The geometry and evolution of magma pathways through migmatites of the Halls Creek Orogen, Western Australia

1997 ◽  
Vol 61 (404) ◽  
pp. 3-14 ◽  
Author(s):  
N. H. S. Oliver ◽  
T. D. Barr
Keyword(s):  
Western Australia ◽  
Mafic Magma ◽  
Shear Zones ◽  
Magma Source ◽  
Felsic Magma ◽  
Melt Migration ◽  
Metasedimentary Rocks ◽  
Fracture Systems ◽  
Magma Migration

AbstractIn the Halls Creek Orogen of north-western Australia, the distance of melt migration through migmatitic metasedimentary rocks and adjacent metabasites is partly constrained by relationships of leucosomes and small mafic magma veins to rock boundaries and structural elements. Stromatic leucosomes in metasediments are cut by a network of small extensional fractures and shear zones, oriented steeply during melt migration. These shear zones allowed cm- to 10 m-scale migration of felsic magma derived by in situ anatexis. In the adjacent metabasite layers, a similar shear array allowed injection of H2O-undersaturated mafic to ultramafic magma, locally dehydrating and chemically modifying these rocks. However, these mafic to ultramafic veinlets are too mafic to be explained by in situ anatexis, necessitating an external magma source. Also, the lack of felsic veinlets cutting metabasites, and mafic veinlets cutting metasediments, requires that vertical inter-connectivity of these fracture systems was restricted. We propose along-layer migration of mafic to ultramafic magma through the metabasite, assisted by horizontal connection of the shear zones. This migration occurred independantly of metre-scale felsic magma migration in the adjacent metasediments, even though these two deformation-assisted magma migration systems may have been operating at the same time.

scholarly journals Early Cambrian U-Pb zircon age and Hf-isotope data from the Guasayán pluton, Sierras Pampeanas, Argentina: implications for the northwestern boundary of the Pampean arc

2016 ◽  
Vol 43 (1) ◽  
pp. 137 ◽  
Author(s):  
Juan A. Dahlquist ◽  
Sebastián O. Verdecchia ◽  
Edgardo G. Baldo ◽  
Miguel A.S. Basei ◽  
Pablo H. Alasino ◽  
...  
Keyword(s):  
Central Area ◽  
Magma Source ◽  
Western Boundary ◽  
Low Grade ◽  
Early Cambrian ◽  
Zircon Age ◽  
Sierras Pampeanas ◽  
Metasedimentary Rocks ◽  
Icp Ms

An Early Cambrian pluton, known as the Guasayán pluton, has been identified in the central area of Sierra de Guasayán, northwestern Argentina. A U-Pb zircon Concordia age of 533±4 Ma was obtained by LA-MC-ICP-MS and represents the first report of robustly dated Early Cambrian magmatism for the northwestern Sierras Pampeanas. The pluton was emplaced in low-grade metasedimentary rocks and its magmatic assemblage consists of K-feldspar (phenocrysts)+plagioclase+quartz+biotite, with zircon, apatite, ilmenite, magnetite and monazite as accessory minerals. Geochemically, the granitic rock is a metaluminous subalkaline felsic granodiorite with SiO2=69.24%, Na2O+K2O=7.08%, CaO=2.45%, Na2O/ K2O=0.71 and FeO/MgO=3.58%. Rare earth element patterns show moderate slope (LaN/YbN=8.05) with a slightly negative Eu anomalies (Eu/Eu*=0.76). We report the first in situ Hf isotopes data (εHft=-0.12 to -4.76) from crystallized zircons in the Early Cambrian granites of the Sierras Pampeanas, helping to constrain the magma source and enabling comparison with other Pampean granites. The Guasayán pluton might provide a link between Early Cambrian magmatism of the central Sierras Pampeanas and that of the Eastern Cordillera, contributing to define the western boundary of the Pampean paleo-arc.

