scholarly journals Metallogenic Setting and Evolution of the Pados-Tundra Cr-Bearing Ultramafic Complex, Kola Peninsula: Evidence from Sm–Nd and U–Pb Isotopes

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 186 ◽  
Author(s):  
Pavel A. Serov ◽  
Tamara B. Bayanova ◽  
Ekaterina N. Steshenko ◽  
Evgeniy L. Kunakkuzin ◽  
Elena S. Borisenko
Keyword(s):  
Kola Peninsula ◽  
Large Scale ◽  
Fennoscandian Shield ◽  
Large Igneous Province ◽  
Layered Series ◽  
Ultramafic Complex ◽  
Granulite Belt ◽  
Igneous Province ◽  
Lapland Granulite Belt ◽  
Four Levels

The article presents new Sm–Nd and U–Pb geochronological data on rocks of the poorly studied Pados-Tundra Cr-bearing complex. It is part of the Notozero mafic–ultramafic complex (western Kola Peninsula) and occurs at the border of the Paleoproterozoic Lapland Granulite Belt and the Archean Belomorian composite terrain. The Pados-Tundra complex hosts two major zones, the Dunite and Orthopyroxenite Blocks. Dunites are associated with four levels of chromite mineralization. Isotope Sm–Nd studies of dunites, harzburgites, and orthopyroxenites from the central part of the complex have been carried out. The isochron Sm–Nd age on 11 whole-rock samples from a rhythmically layered series of the complex is 2485 ± 38 Ma; the mineral Sm–Nd isochron for harzburgites shows the age of 2475 ± 38 Ma. It corresponds with the time of large-scale rifting that originated in the Fennoscandian Shield. When the rhythmically layered series of the intrusion and its chromite mineralization were formed, hornblendite dykes intruded. The U–Pb and Sm–Nd research has estimated their age at ca. 2080 Ma, which is likely to correspond with the occurrence of the Lapland–Kola Ocean. According to isotope Sm–Nd dating on metamorphic minerals (rutile, amphibole), the age of postmetamorphic cooling of rocks in the complex to 650–600 °C is 1872 ± 76 Ma. The U–Pb age on rutile from a hornblendite dyke (1804 ± 10 Ma) indicates further cooling to 450–400 °C. The conducted research has determined the early Proterozoic age of rocks in the rhythmically layered series in the Pados-Tundra complex. It is close to the age of the Paleoproterozoic ore magmatic system in the Fennoscandian Shield that developed 2.53–2.40 Ga ago. Later episodes of alterations in rocks are directly related to main metamorphic episodes in the region at the turn of 1.9 Ga. Results of the current study expand the geography of the vast Paleoproterozoic East Scandinavian Large Igneous Province and can be applied for further studies of similar mafic–ultramafic complexes.

Evolution and metallogenic settings of the Pados-Tundra chrome-bearing ultramafic complex, Kola Peninsula: isotope Sm-Nd and U-Pb evidence

2020 ◽  
Author(s):  
Pavel Serov ◽  
Tamara Bayanova ◽  
Ekaterina Steshenko ◽  
Eugenii Kunakkuzin ◽  
Elena Borisenko
Keyword(s):  
Kola Peninsula ◽  
Layered Series ◽  
North East ◽  
The North ◽  
Ultramafic Complex ◽  
Study Results ◽  
Partially Observed ◽  
North Eastern ◽  
Igneous Province ◽  
Enclosing Rocks

