Pleistocene magmatism in a lithospheric transition area: petrogenesis of alkaline and peralkaline lavas from the Baringo–Bogoria Basin, central Kenya Rift

2003 ◽  
Vol 40 (9) ◽  
pp. 1239-1257 ◽  
Author(s):  
Jean-Philippe Clément ◽  
Martial Caroff ◽  
Christophe Hémond ◽  
Jean-Jacques Tiercelin ◽  
Claire Bollinger ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Geochemical Data ◽  
Mobile Belt ◽  
Crustal Assimilation ◽  
Kenya Rift ◽  
Transition Area ◽  
Short Time Span ◽  
Geochemical Variations ◽  
Short Time ◽  
Central Kenya

New petrological, geochronological, and geochemical data on basalts, mugearites, peralkaline trachytes, and phonolites from the Baringo–Bogoria Basin, central Kenya Rift, are presented. K–Ar dating indicates that the volcanic rocks were emplaced between 894 ± 13 and 92 ± 5 ka. 87Sr/86Sr ranges from 0.70304 to 0.70692, 143Nd/144Nd from 0.51237 to 0.51295, 206Pb/204Pb from 18.4 to 19.8, 207Pb/204Pb from 15.46 to 15.70, and 208Pb/204Pb from 38.2 to 40.5. Despite a rather restricted sampling area and a relatively short time span ([Formula: see text]820 ka), the mineralogical and geochemical variations are not consistent with a simple cogenetic link between the lavas. The studied area is located in a transition zone between two different lithospheric domains (Tanzanian Craton and Panafrican Mobile Belt). We propose that the petrological and geochemical variations of the studied lavas are essentially linked to the nature of the underlying lithosphere. Some basaltic products underwent carbonate contamination, possibly within the crust. Trachytes and phonolites are derived from different basaltic parents through crustal assimilation coupled with fractional crystallization. One phonolite sample contains primary calcite-rich veinlets. Textural relations and geochemical evidence suggest that there is a direct cogenetic link between these carbonate and phonolite melts. The veinlets are the modal expression of a carbonate component included in all the phonolites from the Baringo–Bogoria Basin.

scholarly journals Calc-alkaline volcanic rocks and zircon ages of the late Tonian: early Cryogenian arc-related Big Naryn Complex in the Eastern Djetim-Too Range, Middle Tianshan block, Kyrgyzstan

2020 ◽  
Author(s):  
Baiansuluu Terbishalieva ◽  
Martin Jan Timmerman ◽  
Alexander Mikolaichuk ◽  
Uwe Altenberger ◽  
Jiří Sláma ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Metamorphic Rocks ◽  
Magmatic Arc ◽  
Lower Member ◽  
Short Time Span ◽  
Zircon Crystallization ◽  
Arc Setting ◽  
Late Neoproterozoic ◽  
Continental Magmatic Arc ◽  
Short Time

AbstractThe Big Naryn Complex (BNC) in the East Djetim-Too Range of the Kyrgyz Middle Tianshan block is a tectonized, at least 2 km thick sequence of predominantly felsic to intermediate volcanic rocks intruded by porphyric rhyolite sills. It overlies a basement of metamorphic rocks and is overlain by late Neoproterozoic Djetim-Too Formation sediments; these also occur as tectonic intercalations in the BNC. The up to ca. 1100 m thick Lower Member is composed of predominantly rhyolites-to-dacites and minor basalts, while the at least 900 m thick pyroclastic Upper Member is dominated by rhyolitic-to-dacitic ignimbrites. Porphyric rhyolite sills are concentrated at the top of the Lower Member. A Lower Member rhyolite and a sill sample have LA-ICP-MS U–Pb zircon crystallization ages of 726.1 ± 2.2 Ma and 720.3 ± 6.5 Ma, respectively, showing that most of the magmatism occurred within a short time span in the late Tonian–early Cryogenian. Inherited zircons in the sill sample have Neoarchean (2.63, 2.64 Ga), Paleo- (2.33–1.81 Ga), Meso- (1.55 Ga), and Neoproterozoic (ca. 815 Ma) ages, and were derived from a heterogeneous Kuilyu Complex basement. A 1751 ± 7 Ma 40Ar/39Ar age for amphibole from metagabbro is the age of cooling subsequent to Paleoproterozoic metamorphism of the Kuilyu Complex. The large amount of pyroclastic rocks, and their major and trace element compositions, the presence of Neoarchean to Neoproterozoic inherited zircons and a depositional basement of metamorphic rocks point to formation of the BNC in a continental magmatic arc setting.

