Bimodal Complex Research Articles

Anorogenic plutonism in the West Congo Belt of the Democratic Republic of Congo further supports early Tonian continental rifting in the Congo – São Francisco palaeocontinent

Our paper presents an updated geological map and simplified lithostratigraphy of the West Congo Belt (WCB) in the Democratic Republic of Congo. The WCB holds a key position for understanding the construction of Gondwana and constitutes a larger orogenic system along with its Brazilian counterpart (i.e. Araçuaí orogen). Our current contribution focuses on a newly found and mapped early Tonian small-sized (6 × 4 km) plutonic body (so-called “Shinkakasa intrusive complex”) located in the westernmost amphibolite facies tectono-metamorphic domain of the West Congo fold-and-thrust belt. The complex is hosted by the Kimeza gneissic basement. Our fieldwork, samples and a new geological map provide a solid and updated geological background for more in-depth future work and proves essential for reinterpreting the broader tectonic framework. Our findings show that the Shinkakasa complex comprises felsic, intermediate and mafic to ultramafic rocks displaying mixing-mingling features and well-preserved igneous textures with only limited Panafrican metamorphic and tectonic overprint. According to previously published zircon U–Pb (SHRIMP) data, the Shinkakasa magmatism lasted from 911 Ma to 869 Ma and the complex was hosted by the 2069 Ma Kimeza gneissic basement.We compare the Shinkakasa complex with other small-sized intrusive complexes of the WCB, emplaced in a similar geological setting, such as the contemporaneous Mayumba bimodal complex of southwestern Gabon. This comparison is extended across the Atlantic Ocean to the recently studied early Tonian Salto da Divisa complex of southeastern Brazil. In the African counterpart we correlate the plutonic complexes to the early Tonian eastward arcuate (sub)volcanic bimodal successions (Seke-Banza Group of the DRC) largely exposed along trend of the orogen over a length of ca. 550 km in the greenschist facies domain of the WCB. Finally, we give an updated account of the early Tonian emplacement ages and lithostratigraphic terminology of the multiple bodies constituting this arcuate structure. Our data show that i) the vast majority of the anorogenic magmatism testifying for the aborted early Tonian continental rifting of the Congo - Sao Francisco palaeocontinent is exposed in the African counterpart, and ii) the extent of the (sub)volcanic successions largely predominates compared to the small-sized intrusive bodies such as the Shinkakasa complex.

Neoarchean high-Mg basalt and rhyolite bimodal complex in the Yinshan Block, North China Craton: Petrogenesis and tectonic implications

Plate tectonics plays an important role in Earth’s evolution, but it is a difficult and controversial issue to trace the operation of plate tectonics in the Archean. Calc-alkaline magmas are a diagnostic feature of modern subduction-related magmatism and thus identification of Archean subduction-related calc-alkaline magmas is crucial for understanding when Archean plate tectonics operated. Here we present zircon U-Pb, whole-rock geochemical and Sr-Nd isotopic data for a metamorphosed Neoarchean calc-alkaline bimodal volcanic complex from the Yinshan Block, the North China Craton. Zircon U-Pb dating results indicate that these meta-volcanic rocks were erupted in the late Neoarchean (∼2570 Ma). Its mafic unit is characterized by high contents of K2O (0.68–4.20 wt%), MgO (Mg# = 62.0-73.4), Cr (332-904 ppm), Ni (105-269 ppm), and is enriched in light rare earth elements (REEs), but depleted in heavy REEs and Nb, Ta and Ti. These geochemical features are similar to those of high-Mg basalts in the Phanerozoic arc setting. They have positive εNd(t) values (+1.3 to + 2.4), indicating that they were derived from the depleted mantle wedge. The felsic unit has variable K2O content (1.42–4.95 wt%) and K2O/Na2O ratios of 0.23–1.36 with positive εNd(t) values (+0.7 to + 3.1). They show characteristics of modern adakites with high Sr/Y and LaN/YbN ratios, suggesting that they were generated by partial melting of the thickened juvenile mafic lower crust. We conclude that the studied Neeoarchean bimodal meta-volcanic complex was formed during subduction-zone retreating and root delamination in a Neoarchean arc. Our results further indicate that plate tectonics had already operated in the Neoarchean in the Yinshan Block.

