scholarly journals REINTERPRETAÇÃO DA AMBIÊNCIA TECTÔNICA DE FORMAÇÃO DO LEUCOGRANITO DE GOUVEIA (MINAS GERAIS)

2018 ◽  
Author(s):  
Alexandre de Oliveira Chaves ◽  
Raphael Martins Coelho
Keyword(s):  
Heat Transfer ◽  
Tectonic Setting ◽  
Minas Gerais ◽  
Mantle Plumes ◽  
Crustal Melting ◽  
Type Granite ◽  
Wilson Cycle ◽  
Tectonic Settings

Resumo: Granitoides podem se formar não apenas nos vários ambientes dos diferentes estágios do ciclo de Wilson, como também acima de plumas mantélicas, como resultado da fusão crustal decorrente do calor fornecido pelas plumas. Com base na geoquímica e geocronologia disponível na literatura, este artigo leva em conta essa última possibilidade na reinterpretação do ambiente tectônico de formação do leucogranito de Gouveia (Minas Gerais), que havia sido previamente interpretado como granitoide de ambiente tectônico colisional.Palavras Chave: Granito tipo-A, Gouveia, fusão crustalAbstract:TECTONIC SETTING OF THE GOUVEIA LEUCOGRANITE (MINAS GERAIS) REINTERPRETED. Granitoids can be originated not only in the diverse tectonic settings of the Wilson Cycle, but also above mantle plumes, as a result of the crustal melting promoted by heat transfer from plumes. Based on geochemistry and geochronology available in literature, this paper takes this possibility into account on the reinterpretation of the Gouveia leucogranite tectonic setting, previously interpreted as collisional.Keywords: A-type granite, Gouveia, crustal melting

Petrogenesis and tectonic significance of the middle Neoproterozoic highly fractionated A-type granite in the South Qinling block

2021 ◽  
pp. 1-20
Author(s):  
Xiao-Fei Qiu ◽  
Qiong Xu ◽  
Tuo Jiang ◽  
Shan-Song Lu ◽  
Long Zhao
Keyword(s):  
Tectonic Setting ◽  
Eastern China ◽  
Continental Rift ◽  
The South ◽  
Yangtze Craton ◽  
Dabie Orogen ◽  
Northern Margin ◽  
South Qinling ◽  
Type Granite ◽  
High Alkali

Abstract The South Qinling block, a segment of the Yangtze craton involved in the Qinling–Dabie orogen, is critical for understanding the tectonic evolution of eastern China. However, the tectonic setting of the South Qinling block and the northern margin of the Yangtze block during middle Neoproterozoic time has long been the subject of debate, with two distinctly different models (continental rift or volcanic arc) proposed. Here, a comprehensive study of zircon U–Pb geochronology and geochemistry has been carried out on the Chengwan granitic pluton from the Suizao terrane in the South Qinling block. The granites are monzogranite and syenogranite in lithology, and are mainly composed of potash feldspar, quartz, plagioclase and biotite. This suite has long been regarded as a Palaeozoic magmatic pluton, but zircon U–Pb ages of 809 ± 9 Ma and 816 ± 4 Ma are obtained in this study. The granites are metaluminous to strongly peraluminous with high alkali contents, and exhibit highly fractionated features, including high SiO2, low Zr/Hf ratios, rare earth element tetrad effects and enrichment of K and Rb. They show Hf–Nd isotopic decoupling, which may be genetically related to their petrogenetic process. Based on the geochemical features and the positive εHf(t) values of the zircons, it is indicated that the granites may have been derived from partial melting of juvenile tonalitic rocks by biotite breakdown under fluid-absent conditions. The Chengwan granite geochemically belongs to the A2-subtype granites, suggesting that it might have formed in a post-orogenic tectonic setting. The highly fractionated A-type granite in this study may represent extensional collapse shortly after the collisional events in the South Qinling block, and thus indicate a tectonic regime switch, from compression to extension, as early as middle Neoproterozoic time. Integrating our new data with documented magmatic, metamorphic and sedimentary events during middle Neoproterozoic time in the region may support a continental rift model, and argues against arc models.

