Emplacement and Evolution of The Nlonako Ring Complex in The Southern Domain of The Cameroon Line

The Cameroon Line (CL) appears as a SW-NE straight line characterized by an intense volcanic activity of basaltic composition with alkaline plutonic complexes, including the Nlonako ring complex (NRC) emplaced in the southern part of the CL. Many hypotheses have been proposed to explain the origin and petrogenetic evolution of these complexes but very few of these works focus or attempt to propose their structural emplacement model, though structural data recorded by them can permit such studies. Using petrographic, structural data and space images, we propose an emplacement model of the NRC and other ring complexes along the CL. The NRC is a ring complex of 10 km diameter slightly elongated in the NNE-SSW direction mainly composed of plutonites among which syenites, gabbros, diorites and biotite-amphibole granites, and a few volcanites made up of rhyolites and basalts occurring as veins or boulders in syenites. This complex was emplaced as sill intrusive body within Pan-African k-feldspars megacrysts granites and gneiss host rocks under fractures control. These fractures developed as result of stress release consecutive to the readjustment of the crust during and after the late Cretaceous general extension, therefore facilitating the upwelling of the mantle plume and the generation of magma that vertically uplift. The progressive magmatic pressure decreases after the NRC emplacement in addition to conjugated fractures networks developed at superficial crust level finally lead to the cauldron subsidence of the NRC summit. This subsidence was facilitated by the downward sliding of rocks along the WNW-ESE fault, finally leading to the formation of a caldera at the summit of the NRC. The NRC and other anorogenic complexes aligned along the CL are located in a tension gash form by the Cretaceous sinistral activation of the N70E Adamawa fault. This left lateral wrench movements developed a tension gash, overprinted on pre-existing transcurrent mega-faults with as result, the development of "en-echelon" fractures. Stress release during the late Cretaceous general extensional phase probably accelerated the uplift of magmas and emplacement of ring complexes along the "en-echelon" regional fractures in an extensional setting during the Tertiary (60 - 30 Ma). This therefore explained the alignment of anorogenic complexes along the N30E CL corridor that are highly correlated to lineament networks and Pan-African megafaults

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Architecture of the crust and lithosphere beneath the Semail Ophiolite from ambient noise tomography and receiver functions: insights on the tectonic evolution of eastern Arabia

10.5194/egusphere-egu21-9890 ◽

2021 ◽

Author(s):

Christian Weidle ◽

Lars Wiesenberg ◽

Andreas Scharf ◽

Philippe Agard ◽

Amr El-Sharkawy ◽

...

Keyword(s):

Late Cretaceous ◽

Ambient Noise ◽

Function Analysis ◽

Oceanic Lithosphere ◽

Receiver Functions ◽

Crustal Thickening ◽

Ambient Noise Tomography ◽

First Order ◽

Pan African ◽

Semail Ophiolite

The Semail Ophiolite is the world&#8216;s largest and best exposed oceanic lithosphere on land and a primary reference site for studies of creation of oceanic lithosphere, initiation of subduction, geodynamic models of obduction, subduction and exhumation of continental rocks during obduction. Five decades of geological mapping, structural, petrological and geochronological research provide a robust understanding of the geodynamic evolution of the shallow continental crust in northern Oman and how the late Cretaceous obduction process largely shaped the present-day landscape. Yet, prior to obduction, other first-order tectonic processes have left their imprint in the lithosphere, in particular the Neoproterozoic accretion of Arabia and Permian breakup of Pangea. Due to the scarcity of deep structure imaging below the ophiolite, the presence and significance of inherited structures for the obduction process remain unclear.We discuss a new 3-D anisotropic shear wave velocity model of the crust below northern Oman derived from ambient noise tomography and Receiver Function analysis which allows to resolve some key unknowns in geodynamics of eastern Arabia: (1) Several NE-trending structural boundaries in the middle and lower crust are attributed to the Pan-African orogeny and align with first-order lateral changes in surface geology and topography. (2) The well-known Semail Gap Fault Zone is an upper crustal feature whereas two other deep crustal faults are newly identified. (3) Permian rifting occurred on both eastern and northern margins but large-scale mafic intrusions and/or underplating occurred only in the east. (4) While obduction is inherently lithospheric by nature, its effects are mostly observed at shallow crustal depths, and lateral variations in its geometry and dynamics can be explained by effects on pre-existing Pan-African and Permian structures. (5) Continental subduction and exhumation during late Cretaceous obduction may be the cause for crustal thickening below today&#8216;s topography. (6) Thinning of the continental lithosphere below northern Oman in late Eocene times &#8211; possibly related to thermal effects of the incipient Afar mantle plume - provides a plausible mechanism for the broad emergence of the Oman Mountains and in particular the Jabal Akhdar Dome. Uplift might thus be unrelated to compressional tectonics during Arabia-Eurasia convergence as previously believed.

