scholarly journals Re-Os Geochronology, Whole-Rock and Radiogenic Isotope Geochemistry of the Wulandele Porphyry Molybdenum Deposit in Inner Mongolia, China, and Their Geological Significance

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 374
Author(s):  
Xiaojun Zhang ◽  
Chunliang Yao ◽  
David R. Lentz ◽  
Ying Qin ◽  
Yiwen Wei ◽  
...  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Inner Mongolia ◽  
Isotope Geochemistry ◽  
Minor Component ◽  
Depleted Mantle ◽  
Molybdenum Deposit ◽  
Regional Tectonic ◽  
Northern Inner Mongolia ◽  
A Minor

The Wulandele molybdenum deposit is a porphyry-type Mo deposit in the Dalaimiao area of northern Inner Mongolia, China. Molybdenite Re-Os dating yields a model age of 134.8 ± 1.9 Ma, with the fine-grained monzogranite most closely related to the mineralization. The lithogeochemical data show that the monzogranite is weakly peraluminous, high-K calc-alkaline series, with reduced to slightly oxidized, highly fractionated I-type granite characteristics. The relatively low initial 87Sr/86Sr (range from 0.705347 to 0.705771), weakly negative εNd(t) (range from −2.0 to −1.3), and crust-mantle mixing of Pb isotopes suggest that the monzogranite originated from the partial melting of mafic juvenile lower continental crust derived from the depleted mantle, with a minor component of ancient continental crust. Combined with the regional tectonic evolution, we argue that the partial melting, then injection, of the monzogranite melt was probably triggered by collapse or delamination of the thickened lithosphere, which was mainly in response to the post-orogenic extensional setting of the Mongol–Okhotsk belt; this is possibly coupled with a back-arc extension related to Paleo-Pacific plate subduction. The extensively fractional crystallization of the monzogranite melt is the crucial enrichment process, resulting in magmatic hydrothermal Mo mineralization in the Wulandele deposit, and the Cretaceous granitoids are generally favorable to form Mo mineralization in the Dalaimiao area.

The Early Cretaceous San Juan Plutonic Suite, Ecuador: a magma chamber in an oceanic plateau?

2004 ◽  
Vol 41 (10) ◽  
pp. 1237-1258 ◽  
Author(s):  
Marc Mamberti ◽  
Henriette Lapierre ◽  
Delphine Bosch ◽  
Etienne Jaillard ◽  
Jean Hernandez ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Minor Component ◽  
San Juan ◽  
Type I ◽  
Oceanic Plateau ◽  
Depleted Mantle ◽  
Plutonic Rocks ◽  
Ultramafic Cumulates ◽  
A Minor ◽  
End Members

Sections through an oceanic plateau are preserved in tectonic slices in the Western Cordillera of Ecuador (South America). The San Juan section is a sequence of mafic–ultramafic cumulates. To establish that these plutonic rocks formed in an oceanic plateau setting, we have developed criteria that discriminate intrusions of oceanic plateaus from those of other tectonic settings. The mineralogy and crystallization sequence of the cumulates are similar to those of intra-plate magmas. Clinopyroxene predominates throughout, and orthopyroxene is only a minor component. Rocks of intermediate composition are absent, and hornblende is restricted to the uppermost massive gabbros within the sequence. The ultramafic cumulates are very depleted in light rare-earth elements (LREE), whereas the gabbros have flat or slightly enriched LREE patterns. The composition of the basaltic liquid in equilibrium with the peridotite, calculated using olivine compositions and REE contents of clinopyroxene, contains between 16% and 8% MgO and has a flat REE pattern. This melt is geochemically similar to other accreted oceanic plateau basalts, isotropic gabbros, and differentiated sills in western Ecuador. The Ecuadorian intrusive and extrusive rocks have a narrow range of εNdi (+8 to +5) and have a rather large range of Pb isotopic ratios. Pb isotope systematics of the San Juan plutonic rocks and mineral separates lie along a mixing line between the depleted mantle (DMM) and the enriched-plume end members. This suggests that the Ecuadorian plutonic rocks generated from the mixing of two mantle sources, a depleted mid-oceanic ridge basalt (MORB) source and an enriched one. The latter is characterized by high (207Pb/204Pb)i ratios and could reflect a contamination by recycled either lower continental crust or oceanic pelagic sediments and (or) altered oceanic crust (enriched mantle type I, EMI). These data suggest that the San Juan sequence represents the plutonic components of an Early Cretaceous oceanic plateau, which accreted in the Late Cretaceous to the Ecuadorian margin.