Early Cretaceous redbeds from the Minle Basin, Hexi Corridor, northwest China: Mineralogy and geochemistry implications for paleoweathering, provenance, and tectonic settings

2019 ◽  
Vol 7 (2) ◽  
pp. T525-T545
Author(s):  
Yaxiong Sun ◽  
Wenlong Ding ◽  
Yang Gu ◽  
Gang Zhao ◽  
Siyu Shi ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Lower Cretaceous ◽  
Chemical Weathering ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Northwest China ◽  
Hexi Corridor ◽  
Sediment Supply ◽  
Compositional Variation ◽  
Tectonic Settings

Redbeds with a large thickness in the lower Cretaceous record abundant geologic information in the Minle Basin. We have conducted the paleoweathering conditions, provenance, and tectonic settings based on mineralogy and geochemistry. Our results indicate that mudstone samples are characterized by abundant illite with negligible amounts of K-feldspars and analcime. The lower part of the lower Cretaceous is rich in quartz, whereas the upper part is dominated by dolomite and analcime. We suggest that this is caused by the decreasing input of the clastic influx during the middle-late early Cretaceous. High index of compositional variation values (average 1.33) indicate first-cycle sediment supply, suggesting an overall compositional immaturity and short-distance transportation. These characteristics are consistent with an active regional extension tectonic setting. The [Formula: see text] system ([Formula: see text];[Formula: see text];[Formula: see text]) and Th/U versus Th consistently reveal that the lower Cretaceous experienced a positive gradient in chemical weathering from young to old formations. Although the patterns of trace elements in three formations of the lower Cretaceous are different, those of the rare earth elements (REEs) tend to be consistent. The significant enrichment of light REEs, heavy REEs fractionation, and distinctive negative Eu anomalies suggest derivation from an old, upper continental crust composed of predominantly felsic sediments. This interpretation is supported by several discrimination diagrams such as titanium dioxide-nickel ([Formula: see text]), which shows the characteristics of immature recycled sediments. A few sensitive elements, ratios, and normalized REE patterns indicate a provenance of an active continental margin and a continental island arc (CIA). The La-Th-Sc, Th-Co-Zr/10, and Th-Sc-Zr/10 discrimination plots further confirm the CIA signature. Thus, we conclude that the early Cretaceous redbeds in the Minle Basin, Hexi Corridor, were deposited in a dustpan-shaped half-graben basin in a CIA setting when northwest China was influenced by intense regional extension.

scholarly journals Hotspots and mantle plumes revisited: Towards reconciling the mantle heat transfer discrepancy

2020 ◽  
Vol 542 ◽  
pp. 116317 ◽  
Author(s):  
Mark J. Hoggard ◽  
Ross Parnell-Turner ◽  
Nicky White
Keyword(s):  
Heat Transfer ◽  
Mantle Plumes

scholarly journals Latest Paleoproterozoic (ca. 1.8–1.6 Ga) extensional tectonic setting in the Dunhuang terrane, NW China: Evidence from geochronological and geochemical investigations on A-type granite and metamafic rock

Lithosphere ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 834-854 ◽  
Author(s):  
Yan Zhao ◽  
Wenhao Ao ◽  
Hong Zhang ◽  
Qian Wang ◽  
Mingguo Zhai ◽  
...  
Keyword(s):  
Mantle Source ◽  
Magma Mixing ◽  
Tectonic Setting ◽  
Regional Metamorphism ◽  
Global Scale ◽  
Mixing Processes ◽  
Tectonic Event ◽  
Depleted Mantle ◽  
Type Granite ◽  
T Values

