scholarly journals SHRIMP U-Pb Zircon Geochronology of Volcanic Rocks Hosting World-Class Be-U-Li-F Mineralization, Spor Mountain, Utah, U.S.A

2020 ◽  
Author(s):  
Robert Ayuso ◽  
Nora Foley ◽  
Jorge Vazquez
Keyword(s):  
Volcanic Rocks ◽  
Zircon Geochronology ◽  
World Class

Reconciling zircon and monazite thermometry constrains H2O content in granitic melts

2020 ◽  
Author(s):  
Silvia Volante ◽  
William Collins ◽  
Chris Spencer ◽  
Eleanore Blereau ◽  
Amaury Pourteau ◽  
...  
Keyword(s):  
Water Content ◽  
Volcanic Rocks ◽  
Saturation Temperature ◽  
Granitic Rocks ◽  
Zircon Geochronology ◽  
Bulk Rock ◽  
Independent Evidence ◽  
Water Values ◽  
Host Rocks ◽  
Eastern Domain

<p>In this contribution, we compare and test the reliability of zircon and monazite thermometers and suggest a new and independent method to constrain the H<sub>2</sub>O content in granitic magmas from coeval zircon and monazite minerals. We combine multi-method single-mineral thermometry (bulk-rock zirconium saturation temperature (T<sub>zr</sub>), Ti-in-zircon (T<sub>(Ti-zr</sub><sub>)</sub>) and monazite saturation temperature (T<sub>mz</sub>)) with thermodynamic modelling to estimate water content and P–T conditions for strongly-peraluminous (S-type) granitoids in the Georgetown Inlier, NE Queensland. These granites were generated within ~30 km thick Proterozoic crust, and emplaced during regional extension associated with low-pressure high-temperature (LP–HT) metamorphism.</p><p>SHRIMP U–Pb monazite and zircon geochronology indicates synchronous crystallization ages of c. 1550 Ma for granitic rocks emplaced at different crustal levels—from the eastern deep crustal domain (P = 6–9 kbar), through the middle crustal domain (P = 4–6 kbar), to the western upper crustal domain (P = 0–3 kbar).</p><p>Bulk-rock T<sub>zr</sub> and T<sub>(Ti-zr</sub><sub>)</sub> yielded magma temperature estimates for the eastern domain of ~800°C and ~910–720°C, respectively. Magma temperatures in the central and western domains were ~730°C (T<sub>zr</sub>) and ~870–750°C (T<sub>(Ti-zr)</sub>) in the central domain, and ~810°C (T<sub>zr</sub>) and ~890–720°C (T<sub>(Ti-zr)</sub>) in the western domain, respectively. These temperature estimates were compared with P–T conditions recorded in the host rocks to determine if the magmas had equilibrated thermally with the crust. Similar temperatures were obtained for the middle and lower crust suggesting that the associated magmas thermally equilibrated at their respective depths, whereas the sub-volcanic rocks were, as expected, significantly hotter than the adjacent crust.</p><p>By plotting the results on a P–T–X<sub>H2O</sub> petrogenetic grid, and assuming adiabatic ascent through the crust, the sub-volcanic magmas appear to be drier (~3 wt% H<sub>2</sub>O) than the granitic magmas (~7 wt% H<sub>2</sub>O) which formed at greater depth. Monazite saturation temperatures (which depends on the water content, light–REE content and composition of the granitic melt), are in agreement with the zircon thermometers only if water values of ~3 wt% H<sub>2</sub>O and ~7 wt% H<sub>2</sub>O are assumed for the upper crustal magmas and deeper magmas, respectively. Moreover, melt compositions extracted from a modelled pseudosection of a sillimanite-bearing metapelite, which was interpreted to be the typical source rock for the surrounding granites (P=5 kbar and T=690°C–850°C), show comparable water content values.</p><p>The T<sub>mz</sub> results provide independent evidence for the H<sub>2</sub>O content in magmas, and we suggest that reconciling T<sub>zr</sub> with T<sub>mz</sub> is a new and independent way of constraining H<sub>2</sub>O content in granitic magmas.</p>

Geochemical and scintillometric characterization and correlation of amethyst geode-bearing Paraná lavas from the Quaraí and Los Catalanes districts, Brazil and Uruguay