<p>The Pados-Tundra massif is located in the western Kola Peninsula and included in the Notozero ultrabasic rock complex (Vinogradov, 1971). The intrusion occurs as a body of ca. 13 km<sup>2</sup> stretched out to the north-east. Enclosing rocks are Archaean granite- and granodiorite-gneisses. There are three major areas in the massif structure (Mamontov, Dokuchaeva, 2005): endocontact area, rhythmically layered series, and upper area. The endocontact area with thickness of 10-20 m occurs as schistose amphibole rocks formed during the metamorphism of main rocks. The rhythmically layered series occurs as a number of rocks from dunites to orthopyroxenites and composes most of the massif. There are 7 rhythms in total, each of which starts with dunites and ends with orthopyroxenites. Dykes of mezo- and leucocratic gabbro, diorites, and hornblendites are developed in the series rocks. The upper gabbronorite area can be partially observed in the north-eastern massif. Presumably, its major volume has been overlapped by enclosing rocks as a result of the overthrust. In the massif, there are 4 horizons of disseminated stratiform chromite ores, which are confined to dunites and serpentinites, as well as to a number of lens- and column-like bodies (podiform type) of chromite ores (Mamontov, Dokuchaeva, 2005; Barkov et al., 2017). Previous isotope-geochronological studies have determined the massif rock age of 2.15 Ga (Shapkin et al., 2008). However, further geological field observations and analysis of the obtained data assume that the intrusive is much older.</p><p>New Sm-Nd geochronological data indicate that the massif rocks and its rhythmically layered series are of Paleoproterozoic age, which is similar to the age of the Cu-Ni-Co-Cr-PGE ore-magmatic system of the Fennoscandian Shield (Amelin et al., 1995; Bayanova et al., 2014, 2017, 2019; Hanski et al., 2001; Huhma et al., 1990, 1996; Layered intrusions ...; 2004; Maier, Hanski, 2017; Mitrofanov et al., 2019; Peltonen, Brugmann, 2006; Puchtel et al., 2001; Serov, 2008; Serov et al., 2014; Sharkov, 2006; Sharkov, Smolkin, 1997). Complex Sm-Nd and U-Pb isotope-geochronological studies have allowed determining the major formation and alteration stages of the Pados-Tundra complex rocks:</p><p>–  formation of the rhythmically layered series rocks of the intrusive 2485±77 Ma, harzburgites of the layered series – 2475±38 Ma;</p><p>– metamorphism of the massif rocks at the turn of 1.95 - 1.9 Ga;</p><p>– postmetamorphic cooling of the complex rocks tо 650°-600°С at the turn of 1872±76 Ma (Sm-Nd for metamorphic minerals) and then to 450°-400°С (U-Pb for rutile, 1804±10 Ma).</p><p>Therefore, the study results expand geography the East-Scandinavian large Palaeoproterozoic igneous province and are prospective for further study of analogous ultramafite-mafite complexes.</p><p>All investigations and were supported by the RFBR 18-05-70082, 18-35-00246, Presidium RAS Program #48 and are in frame of the Theme of Scientific Research 0226-2019-0053.</p>

Formation of the North–South Seismic Zone and Emeishan Large Igneous Province in Central China: Insights from P-Wave Teleseismic Tomography

2020 ◽  
Vol 110 (6) ◽  
pp. 3064-3076
Author(s):  
Chuansong He ◽  
M. Santosh
Keyword(s):  
High Velocity ◽  
Large Scale ◽  
P Wave ◽  
Large Igneous Province ◽  
Seismic Zone ◽  
Teleseismic Tomography ◽  
Emeishan Large Igneous Province ◽  
The North ◽  
Igneous Province ◽  
Stress Accumulation

ABSTRACT The geodynamic features of the north–south seismic zone (NSSZ) and the formation of the Emeishan large igneous province (ELIP) in China remain controversial. In this study, we conducted detailed P-wave teleseismic tomography studies in the NSSZ and adjacent regions. The results revealed large high-velocity anomalies beneath the Songpan–Ganzi Block and the South China Block, possibly representing large-scale lithospheric delamination. We further identified low-velocity structures at 50–200 km depths in the western and southern parts of the NSSZ, suggesting an upwelling asthenosphere induced by delamination and the absence of a rigid lithosphere. Two high-velocity structures beneath the Sichuan basin and the Alashan block were also revealed, which may represent the lithospheric roots of these structures. These rigid lithospheric roots may have obstructed the eastward extrusion of the Tibetan plateau and led to stress accumulation and release (triggering earthquakes) in the Longmenshan Orogenic Belt and the northern part of the NSSZ. Because of this obstruction, the eastward extrusion was redirected southeastward to Yunnan in the southern part of the NSSZ, which led to stress accumulation and release causing earthquakes along the Honghe and Xiaojiang faults. The results from this study reveal a high-velocity structure with a subducted slab-like appearance that may represent vestiges of the Paleo-Tethys oceanic lithosphere, which subducted beneath the ELIP and initiating large-scale mantle return flow or mantle upwelling, contributing to the formation of the ELIP.

