction zone on its eastern side.Around 14–13 Ma an extensional tectonic event began in SW Sulawesi, characterized by widespread block-faulting and the onset of potassic volcanism. It reached its peak about 1 Ma year later with the juxtaposition of the Bone Group against the Salokalupang Group along a major strike-slip fault (Walanae Fault Zone). The latter group was sliced up in variously-sized fragments, tilted and locally folded. Potassic volcanism continued up to the end of the Pliocene, and locally into the Quaternary. 相似文献
18.
Yasushi Watanabe 《Mineralium Deposita》2005,40(3):307-323
Kyushu Island, Japan, is located at the junction of the Southwest Japan arc and the Ryukyu arc. There are two major late Cenozoic
epithermal gold-silver provinces in Kyushu, which are termed the Northern and Southern provinces. The provinces are characterized
by: 1) Pliocene volcanism dominated by calc-alkaline andesite, followed by Quaternary volcanism including extrusion of both
calc-alkaline and tholeiitic magmas; 2) formation of extensional grabens; 3) Pliocene to Pleistocene mineralization, which
was dominated by abundant low sulfidation (LS) epithermal deposits with a few high sulfidation (HS) examples. The two epithermal
gold-silver provinces have evolved differently since about 5 Ma; the Northern province has exhibited diminished hydrothermal
activity from the Pliocene to Pleistocene, whereas the Southern province has witnessed increased hydrothermal activity mainly
in easterly and northerly directions. Changes of tectonic setting from the Pliocene to Pleistocene account for the variable
trends in epithermal gold deposit formation. Westward oblique subduction of the Philippine Sea plate beneath the Southwest
Japan arc caused development of the Hohi graben and arc-related volcanism at about 6 Ma. This was associated with widespread
LS mineralization in and surrounding the Hohi graben, as is represented by the Bajo and Taio deposits. The subduction of the
relatively buoyant Kyushu-Palau ridge during the early Pliocene strengthened the coupling between the slab and overriding
Ryukyu arc, leading to polygenetic andesite volcanism with associated HS (Kasuga, Iwato, and Akeshi) and LS (Kushikino) mineral
deposits forming in the Southern province. A change of the subduction direction of the Philippine Sea plate, from west to
north-northwest in the early Pliocene, increased the orthogonal convergence rate between the Southwest Japan arc and the Philippine
Sea plate, resulting in a decrease of volcanic and hydrothermal activity in the Hohi graben of the Northern province. The
more northerly subduction of the Philippine Sea plate shifted the locus of the Kyushu-Palau ridge subduction northward, resulting
in underplating of the older (85–60 Ma), negatively buoyant Amami basin oceanic slab in the Southern province, rather than
continued subduction of the young (27–15 Ma), buoyant Shikoku basin slab. This replacement caused steepening of the slab angle
and slab-rollback in the Southern province, which was associated with regional extension, an eastward shift of the Ryukyu
volcanic front, and development of the Kagoshima and Shimabara grabens, as well as the Okinawa trough. Rhyolite and basalt
volcanism, in addition to andesite volcanism, have occurred since 2 Ma in the area of the Ryukyu back arc; coincident LS mineralization
at Hishikari and Ohkuchi was affiliated with the rhyolite volcanism. Another change of the subduction direction of the Philippine
Sea plate to the northwest occurred at 2–1 Ma. The forearc sliver of the Southwest Japan arc shifted westward, in association
with right-lateral strike-slip faulting along the Median tectonic line, due to the increase of the westward convergence rate.
This shift resulted in shortening and cessation of graben development in the Hohi area, restricting the subsequent volcanism
and related hydrothermal activity to the central part of the graben. 相似文献
19.
《Geodinamica Acta》2001,14(1-3):177-195
The east Anatolian plateau and the Lesser Caucasus are characterised and shaped by three major structures: (1) NW- and NE-trending dextral to sinistral active strike-slip faults, (2) N-S to NNW-trending fissures and /or Plio-Quaternary volcanoes, and (3) a 5-km thick, undeformed Plio-Quaternary continental volcano-sedimentary sequence accumulated in various strike-slip basins. In contrast to the situation in the east Anatolian plateau and the Lesser Caucasus, the Transcaucasus and the Great Caucasus are characterised by WNW-trending active thrust to reverse faults, folds, and 6-km thick, undeformed (except for the fault-bounded basin margins) continuous Oligocene-Quaternary molassic sequence accumulated in actively developing ramp basins. Hence, the neotectonic regime in the Great Caucasus and the Transcaucasus is compressional–contractional, and Oligocene-Quaternary in age; whereas it is compressional–extensional, and Plio-Quaternary in age in the east Anatolian plateau and the Lesser Caucasus.Middle and Upper Miocene volcano-sedimentary sequences are folded and thrust-to-reverse-faulted as a result of compressional–contractional tectonic regime accompanied by mostly calc-alkaline volcanic activity, whereas Middle Pliocene-Quaternary sequences, which rest with angular unconformity on the pre-Middle Pliocene rocks, are nearly flat-lying and dominated by strike-slip faulting accompanied by mostly alkali volcanic activity implying an inversion in tectonic regime. The strike-slip faults cut and displace dykes, reverse to thrust faults and fold axes of Late Miocene age up to maximum 7 km: hence these faults are younger than Late Miocene, i.e., these formed after Late Miocene. Therefore, the time period between late Serravalian (∼ 12 Ma) continent–continent collision of Arabian and Eurasian plates and the late Early Pliocene inversion in both the tectonic regime, basin type and deformation pattern (from folding and thrusting to strike-slip faulting) is here termed as the Transitional period.Orientation patterns of various neotectonic structures and focal mechanism solutions of recent earthquakes that occurred in the east Anatolian plateau and the Caucasus fit well with the N–S directed intracontinental convergence between the Arabian plate in the south and the Eurasian plate in the north lasting since Late Miocene or Early Pliocene in places. 相似文献
20.
Ryuichi Shinjo Takele Chekol Daniel Meshesha Tetsumaru Itaya Yoshiyuki Tatsumi 《Contributions to Mineralogy and Petrology》2011,162(1):209-230
Major and trace element and isotopic ratios (Sr, Nd and Pb) are presented for mafic lavas (MgO > 4 wt%) from the southwestern
Yabello region (southern Ethiopia) in the vicinity of the East African Rift System (EARS). New K/Ar dating results confirm
three magmatic periods of activity in the region: (1) Miocene (12.3–10.5 Ma) alkali basalts and hawaiites, (2) Pliocene (4.7–3.6 Ma)
tholeiitic basalts, and (3) Recent (1.9–0.3 Ma) basanite-dominant alkaline lavas. Trace element and isotopic characteristics
of the Miocene and Quaternary lavas bear a close similarity to ocean island basalts that derived from HIMU-type sublithospheric
source. The Pliocene basalts have higher Ba/Nb, La/Nb, Zr/Nb and 87Sr/86Sr (0.70395–0.70417) and less radiogenic Pb isotopic ratios (206Pb/204Pb = 18.12–18.27) relative to the Miocene and Quaternary lavas, indicative of significant contribution from enriched subcontinental
lithospheric mantle in their sources. Intermittent upwelling of hot mantle plume in at least two cycles can explain the magmatic
evolution in the southern Ethiopian region. Although plumes have been originated from a common and deeper superplume extending
from the core–mantle boundary, the diversity of plume components during the Miocene and Quaternary reflects heterogeneity
of secondary plumes at shallower levels connected to the African superplume, which have evolved to more homogeneous source. 相似文献