2010 ◽  
Vol 147 (6) ◽  
pp. 954-970 ◽  
Author(s):  
LÉO A. HARTMANN ◽  
WILSON WILDNER ◽  
LAUREN C. DUARTE ◽  
SANDRO K. DUARTE ◽  
JULIANA PERTILLE ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Field Studies ◽  
Major And Trace Elements ◽  
Strong Variation ◽  
Stratigraphic Sequence ◽  
Stratigraphic Framework ◽  
World Class ◽  
Geochemical Studies ◽  
Bottom To Top ◽  
Aa Lava

AbstractGeochemical studies of the six lowermost lava flows of the Cretaceous Serra Geral Formation (Paraná volcanic province) in Quaraí (Brazil) and Artigas (Uruguay) were combined with flow-by-flow field studies of structures and scintillometric profiles to establish a consistent regional stratigraphic framework over at least 100 km. This greatly improves exploration capability for amethyst and agate geodes. A basalt, colada Mata Olho (Alegrete facies, Serra Geral Formation), was the first lava to flow over the ancient Botucatu desert in the region, but an andesite, colada Catalán, overstepped this basalt in many places, perhaps palaeohighs. Four basaltic andesites complete the lava stratigraphy in this formation, adding up to 300 m of lavas. The stratigraphic sequence of contrasting lava compositions is 51.0 wt% SiO2 in the first lava, followed by 57.5, 52.5, 56.0, 53.0 and finally 54.5 wt% SiO2. Overall MgO variation is between 2 and 7 wt%. All lavas in the two districts are low-Ti (<2.0 wt% TiO2) of the Gramado type. The characteristic contents of most major and trace elements (124 rock samples analysed) allow the ready identification of each lava. Contrasting rock chemistry also results in strong variation in scintillometric values (270 points measured in the field and nineteen continuous borehole profiles); from bottom to top of the stratigraphy, the cps values are 49±3.2, 123±10.3, 62±4.7, 94±4.6, ~45 and ~85. Colada Catalán has the structure of aa lava, particularly the contorted igneous banding and autobreccias in the upper and lower crusts. In some places, a 2 m thick, silicified sandstone layer lies on top of some coladas, and silicified sandstone forms breccias with volcanic rocks. Geochemistry of the six lavas indicates complex evolution, involving melting of lithospheric mantle, injection into the crust and assimilation of crust followed by fractional crystallization. This study indicates the possibility of world-class deposits of amethyst geodes on the Brazilian side of the border with Uruguay.

scholarly journals Geochronology of the Oliverian Plutonic Suite and the Ammonoosuc Volcanics in the Bronson Hill arc: Western New Hampshire, USA

Geosphere ◽  
2019 ◽  
Vol 16 (1) ◽  
pp. 229-257 ◽  
Author(s):  
Peter M. Valley ◽  
Gregory J. Walsh ◽  
Arthur J. Merschat ◽  
Ryan J. McAleer
Keyword(s):  
High Resolution ◽  
New Hampshire ◽  
Volcanic Rocks ◽  
Late Ordovician ◽  
Zircon Geochronology ◽  
Ion Microprobe ◽  
Lower Section ◽  
The West ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks

Abstract U-Pb zircon geochronology by sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) on 11 plutonic rocks and two volcanic rocks from the Bronson Hill arc in western New Hampshire yielded Early to Late Ordovician ages ranging from 475 to 445 Ma. Ages from Oliverian Plutonic Suite rocks that intrude a largely mafic lower section of the Ammonoosuc Volcanics ranged from 474.8 ± 5.2 to 460.2 ± 3.4 Ma. Metamorphosed felsic volcanic rocks from within the Ammonoosuc Volcanics yielded ages of 460.1 ± 2.4 and 455.0 ± 11 Ma. Younger Oliverian Plutonic Suite rocks that either intrude both the upper and lower Ammonoosuc Volcanics or Partridge Formation ranged in age from 456.1 ± 6.7 Ma to 445.2 ± 6.7 Ma. These new data and previously published results document extended magmatism for &gt;30 m.y. The ages, along with the lack of mappable structural discontinuities between the plutons and their volcanic cover, suggest that the Bronson Hill arc was part of a relatively long-lived composite arc. The Early to Late Ordovician ages presented here overlap with previously determined igneous U-Pb zircon ages in the Shelburne Falls arc to the west, suggesting that the Bronson Hill arc and the Shelburne Falls arc could be part of one, long-lived composite arc system, in agreement with the interpretation that the Iapetus suture (Red Indian Line) lies to the west of the Shelburne Falls–Bronson Hill arc system.