Analysis on bimodal complex permeability spectrum of a noise suppression sheet and single constituent flakes

In recent years, highly integrated active components inside small mobile communication devices have led to serious electromagnetic interference problems. The countermeasure to this problem is covering a noise source with a noise suppression sheet (NSS) which is composed of ferromagnetic flakes and polymers. The NSS absorbs effectively electromagnetic waves due to a large imaginary part of relative permeability μr″ at the specific frequency region. This function is attributed to the bimodal μr″ spectrum of NSS, but its physical origin has not been revealed so far. In this study, the bimodal μr″ spectrum of NSS has been analyzed and its physical mechanism has been discussed. The μr″ spectrum of a constituent single magnetic flake was measured by using a newly developed high-sensitivity permeability measurement system, which showed a bimodal spectrum quite similar to that of NSS. This fact indicates that the physical origin of the bimodal μr″ spectrum is attributed to the magnetization dynamics of each single constituent flake. After measuring the μr″ spectra of single flakes with various materials, such as Fe, Fe-Al, Fe-Co-V, and Fe-Si-Al alloys, these bimodal μr″ spectra were quantitatively explained by the magnetization dynamics of the flux closure states inside the flake. The magnetic domain structure of a single flake was observed by a micro-beam X-ray magnetic circular dichroism microscopy. The result confirmed that the segmented magnetic domains form the local flux closure states inside the flake.

The Ludicovian of the Raahe–Ladoga Zone of the Fennoscandian Shield (Isotope-Geochemical Composition and Geodynamic Nature)

Abstract —In the northern Ladoga area, the age of the Sortavala Group rocks in the southeast of the Raahe–Ladoga zone of junction of the epi-Archean Fenno-Karelian Craton and the Paleoproterozoic Svecofennian province, their relationship with dome granitoids, the age of the provenances, and the time of metamorphic processes were estimated. The study was focused on the Nd isotope composition of rocks, the geochemical and isotope-geochronological parameters of zircon from the granite-gneisses of the Kirjavalakhti dome, the basal graywackes of the lower unit and the trachytes of the middle unit of the Sortavala Group, and the plagio- and diorite-porphyry dikes cutting the volcanosedimentary units of this group. The new isotope-geochemical data show a Neoarchean age of the granitoids of the Kirjavalakhti dome (2695 ± 13 Ma) and their juvenile nature (εNd(T) = +1.5). The granitoids underwent tectonometamorphic transformations (rheomorphism) in the Paleoproterozoic (Sumian) (2.50–2.45 Ga), which are recorded in the U–Th–Pb isotope system of the rims of the ancient cores of zircon crystals. The volcanosedimentary complex of the Sortavala Group formed on the heterogeneous polychronous (3.10–2.46 Ga) continental crust of the epi-Archean Fenno-Karelian Craton. With regard to the errors in determination of the age of clastic zircon, the minimum concordant U–Th–Pb ages of 1940–1990 Ma of detrital zircon from volcanomictic graywackes of the Pitkyaranta Formation can be taken as the upper age bound of terrigenous rocks, which agrees with the maximum age of the Sortavala Group rocks estimated from the U–Th–Pb (SIMS) age of 1922 ± 11 Ma of the Tervaoya diorites (Matrenichev et al., 2006). According to the proposed new tectonic model, the accumulation of the volcanosedimentary complex of the Sortavala Group, its metamorphism, erosion, and overlapping by the Ladoga Group turbidites had already occurred in the pericratonic part of the epi-Archean Fenno-Karelian Craton by the time of the Svecofennian continent–island arc collision, subduction, and formation of bimodal volcanoplutonic complexes of the young Pyhäsalmi island arcs and felsic volcanics of the Savo schist belt (1920–1890 Ma).

Slurry Erosion–Corrosion of Bimodal Complex Concentrated Alloy Composite Cladding

Herein, bimodal‐reinforced AlCoCrFeNi complex concentrated alloy composite cladding on stainless steel 316L substrate using microwave hybrid processing is synthesized. Detailed microstructural analysis of the claddings shows the presence of cellular structure A2 (disordered BCC) with intermetallics (B2 (ordered BCC) and σ phases) at the intercellular regions. The presence of Cr23C6 is also observed for the reinforced claddings due to the dissociation of the SiC particles. The bimodal‐reinforced cladding shows the highest hardness (in excess of 800 HV) and fracture toughness (≈12 MPa√m), followed by micro‐ and nanocomposite claddings. Under slurry erosion condition, the bimodal composite cladding exhibits 10 times better erosion resistance than stainless steel 316L and nonreinforced cladding (1.5–2 times), respectively, at oblique angle followed by nano‐ and microreinforced unimodal counterparts. The outstanding performance of the bimodal composite cladding under both test conditions is related to higher hardness, fracture toughness, and resistance to plastic deformation. The detailed analysis of the eroded samples shows microcutting and ploughing as a dominant mechanism at an oblique angle while platelets, cracks, and microindents being the contributing factors for erosion at the normal impact angle.

