1,721,052 research outputs found
Stratigraphical and structural outline of the Riu Gruppa Tectonic Unit (Southeastern Sardinia) Italy
No full textPreliminary considerations on the lithostratigraphic succession of the Apuane Alps Paleozoic basement (northern Tuscany, Italy)
No full text
L'unità tettonica di Bruncu Nieddu e i suoi rapporti con le unità della Sardegna Sud-Orientale.
No full text
Pre-hecynian Magmatic Activity in the Nappe Zone (External and Internal) of Sardinia:evidences of two Wthin-Plate Basaltic Cycles
No full textRecent data on stratigraphic and structural relationships among the sequences of the "Nappe Zone" of the Variscan Chain in Sardinia , from Sarrabus to Nurra, have made possible to set in a detailed spatial and temporal frame the pre-Variscan intermedite-basic volcanic activity.
The review of the relatioships between metabasites and coutry rocks , the fabrics analysis, the geochemistry and the structural and palaeogeographic setting , allow to propose a new interpretation of the pre-Variscan tectono-magmatic evolution
Osservazioni preliminari sulla successione litostratigrafica del basamento paleozoico apuano
No full textThe overprint of the Alpidic tecto-metamorphic evolution on the Hercynian orogen: an example from the Apuane Alps (northern Apennines, Italy)
No full textGeochemistry and origin of chloritoid schists from the Alpi Apuane, Italy: evidence of a prevailing lateritic signature
No full textChloritoid schist layers frequently occur as the uppermost part of the Rhaetian Brecce di Seravezza Formation, interpreted
as rockfall talus metabreccias intercalated between Norian and Liassic marbles, in the Alpi Apuane Tuscany, Italy. The chloritoid
schist is characterised by mm-sized chloritoid porphyroblasts (20-50 % modal range) and a matrix made up of chlorite, muscovite,
pyrophyllite, chloritoid, hematite, calcite, quartz and epidote. Most chloritoid porphyroblasts show cores with abundant hematite
inclusions. Many pieces of duricrust, pisoid and composite pebbles come from older lateritic bauxite deposits of supposed
Kasimovian to Sakmarian age. Their uneven to well rounded shapes indicate variable duration of transport and multistage reworking.
In comparison with many bauxite and metabauxites, Apuan chloritoid schist shows: great enrichment in SiO2, K2O, Na2O, a slight
increase in CaO, MgO, remarkable depletion in Al2O3 and Fe2O3, a slight decrease in TiO2 and P2O5, strong depletion in Cu, Pb, Zn, Bi,
and As, unexpected Ni, Co and Ba enrichments; slight to strong depletion for Ga, Cr,Nb, Zr, andVreflecting variable dilution of primary
bauxite detritus. The REE spider diagram shows enrichment factors of 2-3 for LREE, of 1-2 for HREE. Strong enrichment to strong
depletion in Sm, Eu, Gd, and Tb is correlated with maximum and minimum contents of duricrust fragments respectively.
Four detrital components were distinguished. Two of them represent about 90-95%of the whole protolith: 1. Fe2O3tot-Al2O3-SiO2-
rich lateritic bauxite detritus; 2. illite-rich desert soil particles with high K2O, SiO2, Al2O3 contents. The calculated relative
proportions are: component 1): 61 %, component 2): 39 %. Minor detrital components are given by: 1) Ba-rich mineralised rock
fragments, a witness to Late Triassic hydrothermal circuits; 2) detritus supplied by Na, Ca, Mg-rich salts abundant in hot desert soils.
The very low TiO2 and very high SiO2 contents of the calculated lateritic bauxite component strongly suggest a granite to rhyolite
protolith for the primary bauxite deposit, the ancestor of the Apuan lateritic bauxite component
- …
