Mesozoic fold structure of the Otago and Alpine Schist Belt and its implications on the tectonic evolution of South Island, New Zealand

Erneute Untersuchungen der mesozoischen Faltenstruktur des Otago Schiefergürtels, Südinsel, Neuseeland, zeigen, dass diese aus zwei aufeinander folgenden, ähnlichen, asymmetrischen, offenen bis mäßig engen Großfaltengenerationen im km- Größenbereich besteht anstatt aus den vorher angenommenen Decken- oder Halbfalten. Hauptproblem der Großfaltenstruktur sind Zonen von durchgreifender Boudinage, die in der Nähe der Großfaltenscharniere entstanden sind. Vorherige Bearbeiter deuteten diese Zonen als 'starke Verformungszonen' oder Überschiebungszonen. Diese Arbeit zeigt, dass in diesen Zonen nur durch die asymmetrische Faltung die unteren liegenden Schenkel der Großfalten boudiniert und somit häufig die ansonsten typischen Faltenstrukturen des liegenden Schenkels einer symmetrischen Faltung überprägt wurden. Ein weiteres Problem dieser mesozoischen Großfaltenstruktur ist die Überprägung einer Faltengeneration auf eine frühere. Weil die Verkürzungsrichtung der überprägenden Faltengeneration nicht subparallel zur älteren Faltenachse ist, sondern einen Winkel von rund 30 Grad einschließt, ist ein Wechsel von orthogonalen zu koaxialen Interferenzmustern der Kleinfalten beobachtbar. Folglich ist die Orientierung der Scheitellinie einer überprägenden und überprägten Kleinfalte nicht unbedingt subparallel zur Orientierung der Faltenachse der Großfalte trotz zylindrischer Faltung. Im letzten Teil dieser Arbeit wird die Überprägung der mesozoischen Großfaltenstruktur durch das känozoisch entstandene, transpressionale Alpine Störungssystem, das einen zweiseitigen Falten- und Überschiebungsgürtel im Otago und im Nordwesten anschließenden Alpinen Schiefergürtel bildet, beschrieben.

Models of hybridization during range expansions and their application to recent human evolution

Several lines of genetic, archeological and paleontological evidence suggest that anatomically modern humans (Homo sapiens) colonized the world in the last 60,000 years by a series of migrations originating from Africa (e.g. Liu et al., 2006; Handley et al., 2007; Prugnolle, Manica, and Balloux, 2005; Ramachandran et al. 2005; Li et al. 2008; Deshpande et al. 2009; Mellars, 2006a, b; Lahr and Foley, 1998; Gravel et al., 2011; Rasmussen et al., 2011). With the progress of ancient DNA analysis, it has been shown that archaic humans hybridized with modern humans outside Africa. Recent direct analyses of fossil nuclear DNA have revealed that 1–4 percent of the genome of Eurasian has been likely introgressed by Neanderthal genes (Green et al., 2010; Reich et al., 2010; Vernot and Akey, 2014; Sankararaman et al., 2014; Prufer et al., 2014; Wall et al., 2013), with Papua New Guineans and Australians showing even larger levels of admixture with Denisovans (Reich et al., 2010; Skoglund and Jakobsson, 2011; Reich et al., 2011; Rasmussen et al., 2011). It thus appears that the past history of our species has been more complex than previously anticipated (Alves et al., 2012), and that modern humans hybridized several times with local hominins during their expansion out of Africa, but the exact mode, time and location of these hybridizations remain to be clarifi ed (Ibid.; Wall et al., 2013). In this context, we review here a general model of admixture during range expansion, which lead to some predictions about expected patterns of introgression that are relevant to modern human evolution.

Tectonic evolution of the Proterozoic Itremo Group metasediments in central Madagascar

The major geologic units of the Itremo region in central Madagascar include: (1) upper amphibolite to granulite facies (higher grade) Precambrian rocks, mainly para- and orthogneisses, and migmatites; (2) the newly defined Itremo Nappes, a fold-and-thrust belt containing the Proterozoic Itremo Group sediments, metamorphosed at greenschist to lower amphibolite facies (lower grade) conditions: (3) Middle Neoproterozoic and Late Neoproterozoic-Cambrian intrusives. The stratigraphic succession of the Itremo Group in the eastern part of the Itremo region is, from bottom to top: quartzites, metapelites, metacarbonates and metapelites overlain by metacarbonates. During D1 the Itremo Group sediments were detached from their continental substratum, deformed into a fold-and-thrust nappe (Itremo Nappes), and transported on top of higher grade rocks that are intruded by Middle Neoproterozoic (c. 797–780 Ma) granites and gabbros. A second phase of deformation shortening (D2) affected both the Itremo Sedimentary Nappes and structurally underlying higher-grade rocksunits, and formed large-scale N-S-trending F2 folds. S1 axial plane foliations in Itremo Group sediments are truncated by Late Neoproterozoic-Cambrian granites (c. 570–540 Ma). The age of the formation of the Itremo Nappes is not well constrained: they formed in Neoproterozoic times between 780 and 570 Ma.