scholarly journals Magmatism of the Kenya Rift Valley: a review

2002 ◽  
Vol 93 (3) ◽  
pp. 239-253 ◽  
Author(s):  
Ray Macdonald
Keyword(s):  
Partial Melting ◽  
Rift Valley ◽  
Volcanic Rocks ◽  
Mobile Belt ◽  
Kenya Rift ◽  
South Central ◽  
Northern Tanzania ◽  
Wide Range ◽  
High Level ◽  
Kenya Rift Valley

ABSTRACTTertiary–Recent magmatism in the Kenya Rift Valley was initiated c. 35 Ma, in the northern part of Kenya. Initiation of magmatism then migrated southwards, reaching northern Tanzania by 5–8 Ma. This progression was accompanied by a change in the nature of the lithosphere, from rocks of the Panafrican Mozambique mobile belt through reworked craton margin to rigid, Archaean craton. Magma volumes and the geochemistry of mafic volcanic rocks indicate that magmatism has resulted from the interaction with the lithosphere of melts and/or fluids from one or more mantle plumes. Whilst the plume(s) may have been characterised by an ocean island basalt-type component, the chemical signature of this component has everywhere been heavily overprinted by heterogeneous lithospheric mantle. Primary mafic melts have fractionated over a wide range of crustal pressures to generate suites resulting in trachytic (silica-saturated and-undersaturated) and phonolitic residua. Various Neogene trachytic and phonolitic flood sequences may alternatively have resulted from volatile-induced partial melting of underplated mafic rocks. High-level partial melting has generated peralkaline rhyolites in the south–central rift. Kenyan magmatism may, at some future stage, show an increasing plume signature, perhaps associated ultimately with continental break-up.

The Mont Saint Hilaire plutonic complex: occurrence of excess 40Ar and short intrusion history

1986 ◽  
Vol 23 (7) ◽  
pp. 948-958 ◽  
Author(s):  
Lisa A. Gilbert ◽  
K. A. Foland
Keyword(s):  
Heating Temperature ◽  
Sedimentary Rocks ◽  
Time Interval ◽  
Crustal Assimilation ◽  
Crustal Rocks ◽  
Short Time Span ◽  
Plutonic Complex ◽  
Widespread Phenomenon ◽  
Short Time ◽  
Western Half

Mont Saint Hilaire is an approximately 10 km2 alkaline plutonic complex in the Monteregian petrographic province of Quebec. The complex consists of an older, western half of alkali gabbros and an eastern portion of nepheline syenites and magmatic breccias. The intrusives were emplaced at depths of no more than a few kilometres into Paleozoic sedimentary rocks through the underlying Grenville basement. 40Ar/39Ar analyses of amphibole yield complex age spectra in which the apparent ages decrease with increasing heating temperature. Conventional K–Ar analyses of amphibole, pyroxene, and feldspar yield anomalously old dates. These data indicate the presence of small yet significant amounts (up to 8 × 10−11 mol/g) of excess 40Ar. The quantities of excess argon are variable between rocks and minerals from the same rock. In contrast, biotites yield concordant plateaus and consistent ages ranging only from 124.1 to 124.6 Ma. These data define the age of the complex (124.4 ± 1.2 Ma) and imply a short time span of emplacement of about 0.5 Ma or less. The restricted time interval suggests the various lithologies are cogenetic. The nature of the amphibole 40Ar/39Ar spectra indicates that excess 40Ar was acquired after crystallization. The 40Ar could have been present in the initial magma either from crustal assimilation or from a mantle source. Alternatively, it could have been derived from outgassing of older crustal rocks. The occurrence of excess 40Ar in epizonal plutons may be a more widespread phenomenon than commonly recognized.

New Cryogenian, Neoproterozoic, and middle Paleozoic U–Pb zircon ages from the Caledonia terrane, southern New Brunswick, Canada: better constrained but more complex volcanic stratigraphy

2020 ◽  
Vol 56 ◽  
pp. 163-187
Author(s):  
Sandra M. Barr ◽  
Susan C. Johnson ◽  
Greg R. Dunning ◽  
Chris E. White ◽  
Adrian F. Park ◽  
...  
Keyword(s):  
New Brunswick ◽  
Volcanic Rocks ◽  
Long Beach ◽  
Volcanic Stratigraphy ◽  
Short Time Span ◽  
Lake Formation ◽  
Middle Paleozoic ◽  
Minimum Age ◽  
Southwestern Usa ◽  
Short Time

