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1.
Studies in the Amundsen Basin have revealed six seismostratigraphic complexes (SSCs) in this region. The horizons bounding
these complexes were dated by identifying the linear magnetic anomalies. The recognized SSCs are correlated with the seismostratigraphic
and lithostratigraphic units of the Lomonosov Ridge. Based on these correlations, the lithological composition of SSCs in
the Amundsen Basin is suggested. The formation of SSC2 is supposed to be due to the diagenetic processes associated with the
transition of opal-A to opal-CT. It is found that, generally, the rate of sedimentation in the Amundsen Basin has consistently
decreased since the beginning of its formation. However, in the Chattian time, the global regression resulted in a sharp increase
in the rate of sedimentation in the basin. Arguments in favor of the duration of the Middle Cenozoic sedimentary hiatus on
the Lomonosov Ridge reduced to 16.3 Ma are presented. It is supposed that the decrease in the intensity of oceanic crustal
accretion in the Eurasian Basin, which is identified by the slowdown in the rate of its opening in the interval from 46 to
20–23 Ma might have resulted in a gradual sea level falling in the Arctic Ocean isolated from the World Ocean. This fact probably
accounts for the Lomonosov Ridge having remained in subaerial conditions over the period from 36.7 to 20.4 Ma. 相似文献
2.
E. V. Verzhbitskii L. I. Lobkovskii A. F. Byakov M. V. Kononov 《Doklady Earth Sciences》2012,444(2):666-670
In order to specify the origin and evolution of the Alpha-Mendeleev and Lomonosov ridges, profiles of the bottom relief and crustal basement were made. Additionally, the coefficients characterizing the rate of subsidence of the crustal basement in different parts of the ridges for the last 25 Ma were calculated and the depth of the crustal basement prior to the beginning of subsidence in the Early Miocene was estimated. The calculation results were compared with the model of thermal subsidence of the Greenland-Iceland and Iceland-Faroe thresholds, which were also formed by plume-tectonic processes. A large dome rise of the basement was found in the central parts of the Alpha-Mendeleev and Lomonosov ridges. It was also found that the coefficients of thermal subsidence of the crustal basement in the central parts of the Alpha-Mendeleev and Lomonosov ridges are close to those for the Greenland-Iceland and Iceland-Faroe thresholds. It was shown that the depth of the crustal basement prior to the beginning of subsidence in the Early Miocene grew going outwards from the central parts of the ridges, analogous to the present-day pattern. All the information given above indicates the thermal origin of subsidence for the Alpha-Mendeleev and Lomonosov ridges starting from the Early Miocene and the substantial influence of the Arctic Plume on the genesis and evolution of these ridges. 相似文献
3.
We have analyzed the geodynamic evolution of the lithosphere and upper mantle of the Amerasian basin based on the stress-strain state simulation. It is shown that the asthenospheric spreading in the return upflow region of the mantle convection, results in formation of two local uplifts, which can be interpreted as Lomonosov Ridge and Mendeleev/Alfa Ridge. The further long-term action of the mantle convection leads to formation of Makarov and Podvodnikov Basins. 相似文献
4.
The integration of information obtained from onshore and offshore geological and geophysical research undertaken in the context
of the International Polar Year has led to the following results. The continental crust is widespread in the Arctic not only
beneath the shelves of polar seas in the framework of the Amerasia Basin but also in the Chukchi-Northwind, Lomonosov, and
Mendeleev ridges; a combination of continental and oceanic crusts is inferred in the Alpha Ridge. The Amerasia Basin is not
an indivisible element of the Arctic Ocean either in genetic or structural terms but consists of variously oriented basins
different in age. The first, Mesozoic “minor ocean” of the Arctic Ocean—the Canada Basin—arose as a result of impact of the
Arctic plume on the high-latitude region of Pangea. This inference is supported by the vast Central Arctic igneous province
that comprises the Jurassic-Mid-Cretaceous within-plate and ocean-island basaltic and associated rocks. The rotational mechanism
of opening of this basin is explained by the slant path of the plume head motion, which resulted in breaking-off and displacement
of a fragment of Pangea. The effect of the Arctic plume was expressed during all stages of the opening of the Canada Basin
and exerted effects on the adjacent part of the Eurasian continent during the formation of the Verkhoyansk-Chukotka tectonic
domain. The Canada Basin was an element of the segmented system of Atlantic spreading ridges, while the Arctic plume that
initiated its evolution was genetically related to the episodically acting African-Atlantic superplume. In comparison with
the Pacific superplume, the low productivity of African-Atlantic lower mantle upwelling became the cause of slow and ultraslow
spreading in the Atlantic and Arctic oceans and determined the passive character of their margins, including the Canada Basin. 相似文献
5.
