1,721,016 research outputs found
Late Hercynian dyke magmatism of Sarrabus (SE Sardinia)
No full textThe late-Hercynian dyke magmatism of Sarrabus reflects the bimodal distribution observed in the other areas of Sardinia, the suite being represented by prevalent basaltic andesites and peraluminous rhyolites. Calcalkaline basalts and andesites are scarce, while dacites are extremely rare. The hypabyssal activity is closed by basaltic dykes with tholeiitic affinity. The chemical composition points out the 'medium-K' and 'high-K' character of the calcalkaline series. Fractionation links are lacking between calcalkaline and the majority of rhyolitic rocks. In comparison with dyke rocks of the other areas of Sardinia, many of the Sarrabus type show a more marked subalkaline character. The compositional variation of calcalkaline rocks can be partly explained by crystal-liquid fractionation processes. Among the rhyolitic rocks, two groups with different peraluminous characters have been recognized
Depositional processes of the mixed carbonate-siliciclastic rhodolith beds of the Miocene Saint-Florent Basin, northern Corsica
No full textMany sedimentary processes can lead to the formation of mixed carbonate-siliciclastic sediments in shallow shelf environments. The Miocene Saint-Florent Basin (Corsica), and in particular the Monte S. Angelo Formation, offers the possibility to analyze coarse mixed sediments produced by erosion of a rocky coast, ephemeral stream input, and shallow-water carbonate production dominated by red algae. The Monte S. Angelo Formation was deposited during the Burdigalian to Langhian interval. During this interval, the island of Corsica experienced increased subsidence related to the development of the Ligurian-Proven double dagger al Basin and associated Sardinia-Corsica block rotation. Four main rhodolith-rich subfacies have been recognized: conglomerate with rhodoliths, massive rhodolith rudstone, well-bedded rhodolith rudstone, and rhodolith floatstone. The four facies have been interpreted as having been deposited in different environments of a gravel-dominated, nearshore to offshore prograding wedge. Deep-water melobesioids dominate the red algal assemblage from shoreface to offshore. Shallow-water subfamilies of lithophylloids and mastophoroids occur in only accessory amounts. Poor illumination is believed to be due to terrigenous input by ephemeral streams and wave- and current-resuspension. Resuspension processes are favored by the limited occurrence of seagrasses. Two types of siliciclastic-carbonate mixing processes characterize the investigated rhodolith-rich deposits: (1) punctuated mixing, produced by the re-deposition of terrigenous sediments by debris-flow processes during flooding events onto carbonate sediments together with rhodoliths of the shoreface environments, and (2) in situ mixing, produced by growth of coralline algae on siliciclastic pebbles to form the rhodoliths.Many sedimentary processes can lead to the formation of mixed carbonate-siliciclastic sediments in shallow shelf environments. The Miocene Saint-Florent Basin (Corsica), and in particular the Monte S. Angelo Formation, offers the possibility to analyze coarse mixed sediments produced by erosion of a rocky coast, ephemeral stream input, and shallow-water carbonate production dominated by red algae. The Monte S. Angelo Formation was deposited during the Burdigalian to Langhian interval. During this interval, the island of Corsica experienced increased subsidence related to the development of the Ligurian-Provençal Basin and associated Sardinia-Corsica block rotation. Four main rhodolith-rich subfacies have been recognized: conglomerate with rhodoliths, massive rhodolith rudstone, well-bedded rhodolith rudstone, and rhodolith floatstone. The four facies have been interpreted as having been deposited in different environments of a gravel-dominated, nearshore to offshore prograding wedge.
Petrologia del magmatismo filoniano tardo-ercinico del Sarrabus (Sardegna sud-orientale)
No full textDottorato di ricerca in scienze della terra. 7. ciclo. A.a. 1991-95. Relatore G. Traversa. Coordinatore G. PialliConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal
Geochronology, Sr-Nd isotope geochemistry and petrology of Late-Hercynian dyke magmatism from Sarrabus (SE Sardinia)
No full textSedimentological analysis of the rhodolith rich deposits of Burdigalian Sant’Angelo Formation (Saint Florant, northern Corsica, France)
No full textDepositional processes of the carbonate-siliciclastic rhodolith rich deposits of Burdigalian Sant'Angelo Formation (Saint Florent, Northern Corsica, France)
No full textPost-Hercynian basic dyke magmatism of the Concas-Alà dei Sardi alignment (Northern Sardinia-Italy)
No full text
The Oligo-Miocene alkaline volcanism of Bahariya (Western Desert, Egypt)
No full textLate Oligocene-Early Miocene volcanic rocks around the Bahariya Oasis in the Western Desert, Egypt occur as
basaltic lava flows, subvolcanic sills and necks in an area of approximately 1800 km2. Five new K-Ar age cluster in a
relatively narrow range from 23.9 to 20.7 Ma. Bahariya rocks are mildly alkaline basic in terms of silica content (SiO2
ranging from 48.4 to 51.4 wt.%), with total alkali content ranging from 4.9 to 5.9 wt.%, and variable amounts of
normative nepheline. The samples are essentially sodic (Na2O-K2O > 2) and can be classified as alkali basalts, hawaiites
or mugerarites. Only the samples from one locality (Qala Siua) can be classified as K-trachybasalts. Samples are usually
porphyritic, with phenocryst assemblage made by olivine + clinopyroxene + plagioclase, and the same minerals along
with alkali feldspar, ilmenite, Ti-magnetite, and eventually intersertal glass in the groundmass. Samples from Qala Siua
can be distinguished also by their petrography, being plagioclase present only in the groundmass. All the samples have
slightly fractionated REE patterns with (La/Yb)N ≈ 10-18, and no Eu anomaly. Primitive mantle-normalized patterns
are bell-shaped, with positive Nb and Ta anomalies, which are more pronounced of Qala Siua samples, and small
troughs for Zr and Hf.
The 143Nd/144Nd initial isotopic ratios are high and constant (≈ 0.51295 for all the samples), whereas some variations
are revealed by 87Sr/86Sr ratios, which are around 0.7028 for two samples, and 0.7036 for the most evolved sample of
Baharyia volcanic field. The 206Pb/204Pb isotope ratios vary from 19.19 to 19.31 and are negatively correlated with the
SiO2 content.
Summing up, all the petrographic, geochemical and isotopic characters of studied rocks, are typical of within plate
magmas, sourced in a depleted asthenospheric mantle unaffected by any subduction imprint. Their composition fully
overlap the field of the other rocks of the Circum-Mediterranean anorogenic Cenozoic igneous rocks (CiMACI
Province). Their relationships with coeval extensional faulting, characterized by NE directed faults, may indicate that
these magmas were erupted in an incipient intracontinental rift, with no geochemical evidence for the involvement of
any deeper mantle sources
- …
