scholarly journals Origin and significance of the antimony mineralisation associated to mafic intrusions in the Iberian Zone and the Central Armorican Domain

2021 ◽  
Author(s):  
Eric Gloaguen ◽  
Héctor Campos ◽  
Anthony Pochon ◽  
Pablo León Higueras ◽  
Saturnino Lorenzo ◽  
...  
Keyword(s):  
Partial Melting ◽  
Spatial Association ◽  
Seismic Profiles ◽  
Volatile Element ◽  
Mafic Intrusions ◽  
Minimum Age ◽  
Southern Border ◽  
Late Neoproterozoic ◽  
Armorican Massif ◽  
Metasomatized Mantle

<p>In the Central Iberian Zone (CIZ) and its French counterpart, the Central Armorican Domain (CAD), widespread swarms of mafic dykes with various ages and compositions are known. Indeed, numerous mafic events are recognized in the late Neoproterozoic, in the Cambrian to the Ordovician, in the Ordovician to the Devonian, at the Devonian-Carboniferous boundary, in the Permian and in the Jurassic. Such a succession of mantle partial melting events, localised or generalized, may have strong consequences (i) on the composition and the homogeneity of the mantle below both the CIZ and CAD, and (ii) on the transfert of metals in the overlying crust. Moreover, the mantle below these domains must have been modified also by the subduction of large to small oceanic crusts from the Iapetus, the Rheic, the Galicia-Moldanubian and the Paleo-tethys. Although the occurrences of paleo-subductions below the CIZ and CAD remain discussed, the southern border of the CIZ, the Ossa-Morena Zone (OMZ), is considered as a suture zone resulting from a subduction followed by a collision between 390 and 360 Ma (D1), according to the 2 opposite structural vergences at the CIZ/OMZ boundary, as well as the location of a NE-dipping slab imaged by seismic profiles. In the Armorican massif, the end of subduction is also dated at 360 Ma and associated to a north-directed subduction. The trace of this subduction below the CAD is visible in the tomographic dataset. Interestingly, these two domains (CIZ and CAD) contain the largest number of Palaeozoic antimony deposits, antimony being a volatile element. In these domains, the large clustering of antimony deposits and occurrences is observed within a ca 100km wide bands along their southern parts. In the two domains, the antimony deposits are frequently spatially associated with diabase dykes. Diabase dykes and associated antimony mineralisation have been dated at 360 Ma in the CAD but remain temporally unconstrained in the CIZ. Nevertheless, since these dykes are strongly affected by the Variscan deformation a minimum age of 350 Ma is inferred. Both, the peculiar composition of these diabase dykes, relatively enriched in Cs, Li, Pb and relatively depleted in K and Rb, the spatial association with antimony at the end of a 360Ma subduction, suggest a link between antimony and a ca 360Ma mafic magmatism which could result from the partial melting of a subduction-related metasomatized mantle.</p><p>This work was funded by the ANR (ANR-19-MIN2-0002), the AEI (MICIU/AEI/REF.: PCI2019-103779), the FCT (ERA-MIN/0005/2018) and author’s institutions in the framework of the ERA-MIN2 AUREOLE project (https://aureole.brgm.fr).</p>

Mechanisms of Partial Melting of Metasomatized Mantle Ultramafic Rocks beneath Avacha Volcano, Kamchatka, and the Growth of Minerals from a Gas Phase in Fractures

Petrology ◽  
2020 ◽  
Vol 28 (6) ◽  
pp. 569-590
Author(s):  
V. N. Sharapov ◽  
A. A. Tomilenko ◽  
G. V. Kuznetsov ◽  
Yu. V. Perepechko ◽  
K. E. Sorokin ◽  
...  
Keyword(s):  
Partial Melting ◽  
Gas Phase ◽  
Ultramafic Rocks ◽  
Metasomatized Mantle

scholarly journals Extensive Sills in the Continental Basement from Deep Seismic Reflection Profiling