A. N. Sukhov V. D. Chekhovich A. V. Lander S. L. Presnyakov E. N. Lepekhina 《Doklady Earth Sciences》2011,439(1):926-932
The Shirshov Ridge holds an important position in the structure of the Bering Sea Basin. Stretching from north to south for
over 500 km, it divides the Bering Sea into two deep water basins, the Aleutian and Komandorsky basins. The age of oceanic
crust of the Aleutian basin based on linear magnetic anomalies is conventionally considered Early Cretaceous, of the Komandorsky
basin — Miocene, according to the K-Ar dating of the basalts (9.8 Ma) exposed in 191 deep water drill borehole. Rocks belonging
to the basement of the Shirshov Ridge were dredged during the 29th cruise of research vessel Dmitrii Mendeleev and are represented by amphibolitic gabbro whose composition is similar to that of gabbroids of mid-oceanic ridges. The age
of metamorphism based on the results of K-Ar dating of amphibole is 47 ± 5 Ma. The U-Pb zircon dating method was used to determine
the age of gabbro. Zircons were extracted from a ∼5 kg combined amphibolitic gabbroid sample, and the age of zircons was determined
using a SHRIMP-II sensitive high resolution secondary ion microprobe (Center of Isotopic Studies, A.P. Karpinskii Russian
Geological Research Institute, St. Petersburg). The average concordant age value for the 25 determinations performed based
on 20 points for 18 grains is 72 ± 1.4 Ma (Late Campanian). For 5 grains, the measured age values are within the range of
88 ± 3.5 Ma to 126.5 ± 4.5 Ma. Given the western vergence of the thrust structure of the Shirshov Ridge, the acoustic basement
of the Shirshov Ridge is most probably a complexly deformed oceanic crust of the Aleutian Trench, which most likely dates
from the Early to Late Cretaceous. 相似文献
6.
Recent multidisciplinary geophysical measurements over the Lomonosov Ridge close to the North Pole support the widely held belief that it was formerly part of Eurasia. The known lithologies, ages, P-wave velocity structure and thickness of the crust along the outer Barents and Kara continental shelves are similar to permitted or measured values of these parameters newly acquired over the Lomonosov Ridge. Seismic, gravity and magnetic data in particular show that the ridge basement is most likely formed of early Mesozoic or older sedimentary or low-grade metasedimentary rocks over a crystalline core that is intermediate to basic in composition. Short-wavelength magnetic anomaly highs along the upper ridge flanks and crest may denote the presence of shallow igneous rocks. Because of the uncertain component of ice-rafted material, seafloor sediments recovered from the ridge by shallow sampling techniques cannot be clearly related to ridge basement lithology without further detailed analysis. The ridge is cut at the surface and at depth by normal faults that appear related to the development of the Makarov Basin. This and other data are consistent with the idea that the Makarov Basin was formed by continental stretching rather than simple seafloor spreading. Hence the flanking Alpha and Lomonosov ridges may originally have been part of the same continental block. It is suggested that in Late Cretaceous time this block was sheared from Eurasia along a trans-Arctic left-lateral offset that may have been associated with the opening of Baffin Bay. The continental block was later separated from Eurasia when the North Altantic rift extended into the Arctic region in the Early Tertiary. The data suggest that the Makarov Basin did not form before the onset of rifting in the Artic. 相似文献
7.