Age constraints on the tectonic evolution of the Itremo region in Central Madagascar

The Itremo region in Central Madagascar comprises a deformed metasedimentary sequence (Itremo Group) that has undergone greenschist to lower amphibolite facies metamorphism. During a first phase of deformation (D1) Itremo Group sediments were deformed into a fold-and-thrust belt and transported toward the E to NE on top of migmatitic gneisses rocks of Anatananarivo block. A second phase of deformation (D2) affected both the fold-and-thrust belt and structurally underlying units, and formed large-scale N-S trending folds with steeply dipping axial planes. A Late Neoproterozoic Th–U–Pb XRF monazite age (565±17 Ma) dates the emplacement of a granite that truncates first-phase structures in the Itremo Group, and indicates that the fold-and-thrust belt formed prior to ≈565 Ma. Th–U–Pb electron microprobe dating was applied to elongated monazites that lie within the first-phase foliation of Itremo Group metapelites. The detrital cores of zoned monazites reveal two distinct age populations at ∼2000 and 1700 Ma, the latter age giving a maximum depositional age for the Itremo Group. Statistical analysis of ages determined from the rims of zoned monazites and from unzoned monazites indicates three Late Proterozoic–Early Paleozoic monazite growth events at about 565–540, 500 and 430 Ma. The oldest age population is contemporaneous within error, with the intrusion of the dated granite. The two younger age populations are found both in the Th–U–Pb and Ar–Ar data; together with the perturbation of the Rb–Sr system we interpret both ages as due to alteration related to fluid circulation events, possibly connected to the emplacement of pegmatite fields in Central Madagascar. Syn-D1 tectonic growth of contact metamorphism minerals such as andalusite has been observed locally in metapelites along the margin of Middle Neoproterozoic (≈800 Ma) granites, suggesting that D1 in the Itremo Group is contemporaneous with the intrusion of granites at ≈800 Ma. The N-S trending D2 folds are associated with ≈E-W shortening during the final assembly of Gondwana in Late Neoproterozoic–Early Cambrian times.

Recent Reticulate Evolution in the Ecologically Dominant Lineage of Coccolithophores

The coccolithophore family Noëlaerhabdaceae contains a number of taxa that are very abundant in modern oceans, including the cosmopolitan bloom-forming Emiliania huxleyi. Introgressive hybridization has been suggested to account for incongruences between nuclear, mitochondrial and plastidial phylogenies of morphospecies within this lineage, but the number of species cultured to date remains rather limited. Here, we present the characterization of 5 new Noëlaerhabdaceae culture strains isolated from samples collected in the south-east Pacific Ocean. These were analyzed morphologically using scanning electron microscopy and phylogenetically by sequencing 5 marker genes (nuclear 18S and 28S rDNA, plastidial tufA, and mitochondrial cox1 and cox3 genes). Morphologically, one of these strains corresponded to Gephyrocapsa ericsonii and the four others to Reticulofenestra parvula. Ribosomal gene sequences were near identical between these new strains, but divergent from G. oceanica, G. muellerae, and E. huxleyi. In contrast to the clear distinction in ribosomal phylogenies, sequences from other genomic compartments clustered with those of E. huxleyi strains with which they share an ecological range (i.e., warm temperate to tropical waters). These data provide strong support for the hypothesis of past (and potentially ongoing) introgressive hybridization within this ecologically important lineage and for the transfer of R. parvula to Gephyrocapsa. These results have important implications for understanding the role of hybridization in speciation in vast ocean meta-populations of phytoplankton.