In Situ Elemental and Sr Isotope Characteristics of Magmatic to Hydrothermal Minerals from the Black Mountain Porphyry Deposit, Baguio District, Philippines

2020 ◽  
Vol 115 (4) ◽  
pp. 927-944 ◽  
Author(s):  
MingJian Cao ◽  
Pete Hollings ◽  
Noreen J. Evans ◽  
David R. Cooke ◽  
Brent I.A. McInnes ◽  
...  
Keyword(s):  
Mafic Magma ◽  
Wall Rock ◽  
Type I ◽  
Felsic Magma ◽  
Sr Isotope ◽  
Magmatic Stage ◽  
Black Mountain ◽  
Late Stages ◽  
Isotope Variation

Abstract At the Black Mountain porphyry Cu-Au deposit in the Baguio district, Northern Luzon (Philippines), pre- and synmineralized rocks preserve magmatic and hydrothermal minerals (e.g., plagioclase, amphibole, titanite, and epidote) spanning the complete paragenesis of the deposit. Strontium isotope values in early crystallized plagioclase phenocrysts from all felsic porphyries can be divided into two types. The type-I plagioclase crystals show relatively homogeneous Sr isotope values (0.7035–0.7038, 1σ <0.0001), indicating crystallization from a relatively stable and long-lived felsic magma chamber. The type-II plagioclase grains have a wider range of Sr isotope compositions (0.7032–0.7039, 1σ <0.0001), indicating mafic and/or felsic magma recharge. In magmatic titanite, Nb/Ta values are higher than those in the whole rock, while Zr/Hf and Y/Ho values are lower. In hydrothermal titanite and epidote, the ratios are similar to those in the whole rock. These patterns reflect crystallization effects imposed during the magmatic stage but an absence of differentiation during the hydrothermal stage. The consistent gradual decrease in total rare earth element, Y, Zr, and U contents in both hydrothermal titanite and epidote from early to late stages indicates the effect of hydrothermal fluid evolution with decreasing temperature. The variation of 87Sr/86Sr values in magmatic amphibole, plagioclase, and hydrothermal epidote in felsic and mafic rocks indicates the addition of mafic magma-derived fluid into the felsic magma-derived fluid. One extra source of fluid (probably derived from wall-rock limestone) was required to generate the highly radiogenic 87Sr/86Sr values of some epidote (0.7038–0.7053). Thus, in situ elemental and Sr isotope variation in minerals from different paragenetic stages can be used to interpret formation process and source for both magmas and hydrothermal fluids.

Geochemical evaluation of the in-situ regolith of Madengi hills of Dodoma, Tanzania. Implication on bedrock mapping and delineating gold mineralization target

2021 ◽  
pp. geochem2021-074
Author(s):  
Godson Godfray
Keyword(s):  
Gold Mineralization ◽  
Early Stage ◽  
Shear Zones ◽  
Soil Geochemistry ◽  
Residual Soils ◽  
Content Type ◽  
Geochemical Evaluation ◽  
Supplementary Material ◽  
Pathfinder Elements

Successful gold exploration projects depend on a piece of clear information on the association between gold, trace elements, and mineralization controlling factors. The use of soil geochemistry has been an important tool in pinpointing exploration targets during the early stage of exploration. This study aimed to establish the gold distribution, the elemental association between gold and its pathfinder elements such as Cu, Zn, Ag, Ni, Co, Mn, Fe, Cd, V, Cr, Ti, Sc, In, and Se and identify lithologies contributing to the overlying residual soils. From cluster analysis, a high similarity level of 53.93% has been shown with Ag, Cd, and Se at a distance level of 0.92. Au and Se have a similarity level of 65.87% and a distance level of 0.68, hence is proposed to be the most promising pathfinder element. PCA, FA, and the Pearson's correlation matrix of transformed data of V, Cu, Ni, Fe, Mn, Cr, and Co and a stronger correlation between Pb and U, Th, Na, K, Sn, Y, Ta and Be shows that source gold mineralization might be associated with both hornblende gneisses interlayered with quartzite, tonalite, and tonalitic orthogneiss. From the contour map and gridded map of Au and its pathfinder elements, it has been noted that their anomalies and target generated are localized in the Northern part of the area. The targets trend ESE to WNW nearly parallel to the shear zones as a controlling factor of Au mineralization emplacement.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5721965

Outbreak densities of the coral predator Drupella in relation to in situ Acropora growth rates on Ningaloo Reef, Western Australia

Coral Reefs ◽  
2018 ◽  
Vol 37 (4) ◽  
pp. 985-993 ◽  
Author(s):  
C. Bessey ◽  
R. C. Babcock ◽  
D. P. Thomson ◽  
M. D. E. Haywood
Keyword(s):  
Western Australia ◽  
Growth Rates ◽  
Ningaloo Reef

scholarly journals Mise En Évidence De Nouvelles Structures Géologiques Dans La Région De Brobo (Centre De La Côte d’Ivoire). Aide À La Compréhension De La Tectonique Du Paléoprotérozoïque Du Craton Ouest Africain