The Early Cambrian bimodal magmatism in the northeastern Siberian Craton

We present new data on geochemistry, isotopic geochemistry, and geochronology of the Early Cambrian igneous rocks of the northeastern Siberian Craton (Kharaulakh anticlinorium, contact between the Siberian Platform and the West Verkhoyansk sector of the Verkhoyansk fold-and-thrust belt united into an Early Cambrian bimodal complex. This complex comprises trachyrhyolites forming pebbles in conglomerates near the base of the Cambrian succession, overlying trachybasalts, and mafic sills and dikes cutting Neoproterozoic strata. According to chemical composition, the felsic rocks are high-alkali rhyolites and correspond to A-type granites. The high contents of Ta, Nb, Hf, Tb, and Zr in these rocks suggest the presence of enriched mantle material in their magmatic sources. The mafic volcanics are high-Ti trachybasalts and trachydolerites with similar geochemical characteristics corresponding to alkali basalts or OIB. The high (Tb/Yb)PM ratios in these volcanics evidence that their magmatic source was the garnet peridotite mantle located at depths more than 90 km and characterized by a low degree of melting. However, the rhyolites, trachybasalts, and trachydolerites show high positive εNd(T) values (4.2–4.7, 7.5–8.9, and 7.2–8.2, respectively) indicating a depleted mantle source and no crustal contamination. The high (Nb/Yb)PM ratio points to the mixing of magmas from enriched and depleted mantle sources. Mafic magmas might have been generated from a heterogeneous source or interacted with the depleted mantle before intrusion. Both the felsic and the mafic rocks formed in within-plate environments. U–Pb zircon dating yielded concordant ages of 525.6 ± 3.9 and 537.0 ± 4.2 Ma, corresponding to the Early Cambrian age of the rhyolites. The date of 546.0 ± 7.7 Ma obtained for one sample points (with regard to the error) to the Late Vendian–Early Cambrian age. Thus, at the Vendian–Early Cambrian boundary, the northeastern Siberian Platform was subjected to continental rifting accompanied by bimodal magmatism of antidrome evolution. According to paleotectonic reconstructions, this part of the Siberian Craton might have been connected with the eastern margin of Laurentia in the Late Neoproterozoic (Late Riphean–Late Vendian), and continental rifting that started at the Vendian–Cambrian boundary led to their separation. The obtained isotope-geochronological data suggest that the studied bimodal complex began to form at the Vendian–Cambrian boundary and this process terminated no earlier than the end of the Terreneuvian (Tommotian), i.e., the complex formed during rifting for about 20 Myr.

Late proterozoic A-type granites of the chernorechenskii massif in the Yenisei ridge: New geochemical and geochronological data

The problems in estimation of the geochronologi� cal boundaries in the history of the breakup of the Rodinia Supercontinent are mostly far from their final solution. This is explained by the lack of precise dat� ings, which limits significantly the possibilities of age correlations for global geological processes. Because of this, the problem of geochemical specifics and dat� ing of Neoproterozoic granitoid complexes, i.e., the main components of the continental crust and indica� tors of geodynamic environments of key significance for reconstruction of events in the lithosphere evolu� tion, is still important. Recently new results on the geochemistry and geo� chronology of granitoids from the Yenisei Ridge formed under contrasting geotectonic environments were obtained (1). These crystalline massifs are located in the axial part of the Central cratonic block, mostly in the Tatarsko-Ishimbinskaya suture zone. In this relation, the western part of the Central block composed of rocks of the Garevka metamorphic com� plex (GMC), the oldest in Transangaria, is the least studied. It consists of a number of intrusive massifs located within the Yenisei regional suture zone (YRSZ), the large deformational metamorphic struc� ture of the lineament type separating the Central cra� tonic block and the Isaakovskii islandarc terrane (2). This zone is a continuation of the Baikal-Yenisei fault and located on the left side of the Yenisei River along the western margin of the Siberian Craton for more than 200 km at a width from 50 to 70 km. Because of the absence of reliable geochemical and geochrono� logical data, the problem of the age and tectonic set� ting of these intrusions is debatable. This is especially important for rocks of the Chernorechenskii massif occurring in the composition of the Posol'nenskii and Ayakhtinskii magmatic complexes of various age and origin (3). To resolve these contradictions, we obtained new data on the geochemistry, age, and nature of these granitoids formed under the environment of extension along the western margin of the Siberian Craton. The Chernorechenskii massif (CM) is located in the GMC, on the western flange of the YRSZ charac� terized by contrast metamorphism, intense foliation, and dynamic recrystallization of rocks (4). This massif occurs on the right side of the Yenisei River, in the Raz� gromnaya River basin, and is located in the same tec� tonic zone as small massifs of rapakivitype granites (5) and bimodal complex of granite and basic dykes (2). The intrusive body of a lenslike shape and an area of ≈140 km 2 occurs at large submeridional faults. With account for the geophysical data (3), it is suggested that the massif has subvertical dipping, a "platelike" shape, and tectonic contacts with host rocks. Three main stages with different thermodynamic regimes and values of geothermal gradients are distin� guished in the evolution of western areas of the YRSZ (6). At the first stage related to the Grenville orogeny (1050-850 Ma), zoned lowpressure metamorphic complexes with a gradient of dT/dH = 20-30°C/km typical of orogenesis were formed. At the second stage in the nappe zone, these rocks underwent Late Riph� ean (801-793 Ma) collisional metamorphism of mod� erate pressures with low dT/dH ≤ 10°С/km. The last stage was accompanied by synexhumation metamor� phism (785-776 Ma) with dT/dH ≤ 12°С/km reflect� ing the tectonic environments of rapid uplift in the dis� location-thrust zones of the crust. The final stages of the orogen evolution in the region include the forma� tion of the bimodal dyke belt with an age of 797- 785 Ma intruding gneiss and crystalline schist of the GMC (2). These events are controlled by the processes of extension along the western margin of the Siberian Craton and consistent with the beginning of breakup of the Rodinia Supercontinent. Later a number of rif� togenic troughs and grabens filled by Neoproterozoic

