The oldest rocks of Greece: first evidence for a Precambrian terrane within the Pelagonian Zone

2005 ◽  
Vol 143 (1) ◽  
pp. 41-58 ◽  
Author(s):  
B. ANDERS ◽  
T. REISCHMANN ◽  
D. KOSTOPOULOS ◽  
U. POLLER
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Magmatic Arc ◽  
Late Proterozoic ◽  
Basement Rocks ◽  
Northwestern Margin ◽  
Single Zircon ◽  
Formed Part ◽  
Terrane Accretion ◽  
Pelagonian Zone

The Pelagonian Zone in Greece represents the westernmost belt of the Hellenide hinterland (Internal Hellenides). Previous geochronological studies of basement rocks from the Pelagonian Zone have systematically yielded Permo-Carboniferous ages. In this study we demonstrate, for the first time, the existence of a Precambrian crustal unit within the crystalline basement of the Pelagonian Zone. The U–Pb single-zircon and SHRIMP ages of these orthogneisses vary from 699 ± 7 Ma to 713 ± 18 Ma, which identify them as the oldest rocks in Greece. These Late Proterozoic rocks, which today occupy an area of c. 20 × 100 km, are significantly different from the neighbouring rocks of the Pelagonian Zone. They are therefore interpreted as delineating a terrane, named here the Florina Terrane. During the Permo-Carboniferous, Florina was incorporated into an active continental margin, where it formed part of the basement for the Pelagonian magmatic arc. The activity of this arc was dated in this study by single-zircon Pb/Pb ages as having taken place at 292 ± 5 Ma and 298 ± 7 Ma. During the Alpine orogeny, Florina, together with the Pelagonian Zone, eventually became a constituent of the Hellenides. Geochemically, the Florina orthogneisses represent granites formed at an active continental margin. Because of the Late Proterozoic ages, this Late Proterozoic active continental margin can be correlated to a Pan-African or Cadomian arc. As the gneisses contain inherited zircons of Late to Middle Proterozoic age, the original location of Florina was probably at the northwestern margin of Gondwana. Similar to other Gondwana-derived terranes, such as East Avalonia, Florina approached the southern margin of Eurasia during Palaeozoic times, where it became part of an active continental margin above the subducting Palaeotethys. These interpretations further indicate that terrane accretion was already playing an important role in the early pre-alpine evolution of the Hellenides.

scholarly journals Late palaeozoic magmatism in the basement rocks Southwest of Mt. Olympos, Central Pelagonian zone, Greece: Remnants of a permo-carboniferous magmatic arc

2001 ◽  
Vol 34 (3) ◽  
pp. 985 ◽  
Author(s):  
T. REISCHMANN ◽  
D. K. KOSTOPOULOS ◽  
S. LOOS ◽  
B. ANDERS ◽  
A. AVGERINAS ◽  
...  
Keyword(s):  
Late Carboniferous ◽  
Early Permian ◽  
Magmatic Evolution ◽  
Geochronological Data ◽  
Magmatic Arc ◽  
Late Palaeozoic ◽  
Basement Rocks ◽  
Evaporation Technique ◽  
Single Zircon ◽  
Pelagonian Zone

We dated basement rocks from several localities southwest of Mt. Olympos, as well as from a locality near the top of the mountain using the single zircon Pb/Pb evaporation technique. For the samples southwest of the mountain, the ages obtained range from ca. 280 to 290 Ma, with only a few zircon grains being around 300 Ma. By contrast, the sample from near the top of the mountain appears to be slightly younger, with ca. 270 Ma. These ages imply that the granitoids crystallized during Late Carboniferous - Early Permian times, and are therefore younger than the basement gneisses of other regions of the Pelagonian zone, which yielded zircon ages of around 300 Ma (e.g. Yarwood & Aftalion 1976, Mountrakis 1983, De Bono 1998, Engel & Reischmann 2001). However, the ages obtained in the present study are identical, within error, to the muscovite Ar-Ar cooling ages from Mt. Ossa (Lips 1998). Our geochronological data show that the magmatic evolution for this part of the basement of the Pelagonian Zone lasted at least 30 Ma.

scholarly journals Metamorfismo de alto gradiente P/T en la Sierra de Pie de Palo (Sierras Pampeanas, Argentina): modelado de equilibrio de fases minerales e implicancias geodinámicas en el antearco famatiniano

2019 ◽  
Vol 46 (3) ◽  
pp. 526
Author(s):  
Carlos Dino Ramacciotti ◽  
César Casquet ◽  
Edgardo Gaspar Baldo ◽  
Sebastián Osvaldo Verdecchia ◽  
Matías Martín Morales ◽  
...  
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Progressive Decrease ◽  
The West ◽  
Sierras Pampeanas ◽  
Magmatic Arc ◽  
Age Related ◽  
Grenvillian Orogeny ◽  
Western Side ◽  
Metasedimentary Sequence