Geochronology, isotopic and Platinum-group elemental geochemistry of lavas and dykes from the western Guangxi in outer zone of Emeishan mantle plume, SW China

2021 ◽  
Author(s):  
Bing Zhao ◽  
Xijun Liu ◽  
Zhenglin Li ◽  
Wenmin Huang ◽  
Chuan Zhao
Keyword(s):  
Partial Melting ◽  
Mantle Source ◽  
Large Scale ◽  
Outer Zone ◽  
Large Igneous Province ◽  
Yangtze Block ◽  
Mafic Rocks ◽  
Emeishan Large Igneous Province ◽  
Low Degree ◽  
Igneous Province

<p>The Emeishan flood basalts are part of an important large igneous province along the western margin of the Yangtze Block, Southwest China. The western Guangxi region in southwestern China is geologically a part of the Yangtze Block. Mafic rocks, comprising mainly lavas and dykes in western Guangxi belong to the outer part of the ~260 Ma Emeishan Large Igneous Province (ELIP). Here we present a systematic study of platinum-group elements (PGEs) combined with the LA-ICP-MS zircon U–Pb age, whole-rock geochemical and isotopic data of the lavas and dykes in the Longlin area of outer zone of ELIP to constraints on their origin. On the basis of petrography and major elements characteristics, mafic lavas and dykes display an enrichment of LREE, LILE, HFSE, high (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> ratios (0.704227~0.705754), low ε<sub>Nd</sub><sub>(t)</sub> values(0.42~0.99), high ε<sub>Hf</sub><sub>(t)</sub> values(5.19~6.04), they are similar to those of Permian Emeishan high-Ti basalts and Ocean island basalts (OIB) features. The Longlin mafic rocks was formed in the Late Permian with the zircon U-Pb dated age of 256.3± 1.7 Ma. The age of the Longlin mafic rocks is close to the formation age of the ELIP large-scale magmatism, suggesting that these lavas and dykes probably belongs to part of the ELIP large-scale magmatism. The Longlin mafic rocks have low total PGE contents ranging from 1.56×10<sup>-9 </sup>to 2.28×10<sup>-9</sup>, with Os, Ir, Ru, Rh, Pt and Pd contents of 0.040~0.076, 0.046~0.076, 0.027~0.079, 0.037~0.056, 0.6374~1.053 and 0.715~1.021ppb, respectively. They show left-leaning primitive mantle-normalized PGE patterns with depletion in Iridium group(IPGE) and enrichment in Palladium group, which also have lower contents than mafic rocks from the inner zone of the ELIP, suggesting that a low degree of partial melting of the mantle source plays an important role. The Longlin mafic rocks exhibit a marked increase in Cu/Pd ratios (>10<sup>5</sup>,84655 to 174785) albeit with a narrow range of lower Pd/Ir ratios (<50,13.4 to 18.7), different from the PGE-enriched basalts of the Siberian Traps, Emeishan Large Igneous Province (ELIP), East Greenland CFBs and Deccan Traps, indicating that their parent magmas was significantly depleted in chalcophile elements. Calculations based on the available trace element geochemistry reveal that the basalts were originated by low degree of partial melting(<5%)，with sulfides remain in the mantle during partial melting. Sulfide segregation could not happen during the evolution of the Longlin mafic rocks, due to the fact that neither significant fractional crystallization nor crustal contamination has been involved in their formation. Overall, mafic rocks from the outer zone of the ELIP show lower PGE contents than those in the inner zones, we find that the PGE contents in igneous rocks are related with the degrees of partial melting in the mantle source and the removal of sulfides before their emplacement.</p><p>This study was financially supported by the Guangxi Natural Science Foundation for Distinguished Young Scholars (2018GXNSFFA281009) and the Fifth Bagui Scholar Innovation Project of Guangxi Province (to XU Ji-feng).</p>