Abstract Latest Paleoproterozoic (ca. 1.8–1.6 Ga) magmatic rocks outcrop in the Dunhuang terrane, represented by A-type granites and mafic (basaltic) rocks that have metamorphosed into amphibolites. The A-type granites, emplaced at ca. 1.79–1.77 Ga, are geochemically characterized by high Na2O + K2O, Fe2O3T, Zr, Nb, and Ce contents, as well as high Fe2O3T/(Fe2O3T + MgO) and Ga/Al ratios. Furthermore, they have Nb/Ta, Y/Nb, Rb/Nb, and Sc/Nb ratios of 12.10–15.56, 1.45–1.79, 3.52–6.51, and 0.11–0.19, respectively, showing affinity to A2-type granite. The A-type granites have negative εNd(t) values (−5.4 to −4.8) with Neoarchean depleted mantle (TDM2) ages (2591–2494 Ma), corresponding to coupling between εHf(t) values (−4.85 to -0.92) and TDM2 ages (2817–2556 Ma) of zircons. Therefore, the A-type granite pluton was mostly generated by partial melting of Neoarchean tonalitic to granodioritic basement rocks of the Dunhuang Complex in a postcollisional tectonic setting following a late Paleoproterozoic continent-continent collisional event. The metamafic rocks have a protolith age of 1605 ± 45 Ma and metamorphic age of 317 ± 20 Ma, indicating a Paleozoic tectonic event. The metamafic rock samples are geochemically characterized by relatively high alkali (Na2O + K2O = 4.39–4.81 wt%) contents and low Nb/Y (0.63–0.66) ratios, and they show steep rare earth element (REE) patterns with light REE enrichment and insignificant Eu anomalies and Nb-Ta, Zr-Hf, and Ti anomalies, resembling subalkaline oceanic-island basalt affinity. They have positive εNd(t) values (+0.8 to +1.8) close to the chondrite evolutionary line and variable εHf(t) values (-1.09 to +9.06) of zircons. Hence, the protolith of the metamafic rocks may have been produced by magma mixing processes between a depleted mantle source and a metasomatized lithospheric mantle source during the initial rifting stage in an extensional setting, completing the formation of the Precambrian Dunhuang Complex. Considering the ca. 1.85–1.80 Ga regional metamorphism in the Dunhuang terrane, the latest Paleoproterozoic (ca. 1.8–1.6 Ga) A2-type granitic magmatism and mafic magmatism documented the postorogenic to initial rifting processes following the global-scale late Paleoproterozoic collisional event, which is comparable with ca. 1.80–1.67 Ga postcollisional and ca. 1.60–1.53 Ga anorogenic magmatism in the North China craton, but different from that of the Tarim craton.

Geochemistry of plutonic spinels from the North Kamchatka Arc: comparisons with spinels from other tectonic settings

1993 ◽  
Vol 57 (389) ◽  
pp. 575-589 ◽  
Author(s):  
Pavel K. Kepezhinskas ◽  
Rex N. Taylor ◽  
Hisao Tanaka
Keyword(s):  
Tectonic Setting ◽  
Transitional Zone ◽  
Late Eocene ◽  
Accessory Mineral ◽  
Volatile Content ◽  
Complex Chemical ◽  
Chemical Zoning ◽  
Magmatic Arc ◽  
The North ◽  
Tectonic Settings

AbstractUltramafic to marie plutons in the Olyutor Range, North Kamchatka, represent the magmatic roots of a late Eocene arc, related to the westward subduction of the Komandorsky Basin beneath the Asian continental margin. Olyutor Range plutons are concentrically zoned with cumulate dunite cores mantled by a wehrlite-pyroxenite transitional zone and, in turn, by a narrow gabbroic rim.Spinel is a common accessory mineral in these arc plutonics, and we present analyses of spinels from a range of lithologies. A continuous compositional trend is observed from Cr-spinel in the ultramafics to Cr-rich magnetite in marginal gabbros. Complex chemical zoning patterns within individual spinel grains suggest an interplay between fO2, fractionation, volatile content and subsequent sub-solidus reequilibration of spinel with co-existing silicates (mainly olivine).In general, the spinels from magmatic arc environments are characterised by high total Fe and high Fe3+ contents compared to MORB and boninitic spinels and higher Cr-values relative to oceanic basin spinels. These differences imply a high oxygen fugacity during arc petrogenesis. Differences are also observed between plutonic spinels from arcs and low-Ti supra-subduction zone ophiolites. Low-Ti ophiolitic spinels are generally poorer in iron and richer in Cr, and hence are similar in composition and perhaps tectonic setting to fore-arc boninitic spinels.

Petrogenesis and tectonic setting of the Devonian Xiqin A-type granite in the northeastern Cathaysia Block, SE China

2017 ◽  
Vol 141 ◽  
pp. 43-58 ◽  
Author(s):  
Da-wei Cai ◽  
Yong Tang ◽  
Hui Zhang ◽  
Zheng-Hang Lv ◽  
Yun-long Liu
Keyword(s):  
Tectonic Setting ◽  
Type Granite ◽  
Cathaysia Block ◽  
Se China

scholarly journals Granitoid plutons in peri-Gondwanaan terranes of Cape Breton Island, Nova Scotia, Canada: new U-Pb (zircon) age constraints

