Density model of the Permo – Triassic lithospheric mantle of the Ivrea Verbano Complex

2021 ◽  
Author(s):  
Luca Faccincani ◽  
Federico Casetta ◽  
Barbara Faccini ◽  
Maurizio Mazzucchelli ◽  
Fabrizio Nestola ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Equations Of State ◽  
Mantle Peridotite ◽  
Radiometric Dating ◽  
Variscan Orogeny ◽  
Spinel Lherzolite ◽  
Density Structure ◽  
Holistic View ◽  
Melt Extraction ◽  
Mafic Complex

<p>The Ivrea – Verbano Zone (IVZ) is a virtually complete lower-to-middle continental crustal section exposed in the Western Italian Alps in result of exhumation processes during the Alpine orogenic cycle. To the northwest, the IVZ is juxtaposed to the basement of the Austro-Alpine Domain by the lnsubric Line; to the southeast, it is separated from the middle-to-upper crustal levels of the Strona – Ceneri Zone by the Pogallo and the Cossato-Mergozzo-Brissago (CMB) lines. The IVZ crustal section is constituted by two main units: the Kinzigite Formation, amphibolite- to granulite-facies sedimentary and igneous metamorphic rocks, and the Mafic Complex, a thick, composite gabbroid-to-dioritic intrusion.</p><p>Additionally, the lower crustal rocks of IVZ embed a series of kilometre-scale peridotite bodies; Baldissero, Balmuccia and Finero are the most relevant. These peridotites are thought to represent remnants of the oldest portion of subcontinental lithospheric mantle (SCLM) beneath Europe. Geochemical and isotopic studies indicate that peridotitic bodies experienced an Upper Devonian partial melting event followed by protracted enrichments while resident in the mantle. Field and structural relationships coupled with radiometric dating suggest that the emplacement of the mantle peridotite bodies at crustal levels has occurred since the end of the Variscan orogeny, prior to the intrusion of the Mafic Complex.</p><p>The Balmuccia Massif is dominated by fresh spinel lherzolites recording moderate degrees of melt extraction, subordinated harzburgites, reactive dunites and diffuse cross-cutting websteritic dykes. The melt extraction and melt-fluid/rock-reactions preserved in the Balmuccia peridotite, together with the lack of substantial low-temperature alteration, enable to track the evolution of the SCLM prior to its uplift and emplacement in crust. Therefore, reconstructing the density structure of the Balmuccia body could have major implications on the comprehension of the geodynamic evolution of the oldest portions of the European lithospheric mantle.</p><p>In this study, we modelled the density structure of the spinel lherzolite from the Balmuccia Massif, starting from the chemical composition and modal abundance of its main phase constituents. It is well known that the bulk density is function of modes, compositions and elastic properties of constituent minerals and can be explored from the perspective of their Equations of State (EoS) (see also Faccincani et al., 2021, abstract to session GD7.3 for a more holistic view of the density structure of the lithospheric mantle). By assuming that the EoS for a polyphase aggregate (e.g., a rock) may be calculated as weighted mean of the EoS of the constituting minerals (in our case olivine, orthopyroxene, clinopyroxene, spinel and garnet at increasing depths), we investigated the density structure of a virtual 1-D vertical profile of the lithospheric mantle below the IVZ at pre-Variscan ages.</p>

Density structure of the lithospheric mantle: upscaling from minerals to peridotites

2021 ◽  
Author(s):  
Luca Faccincani ◽  
Barbara Faccini ◽  
Federico Casetta ◽  
Maurizio Mazzucchelli ◽  
Fabrizio Nestola ◽  
...  
Keyword(s):  
Elastic Properties ◽  
Lithospheric Mantle ◽  
Equations Of State ◽  
Thermal State ◽  
Bulk Composition ◽  
Chemical Compositions ◽  
Density Structure ◽  
Earth Planet ◽  
Mantle Peridotites ◽  
Geodynamic Processes