The Sierra de Pie de Palo (SPP, Western Sierras Pampeanas) shows evidence of two regional metamorphisms: one Mesoproterozoic attributed to the Grenvillian orogeny and other of Ordovician age related to the Famatinian orogeny. The Neoproterozoic-to-Cambrian sedimentary successions that cover the Grenvillian basement only record the Ordovician event. One staurolite-schist from the Ediacaran Difunta Correa Metasedimentary Sequence collected in the southeastern side of the SPP allows to constrain, by means of pseudosections, a prograde evolution from ca. 3 kbar and 515 ºC up to ca. 9 kbar and 640 ºC corresponding to a high P/T gradient. The SPP and the immediately east Loma de Las Chacras outcrop were part of the famatinian forearc which shows a progressive decrease of P (from ca. 13 kbar to 6 kbar), T (from ca. 900 ºC to 450 ºC), and P/T gradient (from ca. 85 ºC/kbar to 35 ºC/kbar) towards the active continental margin on the west. The Caucete Group, in the western side of the SPP, represents the westernmost part of the forearc, near to the active continental margin. Metamorphism was apparently coeval with the Famatinian magmatism and with ductile underthrusting at ca. 470-465 Ma, which led to burial of the forearc beneath the magmatic arc.

U—Pb single zircon data of granitoids from the High Tatra Mountains (Slovakia): implications for the geodynamic evolution

2000 ◽  
Vol 91 (1-2) ◽  
pp. 235-243 ◽  
Author(s):  
Ulrike Poller ◽  
Wolfgang Todt
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Tatra Mountains ◽  
Geodynamic Evolution ◽  
Zircon Age ◽  
Granite Intrusion ◽  
Asthenospheric Mantle ◽  
Subducted Oceanic Crust ◽  
Single Zircon ◽  
High Tatra Mountains

New U/Pb results by cathodoluminescence-controlled single zircon dating of rocks from the High Tatra Mountains (Slovakia) constrain ages for the protolith at 2Ga for the granitoids and 3 Ga for the Koncistá migmatite. Concordant single zircon ages date the intrusion of the migmatite precursor at 3567 Ma and the migmatisation at 332 ± 5 Ma. The intrusion of this precursor corresponds with the major granite intrusion in the Western Tatra Mountains. The geodynamic scenario at this time is described as slab detachment of subducted oceanic crust at the active continental margin of Gondwana. The resulting upwelling of asthenospheric mantle brought enough heat for the anatexis of old metasediments and the production of new H- to S-type granites. High Tatra diorites have an intrusion age of 341 ± 5 Ma, constrained by a concordant single zircon age. This age marks the beginning of the Variscan collision of the two convergent continents Laurasia and Gondwana. The intrusion of granites in the High Tatra was confirmed by concordant data at 314 ± 4 Ma, documenting the final stage of the Variscan continent collision.

U-Pb single zircon grain dating of Present fluvial and Cenozoic aeolian sediments from Gabon: consequences on sediment provenance, reworking, and erosion processes on the equatorial West African margin

2008 ◽  
Vol 179 (1) ◽  
pp. 29-40 ◽  
Author(s):  
Michel Seranne ◽  
Olivier Bruguier ◽  
Mathieu Moussavou
Keyword(s):  
Detrital Zircons ◽  
Sediment Provenance ◽  
Late Proterozoic ◽  
Erosion Processes ◽  
No Formation ◽  
Basement Rocks ◽  
River Bed ◽  
Aeolian Sediments ◽  
Single Zircon ◽  
Mechanical Erosion

Abstract U-Pb ages obtained from detrital zircon from terrigenous sediments are used to determine the sources. Present fluvial sand-bars of the Ogooué river yield age spectra of detrital zircons in agreement with Archean and Early Proterozoic sources found in the drainage. The large proportion of Late Proterozoic zircons cannot be derived from primary erosion of the watershed basement rocks, since there is no formation of that age in the area. This later group of zircons is in good agreement with reworking of the aeolian Paleogene Batéké Sands, by regressive erosion in the upper reaches of the Ogooué river, as they contain a majority of Late Proterozoic age zircons. The sources of Late Proterozoic zircons in the Batéké Sand are very distant, and transported and reworked – at least in part – by aeolian processes. Our results, together with the widely distributed Paleogene sediments over continental Africa, suggests that Paleogene was a time of subdued erosion of the cratonic areas and extensive reworking, transport and deposition within continental Africa. In contrast, our results from the Ogooué river indicate active present incision of the cratonic area, erosion of the previous continental sediments, and export of the river bed-load to the continental margin. This temporal evolution of erosion-transport-deposition is correlated with the drastic climate change that occurred during the Cenozoic, leading to a more efficient mechanical erosion, and it correlates with the increase of terrigenous flux to the margin, observed during the Neogene.