Major hypotheses on the formation of the Iceland region are considered. It is noted that plate- and plume-tectonic genesis
is the most substantiated hypothesis for this region. Model estimations of the effect of hot plume on the formation of genetically
different oceanic ridges are obtained. Computer calculations are performed for the thermal subsidence rate of aseismic ridges
(Ninetyeast and Hawaiian-Emperor) in the asthenosphere of the Indian and Pacific oceans. Comparative analysis of the calculated
subsidence rates of these ridges with those in the Iceland region (Reykjanes and Kolbeinsey ridges) is performed. The results
suggest that the thermophysical processes of formation of the spreading Reykjanes and Kolbeinsey ridges were similar to those
of the aseismic Ninetyeast and Hawaiian-Emperor ridges: the genesis of all these ridges is related to the functioning of a
hotspot. Analysis of the heat flux distribution in the Iceland Island and Hawaiian Rise areas is carried out. Analysis and
numerical calculations indicate that the genesis of Iceland was initially characterized by the plume-tectonic transformation
of a continental rather than oceanic lithosphere. The level of geothermal regime near Iceland was two times higher (100 mW/m2) relative to the Hawaiian Rise area (50 mW/m2) because the average lithosphere thickness of the Reykjanes and Kolbeinsey ridges near the Iceland was approximately two
times less (40 km) relative to the thickness of the Pacific Plate (80 km) in the Hawaiian area. The main stages of evolution
of the Iceland region are based on geological and geothermal data and numerical thermophysical modeling. The Cenozoic tectonic
evolution of the region is considered. Paleogeodynamic reconstructions of the North Atlantic in the hotspot system at 60,
50, and 20 Ma are obtained. 相似文献
8.
Seismic refraction surveys conducted in 1976 and 1979 over the broken ice surface of the Arctic Ocean, reveal distinctly different crustal structures for the Fram, Makarov and Canada basins. The Canada Basin, characterized by a 2–4 km thick sedimentary layer and a distinct oceanic layer 3B of 7.5 km/s velocity has the thickest crust and is undoubtedly the oldest of the three. The crust of the Makarov Basin has a thin sedimentary layer of less than 1 km and is about 9 km in total thickness. The Fram Basin has a similarly thin sedimentary layer but is 3–4 km thicker than the Makarov as it approaches the Lomonosov Ridge near the North Pole. The ridge itself is cored by material with a velocity of 6.6 km/s and may be a metagabbro similar to oceanic layer 3A. This ridge root material extends to a depth of about 27 km, where a change occurs to upper-mantle material with a velocity of 8.3 km/s. The core is overlain by up to 6 km of material with a velocity of about 4.7 km/s which could be oceanic layer 2A basalts or continental crystalline rocks with some sedimentary material.The Fram Basin probably began to open contemporaneously with the North Atlantic about 70 m.y. ago, by spreading along the Nansen-Gakkel Ridge. Although not yet dated, the Makarov Basin is probably no older than the initiation of the Fram Basin and may be much younger. The Alpha Ridge may once have been part of the Lomonosov Ridge, splitting off to form the Makarov Basin between 70 and 25 m.y. ago and possibly contributing to the Eurekan Orogeny of 25 m.y. ago, evident on Ellesmere Island. In contrast, the likely age of the Canada Basin lies in the 125–190 m.y. range and may have been formed by the counter-clockwise rotation of Alaska and the Northwind Ridge away from the Canadian Arctic Islands. The Lomonosov Ridge emerges from this scenario as a block resulting from a strike-slip shear zone on the European continental shelf, related to the opening of the Canada basin (180-120 my) and then becomes an entity broken from this shelf by the opening of the Eurasia Basin (70-0 m.y.). 相似文献
9.
The Siberian–Icelandic hotspot track is the only preserved continental hotspot track. Although the track and its associated age progression between 160 Ma and 60 Ma are not yet well understood, this section of the track is closely linked to the tectonic evolution of Amerasian Basin, the Alpha-Mendeleev Ridge and Baffin Bay. Using paleomagnetic data, volcanic structures and marine geophysical data, the paleogeography of Arctic plates (Eurasian plate, North American Plate, Greenland Plate and Alaska Microplate) was reconstructed and the Siberian–Icelandic hotspot track was interlinked between 160 Ma and 60 Ma. Our results suggested that the Alpha-Mendeleev Ridge could be a part of the hotspot track that formed between 160 Ma and 120 Ma. During this period, the hotspot controlled the tectonic evolution of Baffin Bay and the distribution of mafic rock in Greenland. Throughout the Mesozoic Era, the aforementioned Arctic plates experienced clockwise rotation and migrated northeast towards the North Pacific. The vertical influence from the ancient Icelandic mantle plume broke this balance, slowing down some plates and resulting in the opening of several ocean basins. This process controlled the tectonic evolution of the Arctic. 相似文献
10.