Geosciences ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 449
Author(s):  
Larry D. Brown ◽  
Doyeon Kim
Keyword(s):  
Seismic Reflection ◽  
Country Rock ◽  
High Amplitude ◽  
Tectonic Activity ◽  
Seismic Profiles ◽  
Mafic Intrusions ◽  
Bright Spots ◽  
Crystalline Crust ◽  
Seismic Reflection Profiling ◽  
Fluid Magma

Crustal seismic reflection profiling has revealed the presence of extensive, coherent reflections with anomalously high amplitudes in the crystalline crust at a number of locations around the world. In areas of active tectonic activity, these seismic “bright spots” have often been interpreted as fluid magma at depth. The focus in this report is high-amplitude reflections that have been identified or inferred to mark interfaces between solid mafic intrusions and felsic to intermediate country rock. These “frozen sills” most commonly appear as thin, subhorizontal sheets at middle to upper crustal depths, several of which can be traced for tens to hundreds of kilometers. Their frequency among seismic profiles suggest that they may be more common than widely realized. These intrusions constrain crustal rheology at the time of their emplacement, represent a significant mode of transfer of mantle material and heat into the crust, and some may constitute fingerprints of distant mantle plumes. These sills may have played important roles in overlying basin evolution and ore deposition.

Kimberlite and kimberlitic intrusives of southeastern Australia

1980 ◽  
Vol 43 (330) ◽  
pp. 727-731 ◽  
Author(s):  
John Ferguson
Keyword(s):  
Partial Melting ◽  
Late Jurassic ◽  
Incompatible Element ◽  
Spatial Association ◽  
South Eastern ◽  
Southeastern Australia ◽  
Eastern Australia ◽  
Kimberlite Magma ◽  
Element Contents

SummaryFifteen widely separated occurrences of kimberlite and kimberlitic rocks are now known in south-eastern Australia. Those that have been satisfactorily dated isotopically give ages ranging from Permian to Late Jurassic. One occurrence exhibits an intimate spatial association with carbonatite. The classification of these rocks as ‘kimberlitic’ is partly based on their mode of emplacement, and particularly on the presence of crust/mantle inclusions. Compared with African kimberlitic magmas, the southeastern Australian examples have lower incompatible-element contents. These differences are interpreted as representing slightly greater degrees of partial melting of a four-phase Iherzolite assemblage at shallower depths (∼ 65 km) than typical African kimberlite magma.

scholarly journals Relations between basalts and adakitic–felsic intrusive bodies in a soft-substrate environment: the South Ouessant Visean basin in the Variscan belt, Armorican Massif, France

2016 ◽  
Vol 53 (4) ◽  
pp. 441-456 ◽  
Author(s):  
Martial Caroff ◽  
Bernard Le Gall ◽  
Christine Authemayou ◽  
Denise Bussien Grosjean ◽  
Cyrill Labry ◽  
...  
Keyword(s):  
High Pressure ◽  
Early Stage ◽  
Variscan Orogeny ◽  
Variscan Belt ◽  
Soft Substrate ◽  
Mafic Intrusions ◽  
Partial Remelting ◽  
Pressure Fractionation ◽  
Peraluminous Granites ◽  
Armorican Massif

The metasedimentary and magmatic terranes in the southern part of the Ouessant Island (Western Brittany, France) are the offshore prolongation of the Léon Variscan metamorphic domain. They mainly consist of micaschists and subordinate amphibolitic lenses (meta-pillow lavas and volcaniclastic successions) cut by a swarm of trondhjemite sills, together with a large porphyritic monzogranite body, newly dated at 336 Ma, and later syeno-leucogranitic intrusions. A large spectrum of fluidal peperites, including spectacular “fiamme”-bearing breccias, is observable at the contact between metasediments and most of the intrusives. The coexistence of amphibolitized basalts, adakitic trondhjemites, and peraluminous granites in the inferred South Ouessant basin is assigned to a variety of deep subcontemporaneous processes, including asthenospheric partial melting, high-pressure fractionation in lithospheric reservoirs (or partial remelting of deep crystallized mafic intrusions), and continental crust melting. Implications of these new results are discussed in the Visean basinal framework of the Armorican Massif, formed at an early stage of the Variscan orogeny.