Correlation between compositions of ore and host rocks in volcanogenic massive sulfide deposits of the Southern Urals

The geology and typification of volcanogenic massive sulfide (VMS) deposits of the Southern Urals are considered. The mineralogical-geochemical types of these deposits correlate with the composition of the underlying igneous rocks: Ni-Co-Cu deposits correlatedwith serpentinites (Ivanovka type); (Co)-Cu deposits, with basalts (Dombarovka type); Cu-Zn deposits, with basalt-rhyolite and basalt-andesite-rhyolite complexes (Ural type); and Au-Ba-Pb-Zn-Cu deposits, with basalt-andesite-rhyolite complexes with predominance of andesitic and felsic volcanics (Baimak type). The Ural-type deposits are subdivided into three subtypes: I, underlain by basalts (Zn-Cu deposits); II, hosted in felsic volcanic rocks of bimodal complexes (Cu-Zn deposits); and III, hosted in felsic volcanic rocks of continuously differentiated complexes (Zn-Cu deposits with Ba, Pb, and As). The above types and subtypes bearing local names are compared with global types of VMS deposits (MAR, Cyprus, Noranda, and Kuroko), to which they are close but not identical.

Aptian bimodal volcanic associations and granitoids in the northern margin of the Amur microcontinent: Age, sources of material, and geodynamic environments

Data on the composition, age, and source of material of Aptian rocks composing a bimodal volcanic complex and related granitoids in the northern margin of the Amur microcontinent indicate that the granodiorites of the Talalinskii Massif and subalkaline granites of the Dzhiktandiunskii Massif crystallized at 117 ± 2 and 119 ± 2 Ma, respectively (40Ar/39Ar method), and their crystallization ages coincide with the age of volcanic rocks of the Gal’kinskii bimodal complex. These data make it possible to combine the rocks within a single volcano-plutonic association. Geochemical and isotopic-geochemical features of trachybasaltic andesites of the Gal’kinskii bimodal complex suggest that the parental melts were derived from such sources as PREMA (or DM) and an enriched source of the EMII type at a subordinate contribution of a crustal source. The parental melts of rhyolites of the Gal’kinskii Complex and granitoids of the Talalinskii and Dzhiktandinskii massifs were derived from crustal material with minor amounts of juvenile material. The bimodal volcanic association and related granitoids dated at 119–115 Ma were most likely formed in geodynamic environments implying the ascent of the asthenospheric mantle.

Geochronology–geochemistry of the Cida bimodal intrusive complex, central Emeishan large igneous province, southwest China: petrogenesis and plume–lithosphere interaction

