1,721,167 research outputs found
Long-lived orogenic construction along the paleo-Pacific margin of Gondwana (Deep Freeze Range, North Victoria Land, Antarctica)
No full textThe paleo‐Pacific margin of Gondwana records a prolonged history of convergence
during the Cambrian–Early Ordovician Ross‐Delamerian and the Middle Ordovician–
Early Silurian Lachlan orogenies. This study describes structure, petrology, and
geochronology of a set of NW‐SE striking ductile shear zones that crosscut the Ross
age, Early Cambrian granitoid rocks of the Wilson Terrane in the Deep Freeze Range
(North Victoria Land, Antarctica). The shear zones developed under amphibolite facies
metamorphic conditions (650–700°C and 0.5–0.7 GPa) and show a systematic top‐to‐the‐
NE sense of shear. The shear zone activity interferes with emplacement of late,
subhorizontal leucocratic dikes and combined U‐(Th)‐Pb (zircon and monazite) and
40Ar‐39Ar (biotite and phengite) geochronology constrains the shearing event at ∼470 Ma,
with the sheared granite yielding U‐Pb zircon crystallization ages of ∼508 Ma. The
reconstructed P‐T path followed by the granite protoliths indicates an anticlockwise
trajectory, suggesting the synshearing amphibolite metamorphism was associated with the
burial of an early formed, Ross continental crustal section. These new findings are
interpreted as evidence of a renewed, Ordovician episode of orogenic construction at
the paleo‐Pacific margin of Gondwana that predated the onset of the Lachlan orogeny in
the region. A polycyclic reactivation of the Ross age Wilson Terrane of North Victoria
Land is suggested, which is used to propose a unitary framework for the space‐time
transition from the Ross‐Delamerian to the Lachlan orogeny along the proto‐Pacific active
margin of Gondwana
Fluid flow within the damage zone of the Boccheggiano extensional fault (Larderello-Travale geothermal field, central Italy): structures, alteration and implications for hydrothermal mineralization in extensional settings
No full textThe Neogene extensional province of southern Tuscany in central Italy provides an outstanding example of fossil and active structurally controlled fluid flow and epithermal ore mineralization associated with post-orogenic silicic magmatism. Characterization of the hydrodynamic regime leading to the genesis of the polysulphide deposit (known as Filone di Boccheggiano) hosted within the damage zone of the Boccheggiano Fault is a key target to assess modes of fossil hydrothermal fluid circulation in the region and, more generally, to provide inferences on fault-controlled hydrothermal fluid flow in extensional settings. We provide a detailed description of the fault zone architecture and alteration/mineralization associated with the Boccheggiano ore deposit and report the results of fluid inclusion and stable oxygen isotope studies. This investigation shows that the Boccheggiano ore consists of an adularia/illite-type epithermal deposit and that sulphide ore deposition was controlled by channelling of hydrothermal fluids of dominantly meteoric origin within the highly anisotropic permeability structure of the Boccheggiano Fault. The low permeability structure of the fault core compartmentalized the fluid outflow preventing substantial cross-fault flow, with focused fluid flow occurring at the hangingwall of the fault controlled by fracture permeability. Fluid inclusion characteristics indicate that ore minerals were deposited between 280° and 350°C in the upper levels of the brittle extending crust (lithostatic pressure in the order of 0.1 GPa). Abundant vapour-rich inclusions in ore-stage quartz are consistent with fluid immiscibility and boiling, and quartz ore vein textures suggest that mineralization in the Boccheggiano ore deposit occurred during cyclic fluid flow in a deformation regime regulated by transient and fluctuating fluid pressure conditions. Results from this study (i) predict a strongly anisotropic permeability structure of the fault damage zone during crustal extension, and (ii) indicate the rate of secondary (structural) permeability creation and maintenance by active deformation in the hangingwall of extensional faults as the major factor leading to effective hydraulic transmissivity in extensional terranes. These features intimately link ore-grade mineralization in extensional settings to telescoping of hydrothermal flow along the hangingwall block(s) of major extensional fault zones
Brittle deformation of the Beacon and Ferrar rocks in the Eisenhower Range-Deep Freeze Range area, northern Victoria Land, Antarctica
No full textMonte Argentario and Isola del Giglio (Southern Tuscany, Italy): a record from continental break-up to subduction-orogenic wedge formation, and post-orogenic extension
No full textSi tratta della Guida all'escursione post-Congresso P61 del 32nd International Geological Congres
Late Ross ductile deformation features in the Wilson "Terrane" of northern Victoria Land (Antarctica) and their implications for the western boundary of the Ross Orogen
No full textCarbonatisation and overprinting mineralisation in Siah-Kamar porphyry molybdenum deposit, NW Iran
No full textThe Siah-Kamar porphyry Mo deposit (SKD) is located at the north-western termination of the Urumieh-Dokhtar magmatic arc and it is the only known porphyry Mo ore reserve in Iran. The SKD formed in two main mineralisation stages, at ~33–32 Ma (late-stage, disseminated) and ~ 29–28 Ma (late-stage, high-grade), within a context of a long-lived magmatism. We integrate results from the whole-rock geochemistry, the Osingle bondC stable and Sr isotope systematics across the mineralised alteration zones with the available drilling data (ore element concentration) to define the ore-forming processes leading to Mo enrichment in the SKD. Our investigation shows that CO2 bearing magmatic fluids had the major role in both early and late-stage mineralisation. The Mo shows positive correlation with SiO2 content but a clear negative correlation with W, Cu, and S, due to a delayed precipitation of Mo during the early-stage mineralisation. The released fluids from the new acidic magmas and subsequent fluid-rock interaction in an open-system, primarily assisted by brittle fracturing, and accompanied by cooling and mixing with various amounts of meteoric water and fluid neutralisation, was responsible for the selective ore depletion and Mo-ore enhancement during carbonatisation along structurally-controlled pathways
Re-equilibration textures of fluid inclusions in exhumed high-pressure rocks: the example of the Tuscan Archipelago (Northern Tyrrhenian Sea, Italy)
No full textCenozoic Tectonics in the Yule Bay Area: An Alternative Approach to the Structural Evolution of the Enigmatic Surgeon Island Block (Northern Victoria Land, Antarctica)
No full textLate Ross structures between Kleinschmidt Bluffs and Outback Nunataks in northern Victoria Land (Antarctica).
No full textLate-Ross structures in the Wilson Terrane in the Rennick Glacier area (northern Victoria Land, Antarctica)
No full text- …