Recent Reticulate Evolution in the Ecologically Dominant Lineage of Coccolithophores

The coccolithophore family Noëlaerhabdaceae contains a number of taxa that are very abundant in modern oceans, including the cosmopolitan bloom-forming Emiliania huxleyi. Introgressive hybridization has been suggested to account for incongruences between nuclear, mitochondrial and plastidial phylogenies of morphospecies within this lineage, but the number of species cultured to date remains rather limited. Here, we present the characterization of 5 new Noëlaerhabdaceae culture strains isolated from samples collected in the south-east Pacific Ocean. These were analyzed morphologically using scanning electron microscopy and phylogenetically by sequencing 5 marker genes (nuclear 18S and 28S rDNA, plastidial tufA, and mitochondrial cox1 and cox3 genes). Morphologically, one of these strains corresponded to Gephyrocapsa ericsonii and the four others to Reticulofenestra parvula. Ribosomal gene sequences were near identical between these new strains, but divergent from G. oceanica, G. muellerae, and E. huxleyi. In contrast to the clear distinction in ribosomal phylogenies, sequences from other genomic compartments clustered with those of E. huxleyi strains with which they share an ecological range (i.e., warm temperate to tropical waters). These data provide strong support for the hypothesis of past (and potentially ongoing) introgressive hybridization within this ecologically important lineage and for the transfer of R. parvula to Gephyrocapsa. These results have important implications for understanding the role of hybridization in speciation in vast ocean meta-populations of phytoplankton.

Tectonic evolution of Variscan Iberia: Gondwana–Laurussia

An integrated interpretation of the late Paleozoic structural and geochronological record of the Iberian Massif is presented and discussed under the perspective of a Gondwana-Laurussia collision giving way to the Variscan orogen. Compressional and extensional structures developed during the building of the Variscan orogenic crust of Iberia are linked together into major tectonic events operating at lithosphere scale. A review of the tectonometamorphic and magmatic evolution of the IberianMassif reveals backs and forths in the overall conver- gence between Gondwana and Laurussia during theamalgamation of Pangea in late Paleozoic times. Stages dom- inated by lithosphere compression are characterized by subduction, both oceanic and continental, development of magmatic arcs, (over- and under-) thrusting of continental lithosphere, and folding. Variscan convergence re- sulted in the eventual transference of a large allochthonous set of peri-Gondwanan terranes, the Iberian Allochthon, onto the Gondwana mainland. The Iberian Allochthon bears the imprint of previous interaction be- tween Gondwana and Laurussia, including their juxtaposition after the closure of the Rheic Ocean in Lower De- vonian times. Stages governed by lithosphere extension are featured by the opening of two short-lived oceanic basins that dissected previous Variscan orogenic crust, first in the Lower-Middle Devonian, following the closure of the Rheic Ocean, and then in the early Carboniferous, following the emplacement of the peri-Gondwanan allochthon. An additional, major intra-orogenic extensional event in the early-middle Carboniferous dismem- bered the Iberian Allochthon into individual thrust stacks separated by extensional faults and domes. Lateral tec- tonics played an important role through the Variscan orogenesis, especially during the creation of new tectonic blocks separated by intracontinental strike-slip shear zones in the late stages of continental convergence.

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes in central Iran: New geological data, relationships and tectonic implications

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes occupy the NW part of the Central-East Iranian Microcontinent and are juxtaposed with the Great Kavir block and Sanandaj-Sirjan zone. Our recent findings redefine the origin of these complexes, so far attributed to the Precambrian-Early Paleozoic orogenic episodes, and now directly related to the tectonic evolution of the Paleo-Tethys Ocean. This tectonic evolution was initiated by Late Ordovician-Early Devonian rifting events and terminated in the Triassic by the Eocimmerian collision event due to the docking of the Cimmerian blocks with the Asiatic Turan block. The ``Variscan accretionary complex'' is a new name we proposed for the most widely distributed metamorphic rocks connected to the Anarak and Jandaq complexes. This accretionary complex exposed from SW of Jandaq to the Anarak and Kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal-sea ophiolitic remnants, including gabbro-basalts with a supra-subduction-geochemical signature. New Ar-40/Ar-39 ages are obtained as 333-320 Ma for the metamorphism of this sequence under greenschist to amphibolite facies. Moreover, the limy intercalations in the volcano-sedimentary part of this complex in Godar-e-Siah yielded Upper Devonian-Tournaisian conodonts. The northeastern part of this complex in the Jandaq area was intruded by 215 +/- 15 Ma arc to collisional granite and pegmatites dated by ID-TIMS and its metamorphic rocks are characterized by Some Ar-40/Ar-39 radiometric ages of 163-156 Ma. The ``Variscan'' accretionary complex was northwardly accreted to the Airekan granitic terrane dated at 549 +/- 15 Ma. Later, from the Late Carboniferous to Triassic, huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the Anarak and Kabudan. This new period of accretion is supported by the 280-230 Ma Ar-40/Ar-39 ages for the Anarak mild high-pressure metamorphic rocks and a 262 Ma U-Pb age for the trondhjemite-rhyolite association of that area. The Triassic Bayazeh flysch filled the foreland basin during the final closure of the Paleo-Tethys Ocean and was partly deposited and/or thrusted onto the Cimmerian Yazd block. The Paleo-Tethys magmatic arc products have been well-preserved in the Late Devonian-Carboniferous Godar-e-Siah intra-arc deposits and the Triassic Nakhlak fore-arc succession. On the passive margin of the Cimmerian block, in the Yazd region, the nearly continuous Upper Paleozoic platform-type deposition was totally interrupted during the Middle to Late Triassic. Local erosion, down to Lower Paleozoic levels, may be related to flexural bulge erosion. The platform was finally unconformably covered by Liassic continental molassic deposits of the Shemshak. One of the extensional periods related to Neo-Tethyan back-arc rifting in Late Cretaceous time finally separated parts of the Eocimmerian collisional domain from the Eurasian Turan domain. The opening and closing of this new ocean, characterized by the Nain and Sabzevar ophiolitic melanges, finally transported the Anarak-Jandaq composite terrane to Central Iran, accompanied by large scale rotation of the Central-East Iranian Microcontinent (CEIM). Due to many similarities between the Posht-e-Badam metamorphic complex and the Anarak-Jandaq composite terrane, the former could be part of the latter, if it was transported further south during Tertiary time. (C) 2007 Elsevier B.V. All rights reserved.