<p>The knowledge of the density structure of the lithospheric mantle is critical to our comprehension of tectonic and magmatic events occurring within the lithosphere and crucial to model the evolution of complex geodynamic processes (e.g., subduction dynamics, mantle plume upwelling etc). Furthermore, a thorough understanding of the density evolution at mantle conditions is essential to interpret geophysical data such as seismic tomography (e.g., Afonso et al., 2008; Stixrude and Lithgow-Bertelloni, 2012).</p><p>The density of mantle peridotites is related to chemical composition, modal abundance and elastic properties of their constituent minerals, which in turn are controlled by pressure, temperature and bulk composition of the system. Accordingly, the elastic properties of mantle minerals combined with the thermal state of the lithosphere can predict how the physical properties (e.g., density, elastic <em>moduli</em>) of mantle peridotites vary with depth. To this aim, (i) we examined the existing literature data (compressibility, thermal expansion and elasticity) suitable to constrain the elastic properties of peridotite minerals and (ii) we addressed the density structure of two potential lithospheric mantle sections (fertile and depleted) across different thermal regimes from the perspective of the Equations of State (EoS) of their constituent minerals.</p><p>In a mantle characterized by a relatively cold geotherm (45 mWm<sup>-2</sup>), the density of a depleted peridotitic system remains nearly constant up to about 4 GPa, while it moderately increases in a fertile system. In a mantle characterized by a relatively hot geotherm (60 mWm<sup>-2</sup>), the density of both depleted and fertile systems decreases up to about 3 GPa, due to the more rapid raise of temperature compared to pressure, and then it increases downwards.</p><p>These preliminary results show that the thermal state of the lithosphere produces a first-order signature in its density structure, with few differences owing to different modes and crystal chemical compositions.</p><p><strong>References</strong></p><p>Afonso, J.C., Fernàndez, M., Ranalli, G., Griffin, W.L., Connolly, J.A.D., 2008. Integrated geophysical-petrological modeling of the lithosphere and sublithospheric upper mantle: Methodology and applications. Geochemistry, Geophys. Geosystems 9, Q05008.</p><p>Stixrude, L., Lithgow-Bertelloni, C., 2012. Geophysics of Chemical Heterogeneity in the Mantle. Annu. Rev. Earth Planet. Sci. 40, 569–595.</p>

Microscale effects of melt infiltration into the lithospheric mantle: Peridotite xenoliths from Xilong, South China

Lithos ◽  
2015 ◽  
Vol 232 ◽  
pp. 111-123 ◽  
Author(s):  
Jianggu Lu ◽  
Jianping Zheng ◽  
William L. Griffin ◽  
Suzanne Y. O'Reilly ◽  
Norman J. Pearson
Keyword(s):  
South China ◽  
Lithospheric Mantle ◽  
Mantle Peridotite ◽  
Peridotite Xenoliths ◽  
Melt Infiltration

scholarly journals Elemental and Sr–Nd–Pb isotopic geochemistry of Mesozoic mafic intrusions in southern Fujian Province, SE China: implications for lithospheric mantle evolution

2007 ◽  
Vol 144 (6) ◽  
pp. 937-952 ◽  
Author(s):  
JUN-HONG ZHAO ◽  
RUIZHONG HU ◽  
MEI-FU ZHOU ◽  
SHEN LIU
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Lithospheric Mantle ◽  
Type A ◽  
Primitive Mantle ◽  
Trace Element Geochemistry ◽  
Spinel Lherzolite ◽  
Fujian Province ◽  
Mafic Rocks ◽  
Se China

AbstractCretaceous mafic dykes in Fujian province, SE China provide an opportunity to examine the nature of their mantle source and the secular evolution of the Mesozoic lithospheric mantle beneath SE China. The mafic rocks have SiO2 ranging from 47.42 to 55.40 wt %, Al2O3 from 14.0 wt % to 20.4 wt %, CaO from 4.09 to 11.7 wt % and total alkaline (K2O+Na2O) from 2.15 wt % to 6.59 wt %. Two types are recognized based on their REE and primitive mantle-normalized trace element patterns. Type-A is the dominant Mesozoic mafic rock type in SE China and is characterized by enrichment of light rare earth elements (LREE) ((La/Yb)n = 2.85–19.0) and arc-like trace element geochemistry. Type-P has relatively flat REE patterns ((La/Yb)n = 1.68–3.43) and primitive mantle-like trace element patterns except for enrichment of Rb, Ba and Pb. Type-A samples show EMII signatures on the Sr-Nd isotopic diagram, whereas type-P rocks have high initial 143Nd/144Nd ratios (0.5126–0.5128) relative to the type-A rocks (143Nd/144Nd = 0.5124–0.5127). The type-A rocks have 207Pb/204Pb ranging from 15.47 to 15.67 and 206Pb/204Pb from 18.26 to 18.52. All the type-A rocks show a negative correlation between 143Nd/144Nd and 206Pb/204Pb ratios and a positive relationship between 87Sr/86Sr and 206Pb/204Pb ratios, indicating mixing of a depleted mantle source and an EMII component. Geochemical modelling shows that the parental magmas were formed by 5–15 % partial melting of a spinel lherzolite, and contaminated by less than 1 % melt derived from subducted sediment. The type-P magmas were derived from a mantle source unmodified by subduction components. The wide distribution of type-A dykes in SE China suggests that subduction-modified lithospheric mantle was extensive beneath the Cathaysia Block. Geochemical differences between Mesozoic and Cenozoic mafic rocks indicate that lithospheric thinning beneath SE China occurred in two episodes: firstly by heterogeneous modification by subducted components in early Mesozoic times, and later by chemical–mechanical erosion related to convective upwelling of the asthenosphere during Cenozoic times.