2018 ◽  
Vol 14 (18) ◽  
pp. 305
Author(s):  
Daï Bi Seydou Mathurin ◽  
Ouattara Gbele ◽  
Koffi Gnammytchet Barthélémy ◽  
Gnanzou Allou ◽  
Coulibaly Inza
Keyword(s):  
Cote D'ivoire ◽  
Field Data ◽  
Côte D’Ivoire ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Cote D’Ivoire ◽  
Metasedimentary Rocks ◽  
Large Structures ◽  
Côte D'ivoire ◽  
Ductile Shear Zones

The lithological and structural observations of the region of Brobo (Central Côte d'Ivoire) indicate a succession of metasedimentary rocks (micaschists with cordierite, silstones, graphitic sediments, sandstones with amphibole-garnet, etc.) intermixed with volcanic rocks (rhyolite, dacite, andesite, basalt and the volcanoclastics). The whole is intruded by granites with one or two micas, sometimes porphyries, granodiorites, gabbros, and granite gneisses. Interpretations of Landsat ETM+ , RadarSat-1 and SRTM remote sensing imageries, as well as field data, revealed several lineament directions which, after field control, correspond to major faults and shear zones. These large structures show the N-S, NE-SW, NNE-SSW, E-W, NWSE, and NNW-SSE orientations. The field data also made it possible to describe several structures and to propose a preliminary geodynamic model for the setting and structuring of the formations of this region. This model suggests that the geodynamic took place in three stages: distension with a deformation of basement formations generating a gneissocity (D1), as well as deposits of sediments in the basins; followed by a NW-SE to E-W convergence generating a cleavage in the volcanogenic series (D2). This phase of deformation continues while creating, locally, a strain slip cleavage or a transposed schistosity. The third cleavage affects the volcanogenic series (fractures cleavages, D3) and ends in large corridors of ductile shear zones and associated faults.

scholarly journals Origins and characterization of CO and O<sub>3</sub> in the African upper troposphere

2021 ◽  
Author(s):  
Victor Lannuque ◽  
Bastien Sauvage ◽  
Brice Barret ◽  
Hannah Clark ◽  
Gilles Athier ◽  
...  
Keyword(s):  
Wind Shear ◽  
Asian Monsoon ◽  
Shear Zones ◽  
Hadley Cell ◽  
Trade Winds ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Hadley Cells

Abstract. Between December 2005 and 2013, the In-service Aircraft for a Global Observing System (IAGOS) program produced almost daily in situ measurements of CO and O3 between Europe and southern Africa. IAGOS data combined with measurements from the IASI instrument onboard the Metop-A satellite (2008–2013) are used to characterize meridional distributions and seasonality of CO and O3 in the African upper troposphere (UT). The FLEXPART particle dispersion model and the SOFT-IO model which combines the FLEXPART model with CO emission inventories are used to explore the sources and origins of the observed transects of CO and O3. We focus our analysis on two main seasons: December to March (DJFM) and June to October (JJASO). These seasons have been defined according to the position of Intertropical Convergence Zone (ITCZ), determined using in situ measurements from IAGOS. During both seasons, the UT CO meridional transects are characterized by maximum mixing ratios located 10° from the position of the ITCZ above the dry regions inside the hemisphere of the strongest Hadley cell (132 to 165 ppb at 0–5° N in DJFM and 128 to 149 ppb at 3–7° S in JJASO), and decreasing values south- and north-ward. The O3 meridional transects are characterized by mixing ratio minima of ~ 42–54 ppb at the ITCZ (10–16° S in DJFM and 5–8° N in JJASO) framed by local maxima (~ 53–71 ppb) coincident with the wind shear zones North and South of the ITCZ. O3 gradients are strongest in the hemisphere of the strongest Hadley cell. IASI UT O3 distributions in DJFM have revealed that the maxima are a part of a crescent-shaped O3 plume above the Atlantic Ocean around the Gulf of Guinea. CO emitted at the surface is transported towards the ITCZ by the trade winds and then convectively uplifted. Once in the upper troposphere, CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maximum CO mixing ratios are found. Anthropogenic and fires both contribute, by the same order of magnitude, to the CO budget of the African upper troposphere. Local fires have the highest contribution, drive the location of the observed UT CO maxima, and are related to the following transport pathway: CO emitted at the surface is transported towards the ITCZ by the trade winds and further convectively uplifted. Then UT CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maxima are located. Anthropogenic CO contribution is mostly from Africa during the entire year, with a low seasonal variability, and is related to similar transport circulation than fire air masses. There is also a large contribution from Asia in JJASO related to the fast convective uplift of polluted air masses in the Asian monsoon region which are further westward transported by the tropical easterly jet (TEJ) and the Asian monsoon anticyclone (AMA). O3 minima correspond to air masses that were recently uplifted from the surface where mixing ratios are low at the ITCZ. The O3 maxima correspond to old high altitude air masses uplifted from either local or long distance area of high O3 precursor emissions (Africa and South America during all the year, South Asia mainly in JJASO), and must be created during transport by photochemistry. This analysis of meridional transects contribute to a better understanding of distributions of CO and O3 in the intertropical African upper troposphere and the processes which drive these distributions. Therefore, it provides a solid basis for comparison and improvement of models and satellite products in order to get the good O3 for the good reasons.