Katalin Báldi 《International Journal of Earth Sciences》2006,95(1):119-142
Benthic foraminifera and stable isotopes analyses revealed changes emerging in the paleoceanographic scenery in the Paratethys.
The percentage of inbenthic, oxyphylic taxa and diversity in the benthic foraminiferal assemblage showed increasing food supply
(organic matter), decreasing oxygen level and growing stress on the sea floor. Oxygen isotopes measured in planktonic and
benthic foraminifera pointed to strengthening stratification during the Badenian period. The carbon isotopes indicated intensified
accumulation of light marine organic matter. This increasing stratification trend is especially pronounced by Late Badenian
(13.5–13 Ma) when surface water oxygen isotope values are rather negative. A simple two-layer circulation model was worked
out for the Badenian Paratethys explaining these characteristic environmental changes. An antiestuarine (lagoonal) circulation is assumed for the Central Paratethys during the Early (16.4–15 Ma) and mid Badenian (15–13.5 Ma). The mid Badenian
period of time comprises the short episode of evaporite formation in the Carpathian Foredeep and the Transylvanian Basin.
Evidence presented here supported a reversal of circulation to estuarine type after the deposition of salts by Late Badenian (13.5–13 Ma). The Early Badenian antiestuarine circulation is suggested
to associate with the high temperatures of the Mid-Miocene Climatic Optimum, and the Late Badenian estuarine circulation with
the cooler period following it. 相似文献
11.
Cenozoic geodynamics of the Bering Sea region 总被引：1，自引：0，他引：1
In the Early Cenozoic before origination of the Aleutian subduction zone 50–47 Ma ago, the northwestern (Asian) and northeastern (North American) parts of the continental framework of the Pacific Ocean were active continental margins. In the northwestern part, the island-arc situation, which arose in the Coniacian, remained with retention of the normal lateral series: continent-marginal sea-island arc-ocean. In the northeastern part, consumption of the oceanic crust beneath the southern margin of the continental Bering shelf also continued from the Late Cretaceous with the formation of the suprasubduction volcanic belt. The northwestern and northeastern parts of the Paleopacific were probably separated by a continuation of the Kula-Pacific Transform Fracture Zone. Change of the movement of the Pacific oceanic plates from the NNW to NW in the middle Eocene (50–47 Ma ago) was a cause of the origin of the Aleutian subduction zone and related Aleutian island arc. In the captured part of the Paleopacific (proto-Bering Sea), the ongoing displacement of North America relative to Eurasia in the middle-late Eocene gave rise to the formation of internal structural elements of the marginal sea: the imbricate nappe structure of the Shirshov Ridge and the island arc of the Bowers Ridge. The Late Cenozoic evolution was controlled by subduction beneath the Kamchatka margin and its convergence with the Kronotsky Terrane in the south. A similar convergence of the Koryak margin with the Goven Terrane occurred in the north. The Komandorsky minor oceanic basin opened in the back zone of this terrane. Paleotectonic reconstructions for 68–60, 56–52, 50–38, 30–15, and 15–6 Ma are presented. 相似文献
12.