Partial melting of subducted oceanic crust and isolation of its residual eclogitic lithology

1991 ◽  
Vol 335 (1638) ◽  
pp. 407-418 ◽  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Oceanic Crust ◽  
Significant Proportion ◽  
Oceanic Lithosphere ◽  
Rutile Phase ◽  
Island Arc ◽  
Plate Boundaries ◽  
Water Release ◽  
Depleted Mantle

Oceanic lithosphere is produced at mid-ocean ridges and reinjected into the mantle at convergent plate boundaries. During subduction, this lithosphere goes through a series of progressive dehydration and melting events. Initial dehydration of the slab occurs during low pressure metamorphism of the oceanic crust and involves significant dewatering and loss of labile elements. At depths of 80-120 km water release by the slab is believed to lead to partial melting of the oceanic crust. These melts, enriched in incompatible elements (excepting Nb, Ta and Ti), fertilize the overlying mantle wedge and produce the enriched peridotitic sources of island arc basalts. Retention of Nb, Ta and Ti by a residual mineral (e.g. in a rutile phase) in a refractory eclogitic lithology within the sinking slab are considered to cause their characteristic depletions in island arc basalts. These refractory eclogitic lithologies, enriched in Nb, Ta and Ti, accumulate at depth in the mantle. The continued isolation of this eclogitic residuum in the deep mantle over Earth ’s history produces a reservoir which contains a significant proportion of the Earth’s Ti, Nb and Ta budget. Both the continental crust and depleted mantle have subchondritic Nb /La and Ti/Zr ratios and thus they cannot be viewed strictly as complementary geochemical reservoirs. This lack of complementarity between the continental crust and depleted mantle can be balanced by a refractory eclogitic reservoir deep in the mantle, which is enriched in Nb, Ta and Ti. A refractory eclogitic reservoir amounting to ca . 2% of the mass of the silicate Earth would also contain significant amounts of Ca and Al and may explain the superchondritic Ca/Al value of the depleted mantle.

Geochemical constraints on the petrogenesis of the Proterozoic granitoid gneisses from the eastern segment of the Central Tianshan Tectonic Zone, northwestern China

2007 ◽  
Vol 144 (2) ◽  
pp. 305-317 ◽  
Author(s):  
QIUGEN LI ◽  
SHUWEN LIU ◽  
ZONGQI WANG ◽  
QUANREN YAN ◽  
ZHAOJIE GUO ◽  
...  
Keyword(s):  
Partial Melting ◽  
Minor Amount ◽  
Tectonic Zone ◽  
Depleted Mantle ◽  
Eastern Segment ◽  
Tectonic Zones ◽  
Granitoid Gneisses ◽  
A Minor ◽  
T Values ◽  
Ree Patterns

The Tianshan orogen is divided into the Northern, Central and Southern Tianshan tectonic zones by the northern and southern sutures on both sides of the Central Tianshan Tectonic Zone. The eastern segment of the Central Tianshan Tectonic Zone is characterized by the presence of numerous Precambrian metamorphic blocks and is unconformably overlain by Ordovician–Silurian and late Palaeozoic strata. The Precambrian Kumishi and Pargantag metamorphic blocks are the largest older blocks in the eastern segment of the Central Tianshan Tectonic Zone, consisting mainly of metamorphic granitoids and sedimentary rocks in greenschist to amphibolite facies. There are two major lithological assemblages of the metamorphic granitoids: (1) quartz dioritic gneisses, and (2) granodioritic–monzogranitic gneisses with a minor amount of tonalitic and syenogranitic gneisses in both the Kumishi and Pargantag blocks. The quartz dioritic gneisses are characterized by low Sr/Ce (<5.3) and Sr/Y (<28), relatively high Mg no. (51.0–57.0), K2O (2.65–4.04 wt %) contents and εNd(t) values (−2.37–5.84), and negative Nb and Zr–Hf anomalies, as well as relatively flat chondrite-normalized REE patterns with slightly negative Eu anomalies, suggesting that the quartz dioritic gneisses were derived from partial melting of a depleted mantle source enriched by fluids and sedimentary melts from the subducted slab. However, most of granitic gneiss samples display high K2O contents, low Al2O3/(FeO* + MgO + TiO2) values, and relatively flat chondrite-normalized REE patterns with intensively negative Eu anomalies. Integrated low εNd(t) values and older TDM model ages suggest that crustal materials played a significant role in the petrogenesis of these granitoid gneisses and that they were mainly derived from the partial melting of calc-alkaline mafic to intermediate rocks in the crust. Also, variations in geochemical features between the Kumishi–Gangou and Pargantag regions, such as Zr and Hf, may reflect geographic variability in the development of coeval granitic magmas. Tectonic discrimination for granitoid, using trace elements, together with Nd isotopic data, demonstrates that these granitoid gneisses in the eastern segment of the Central Tianshan Tectonic Zone formed in a continental margin arc during late Mesoproterozoic times.