New U–Pb zircon ages from volcanic, plutonic, and sedimentary units in the Avalonian Caledonia terrane of southern New Brunswick provide better timing constraints in this geologically complex area. Previous ca. 620 Ma ages from the Broad River Group are now corroborated by additional dates from felsic tuff in the Gordon Falls Formation and rhyolite in the former Fairfield (now East Branch Black River) Formation of 620 ± 5 Ma and 622 ± 1.9 Ma, respectively. Combined with ages ranging from ca. 625 Ma to 615 Ma from crosscutting plutons, the data suggest that the minimum age of the Broad River Group is about 615 Ma. A quartzfeldspar porphyry dyke in mafic volcanic rocks of the previously undated Long Beach Formation yielded an igneous crystallization age of 685 ± 10 Ma, the oldest unit yet dated in the Caledonia terrane but similar in age to porphyry in the Stirling belt in the Avalonian Mira terrane of Nova Scotia. The age of the Coldbrook Group was constrained previously by U–Pb (zircon) ages of volcanic rocks between 560 and 550 Ma as well as by similar ages from comagmatic plutons. Five additional samples from both volcanic and plutonic units lie in the same range of 560–550 Ma, including errors, demonstrating that the Coldbrook Group and related plutons formed in less than 10 million years. Such a large volume of mainly felsic magma erupted and emplaced in a short time span suggests a “supereruption/supervolcano” environment such as the late Cenozoic southwestern USA but not yet recognized at ca. 560–550 Ma elsewhere in Avalonia. Two units yielded Paleozoic ages: felsite of the Bloomsbury Mountain Formation with a zircon population at 427 ± 9 Ma, indicating a Silurian maximum emplacement age, and dacite of the Grassy Lake Formation with several zircon grains at 382.8 ± 8.3 Ma, indicating a maximum age of middle Devonian, the first rocks of this age to be identified in the Caledonia terrane.

scholarly journals ‘Scrupulous and Timid Conformism’: Ireland and the Reception of the Liturgical Changes of Vatican II

Religions ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 545
Author(s):  
Gary Carville
Keyword(s):  
Vatican Ii ◽  
Time Span ◽  
Second Vatican Council ◽  
The People ◽  
Vatican Council ◽  
Short Time Span ◽  
Irish Catholics ◽  
Catholic Tradition ◽  
Short Time ◽  
The Church

The Second Vatican Council and, in particular, its Constitution on the Sacred Liturgy, changed much in the daily life of the Church. In Ireland, a country steeped in the Catholic tradition but largely peripheral to the theological debates that shaped Vatican II, the changes to liturgy and devotional practice were implemented dutifully over a relatively short time span and without significant upset. But did the hierarchical manner of their reception, like that of the Council itself, mean that Irish Catholics did not receive the changes in a way that deepened their spirituality? And was the popular religious memory of the people lost through a neglect of liturgical piety and its place in the interior life, alongside what the Council sought to achieve? In this essay, Dr Gary Carville will examine the background to the liturgical changes at Vatican II, the contribution to their formulation and implementation by leaders of the Church in Ireland, the experiences of Irish Catholic communities in the reception process, and the ongoing need for a liturgical formation that brings theology, memory, and practice into greater dialogue.

scholarly journals A 20-Year Follow-Up Study of Objectively Measured Physical Activity

2021 ◽  
Vol 18 (6) ◽  
pp. 3076
Author(s):  
Anders Raustorp ◽  
Andreas Fröberg
Keyword(s):  
Physical Activity ◽  
Early Adolescence ◽  
Total Sample ◽  
Short Time Span ◽  
Steps Per Day ◽  
Objectively Measured ◽  
Short Time ◽  
Objectively Measured Physical Activity

Background: The objectives of this study were to explore the effect of time, long-term tracking, and the proportion of objectively measured physical activity (PA) from early adolescence to the mid-thirties. Methods: PA was measured as mean steps per day (SPD) with pedometers during 2000 (T1), 2003 (T2), 2005 (T3), 2010 (T4), 2016 (T5) and 2020 (T6). Data from 64 participants (n = 32 males) were analysed from their early adolescence (T1) to their mid-thirties (T6). Results: SPD decreased in the total sample and among males and females (all, p < 0.001). Males took more mean SPD than females during T1 (p = 0.002), whereas females took more mean SPD during T2 (p = 0.009) and T6 (p = 0.008). Males’ mean SPD tracked between T1 and T2 (p = 0.021), T2 and T3 (p = 0.030), T3 and T4 (p = 0.015) and T4 and T5 (p = 0.003). Females’ mean SPD tracked between T3 and T4 (p = 0.024) and T5 and T6 (p < 0.001). In the total sample, more mean SPD were found on weekdays compared to weekend days at T3 (p = 0.017) and T5 (p < 0.001). Conclusions: SPD decreased between T1 and T6. Mean SPD tracked low-to-moderate in the short time span. From late adolescence to the mid-thirties, more mean SPD was observed during weekdays compared to weekend days.