scholarly journals A Mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan

Solid Earth ◽  
2011 ◽  
Vol 2 (1) ◽  
pp. 25-33 ◽  
Author(s):  
M. J. Pankhurst ◽  
B. F. Schaefer ◽  
P. G. Betts ◽  
N. Phillips ◽  
M. Hand
Keyword(s):  
Physicochemical Properties ◽  
Large Scale ◽  
South Australia ◽  
Large Igneous Province ◽  
Melt Viscosity ◽  
Volcanic Province ◽  
Low Viscosity ◽  
Geophysical Interpretation ◽  
The Family ◽  
Igneous Province

Abstract. Rhyolite and dacite lavas of the Mesoproterozoic upper Gawler Range Volcanics (GRV) (>30 000 km3 preserved), South Australia, represent the remnants of one of the most voluminous felsic magmatic events preserved on Earth. Geophysical interpretation suggests eruption from a central cluster of feeder vents which supplied large-scale lobate flows >100 km in length. Pigeonite inversion thermometers indicate eruption temperatures of 950–1100 °C. The lavas are A-type in composition (e.g. high Ga/Al ratios) and characterised by elevated primary halogen concentrations (~1600 ppm fluorine, ~400 ppm chlorine). These depolymerised the magma such that temperature-composition-volatile non-Arrhenian melt viscosity modelling suggests they had viscosities of <3.5 log η (Pa s). These physicochemical properties have led to the emplacement of a Large Rhyolite Province, which has affinities in emplacement style to Large Basaltic Provinces. The low viscosity of these felsic magmas has produced a unique igneous system on a scale which is either not present or poorly preserved elsewhere on the planet. The Gawler Range Volcanic Province represents the erupted portion of the felsic end member of the family of voluminous, rapidly emplaced terrestrial magmatic provinces.

scholarly journals A mesoproterozoic continental flood rhyolite province, the Gawler Ranges, Australia: the end member example of the Large Igneous Province clan

2010 ◽  
Vol 2 (2) ◽  
pp. 251-274 ◽  
Author(s):  
M. J. Pankhurst ◽  
B. F. Schaefer ◽  
P. G. Betts ◽  
N. Phillips ◽  
M. Hand
Keyword(s):  
Physicochemical Properties ◽  
Large Scale ◽  
South Australia ◽  
Large Igneous Province ◽  
Melt Viscosity ◽  
Volcanic Province ◽  
Low Viscosity ◽  
Geophysical Interpretation ◽  
The Family ◽  
Igneous Province

Abstract. Rhyolite and dacite lavas of the Mesoproterozoic upper Gawler Range Volcanics (GRV) (>30 000 km3 preserved), South Australia, represent the remnants of one of the most voluminous felsic magmatic events preserved on Earth. Geophysical interpretation suggests eruption from a central cluster of feeder vents which supplied large-scale lobate flows >100 km in length. Pigeonite inversion thermometers indicate eruption temperatures of 950–1100 °C. The lavas are A-type in composition (e.g. high Ga/Al ratios) and characterised by elevated primary halogen concentrations (~1600 ppm Fluorine, ~400 ppm Chlorine). These depolymerised the magma such that temperature-composition-volatile non-Arrhenian melt viscosity modelling suggests they had viscosities of <3.5 log η (Pa s). These physicochemical properties have led to the emplacement of a Large Rhyolite Province, which has affinities in emplacement style to Large Basaltic Provinces. The low viscosity of these felsic magmas has produced a unique igneous system on a scale which is either not present or poorly preserved elsewhere on the planet. The Gawler Range Volcanic Province represents the erupted portion of the felsic end member of the family of voluminous, rapidly emplaced terrestrial magmatic provinces.