Crustal assimilation in the Burnt Lake metavolcanics, Grenville Province, southeastern Ontario, and its tectonic significance

1997 ◽  
Vol 34 (9) ◽  
pp. 1272-1285 ◽  
Author(s):  
T. E. Smith ◽  
P. E. Holm ◽  
N. M. Dennison ◽  
M. J. Harris
Keyword(s):  
Rare Earth ◽  
Trace Element ◽  
Partial Melting ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Lake Area ◽  
Depleted Mantle ◽  
Mafic Magmas ◽  
Back Arc

Three intimately interbedded suites of volcanic rocks are identified geochemically in the Burnt Lake area of the Belmont Domain in the Central Metasedimentary Belt, and their petrogenesis is evaluated. The Burnt Lake back-arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back-arc basins formed in continental crust. The Burnt Lake continental tholeiitic suite comprises basalts and andésites similar in trace element composition to continental tholeiitic sequences. The Burnt Lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts. Rare earth element models suggest that the Burnt Lake back-arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5% partial melting of an amphibole-bearing depleted mantle, enriched in light rare earth elements by a subduction component. The modelling also suggests that the Burnt Lake continental tholeiitic rocks were formed by contamination – fractional crystallization of mixtures of mafic magmas, derived by ~3% partial melting of the subduction-modified source, and rhyolitic crustal melts. These models are consistent with the suggestion that the Belmont Domain of the Central Metasedimentary Belt formed as a back-arc basin by attenuation of preexisting continental crust above a westerly dipping subduction zone.

INFLUENCE OF PULSED MAGMATIC ACTIVITY, LATENT HEAT, AND PARTIAL MELTING ON THE STRENGTH OF THE CONTINENTAL CRUST

2020 ◽  
Author(s):  
Aleksi Rantanen ◽  
◽  
David Whipp ◽  
Jussi S. Heinonen ◽  
Lars Kaislaniemi ◽  
...  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Latent Heat ◽  
Magmatic Activity

Protonation effects on dynamic flux properties of aqueous metal complexes

2009 ◽  
Vol 74 (10) ◽  
pp. 1543-1557 ◽  
Author(s):  
Herman P. Van Leeuwen ◽  
Raewyn M. Town
Keyword(s):  
Complex Formation ◽  
Metal Ion ◽  
Good Description ◽  
Minor Component ◽  
Outer Sphere ◽  
Metal Species ◽  
Central Metal ◽  
Inner Sphere ◽  
A Minor ◽  
Protonated Ligand

The degree of (de)protonation of aqueous metal species has significant consequences for the kinetics of complex formation/dissociation. All protonated forms of both the ligand and the hydrated central metal ion contribute to the rate of complex formation to an extent weighted by the pertaining outer-sphere stabilities. Likewise, the lifetime of the uncomplexed metal is determined by all the various protonated ligand species. Therefore, the interfacial reaction layer thickness, μ, and the ensuing kinetic flux, Jkin, are more involved than in the conventional case. All inner-sphere complexes contribute to the overall rate of dissociation, as weighted by their respective rate constants for dissociation, kd. The presence of inner-sphere deprotonated H2O, or of outer-sphere protonated ligand, generally has a great impact on kd of the inner-sphere complex. Consequently, the overall flux can be dominated by a species that is a minor component of the bulk speciation. The concepts are shown to provide a good description of experimental stripping chronopotentiometric data for several protonated metal–ligand systems.

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