Zircon geochronology of the Mashak volcanic rocks and the problem of the age of the lower-middle Riphean boundary (Southern Urals)

2013 ◽  
Vol 21 (5) ◽  
pp. 465-481 ◽  
Author(s):  
A. A. Krasnobaev ◽  
V. I. Kozlov ◽  
V. N. Puchkov ◽  
S. V. Busharina ◽  
N. D. Sergeeva ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Southern Urals ◽  
Zircon Geochronology

scholarly journals Reconstructing the Physical and Chemical Development of a Pluton-Porphyry Complex in a Tectonically Reorganized Arc Crustal Section, Tioga Pass, Sierra Nevada

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
pp. 1-26
Author(s):  
Katie Ardill ◽  
Valbone Memeti ◽  
Scott Paterson
Keyword(s):  
Sierra Nevada ◽  
Volcanic Rocks ◽  
Zircon Geochronology ◽  
Magmatic System ◽  
East Central ◽  
Hypabyssal Intrusions ◽  
Magmatic Processes ◽  
History Of ◽  
Scale Structures ◽  
Physical And Chemical

Abstract In ancient or partially eroded arc sections, a protracted history of tectonism and deformation makes interpretation of local volcanic-plutonic relationships challenging. The fragmentary preservation of volcanic rocks relative to the extensive plutonic record in upper-crustal arc sections also suggests that a broader-scale approach that includes volcanic-hypabyssal-plutonic “fields” is useful. In this context, studies of hypabyssal intrusions emplaced at the intersection of volcanic and plutonic fields provide additional physical and chemical constraints on shallow-level magmatic processes. New mapping, U-Pb zircon geochronology, and geochemistry at Tioga Pass, in the central Sierra Nevada arc section, document the physical and chemical evolution of the Tioga Pass hypabyssal complex, a ca. 100 Ma system that includes an intrusive dacite-rhyolite porphyry unit and comagmatic Tioga Lake quartz monzodiorite. We interpret these units as a Cretaceous subvolcanic magma feeder system intruding a package of tectonically displaced Triassic and Jurassic volcanic and sedimentary rocks, rather than the previous interpretation of a Triassic caldera. The Tioga Pass magmatic system is a well-exposed example of a hypabyssal complex with meso- to micro-scale structures that are consistent with rapid cooling and emplacement between 0–6 km depth and compositions suggestive of extensive fractionation of largely mantle-derived magma. The Tioga Pass porphyry unit is one of many hypabyssal intrusions scattered along a ~50-kilometer-wide belt of the east-central Sierra Nevada that are spatially associated with coeval volcanic and plutonic rocks due to tectonic downward transfer of arc crust. They provide a valuable perspective of shallow magmatic processes that may be used to test upper-crustal plutonic-volcanic links in tectonically reorganized arc sections.

U–Pb zircon geochronology of Lower Jurassic and Paleozoic Stikinian strata and Tertiary intrusions, northwestern British Columbia

1995 ◽  
Vol 32 (8) ◽  
pp. 1155-1171 ◽  
Author(s):  
C. J. Greig ◽  
G. E. Gehrels
Keyword(s):  
Volcanic Rocks ◽  
Lower Jurassic ◽  
Detrital Zircons ◽  
Zircon Geochronology ◽  
Fold Belt ◽  
Isotopic Data ◽  
The West ◽  
Juvenile Crust ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks

New U–Pb zircon ages are reported from western Stikinia. Devonian and Pennsylvanian ages of volcanic rocks at Oweegee dome confirm the presence of pre-Permian strata, and with Paleozoic and Triassic detrital zircons from Lower Jurassic sandstone, they help to demonstrate pre-Lower Jurassic deformation and uplift. The absence of pre-Paleozoic inherited zircon from all samples is consistent with Nd–Sr isotopic data which suggest that Stikinia consists mainly of juvenile crust. U–Pb ages for posttectonic intrusions suggest that structures in Skeena Fold Belt in the Kinskuch area formed prior to Eocene time. Five ages for felsic volcanic rocks from stratigraphically well-constrained upper parts of the Hazelton arc are approximately 196–199 Ma and suggest near-contemporaneity for cessation of volcanism in the areas studied. The Sinemurian or late Sinemurian – early Pliensbachian ages are older than previously reported U–Pb and biostratigraphic ages for presumed correlative rocks to the west, and westward-migrating volcanism is implied. Together with Toarcian fossils from overlying sandstone, the new ages suggest that a hiatus of moderate duration preceded regionally extensive sedimentation.

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