Early Cretaceous crust–mantle interaction linked to rollback of the Palaeo-Pacific flat-subducting slab: constraints from the intermediate–felsic volcanic rocks of the northern Great Xing’an Range, NE China

2021 ◽  
pp. 1-22
Author(s):  
Jia-Hao Jing ◽  
Hao Yang ◽  
Wen-Chun Ge ◽  
Yu Dong ◽  
Zheng Ji ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Ne China ◽  
Asthenospheric Mantle ◽  
High K ◽  
Wide Range ◽  
Great Xing’An Range ◽  
Subducting Slab

Abstract Late Mesozoic igneous rocks are important for deciphering the Mesozoic tectonic setting of NE China. In this paper, we present whole-rock geochemical data, zircon U–Pb ages and Lu–Hf isotope data for Early Cretaceous volcanic rocks from the Tulihe area of the northern Great Xing’an Range (GXR), with the aim of evaluating the petrogenesis and genetic relationships of these rocks, inferring crust–mantle interactions and better constraining extension-related geodynamic processes in the GXR. Zircon U–Pb ages indicate that the rhyolites and trachytic volcanic rocks formed during late Early Cretaceous time (c. 130–126 Ma). Geochemically, the highly fractionated I-type rhyolites exhibit high-K calc-alkaline, metaluminous to weakly peraluminous characteristics. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depleted in high-field-strength elements (HFSEs), with their magmatic zircons ϵHf(t) values ranging from +4.1 to +9.0. These features suggest that the rhyolites were derived from the partial melting of a dominantly juvenile, K-rich basaltic lower crust. The trachytic volcanic rocks are high-K calc-alkaline series and exhibit metaluminous characteristics. They have a wide range of zircon ϵHf(t) values (−17.8 to +12.9), indicating that these trachytic volcanic rocks originated from a dominantly lithospheric-mantle source with the involvement of asthenospheric mantle materials, and subsequently underwent extensive assimilation and fractional crystallization processes. Combining our results and the spatiotemporal migration of the late Early Cretaceous magmatic events, we propose that intense Early Cretaceous crust–mantle interaction took place within the northern GXR, and possibly the whole of NE China, and that it was related to the upwelling of asthenospheric mantle induced by rollback of the Palaeo-Pacific flat-subducting slab.

Geochemistry and original nature of Precambrian khondalites in the Eastern Ghats, Orissa: a discussion

1991 ◽  
Vol 82 (1) ◽  
pp. 87-88 ◽  
Author(s):  
J. K. Nanda ◽  
U. C. Pati
Keyword(s):  
Major Part ◽  
Eastern Ghats ◽  
Geochemical Data ◽  
Mobile Belt ◽  
Indian Peninsula ◽  
Eastern Ghats Mobile Belt

While congratulating the authors for the wealth of geochemical data on a very important Precambrian lithological assemblage of India, known commonly as khondalites, which constitute a major part of the Eastern Ghats mobile belt bordering the eastern fringes of the Indian Peninsula, we have a few comments to offer on the hypothesis propounded by the authors (Dash et al. 1987).

Three stages of arc migration in the Carboniferous-Triassic in northern Qiangtang, central Tibet, China: Ridge subduction and asynchronous slab rollback of the Jinsha Paleotethys

2021 ◽  
Author(s):  
Yin Liu ◽  
Wenjiao Xiao ◽  
Brian F. Windley ◽  
Kefa Zhou ◽  
Rongshe Li ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Volcanic Rocks ◽  
Late Triassic ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
Ridge Subduction ◽  
Temporal Relationships ◽  
Slab Rollback ◽  
Geodynamic Processes ◽  
Central Tibet

Carboniferous-Triassic magmatism in northern Qiangtang, central Tibet, China, played a key role in the evolution of the Tibetan Plateau yet remains a subject of intense debate. New geochronological and geochemical data from adakitic, Nb-enriched, and normal arc magmatic rocks, integrated with results from previous studies, enable us to determine the Carboniferous-Triassic (312−205 Ma), arc-related, plutonic-volcanic rocks in northern Qiangtang. Spatial-temporal relationships reveal three periods of younging including southward (312−252 Ma), rapid northward (249−237 Ma), and normal northward (234−205 Ma) migrations that correspond to distinct slab geodynamic processes including continentward slab shallowing, rapid trenchward slab rollback, and normal trenchward rollback of the Jinsha Paleotethys rather than the Longmuco-Shuanghu Paleotethys, respectively. Moreover, varying degrees of coexistence of adakites/High-Mg andesites (HMAs)/Nb-enriched basalt-andesites (NEBs) and intraplate basalts in the above-mentioned stages is consistent with the magmatic effects of slab window triggered by ridge subduction, which probably started since the Late Carboniferous and continued into the Late Triassic. The Carboniferous-Triassic multiple magmatic migrations and ridge-subduction scenarios provide new insight into the geodynamic processes of the Jinsha Paleotethys and the growth mechanism of the Tibetan Plateau.

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