scholarly journals Petrology of potassic alkaline ultramafic and carbonatitic rocks from Planalto da Serra (Mato Grosso State), Brazil

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Piero Comin-Chiaramonti ◽  
Celso Gomes ◽  
Angelo Min ◽  
Excelso Ruberti ◽  
Vicente Girardi ◽  
...  
Keyword(s):  
Mantle Source ◽  
Crustal Contamination ◽  
Alkaline Magmatism ◽  
Mato Grosso ◽  
Rock Types ◽  
Long Time ◽  
Late Neoproterozoic ◽  
Rock Association ◽  
Rule Out ◽  
Metasomatized Mantle

AbstractThe Planalto da Serra igneous rocks form plugs, necks and dykes of carbonate-rich ultramafic lamprophyres (aillikites and glimmerites with kamafugitic affinity) and carbonatites (alvikites and beforsites). Phlogopite and/or tetraphlogopite, diopside and melanitic garnet are restricted to aillikitic rock-types, whereas pyroclore occurs only in carbonatites. Aillikites and carbonatites are altered to hydrotermalites, having chlorite and serpentine as dominant minerals. Planalto da Serra igneous rock association has kamafugitic affinity (i.e. effusive, ultrapotassic. High LREE/HREE fractionation, incompatible elements data and Sr-Nd isotopes, suggest that the K-ultramafic alkaline and carbonatite rocks originated from a variably metasomatized mantle source enriched in radiogenic Sr. Crustal contamination is negligible or absent. Age values of 600 Ma rule out the geochronological relationship between the investigated intrusions and the Mesozoic alkaline bodies from the Azimuth 125° lineament. The TDM model ages allow to conclude that Planalto da Serra magma is derived from the partial melting of a mantle source metasomatised by K-rich carbonatated melt during the Early to Late Neoproterozoic. On the basis of alkaline magmatism repetitions at 600 Ma and 90–80 Ma we question the subsistence of a stationary mantle plume for so long time.

Late Neoproterozoic granulite facies metamorphism of the Upper Gneiss unit (Seve Nappe Complex) in the Váivančohkka-Salmmečohkat area, northern Scandinavian Caledonides 

2021 ◽  
Author(s):  
Riccardo Callegari ◽  
Katarzyna Walczak ◽  
Grzegorz Ziemniak ◽  
Christopher Barnes ◽  
Jaroslaw Majka
Keyword(s):  
Partial Melting ◽  
Thermal Evolution ◽  
Granulite Facies ◽  
Stability Field ◽  
Granulite Facies Metamorphism ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
Seve Nappe Complex ◽  
Break Up ◽  
Late Neoproterozoic