2018 ◽  
pp. 021-080 ◽  
Author(s):  
Sandra M. Barr ◽  
Deanne Van Rooyen ◽  
Chris E. White
Keyword(s):  
Tectonic Setting ◽  
Magmatic Activity ◽  
Zircon Age ◽  
Cape Breton Island ◽  
The Past ◽  
Late Cambrian ◽  
Cape Breton ◽  
History Of ◽  
Tectonic Settings ◽  
Age Constraints

Granitoid plutons are a major component of pre-Carboniferous rocks in Cape Breton Island and knowledge of the time and tectonic setting of their emplacement is crucial for understanding the geological history of the island, guiding exploration for granite-related economic mineralization, and making along-orogen correlations. The distribution of these plutons and their petrological characteristics have been used in the past for recognizing both Laurentian and peri-Gondwanan components in Cape Breton Island, and for subdividing the peri-Gondwanan components into Ganderian and Avalonian terranes. However, ages of many plutons were assumed on the basis of field relations and petrological features compared to those of the relatively few reliably dated plutons. Seventeen new U–Pb (zircon) ages from igneous units reported here provide enhanced understanding of the distribution of pluton ages. Arc-related plutons in the Aspy terrane with ages of ca. 490 to 475 Ma likely record the Penobscottian tectonomagmatic event recognized in the Exploits subzone of central Newfoundland and New Brunswick but not previously recognized in Cape Breton Island. Arc-related Devonian plutonic activity in the same terrane is more widespread, continuous, and protracted (445 Ma to 395 Ma) than previously known. Late Devonian magmatism in the Ganderian Aspy terrane is similar in age to that in the Avalonian Mira terrane (380 to 360 Ma) but the tectonic settings are different. In contrast, magmatic activity in the Bras d’Or terrane is almost exclusively arc-related in the Late Ediacaran (580 to 540 Ma) and rift-related in the Late Cambrian (520 to 490 Ma). The new data support the terrane distinctions previously documented.

scholarly journals Petrogenesis of Volcanic Arc Granites from Bayah Complex, Banten, Indonesia

2019 ◽  
Vol 4 (2) ◽  
pp. 104
Author(s):  
Jemi Saputra Ahnaf ◽  
Aton Patonah ◽  
Haryadi Permana
Keyword(s):  
Tectonic Setting ◽  
Crustal Contamination ◽  
Polarized Light ◽  
Granitic Rocks ◽  
Tectonic Activity ◽  
Molar Ratio ◽  
Petrographic Analysis ◽  
Volcanic Arc ◽  
Regional Tectonic ◽  
Type Granite

This research aimed to reveal the petrogenesis of granitic rocks of Bayah Complex starting from magma differentiation to exposing event, this research also intended to determine the tectonic environment. The methods carried out in this research include field observation, petrographic analysis using polarized light microscopy, and geochemical analysis using X-Ray Fluorescence (XRF) and Inductively Coupled Mass Spectrometry (ICP-MS). Petrographic analysis shows that Bayah granitic rocks are composed of quartz, plagioclase, and K-feldspar while the rest are amphibole, biotite, sericite, chlorite, epidote, and opaque. Based on its major oxide concentrations, Bayah granitic rocks classified as granite and diorite-quartz which have high-K calc-alkaline magma. 4 samples of granitic rocks showed the A/N+K+C > 1 molar ratios belonging to the peraluminous S-type granite index while the remaining 1 sample showed a molar ratio of A/N+ K+C < 1 and A/N+K > 1 which classified as metaluminous I-type granite. Accordingly, Bayah granitic rocks are S-type granite which crystallized from sediment-derived magma, the sediments itself estimated sourced from continental especially Malay Peninsula, Indonesian Tin Island, and Schwaner Mountains. During differentiation, the magma undergone crustal contamination reflected by the increase in both SiO2 0.51 wt% and Al2O3 1.95 wt%, and decrease in Fe2O3 + MgO 0.61 wt% from the pure composition of sediment-derived magma. Furthermore, the occurrence of crustal contamination also recognized from high concentrations of Rb and Ba which indicate the interaction of magma with the materials of continental crust. Regard to the exposing event, Bayah granitic rocks approximated to be exposed due to regional tectonic activity which caused Orogenesa I in the Early Oligocene to the Late Oligocene. Moreover, based on the plot of trace elements especially Rb, Y, Nb, Ta, and Yb on Harker and tectonic discriminant diagrams, Bayah granitic rocks are formed on volcanic-arc active continental margins in accordance with regional tectonic setting.           

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