Search results for "Conti"
showing 10 items of 3486 documents
Late Paleozoic Ice Age glaciers shaped East Antarctica landscape
2019
International audience; The erosion history of Antarctica is fundamental to our understanding of interlinks between climate and glacier dynamics. However, because of the vast polar ice sheet covering more than 99% of Antarctica land mass, the continental surface response to glacial erosion remains largely unknown. Over the last decade the subglacial topography of Antarctica has been imaged by airborne radar surveys. These studies revealed high and complex sub-glacial relief in the core of the East Antarctic shield, interpreted as resulting from rifting episodes and low long-term erosion rates, or repeated large-scale glacial retreats and advances. In East Antarctica, thermochronology studie…
Impact of Holocene tsunamis detected in lagoonal environments on Corfu (Ionian Islands, Greece): Geomorphological, sedimentary and microfaunal eviden…
2016
Abstract In this paper, we present for the first time geomorphological, sedimentary and microfaunal evidence of palaeotsunami impact on Corfu (Ionian Islands, Greece). The island of Corfu is located in an area of exceptional tectonic stress: towards the south, the African oceanic plate is being subducted underneath the Aegean plate, whereas towards the north, the Adriatic and European plates form a continental collision zone. Recent publications provide evidence of earthquake related co-seismic movements that potentially trigger extreme wave events as well as relative sea level fluctuations. In this context, we investigated two selected near-coast geological archives – the Chalikiopoulou La…
Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: an integrated geodynamic and petrological modelling approach
2017
The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India–Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure–temperature–time (P–T–t) path has been derived from thermomechanical simulations tailored for E…
On the Mesozoic Ionian Basin
2001
SUMMARY New seismic reflection profiles of the Italian deep crust project CROP provide new insights on the structure of the Ionian sea. In spite of the Apennines and Hellenides Neogene subduction zones, two conjugate passive continental margins are preserved at the margins of the Ionian sea, along the Malta escarpment to the southwest and the Apulian escarpment to the northeast. The Ionian sea is likely to be a remnant of the Mesozoic Tethys Ocean, confined by these two conjugate passive continental margins. The transition from continental to oceanic crust appears sharper to the northeast than to the southwest. The basin between southeast Sicily and southwest Puglia was about 330 km wide an…
Archean-Paleoproterozoic crustal evolution of the Ordos Block in the North China Craton: Constraints from zircon U–Pb geochronology and Hf isotopes f…
2015
Abstract The Ordos Block has been considered as an Archean micro-block in North China Craton. However, its formation and evolution are poorly understood for a long time due to lack of available basement rocks. Our LA-ICPMS and SIMS zircon U–Pb dating of gneissic granitoids from the Ordos Block basement identified two distinct periods of granitic magmatism at ∼2.5 Ma and 2.2–2.0 Ga, and two phases of metamorphisms at ∼1.95 Ga and ∼1.85 Ga, respectively. Of which most zircons of ∼2.5 Ga granitoids show positive ɛ Hf ( t ) values ranging from +0.1 to +4.1 with a peak T DM of ∼2.7 Ga. Minor zircons have negative ɛ Hf ( t ) values from −3.8 to −0.02 and T Hf C of 2.8–3.1 Ga. Moreover, the 3.40 G…
Zircon REE patterns and geochemical characteristics of Paleoproterozoic anatectic granite in the northern Tarim Craton, NW China: Implications for th…
2012
Abstract Because Archean basement rocks are sparsely distributed around the Tarim Basin, little is known of the relationship between the Tarim Craton and the Paleo- to Mesoproterozoic Columbia supercontinent. Zircon U–Pb dating of a Paleoproterozoic gneissic granite in the northern Tarim Craton yielded a crystallization age of 1915 ± 13 Ma, consistent with global Paleoproterozoic collisional events (ca. 2.1–1.8 Ga) recorded in most cratons. Despite the fact that some zircons display discordant U–Pb ages with a distinct loss of radiogenetic Pb, all grains have similar 176Lu/177Hf and 176Hf/177Hf(t) values. Zircons from this granite have high Th/U ratios (0.15–0.95), but contrasting rare eart…
Structural variables drive the distribution of the sensitive lichen Lobaria pulmonaria in Mediterranean old-growth forests
2015
a b s t r a c t We tested the hypothesis that structural variables related to old-growth features affect the distribution of Lobaria pulmonaria in a Mediterranean National Park of Italy. A total of 36 plots, with old-growth characteristics and representing overall three forest types (beech- oak- and mixed- forests) were studied. The lichen was absent in about half of the sites, suggesting that the selection of old-growth forests based solely on structural features is not sufficient to predict the presence of this species, which therefore proves to be rather sensitive and selective. Its abundance was related to high tree circumference and basal area, and to availability of deadwood, confirmi…
A ∼700 Ma Sm–Nd garnet–whole rock age from the granulite facies Central Kaoko Zone (Namibia): Evidence for a cryptic high-grade polymetamorphic histo…
2007
Continental collision of the Kalahari and the Congo craton in Africa and the Rio de la Plata Craton in South America resulted in a structurally complex Neoproterozoic belt system, the Kaoko–Dom Feliciano–Ribeira belt. It is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at ∼580–550 Ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events. The Kaoko Belt (NW Nambia), representing the belt system between the southern Congo Craton and the Rio de la Plata Craton, is an ideal object to study these complexities. Within this belt, high-grade meta-igneous and metasedimentary rocks of t…
Single zircon ages from high-grade rocks of the Jianping Complex, Liaoning Province, NE China
1998
Abstract The high-grade rocks of the Jianping Complex in Liaoning Provi nce, NE China, belong to the late Archaean to earliest Proterozoic granulite belt of the North China craton. Single zircon ages obtained by the Pb–Pb evaporation method and SHRIMP analyses document an evolutionary history that began with deposition of a cratonic supracrustal sequence some 2522–2551 Ma ago, followed by intrusion of granitoid rocks beginning at 2522 Ma and reaching a peak at about 2500 Ma. This was followed by high-grade metamorphism, transforming the existing rocks into granulites, charnockites and enderbites some 2485–2490 Ma ago. The intrusion of post-tectonic granites at 2472 Ma is associated with wid…
Ca. 1318 Ma A-type granite on the northern margin of the North China Craton: Implications for intraplate extension of the Columbia supercontinent
2012
Abstract Identification of the Mesoproterozoic A-type Jining granite and granite porphyry, which with abundant coeval mafic dike sills and volcanic rocks on the northern margin of the Precambrian North China Craton (NCC), may suggest intraplate extension of Columbia supercontinent. Major and trace elements of the Jining granite show an affinity to A-type granites, and may reflect an intraplate rift setting (A 1 ‐type granite). High Rb, Y, Yb, and Ta contents also show features of within-plate granites. SHRIMP zircon dating yielded concordant weighted mean 207 Pb/ 206 Pb ages of 1318 ± 7 Ma and 1321 ± 15 Ma, which define a Mesoproterozoic magmatic event. The zircons have negative e Hf(t) of …