Evolution of the Pelagonian carbonate platform complex and the adjacent oceanic realm in response to plate tectonic forcing (Late Triassic and Jurassic), Evvoia, Greece

The Late Triassic and Jurassic platform and the oceanic complexes in Evvoia, Greece, share a complementary plate-tectonic evolution. Shallow marine carbonate deposition responded to changing rates of subsidence and uplift, whilst the adjacent ocean underwent spreading, and then convergence, collision and finally obduction over the platform complex. Late Triassic ocean spreading correlated with platform subsidence and the formation of a long-persisting peritidal passive-margin platform. Incipient drowning occurred from the Sinemurian to the late Middle Jurassic. This subsidence correlated with intra-oceanic subduction and plate convergence that led to supra-subduction calc-alkaline magmatism and the formation of a primitive volcanic arc. During the Middle Jurassic, plate collision caused arc uplift above the carbonate compensation depth (CCD) in the oceanic realm, and related thrust-faulting, on the platform, led to sub-aerial exposures. Patch-reefs developed there during the Late Oxfordian to Kimmeridgian. Advanced oceanic nappe-loading caused platform drowning below the CCD during the Tithonian, which is documented by intercalations of reefal turbidites with non-carbonate radiolarites. Radiolarites and bypass-turbidites, consisting of siliciclastic greywacke, terminate the platform succession beneath the emplaced oceanic nappe during late Tithonian to Valanginian time.

Structural analysis, clay mineralogy and K-Ar dating of fault gouges from Centovalli Line (Central Alps) for reconstruction of their recent activity

Between the cities of Domodossola and Locarno, the complex ``Centovalli Line'' tectonic zone of the Central Alps outlines deformation phases over a long period of time (probably starting similar to 30 Ma ago) and under variable P-T conditions. The last deformation phases developed gouge-bearing faults with a general E-W trend that crosscuts the roots of the Alpine Canavese zone and the Finero ultramafic body. Kinematic indicators show that the general motion was mainly dextral associated with back thrusting towards the S. The <2 mu m clay fractions of fault gouges from Centovalli Line consist mainly of illite, smectite and chlorite with varied illite-smectite, chlorite-smectite and chlorite-serpentine mixed-layers. Constrained with the illite crystallinity index, the thermal conditions induced by the tectonic activity show a gradual trend from anchizonal to diagenetic conditions. The <2 and <0.2 mu M clay fractions, and hydrothermal K-feldspar separates all provide K-Ar ages between 14.2 +/- 2.9 Ma and roughly 0 Ma, with major episodes at about 12,8, 6 and close to 0 Ma These ages set the recurrent tectonic activity and the associated fluid circulations between Upper Miocene and Recent. On the basis of the K-Ar ages and with a thermal gradient of 25-30 degrees C/km, the studied fault zones were located at a depth of 4-7 km. If they were active until now as observed in field, the exhumation was approximately 2.5-3.0 km for the last 12 Ma with a mean velocity of 0.4 mm/y. Comparison with available models on the recent Alpine evolution shows that the tectonic activity in the area relates to a continuum of the back-thrusting movements of the Canavese Line, and/or to several late-extensional phases of the Rhone-Simplon line. The Centovalli-Val Vigezzo zone therefore represents a major tectonic zone of the Central-Western Alps resulting from different interacting tectonic events. (C) 2011 Elsevier B.V. All rights reserved.