The Cida complex is situated in the Panxi region and is predominantly composed of mafic-ultramafic and syenitic rock units; minor amounts of intermediate rocks occupy the contact zone between the two major rock types. The intermediate unit is mineralogically heterogeneous and typically exhibits a mottled structure. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb zircon dating shows that the mafic-ultramafic rocks and syenitic rocks formed almost coevally (243 ± 0.77 Ma and 240.5 ± 0.76 Ma, respectively). These ages may represent the end phase of the Emeishan large igneous province (ELIP) magmatism. Most of these three rock types possess alkaline and metaluminous affinities. The mafic-ultramafic, syenitic, and intermediate units have K2O + Na2O contents of 1.85–5.16, 6.55–10.46, and 9.55–11.54 wt.%, and SiO2 contents of 40.06–46.70, 61.74–68.54, and 51.57–54.13 wt.%, respectively. The mafic-ultramafic unit displays ocean-island basalt (OIB)-like primitive-mantle-normalized incompatible element patterns, coupled with low initial 87Sr/86Sr ratios (0.7048–0.7064), positive ϵNd(t) (0.32–2.23), and zircon ϵHf(t) (4.53–14.17) values, consistent with a mafic plume-head origin, whereas one exceptional sample with negative ϵNd(t) (–0.22) can be interpreted as due to the involvement of considerable amounts of enriched subcontinental lithospheric mantle. The relatively low (La/Yb) N ratios (3.40–7.69) reflect a spinel-facies lherzolite source. The syenitic unit is characterized by enrichment in large ion lithophile elements (e.g. Rb, K, Pb) and light rare earth elements (LREEs), relative to high field strength elements (e.g. Nb, Ta, P, Ti) and heavy rare earth elements (HREEs), respectively. These features, together with their metaluminous affinities, low SiO2 contents, lower initial 87Sr/86Sr ratios (0.7043), positive ϵNd(t) (0.18), and zircon ϵHf(t) (2.63–10.09) values as well as modelling of REEs, can be plausibly explained by crustal partial melting of juvenile basic materials beneath the Yangtze Block. In contrast, the field, petrographic observations, and geochemical signatures (e.g. the linear correlations between FeO* and MgO, K/Ba and Rb/Ba ratios) suggest that the intermediate unit may have resulted from magma mixing between the syenitic and basaltic magmas that in turn had evolved from a parental mafic-ultramafic liquid. Thus, the formation of the Cida complex can be attributed to the plume–lithosphere interaction plus partial melting of juvenile basic lower crust in response to heating of underplated plume-derived basaltic magma.

Multiple phases of the Neoproterozoic igneous activity in Quruqtagh of the northeastern Tarim Block, NW China: Interaction between plate subduction and mantle plume?

Neoproterozoic igneous rocks are widely distributed in the Quruqtagh along the northern margin of the Tarim, NW China. Here we report ages, petrography, and geochemistry of two (No. I and No. IV) Neoproterozoic bimodal intrusive complexes and Zhongtuzhan ultramafic dykes in the Quruqtagh, in order to construct a new model of Neoproterozoic tectonic evolution of the Tarim during the breakup of Rodinia. The No. I (∼20km2) and No. IV (∼10km2) bimodal intrusive complexes in Quruqtagh are composed of gabbroic and granitic rocks. New U–Pb ages of the zircons from the two intrusive complexes demonstrate that they were coevally emplaced at ca. 735Ma. The Zhongtuzhan ultramafic dykes were emplaced at ca. 802Ma, broadly coeval with the nearby Qieganbulake ultamafic-mafic–carbonatite complex.The gabbroic rocks from both No. I and No. IV complexes exhibit tholeiitic characters, enrichment in LILE and LREE, and depletion in HFSE and HREE. Isotopically, they are characterized by wide range of whole-rock ɛNd(t) values (0 to −0) and variable high (87Sr/86Sr)i (0.7095–0.7059). Zircons from the gabbroic samples of the No. I and No. IV complexes have slightly different ɛHf(t) (−1.5–0.9 and −2.5 to −0.5, respectively), indicating Nd–Hf isotopic decoupling. Zircons from Zhongtuzhan ultramafic dykes have pronounced negative ɛHf(t) (−14.9 to −11.9), resembling the Hf isotopic compositions of the baddeleyites from the Qieganbulake carbonatite. These features, combined with the presence of the primary phlogopite and hornblende, suggest that the gabbroic rocks were likely formed via combined crustal assimilation and crystal fractionation/cumulation (AFC effects) of a tholeiitic magma originally derived from a metasomatized subcontinental lithosphere mantle (SCLM). In comparison, the granites mingled into the No. I complex display adakitic signatures and pronounced negative ɛNd(t) values (≤−12), and were derived from partial melting of mafic lower crust due to the underplating of the coeval mafic magma.Our results, in conjunction with previous data in literature, indicate that the Neoproterozoic igneous activities in Quruqtagh could be broadly divided into four phases. They are as follows: (1) the ca. 820–800Ma ultramafic–mafic–carbonatite complex and voluminous adakitic granites and mafic dyke swarm; (2) the ca. 780–760Ma tholeiitic ultramafic–mafic complex and voluminous mafic dyke swarm; (3) the ca. 740–735Ma bimodal complex and bimodal volcanic series; and (4) minor 650–635Ma mafic dykes. The Neoproterozoic igneous activities waned since 740Ma as a result of the dispersing of Tarim from Rodinia. The presence of voluminous mafic rocks of arc-signature and the calc-alkaline granites in this area is due to the interaction between the Rodinian plume and oceanic crust subduction under the Tarim continent before 760Ma. As the Tarim Block was at the periphery of the Rodinia, subduction along the northern margin of the Tarim could last from late Mesoproterozoic to mid-Neoproterozoic (ca. 760Ma). During the subduction, the Rodinian plume (pulses of 825–800 and 780–740Ma) could heat the lithospheric mantle under the continental arc along the northern margin of Tarim, leading to the formation of the voluminous and diverse igneous rocks of arc-signatures. The subduction ceased at ca. 760Ma. The ca. 735Ma bimodal intrusive complex and the coeval Beiyixi basalt unconformably overlying on the ca. 820–800Ma granites, might indicate the dispersing of the Tarim from Australia.