scholarly journals Cenozoic deformation in the Tauern Window (Eastern Alps) constrained by in situ Th-Pb dating of fissure monazite

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 437-467 ◽  
Author(s):  
Emmanuelle Ricchi ◽  
Christian A. Bergemann ◽  
Edwin Gnos ◽  
Alfons Berger ◽  
Daniela Rubatto ◽  
...  
Keyword(s):  
Thermal Evolution ◽  
Structural Data ◽  
Shear Zones ◽  
Eastern Alps ◽  
Strike Slip ◽  
Major Peak ◽  
Tauern Window ◽  
Two Phases ◽  
Fissure Formation

Abstract. Thorium–lead (Th-Pb) crystallization ages of hydrothermal monazites from the western, central and eastern Tauern Window provide new insights into Cenozoic tectonic evolution of the Tauern metamorphic dome. Growth domain crystallization ages range from 21.7 ± 0.4 to 10.0 ± 0.2 Ma. Three major periods of monazite growth are recorded between ∼ 22–20 (peak at 21 Ma), 19–15 (major peak at 17 Ma) and 14–10 Ma (major peak around 12 Ma), respectively, interpreted to be related to prevailing N–S shortening, in association with E–W extension, beginning strike-slip movements and reactivation of strike-slip faulting. Fissure monazite ages largely overlap with zircon and apatite fission track data. Besides tracking the thermal evolution of the Tauern dome, monazite dates reflect episodic tectonic movement along major shear zones that took place during the formation of the dome. Geochronological and structural data from the Pfitschtal area in the western Tauern Window show the existence of two cleft generations separated in time by 4 Ma and related to strike-slip to oblique-slip faulting. Moreover, these two phases overprint earlier phases of fissure formation. Highlights. In situ dating of hydrothermal monazite-(Ce). New constraints on the exhumation of the Tauern metamorphic dome. Distinct tectonic pulses recorded from east to west.

scholarly journals Cenozoic deformation in the Tauern Window (Eastern Alps, Austria) constrained by in-situ Th-Pb dating of fissure monazite

2019 ◽  
Author(s):  
Emmanuelle Ricchi ◽  
Christian A. Bergemann ◽  
Edwin Gnos ◽  
Alfons Berger ◽  
Daniela Rubatto ◽  
...  
Keyword(s):  
Thermal Evolution ◽  
Structural Data ◽  
Shear Zones ◽  
Eastern Alps ◽  
Strike Slip ◽  
Tauern Window ◽  
Dome Growth ◽  
Two Phases ◽  
Fissure Formation

Abstract. Thorium-Pb crystallization ages of hydrothermal monazites from the western, central and eastern Tauern Window provide new insights into Cenozoic tectonic evolution of the Tauern metamorphic dome. Growth domain crystallization ages range from 22.3 ± 0.6 Ma to 7.7 ± 0.9 Ma. Three major periods of monazite growth are recorded between ~ 22–19 (peak at 21 Ma), 19–15 (major peak at 17 Ma) and 13–8 Ma (major peaks at 12, 10 and 8 Ma), respectively interpreted to be related to prevailing N-S shortening, in association with E-W extension, beginning strike-slip movements, and reactivation of strike-slip faulting. Fissure monazite ages largely overlap with zircon and apatite fission tracks data. Besides tracking the thermal evolution of the Tauern dome, monazite dates reflect episodic tectonic movement along major shear zones that took place during the formation of the dome. Geochronological and structural data from the Pfitschtal area in the western Tauern Window show the existence of two cleft generations separated in time by 4 Ma and related to strike-slip to oblique-slip faulting. Moreover, these two phases overprint earlier phases of fissure formation.

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