<p>Here, we present preliminary petrochronological results of paragneisses and schists containing bodies of metamafic rocks belonging the Upper Gneiss unit that occurs within the Seve Nappe Complex (SNC) in the Váivančohkka-Salmmečohkat area, north of the lake Torneträsk in northern Sweden and Norway.</p><p>At the outcrop scale, the paragneiss is pervasively foliated and bears features of migmatization. It hosts garnet amphibolite bodies that are locally transected by leucocratic veins. Thin section observations of the paragneiss reveal a mineral assemblage composed of Q+Grt+Amp+Bi±Pl±Ms±Sil±Ru. The leucocratic vein contains Q+Pl+Ms+Bi+Grt+Kfs±Sil. Importantly, some of the studied gneisses contain quartz, exhibiting lobate boundaries, as well as garnet surrounded by melt rim. The presence of quartz forming pseudomorphs after melt was also identified and observed to host both monophase and fluid inclusions. All of these microtextures are indicative of partial melting.</p><p>Preliminary pressure-temperature estimates derived using conventional geothermobarometry and phase equilibrium modelling corroborated petrographic observations. The peak metamorphic conditions were estimated to 8–10kbar and 800–850°C, i.e., in the stability field of melt.</p><p>Uranium-Pb zircon and Th-U-total Pb monazite dating of the migmatitic paragneiss yielded consistent age estimates of 602±5Ma and 599±3Ma, respectively. Nearly the same U-Pb age of 604±7Ma was obtained for the zircon from the leucocratic vein transecting the amphibolite within the studied gneiss. Interestingly, no Caledonian zircon nor monazite were identified. Considering the textural position of the dated zircon and monazite, as well as their chemical character, we suggest that these minerals date the partial melting event recorded by the rocks.</p><p>Regionally, we interpret that the Upper Gneiss unit of SNC in the Váivančohkka-Salmmečohkat area could be a northern continuation of the Leavasvággi gneiss associated with the Vassačoru Igneous Complex of SNC in the Kebnekaise region. Notably, the latter reveals evidence of high temperature metamorphism at c. 600Ma (Paulsson and Andréasson 2002) and its mafic component (see also Rousku et al. in this session) could be an equivalent to the metamafic rocks enclosed within the Upper Gneiss unit. The Leavasvággi gneiss and the Upper Gneiss unit together with similar rocks farther north in Indre Troms and in Corrovare which also yield a c. 610-600Ma age of high grade overprint (Gee et al. 2016; Kjøll et al. 2019). Altogether, these areas with only localized Caledonian influence diverge from traditional models developed for the SNC farther south and offer an additional insight into the development of the late Neoproterozoic margin of Baltica at the early stages of Iapetus opening.</p><p>This study was supported by the National Science Centre (Poland) grant no. 2019/33/B/ST10/01728 to J. Majka.</p><p>References</p><p>Gee et al. 2016. Baltoscandian margin, Sveconorwegian crust lost by subduction during Caledonian collisional orogeny. GFF 139, 36–51.</p><p>Kjøll et al. 2019. Timing of break-up and thermal evolution of a pre-Caledonian  Neoproterozoic exhumed magma-rich rifted margin. Tectonics 38, 1843-1862.</p><p>Paulsson & Andréasson 2002. Attempted break-up of Rodinia at 850 Ma: geochronological evidence from the Seve–Kalak Superterrane, Scandinavian Caledonides. JGS, 159, 751-761.</p>

scholarly journals Geochemistry of the Neoarchaean Volcanic Rocks of the Kilimafedha Greenstone Belt, Northeastern Tanzania

2012 ◽  
Vol 2012 ◽  
pp. 1-18 ◽  
Author(s):  
Charles W. Messo ◽  
Shukrani Manya ◽  
Makenya A. H. Maboko
Keyword(s):  
Partial Melting ◽  
Greenstone Belt ◽  
Mantle Wedge ◽  
Spatial Association ◽  
Volcanic Rocks ◽  
Low Concentrations ◽  
Peridotite Mantle ◽  
Ree Patterns ◽  
Subducting Slab ◽  
Oceanic Slab

The Neoarchaean volcanic rocks of the Kilimafedha greenstone belt consist of three petrological types that are closely associated in space and time: the predominant intermediate volcanic rocks with intermediate calc-alkaline to tholeiitic affinities, the volumetrically minor tholeiitic basalts, and rhyolites. The tholeiitic basalts are characterized by slightly depleted LREE to nearly flat REE patterns with no Eu anomalies but have negative anomalies of Nb. The intermediate volcanic rocks exhibit very coherent, fractionated REE patterns, slightly negative to absent Eu anomalies, depletion in Nb, Ta, and Ti in multielement spidergrams, and enrichment of HFSE relative to MORB. Compared to the other two suites, the rhyolites are characterized by low concentrations of TiO2 and overall low abundances of total REE, as well as large negative Ti, Sr, and Eu anomalies. The three suites have a εNd (2.7 Ga) values in the range of −0.51 to +5.17. The geochemical features of the tholeiitic basalts are interpreted in terms of derivation from higher degrees of partial melting of a peridotite mantle wedge that has been variably metasomatized by aqueous fluids derived from dehydration of the subducting slab. The rocks showing intermediate affinities are interpreted to have been formed as differentiates of a primary magma formed later by lower degrees of partial melting of a garnet free mantle wedge that was strongly metasomatized by both fluid and melt derived from the subducting oceanic slab. The rhyolites are best interpreted as having been formed by shallow level fractional crystallization of the intermediate volcanic rocks involving plagioclase and Ti-rich phases like ilmenite and magnetite as well as REE-rich phases like apatite, zircon, monazite, and allanite. The close spatial association of the three petrological types in the Kilimafedha greenstone belt is interpreted as reflecting their formation in an evolving late Archaean island arc.