Generic Prediction Rules for Regime Change in Bimodal Processes

Several bimodal complex processes having great socio-economic impact exist in nature, yet more often than not it is non-trivial to find prediction rules for their regime change. Generic prediction rules for regime transition and duration of subsequent regime are given for several two-regime models. It is demonstrated that prediction rules are a universal property of a large class of bimodal processes. An effort is made to explore the applicability of generic prediction rules to real-world bimodal processes, namely the Indian summer monsoon rainfall and the Indian Ocean Dipole event. Time series representative of these phenomena are analyzed to establish their bimodality and to show that prediction rules hold well for these time series also.

Age and lithotectonic correlations of igneous complexes of the Nyavlenga volcanoplutonic structure, Northeast Russia

According to paleofloral and Rb-Sr isotope data, the Nyavlenga structure was rapidly formed in the initial Albian (Buor-Kemyus phytostratigraphic horizon). Igneous rocks of this structure belong to the calcalkaline series characteristic of the early development stage of the Okhotsk-Chukotka volcanogenic belt (OCHVB), owing to which it differs distinctly from the bimodal riftogenic complex of the Omsukchan Graben (Silyap Horizon). The early development stage of the OCHVB outer zone (Buor-Kemyus, Arman, and Amka horizons) was accompanied by multiple volcanic cycles (andesitic → dacitic-rhyolitic associations) with the formation of corresponding structures. There is a need for elaborating a special nomenclature for identifying volcanic cycles and related structures.

Glu 87 of Channelrhodopsin‐1 Causes pH‐dependent Color Tuning and Fast Photocurrent Inactivation†

Channelrhodopsins (ChR1 and ChR2) are directly light-gated ion channels acting as sensory photoreceptors in the green alga Chlamydomonas reinhardtii. These channels open rapidly after light absorption and both become permeable for cations such as H(+), Li(+), Na(+), K(+) and Ca(2+). K(m) for Ca(2+) is 16.6 mm in ChR1 and 18.3 mm in ChR2 whereas the K(m) values for Na(+) are higher than 100 mm for both ChRs. Action spectra of ChR1 peak between 470 and 500 nm depending on the pH conditions, whereas ChR2 peaks at 470 nm regardless of the pH value. Now we created two chimeric ChRs possessing helix 1-5 of ChR1 and 6, 7 of ChR2 (ChR1/2(5/2)), or 1, 2 from ChR1 and 3-7 from ChR2 (ChR1/2(2/5)). Both ChR-chimera still showed pH-dependent action spectra shifts. Finally, a mutant ChR1E87Q was generated that inactivated only slowly in the light and showed no spectral shift upon pH change. The results indicate that protonation/deprotonation of E87 in helix 1 alters the chromophore polarity, which shifts the absorption and modifies channel inactivation accordingly. We propose a trimodal counter ion complex for ChR1 but only a bimodal complex for ChR2.

Geochronology of igneous rocks and formation of the Late Paleozoic south Mongolian active margin of the Siberian continent