Two belts of subaerial volcanic rocks—the Eocene Kinkil belt and the Neogene belt of the Sredinny Range—extend along the Kamchatka
Isthmus. It is suggested that their formation is related to subduction of the oceanic lithosphere beneath the continental
margin of North Kamchatka. The oceanic lithosphere consumed in the subduction zones could have been formed as a result of
active spreading in the Komandorsky Basin. In the simplest case, both spreading and subduction reflect the northwestward motion
of the lithosphere of the Komandorsky Plate relative to Kamchatka, the Shirshov Ridge, and the Aleutian Basin combined into
one relatively immobile plate conventionally called the North American Plate. The authors perform a simulation of conjugate
spreading and subduction. The most important parameter determining the regional geodynamics—the velocity of the Komandorsky
Plate moving relative to the North American Plate—is taken as 2.5, 5.0, and 7.5 cm/yr. The calculated ages of the onset and
end of volcanic activity in the aforementioned belts are compared with the dates obtained with the isotopic and paleontological
methods. For the Eocene Kinkil belt, where volcanism started 44 Ma ago, the model age of the onset of subduction depends on
the accepted velocity of the motion of the Komandorsky Plate and varies from 54 Ma at the velocity of 2.5 cm/yr to 47.5 Ma
at the velocity of 7.5 cm/yr. It can be assumed that the model of fast subduction in this age interval is most consistent
with the geological data. For the Miocene-Pliocene belt of the Sredinny Range, assuming the velocity of the motion of the
Komandorsky Plate at 5.0 and 7.5 cm/yr, multiple rifting at the boundary with the Shirshov Ridge should be assumed. Therefore,
for the end of the Neogene, a model with low velocity (2.5–5.0 cm/yr, i.e., about 4.0 cm/yr) is preferable. 相似文献
13.
Rb-Sr isochron age of fluid inclusions in quartz from the Fuwan super-large silver deposit is 68 - 6 Ma, the silver deposit is characterized by high μ values (10.67 - 10.95 ), which are much higher than those of the ore-hosted Paleozoic strata and are close to those of ores hosted in the Proterozoic metamorphic basement in western Guangdong Province. Based on the Pb isotopic characteristics, coupled with much high background silver contents (200-1000ng/g) in the Proterozoic basement and relatively low silver contents in the Paleozoic strata in the region of the Sanshui Basin, it is concluded that the ore-forming material of the super-large silver deposit came mainly from the old basement. The super-large silver deposit related genetically to the intense volcanic activities during the Upper Cretaceous to Eogene. The formation of the Fuwan super-large silver deposit is controlled by the following favorable geological conditions : ( 1 ) The intersection of deep faults and contemporaneous faults at the margin of the Sanshui Basin led to the formation of an excellent structure as passageway for ore fluids; (2) The special ore-hosted rock association forms a ore gathering-trap structure that favors the precipitation of ore; (3) The silver-rich old basement, multi-stage mineralization and multi-episode volcanic activities which constitute a geothermal convection system. 相似文献
14.
M. I. Kuzmin E. B. Karabanov A. A. Prokopenko V. F. Gelety V. S. Antipin D. F. Williams A. N. Gvozdkov 《International Journal of Earth Sciences》2000,89(2):183-192
With this paper we present a first attempt to combine the direct results on lithology, composition and age dating in the
boreholes BDP-93, BDP-96 and BDP-97 with geological and seismic data from the areas where those sections were drilled. The
sedimentary environments represented by the BDP boreholes are markedly different and possess characteristic lithological features.
The results of the deep drilling provide the essential means for testing numerous age models used in geological reconstructions
of the Lake Baikal rifting dynamics. Neither the basin-wide unconformity interpreted from seismic data, nor the interpreted
change from shallow-water to deep-water facies at the boundary of the seismic stratigraphic complexes were found in the BDP-96
boreholes on Academician Ridge. Also, lithology does not support the proposed reconstructions of intense lake level fluctuations
and transgressions during the Pliocene at Academician Ridge. The continuous deep-water hemipelagic sedimentation at Academician
Ridge has existed for the past 5 Ma. The beginning of an intense rifting phase of the Neobaikalian sub-stage and related drastic
changes in sedimentation processes were interpreted on seismic sections as the basin-wide unconformity B10. Different age
estimates for this boundary ranged from Late Pliocene (3.5 Ma) to Plio-Pleistocene boundary. As shown by BDP-96 borehole,
B10 is associated with a lithological change from diatomaceous ooze to dense silty clay and not with an erosional contact.
The new age for this boundary in BDP-96 is approximately 2.5 Ma. This new age constraint suggests that the upper sedimentary
strata of Northern Baikal (1.5–1.7 km thick) have formed during the past 2.5 Ma with average sedimentation rates of 60–70 cm/ka.