scholarly journals Volcanically driven lacustrine ecosystem changes during the Carnian Pluvial Episode (Late Triassic)

2021 ◽  
Vol 118 (40) ◽  
pp. e2109895118 ◽  
Author(s):  
Jing Lu ◽  
Peixin Zhang ◽  
Jacopo Dal Corso ◽  
Minfang Yang ◽  
Paul B. Wignall ◽  
...  
Keyword(s):  
Climate Change ◽  
Large Scale ◽  
North China ◽  
Climatic Changes ◽  
Large Igneous Province ◽  
Late Triassic ◽  
C Cycle ◽  
Igneous Province ◽  
Ecosystem Changes ◽  
Lacustrine Ecosystem

The Late Triassic Carnian Pluvial Episode (CPE) saw a dramatic increase in global humidity and temperature that has been linked to the large-scale volcanism of the Wrangellia large igneous province. The climatic changes coincide with a major biological turnover on land that included the ascent of the dinosaurs and the origin of modern conifers. However, linking the disparate cause and effects of the CPE has yet to be achieved because of the lack of a detailed terrestrial record of these events. Here, we present a multidisciplinary record of volcanism and environmental change from an expanded Carnian lake succession of the Jiyuan Basin, North China. New U–Pb zircon dating, high-resolution chemostratigraphy, and palynological and sedimentological data reveal that terrestrial conditions in the region were in remarkable lockstep with the large-scale volcanism. Using the sedimentary mercury record as a proxy for eruptions reveals four discrete episodes during the CPE interval (ca. 234.0 to 232.4 Ma). Each eruptive phase correlated with large, negative C isotope excursions and major climatic changes to more humid conditions (marked by increased importance of hygrophytic plants), lake expansion, and eutrophication. Our results show that large igneous province eruptions can occur in multiple, discrete pulses, rather than showing a simple acme-and-decline history, and demonstrate their powerful ability to alter the global C cycle, cause climate change, and drive macroevolution, at least in the Triassic.

scholarly journals The formation of North-South Seismic Zone and Emeishan large igneous province in Western China: Insight from teleseismic tomography

2019 ◽  
Author(s):  
Chuansong He
Keyword(s):  
High Velocity ◽  
Large Scale ◽  
Western China ◽  
Large Igneous Province ◽  
The Tibetan Plateau ◽  
Seismic Zone ◽  
Study Region ◽  
Teleseismic Tomography ◽  
Emeishan Large Igneous Province ◽  
Igneous Province

Abstract. Several models have been suggested to explain the earthquake mechanism of the North-South Seismic Zone (NSSZ) and the formation of the Emeishan Large Igneous Province (ELIP). In this study, I extended the study region and carried out detailed teleseismic tomography in the NSSZ and near-by regions. Results identified by this study reveal large plate-like high-velocity anomalies beneath the Songpan-Ganzi Block and the South China Block, which may be associated with large-scale lithospheric delamination, and low-velocity structures at 50–200 km depths in the western and southern parts of this study region, which imply upwelling asthenosphere induced by delamination and the absence of the rigid lithosphere there. Two high-velocity structures beneath the Sichuan Basin and the Alashan Block are revealed, which might be the lithospheric roots of these structures. These rigid lithospheric roots obstructed the eastward extrusion of the Tibetan Plateau and led to stress accumulations and releases (earthquakes) in the Longmenshan Orogenic Belt and the northern part of the NSSZ. Due to obstruction by the Sichuan Basin’s lithosphere, eastward extrusion was redirected southeastward to Yunnan in the southern part of the NSSZ, which led to stress accumulations and releases (earthquakes) along the Honghe and Xiaojiang Faults. This study provide velocity images reveal a slab-like high-velocity structure, which might be associated with the lithospheric vestige of the Paleo-Tethys Ocean that subducted beneath the ELIP, which resulted in large-scale return mantle flow or mantle upwelling and contribute to the LIP formation in early Mesozoic.

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