The succession of magmatic events associated with development of the Early Carboniferous-Early Permian marginal continental magmatic belt of southern Mongolia is studied. In the belt structure there are defined the successive rock complexes: the older one represented by differentiated basalt-andesite-rhyodacite series and younger bimodal complex of basalt-comendite-trachyrhyolite composition. The granodiorite-plagiogranite and banatite (diorite-monzonite-granodiorite) plutonic massifs are associated with the former, while peralkaline granite massifs are characteristic of the latter. First systematic geochronological study of igneous rock associations is performed to establish time succession and structural position of both complexes. Geochronological results and geological relations between rocks of the bimodal and differentiated complexes showed first that rocks of the differentiated complex originated 350 to 330 Ma ago at the initial stage of development of the marginal continental belt. This is evident from geochronological dates obtained for the Adzh-Bogd and Edrengiyn-Nuruu massifs and for volcanic associations of the complex. The dates are consistent with paleontological data. The bimodal association was formed later, 320 to 290 Ma ago. The time span separating formation of two igneous complexes ranges from several to 20–30 m.y. in different areas of the marginal belt. The bimodal magmatism was interrelated with rifting responsible for development of the Gobi-Tien Shan rift zone in the belt axial part and the Main Mongolian lineament along the belt northern boundary. Loci of bimodal rift magmatism likely migrated with time: the respective magmatic activity first initiated on the west of the rift system and then advanced gradually eastward with development of rift structures. Normal granitoids untypical but occurring nevertheless among the products of rift magmatism in addition to peralkaline massifs are assumed to have been formed, when the basic magmatism associated with rifting stimulated crustal anatexis and generation of crustal granitoid magmas under specific conditions of rifting within the active continental margin.

Geology, Geochronology, and Geodynamics of the Khan Bogd alkali granite pluton in southern Mongolia

The Khan Bogd alkali granite pluton, one of the world’s largest, is situated in the southern Gobi Desert, being localized in the core of the Late Paleozoic Syncline, where island-arc calc-alkaline differentiated volcanics (of variable alkalinity) give way to the rift-related bimodal basalt-comendite-alkali granite association. The tectonic setting of the Khan Bogd pluton is controlled by intersection of the near-latitudinal Gobi-Tien Shan Rift Zone with an oblique transverse fault, which, as the rift zone, controls bimodal magmatism. The pluton consists of the eastern and the western ring bodies and comes into sharp intrusive contact with rocks of the island-arc complex and tectonic contact with rocks of the bimodal complex. The inner ring structure is particularly typical of the western body and accentuated by ring dikes and roof pendants of the country island-arc complex. According to preliminary gravity measurements, the pluton is a flattened intrusive body (laccolith) with its base subsiding in stepwise manner northwestward. Reliable geochronologic data have been obtained for both plutonic and country rocks: the U-Pb zircon age of alkali granite belonging to the main intrusive phase is 290 ± 1 Ma, the 40Ar/39Ar ages of amphibole and polylithionite are 283 ± 4 and 285 ± 7 Ma, and the Rb-Sr isochron yields 287 ± 3 Ma; i.e., all these estimates are close to 290 Ma. Furthermore, the U-Pb zircon age of red normal biotite granite (290 ± 1 Ma) and the Rb-Sr age of the bimodal complex in the southern framework of the pluton are the same. The older igneous rocks of the island-arc complex in the framework and roof pendants of the pluton are dated at 330 Ma. The geodynamic model of the Khan Bogd pluton formation suggests collision of the Hercynian continent with a hot spot in the paleoocean; two variants of this model are proposed. According to the first variant, the mantle plume, after collision with the margin of the North Asian paleocontinent, reworked the subducted lithosphere and formed a structure similar to an asthenospheric window, which served as a source of rift-related magmatism and the Khan Bogd pluton proper. In compliance with the second variant, the emergence of hot mantle plume resulted in flattening of the subducted plate; cessation of the island-arc magmatism; and probably in origin of a local convective system in the asthenosphere of the mantle wedge, which gave rise to the formation of a magma source. The huge body of the Khan Bogd alkali granite pluton and related volcanic rocks, as well as its ring structure, resulted from the caldera mechanism of the emplacement and evolution of magmatic melts.

Bimodal Loop−Loop Interactions Increase the Affinity of RNA Aptamers for HIV-1 RNA Structures

Multiple loop-loop interactions between adjacent RNA hairpins regulate gene expression in different organisms. To demonstrate that such natural interactions could be mimicked for generating RNA ligands that are able to recognize simultaneously at least two structured RNA targets, a double kissing complex model was designed. The target consisted of two HIV-1 transactivating responsive (TAR) RNA variants, BRU and MAL, connected by a non-nucleotidic linker. The double ligand was generated by combining the corresponding hairpin aptamers, R06BRU and R06MAL, identified previously by in vitro selection [Ducongé, F., and Toulmé, J. J (1999) RNA 5, 1605-1614]. The resulting interaction was analyzed by thermal denaturation monitored by UV spectroscopy, electrophoretic mobility shift assays (EMSAs), and surface plasmon resonance (SPR) experiments. The bimodal complex was characterized by a binding equilibrium constant increased by at least 1 order of magnitude compared to that of the complexes between the individual parent hairpins. This resulted from a slower dissociation rate. We then made use of such a strategy for targeting two structured functional motifs of the folded 5' untranslated region (5'UTR) of HIV-1. Two bivalent RNA ligands were designed that targeted simultaneously the TAR and dimerization initiation site (DIS) hairpins or the TAR and poly(A) ones. The results show that these ligands also displayed enhanced affinity for their target compared to the individual molecules. The work reported here suggests that bimodal structured RNA ligands might provide a way of increasing the affinity of aptamers for folded RNA targets.