The BDP-93 boreholes at Buguldeika suggest that uplift in Primorsky Range took place prior to 1.07–1.31 Ma, a date which exceeds
the age of previous geological models.
Received: 12 March 1999 / Accepted: 10 February 2000 相似文献
15.
J. N. Pattan M. Shyam Prasad E. V. S. S. K. Babu 《Journal of Earth System Science》2010,119(4):531-539
We have identified an ash layer in association with Australasian microtektites of ∼0.77 Ma old in two sediment cores which
are ∼450 km apart in the central Indian Ocean Basin (CIOB). Morphology and chemical composition of glass shards and associated
microtektites have been used to trace their provenance. In ODP site 758 from Ninetyeast Ridge, ash layer-D (13 cm thick, 0.73–0.75
Ma) and layer-E (5 cm thick, 0.77–0.78 Ma) were previously correlated to the oldest Toba Tuff (OTT) eruptions of the Toba
caldera, Sumatra. In this investigation, we found tephra ∼3100 km to the southwest of Toba caldera that is chemically identical
to layer D of ODP site 758 and ash in the South China Sea correlated to the OTT. Layer E is not present in the CIOB or other
ocean basins. The occurrence of tephra correlating to layer D suggests a widespread distribution of OTT tephra (∼3.6 × 107 km2), an ash volume of at least ∼1800 km3, a total OTT volume of 2300 km3, and classification of the OTT eruption as a super-eruption. 相似文献
16.
Seismic data on the southern (Laptev Sea) extremity of the Lomonosov Ridge were used to develop a new structural model for the sedimentary cover. It permitted a correlation between the seismic cross-sections of the ridge crest and two deep-sea basins: the Podvodnikov Basin and the Amundsen Plain. It is the first time that a seismic model has taken into account both regional seismic-reflection profiles obtained from NP drifting ice stations and recent high-resolution CDP data. Our seismic model agrees both with geological data on the Laptev Sea continental margin and the data obtained from deep-sea drilling into the Lomonosov Ridge under the IODP-302 project. The sedimentary cover of the southern Lomonosov Ridge and adjacent parts of the Amundsen Plain and Podvodnikov Basin was dated at the Aptian–Cenozoic. The sedimentary section is divided by two main unconformities, of Campanian–Paleocene and Oligocene–Early Miocene ages. The cover contains a structurally complicated graben system, which is an extension of the New Siberian system of horsts and grabens, recognized in the shelf. Sedimentation began in the grabens in the Aptian–Albian and ended with their complete compensation in the Paleocene. 相似文献
17.
K.M. Haase C. Beier S. Fretzdorff P.T. Leat R.A. Livermore T.L. Barry J.A. Pearce F. Hauff 《Chemical Geology》2011,280(1-2):115-125
New 40Ar–39Ar ages of 5.6 to 1.3 Ma for lavas from the fossil Phoenix Ridge in the Drake Passage show that magmatism continued for at least 2 Ma after the cessation of spreading at 3.3 ± 0.2 Ma. The Phoenix Ridge lavas are incompatible element-enriched relative to average MORB and show an increasing enrichment with decreasing age, corresponding to progressively decreasing degrees of partial melting of spinel peridotite after spreading stopped. The low-degree partial melts increasingly tap a mantle source with radiogenic Sr and Pb but unradiogenic Nd isotope ratios implying an ancient enrichment. The post-spreading magmas apparently form by buoyant ascent of enriched and easily fusible portions of the upper mantle. Only segments of fossil spreading ridges underlain by such enriched and fertile mantle show post-spreading volcanism frequently forming bathymetric highs. The Phoenix Ridge lavas belong to the Pacific, rather than the Atlantic, mantle domain in regional Sr–Nd–Pb space. Our new data show that the southern Pacific Ocean mantle is heterogeneous containing significant enriched portions that are preferentially tapped at low melt fractions. Isotopic mapping reveals that Pacific-type upper mantle flows eastward through Drake Passage and surrounds the subducting Phoenix Plate beneath the Bransfield Basin. 相似文献
18.