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K-Ar ages of a Late Cretaceous granitic ring complex around southern Lake Biwa. Southwest Japan. Cooling history of a huge cauldron.

The Journal of the Geological Society of Japan ◽

10.5575/geosoc.99.975 ◽

1993 ◽

Vol 99 (12) ◽

pp. 975-990 ◽

Cited By ~ 17

Author(s):

Yoshihiro Sawada ◽

Tetsumaru Itaya

Keyword(s):

Late Cretaceous ◽

Lake Biwa ◽

Southwest Japan ◽

Cooling History ◽

Ring Complex ◽

History Of

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From arc evolution to arc-continent collision: Late Cretaceous–middle Eocene geology of the Eastern Pontides, northeastern Turkey

Geological Society of America Bulletin ◽

10.1130/b31913.1 ◽

2019 ◽

Vol 131 (11-12) ◽

pp. 1889-1906 ◽

Cited By ~ 7

Author(s):

Özgür Kandemir ◽

Kenan Akbayram ◽

Mehmet Çobankaya ◽

Fatih Kanar ◽

Şükrü Pehlivan ◽

...

Keyword(s):

Late Cretaceous ◽

Middle Eocene ◽

Structural Data ◽

Massive Sulfide ◽

Arc Volcanism ◽

Eastern Pontides ◽

The North ◽

Fold And Thrust Belt ◽

Volcaniclastic Rocks ◽

Back Arc

Abstract The Eastern Pontide Arc, a major fossil submarine arc of the world, was formed by northward subduction of the northern Neo-Tethys lithosphere under the Eurasian margin. The arc’s volcano-sedimentary sequence and its cover contain abundant fossils. Our new systematical paleontological and structural data suggest the Late Cretaceous arc volcanism was initiated at early-middle Turonian and continued uninterruptedly until the end of the early Maastrichtian, in the northern part of the Eastern Pontides. We measured ∼5500-m-thick arc deposits, suggesting a deposition rate of ∼220 m Ma–1 in ∼25 m.y. We have also defined four different chemical volcanic episodes: (1) an early-middle Turonian–Santonian mafic-intermediate episode, (2) a Santonian acidic episode; when the main volcanic centers were formed as huge acidic domes-calderas comprising the volcanogenic massive sulfide ores, (3) a late Santonian–late Campanian mafic-intermediate episode, and (4) a late Campanian–early Maastrichtian acidic episode. The volcaniclastic rocks were deposited in a deepwater extensional basin until the late Campanian. Between late Campanian and early Maastrichtian, intra-arc extension resulted in opening of back-arc in the north, while the southern part of the arc remained active and uplifted. The back-arc basin was most probably connected to the Eastern Black Sea Basin. In the back-arc basin, early Maastrichtian volcano-sedimentary arc sequence was transitionally overlain by pelagic sediments until late Danian suggesting continuous deep-marine conditions. However, the subsidence of the uplifted-arc-region did not occur until late Maastrichtian. We have documented a Selandian–early Thanetian (57–60 Ma) regional hiatus defining the closure age of the İzmir-Ankara-Erzincan Ocean along the Eastern Pontides. Between late Thanetian and late Lutetian synorogenic turbidites and postcollisional volcanics were deposited. The Eastern Pontide fold-and-thrust belt started to form at early Eocene (ca. 55 Ma) and thrusting continued in the post-Lutetian times.

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A MOLECULAR RECOGNITION MODEL FOR ENANTIOSELECTIVITY AND AUTOINDUCTION IN CYANOHYDRIN FORMATION CATALYZED BY CYCLO[(S)-HIS-(S)-PHE]

Journal of Theoretical and Computational Chemistry ◽

10.1142/s0219633610005803 ◽

2010 ◽

Vol 09 (02) ◽

pp. 495-510

Author(s):

JIAHAI WANG

Keyword(s):

Molecular Recognition ◽

Hydrogen Bonds ◽

Theoretical Calculation ◽

Am1 Method ◽

Cyanide Ion ◽

Recognition Mechanism ◽

Ring Complex ◽

Ring Complexes ◽

Experimental Findings ◽

Intramolecular Hydrogen

A molecular recognition mechanism based on dimeric model for cyclic dipeptide Cyclo[(S)-His-(S)-Phe] (abridged CHP) catalyzed autoinduction is proposed according to the inference of previous experimental findings, which is supported by theoretical calculation with Oniom(B3LYP/3-21G*:AM1) method. The most unstable CHP dimer whose intermolecular hydrogen bonds are immensely lessened by two intramolecular hydrogen bonds is defined as the highest active component (IIa) existing in solid among the three possible dimers (Ia, IIa, and IIb). The carbonyl group of benzaldehyde coordinates to CHP dimer (IIa) by a hydrogen bond with Phe–NαH rather than His–NαH and HCN interacted with the imidazole moiety of His residue to form cyanide ion. In view of the theoretical calculation and experimental results, the structures of the nine-ring complexes derived from interaction between catalytic active dimer CHP(IIa) and cyanohydrins were postulated to explain the enantioselective autoinduction: The structure of no nitrile involved six-ring complex derived from interaction between catalytic active dimer CHP(IIa) and cyanohydrins were postulated to explain the elimination of enantioselective autoinduction.