Chiral recognition of aromatic compounds by β-cyclodextrin based on bimodal complexation

The chiral recognition of the selected aromatic chiral compounds by native beta-cyclodextrin (beta-CD) based on bimodal complexation was studied using a flexible docking algorithm FDOCK. A quantitative empirical free energy relationship model was employed to predict the complex stability constants and the preferred binding modes. The results showed that the calculated complex stability constants are in good agreement with the experimental data. Furthermore, the main force responsible for host-guest complexation is the van der Waals force and the chiral molecules are completely included into the beta-CD cavity. The chiral recognition for the selected aromatic chiral compounds is the result of the van der Waals force counterbalancing with the other effects, such as the electrostatic interaction and the hydrophobic effect.

Bi-directional Inclusion Complexation of Methylalkyl Viologens with -Cyclodextrin and Naphthyl group-Tethered β-Cyclodextrins

Inclusion complexation of methylalkyl viologens(C1CnV2+; n = 7–10, 12) withmono-6-O-(2-sulfonato-6-naphthyl)-β-CD (1)and mono-6-O-(2-naphthyl)-β-CD (2) werestudied by steady-state and time-resolved fluorescencespectroscopies and compared with the binding of theviologens with native β-CD investigated by induced circulardichroism. The viologens form bimodal complexes with1 and 2, in which the bipyridinium group of theviologens is placed on the primary side (type I complex) andsecondary side (type II complex) of β-CD cavity, while thegroup is predominantly on the secondary side in complexeswith native β-CD. The microscopic binding constantsKI and K II were calculated from theanalysis of fluorescence data. The formation of the type Icomplexes with 1 and 2 appears to be largely dueto the charge–transfer interaction between the bipyridinium andnaphthyl groups in the complexes. This work shows thatthe location of the bipyridinium group in β-CDcomplexes and in the type II complexes of the viologens with1 and 2 depends little on the length of alkyl chainof the viologens.

Short-lived magmatic activity in an anorogenic subvolcanic complex: 40Ar/ 39Ar and ion microprobe U–Pb zircon dating of the Erongo, Damaraland, Namibia

The Erongo subvolcanic center in Namibia is the largest composite, bimodal complex in the Mesozoic Etendeka igneous province of Namibia. This study of 40Ar/ 39Ar and high spatial resolution U–Pb zircon dating demonstrates that emplacement of the various igneous units at Erongo took place within a time span equivalent to or shorter than geochronologically resolvable age differences (ca. 2 Ma), and at the peak of regional flood-basalt activity in the Etendeka–Paraná province. The Erongo complex comprises a series of felsic volcanic and intrusive units that overlie or intrude basaltic lavas attributed to the Etendeka Group. The stratigraphically oldest rhyodacite (Erongorus unit) yielded U–Pb zircon ages of 131.8±1.1 Ma (1σ). The overlying Ombu rhyodacite was previously dated at 135.0±1.6 Ma and our new ages for a resurgent intrusion of the same magma type (Ombu granodiorite) in the vent area are 132.6±1.1 Ma ( 40Ar/ 39Ar) and 132.3±1.9 Ma (U–Pb zircon) respectively. The youngest felsic magmas at Erongo are the high-silica Ekuta rhyolite and compositionally equivalent Erongo granite. These units yielded U–Pb zircon ages of 131.9±2.9 and 130.3±1.4 Ma, respectively. Concordant 40Ar/ 39Ar biotite ages from two samples of the granite average 132.2±0.8 Ma. The final stage of magmatism at Erongo involved emplacement of basic alkaline plugs and dikes. Phlogopite and kaersutite from foidite plugs of this series yielded 40Ar/ 39Ar ages of 130.8±1.0 and 132.0±1.0 Ma. In a regional context, these age results indicate that silicic magmatism in the largest complexes of the Damaraland (Erongo, Brandberg, Paresis, Messum) began simultaneously with the peak of flood-basalt effusion at about 132 Ma throughout the Etendeka province and ceased by about 130 Ma. The silicic magmas are hybrid, with varying contributions of crustal and mantle-derived melts, and the age constraints suggest that crustal melting was caused by a short-lived thermal pulse related to the main flood-basalt event. Basic magmatism in the Damaraland complexes continued sporadically thereafter to about 123 Ma, but lacked the power to create further crustal melting.