Several spindle-shaped grains of zircon, which have a small size (<0.25 mm) and a distinct purplish pink coloration were found
in the crushed samples of kimberlites from the Aykhal, Komsomolskaya-Magnitnaya, Botuobinskaya (Siberian platform), and Nyurbinskaya
(Yakutia) pipes and olivine lamproites of the Khani massif (West Aldan). U-Pb SHRIMP II zircon dating performed at the VSEGEI
Center for Isotopic Research yielded the ages of 1870–1890 Ma for the pipes of the Western province (Aykhal and Komsomolskaya)
and 2200–2750 Ma for the pipes of the eastern province (Nyurbinskaya and Botuobinskaya), which allowed us to consider these
zircons to be xenogenic to kimberlites. Although these zircons resemble in their age and color those from the granulite xenoliths
in the Udachnaya pipe [2], no other granulite minerals are found there. Thus, major geological events in the mantle and lower
crust, which led to the formation of zircon-bearing rocks, happened at 1800–1900 Ma in the northern part of the kimberlite
province, whereas in the Eastern part of the province (Nakyn field) these events were much older (2220–2700 Ma). It is known
that the period of 1800–1900 Ma in the Earth’s history was accompanied by intense tectonic movements and widespread alkaline-carbonatite
magmatism. This magmatism was related to plume activity responsible for overheating the large portions of the mantle to the
temperatures at which some diamonds in mantle rocks would burn (northern part of the kimberlite province). In the Nakyn area,
the mantle underwent few or no geological processes at that time, and perhaps for this reason this area hosts more diamondiferous
kimberlites. The age of olivine lamproites from the Khani massif is 2672–2732 Ma. Thus, these are some of the world’s oldest
known K-alkaline rocks. 相似文献
19.
V. A. Vernikovsky A. E. Vernikovskaya N. Yu. Matushkin I. V. Romanova N. G. Berezhnaya A. N. Larionov A. V. Travin 《Doklady Earth Sciences》2010,432(1):547-552
This study characterizes some issues of the Paleozoic and Mesozoic tectonomagmatic evolution of Precambrian structures from
the southwestern margin of the Siberian craton. The relationship between the Devonian and Triassic magmatic events is demonstrated
from the example of the Severnaya rift-related structure, South Yenisei Ridge. U-Pb SHRIMP dating yielded ages of 387 ± 5
Ma for leucogranites and 240 ± 3 Ma for the overlying alkaline trachytes. These ages show good agreement with Ar-Ar geochronological
data (392–387 Ma) obtained for micas from paragneisses and leucogranite dykes of the Yenisei suture zone, the extension of
which is superimposed by the studied rift-related structure. The previous geological evidence and the Devonian age estimate
first obtained for magmatic rocks of the Yenisei Ridge allow us to interpret the studied leucogranites as products of Devonian
continental rifting, similar to volcanic and intrusive rocks of the North Minusa depression and Agul graben. Like other localities
within the western margin of Siberian craton, the formation of Triassic alkaline rocks may be related to the Siberian superplume
activity. 相似文献
20.
Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia 总被引：30，自引：1，他引：30
Daniela Rubatto Ian S. Williams Ian S. Buick 《Contributions to Mineralogy and Petrology》2001,140(4):458-468
We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central
Australia), where greenschist- to granulite-facies metamorphism is recorded over a continuous crustal section. Detailed cathodoluminescence
and back-scattered electron imaging, supported by SHRIMP U–Pb dating, has revealed the different behaviours of zircon and
monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 ± 5 Ma), at amphibolite-facies grade,
at ∼600 °C. Abundant monazite yielding similar ages (1557 ± 2 to 1585 ± 3 Ma) is found at granulite-facies conditions in both
partial melt segregations and restites. New zircon growth occurred between 1562 ± 4 and 1587 ± 4 Ma, but, in contrast to monazite,
is only recorded in granulite-facies rocks where melt was present (≥700 °C). New zircon appears to form at the expense of
pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals
increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven
by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these
accessory phases in response to metamorphism extends over the 30 Ma period of melt crystallisation (1557–1587 Ma) in a stable
high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the
protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature
(750–800 °C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found
in monazite, indicating that the closure temperature of the U–Pb system in relatively large monazite crystals can exceed 750–800 °C.
Received: 7 April 2000 / Accepted: 12 August 2000 相似文献