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γ-Tubulin ring complexes regulate microtubule plus end dynamics

The Journal of Cell Biology ◽

10.1083/jcb.200905060 ◽

2009 ◽

Vol 187 (3) ◽

pp. 327-334 ◽

Cited By ~ 42

Author(s):

Anaïs Bouissou ◽

Christel Vérollet ◽

Aureliana Sousa ◽

Paula Sampaio ◽

Michel Wright ◽

...

Keyword(s):

Drosophila Melanogaster ◽

Rna Interference ◽

Live Imaging ◽

S2 Cells ◽

Imaging Analysis ◽

Mitotic Progression ◽

Small Complex ◽

Drosophila S2 Cells ◽

Ring Complex ◽

Ring Complexes

γ-Tubulin is critical for the initiation and regulation of microtubule (MT) assembly. In Drosophila melanogaster, it acts within two main complexes: the γ-tubulin small complex (γ-TuSC) and the γ-tubulin ring complex (γ-TuRC). Proteins specific of the γ-TuRC, although nonessential for viability, are required for efficient mitotic progression. Until now, their role during interphase remained poorly understood. Using RNA interference in Drosophila S2 cells, we show that the γ-TuRC is not critical for overall MT organization. However, depletion of any component of this complex results in an increase of MT dynamics. Combined immunofluorescence and live imaging analysis allows us to reveal that the γ-TuRC localizes along interphase MTs and that distal γ-tubulin spots match with sites of pause or rescue events. We propose that, in addition to its role in nucleation, the γ-TuRC associated to MTs may regulate their dynamics by limiting catastrophes.

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The early magmatic chronology of Fuerteventura, Canary Islands

Geological Magazine ◽

10.1017/s0016756800034762 ◽

1986 ◽

Vol 123 (3) ◽

pp. 287-298 ◽

Cited By ~ 87

Author(s):

M. J. Le Bas ◽

D. C. Rex ◽

C. J. Stillman

Keyword(s):

Canary Islands ◽

Late Cretaceous ◽

Middle Miocene ◽

Early Miocene ◽

Volcanic History ◽

Early Tertiary ◽

Ring Complex ◽

High Level

AbstractEight new K-Ar determinations are presented which, together with field relations and previous studies, are used to construct a chronology of the volcanic build-up of Fuerteventura. The earliest island-building volcanics are late Cretaceous to early Tertiary alkaline basaltic volcaniclastic sediments, and these may be correlated with the early gabbro/pyroxenite intrusions which were probably subvolcanic to the early edifice. This was followed by a carbonatitic subvolcanic complex then by two later high-level gabbro/pyroxenite plutons, the latter being early Miocene or older. The emplacement of a subsequent middle Miocene gabbro/syenite ring complex caused widespread resetting of the Ar contents of the earlier rocks, but nevertheless consideration of the mineralogy of the rocks in conjunction with the field relations enables the long volcanic history (c. 80 Ma) to be reconstructed.

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Origin of Iforas alkaline ring complexes in the Pan-African context

Journal of African Earth Sciences (1983) ◽

10.1016/0899-5362(85)90062-4 ◽

1985 ◽

Vol 3 (1-2) ◽

pp. 276

Keyword(s):

Pan African ◽

African Context ◽

Ring Complexes

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Towards the Stepwise Assembly of Molecular Borromean Rings. A Donor-Acceptor Ring-in-Ring Complex

Journal of the Mexican Chemical Society ◽

10.29356/jmcs.v53i3.995 ◽

2019 ◽

Vol 53 (3) ◽

Author(s):

Ross S. Forgan ◽

Jason M. Spruell ◽

John-Carl Olsen ◽

Charlotte L. Stern ◽

J. Fraser Stoddart

Keyword(s):

Borromean Rings ◽

Stepwise Manner ◽

Ring Complex ◽

Donor Acceptor ◽

Ring Complexes ◽

Stepwise Assembly

The assembly of molecular Borromean Rings from constitutionally independent rings in a stepwise manner depends on the preparation of robust “ring-in-ring” complexes. The π-electron rich macrocycle bis-1,5-dinaphtho[50]crown-14 (1) is shown to form a donor-acceptor ring-in-ring complex with the π-electron poor cyclophane cyclobis(paraquat-4,4'-biphenylene) (24+) in solution. In the crystal superstructure of [1⊂2]·4PF6, CH···O interactions between the polyether loops of 1 and the bipyridinium units of 24+ could disfavor the threading of dialkylammonium components of a third ring.

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