Late-glacial fluctuations of two southern Patagonia outlet glaciers revealed by high-resolution seismic surveys

2020 ◽  
Vol 97 ◽  
pp. 111-124 ◽  
Author(s):  
Emanuele Lodolo ◽  
Jorge Lozano ◽  
Federica Donda ◽  
Donald Bran ◽  
Luca Baradello ◽  
...  
Keyword(s):  
High Resolution ◽  
Late Pleistocene ◽  
Late Glacial ◽  
Seismic Profiles ◽  
Seismic Surveys ◽  
Southern Patagonia ◽  
Minimum Age ◽  
General Phase ◽  
Lake Floor ◽  
Bathymetric Map

AbstractLago Argentino hosts various calving glaciers, among them the famous Perito Moreno. Whereas the onland late Pleistocene–Holocene glacial history is rather well constrained, the submerged glacier-related features were until now undisclosed. Here we present a series of high-resolution seismic profiles revealing moraine bodies associated with the late-glacial glacier dynamics and the first bathymetric map of the Brazo Rico and Brazo Sur, the two southern arms of Lago Argentino. At the eastern termination of Brazo Rico, we identified at the lake floor the submerged expression of the Puerto Bandera 3 moraine mapped onshore, which represents the oldest event (12,660 ± 70 cal yr BP oldest minimum age) recognized in this lake arm, and seven other younger events expressed by a series of terminal and recessional moraines. Along the Brazo Sur, few moraine bodies have been imaged by seismic data. Here, the youngest temporal constraint comes from the Frías moraine (ca. 6000 cal yr BP), which closes off the southern end of the Brazo Sur. At the confluence of the two arms, the Perito Moreno and the former Frías glacier merged and flowed toward east during their late-glacial maximum advance (i.e., Puerto Bandera 1 moraine). The subaqueous evidence of moraine bodies testifies to the occurrence of previously undocumented pulses of the Perito Moreno and former Frías glaciers within the general phase of late Pleistocene–Holocene regression.

Archean granitoids of the Aravalli Craton, northwest India

2020 ◽  
Vol 489 (1) ◽  
pp. 215-234 ◽  
Author(s):  
Iftikhar Ahmad ◽  
M. E. A. Mondal ◽  
Md Sayad Rahaman ◽  
Rajneesh Bhutani ◽  
M. Satyanarayanan
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Mantle Wedge ◽  
Nd Isotope ◽  
Oceanic Plateau ◽  
Slab Breakoff ◽  
Northwest India ◽  
Aravalli Craton ◽  
Metasomatized Mantle ◽  
Asthenospheric Upwelling

AbstractThe Archean granitoids of the Aravalli Craton (NW India) are represented by orthogneisses (3.3–2.6 Ga) and undeformed granitoids (c. 2.5 Ga). Here we present whole-rock geochemical (elemental and Nd-isotope) data of the granitoids from the Aravalli Craton with an aim of understanding the evolution of the continental crust during the Archean. These Archean granitoids have been classified into three compositional groups: (1) TTG – tonalite–trondhjemite–granodiorite; (2) t-TTG – transitional TTG; and (3) sanukitoids. Based on the geochemical characteristics, it is proposed that the TTGs have formed from the partial melting of subducting oceanic plateau. The t-TTG formed owing to reworking of an older continental crust (approximately heterogeneous) in response to tectonothermal events in the craton. For the formation of the sanukitoids, a two-stage petrogenetic model is invoked which involves metasomatization of the mantle wedge, followed by slab breakoff and asthenospheric upwelling, which leads to the melting of asthenosphere and the metasomatized mantle wedge. It is also proposed that subducted sediments contributed to the genesis of sanukitoid magma.

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