scholarly journals Sedimentary provenance study of the post-Early Permian to pre-Early Cretaceous metasedimentary Duque de York Complex, Chile

2010 ◽  
Vol 33 (2) ◽  
pp. 199
Author(s):  
Juan Pablo Lacassie ◽  
Francisco Herve ◽  
Barry Roser
Keyword(s):  
Early Cretaceous ◽  
Continental Margin ◽  
Active Continental Margin ◽  
Source Area ◽  
Mineralogical Composition ◽  
Late Triassic ◽  
Low Grade ◽  
Early Permian ◽  
Magmatic Arc ◽  
Geochemical Analyses

The Duque de York Complex constitutes a post-Early Permian to pre-Early Cretaceous metasedimentary succession that crops out at the Madre de Dios and Diego de Almagro archipelagos along the Chilean Patagonian Andes. The petrography and geochemistry of sandstones and mudstones of this complex have been analyzed to characterize its source and depositional tectonic regime. Sandstone modal compositions are dominated by feldspar and, in similar but smaller proportions, by quartz. The mineralogical composition of the sandstones and mudstones is compatible with a low-grade sub-greenschist facies metamorphism. This did not affect significantly the geochemical compositions of these rocks. Nevertheless, the geochemical analyses reveal variable K+ enrichment, especially in the mudstones. Chemical Index of Alteration values of the sandstones and mudstones range between 58 and 71, indicating that the sediment underwent moderate chemical alteration in the source area or during transportation. Sandstone modal compositions are consistent with erosion of the plutonic roots of a magmatic arc. Geochemical provenance indices suggest a relatively evolved source, close in composition to typical continental magmatic arc granodiorite. Deposition of the detritus is most likely to have occurred within an active continental margin. Geochronological, petrographic, and geochemical similarities between the metasediments of the Duke de York Complex, the LeMay Group (Western Antarctica) and the Permian-Late Triassic Rakaia terrane (New Zealand) suggest a common geodynamic set-up for these three successions. This likely constituted an extensive late Paleozoic-early Mesozoic active continental margin, possibly along the Antarctic sector of Gondwana.

Nature and origin of the volcanic ash beds near the Permian–Triassic boundary in South China: new data and their geological implications

2019 ◽  
Vol 157 (4) ◽  
pp. 677-689 ◽  
Author(s):  
Binsong Zheng ◽  
Chuanlong Mou ◽  
Renjie Zhou ◽  
Xiuping Wang ◽  
Zhaohui Xiao ◽  
...  
Keyword(s):  
Trace Element ◽  
Continental Margin ◽  
South China ◽  
Volcanic Ash ◽  
Active Continental Margin ◽  
Main Body ◽  
Early Triassic ◽  
Late Permian ◽  
Triassic Boundary ◽  
Permian Triassic Boundary

AbstractPermian–Triassic boundary (PTB) volcanic ash beds are widely distributed in South China and were proposed to have a connection with the PTB mass extinction and the assemblage of Pangea. However, their source and tectonic affinity have been highly debated. We present zircon U–Pb ages, trace-element and Hf isotopic data on three new-found PTB volcanic ash beds in the western Hubei area, South China. Laser ablation inductively coupled plasma mass spectrometry U–Pb dating of zircons yields ages of 252.2 ± 3.6 Ma, 251.6 ± 4.9 Ma and 250.4 ± 2.4 Ma for these three volcanic ash beds. Zircons of age c. 240–270 Ma zircons have negative εHf(t) values (–18.17 to –3.91) and Mesoproterozoic–Palaeoproterozoic two-stage Hf model ages (THf2) (1.33–2.23 Ga). Integrated with other PTB ash beds in South China, zircon trace-element signatures and Hf isotopes indicate that they were likely sourced from intermediate to felsic volcanic centres along the Simao–Indochina convergent continental margin. The Qinling convergent continental margin might be another possible source but needs further investigation. Our data support the model that strong convergent margin volcanism took place around South China during late Permian – Early Triassic time, especially in the Simao–Indochina active continental margin and possibly the Qinling active continental margin. These volcanisms overlap temporally with the PTB biocrisis triggered by the Siberian Large Igneous Province. In addition, our data argue that the South China Craton and the Simao–Indochina block had not been amalgamated with the main body of Pangea by late Permian – Early Triassic time.

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