scholarly journals Contaminating melt flow in magmatic peridotites from the lower continental crust (Rocca d'Argimonia sequence, Ivrea–Verbano Zone)

2020 ◽  
Vol 32 (6) ◽  
pp. 587-612
Author(s):  
Marta Antonicelli ◽  
Riccardo Tribuzio ◽  
Tong Liu ◽  
Fu-Yuan Wu
Keyword(s):  
Continental Crust ◽  
Granulite Facies ◽  
Variscan Orogeny ◽  
Lower Permian ◽  
Melt Flow ◽  
Slow Cooling ◽  
Lower Continental Crust ◽  
Magmatic Origin ◽  
Mafic Complex ◽  
Geochemical Investigation

Abstract. The lower continental crust section of the Ivrea–Verbano Zone (Italian Alps) was intruded by a ∼ 8 km thick gabbroic–dioritic body (Ivrea Mafic Complex) in the Upper Carboniferous–Lower Permian, in conjunction with the post-collisional transtensional regime related to the Variscan orogeny. In the deepest levels of the Ivrea Mafic Complex, several peridotite–pyroxenite sequences considered of magmatic origin are exposed. We present here a petrological–geochemical investigation of the peridotites from the largest magmatic ultramafic sequence of the Ivrea Mafic Complex, locally called Rocca d'Argimonia. In spite of the widespread subsolidus re-equilibration under granulite facies conditions, most likely reflecting a slow cooling evolution in the lower continental crust, the Rocca d'Argimonia peridotites (dunites to harzburgites and minor clinopyroxene-poor lherzolites) typically retain structures and microstructures of magmatic origin. In particular, the harzburgites and the lherzolites typically show poikilitic orthopyroxenes enclosing partially dissolved olivine and minor spinel. Olivine has forsterite proportion diminishing from the dunites to the harzburgites and the lherzolites (90 mol % to 85 mol %) and negatively correlating with δ18O (+5.8 ‰ to +6.6 ‰). Gabbronorite dykes locally crosscut the peridotites and show millimetre-scale thick, orthopyroxenite to websterite reaction zones along the contact with host rocks. We propose that the Rocca d'Argimonia peridotites record a process of reactive melt flow through a melt-poor olivine-rich crystal mush or a pre-existing dunite. This process was most likely responsible for the olivine dissolution shown by the poikilitic orthopyroxenes in the harzburgites–lherzolites. We infer that the reactively migrating melts possessed a substantial crustal component and operated at least at the scale of ∼ 100 m.

Petrochemistry of late Palaeozoic alkali lamprophyre dykes from N Scotland

1987 ◽  
Vol 77 (4) ◽  
pp. 267-277 ◽  
Author(s):  
A. N. Baxter
Keyword(s):  
Lithospheric Mantle ◽  
Incompatible Element ◽  
Fluid Phase ◽  
Spinel Lherzolite ◽  
Lower Carboniferous ◽  
Scottish Highlands ◽  
Basic Series ◽  
Dyke Swarms ◽  
Element Variation ◽  
Primary Magmas

ABSTRACTThe lower Carboniferous–late Permian dyke swarms of the Scottish Highlands and Islands comprise a mild-strongly alkaline basic series of dolerites, camptonites and monchiquites. Differentiation within the suite was largely controlled by olivine + clinopyroxene fractionation. Major and trace element data indicate that dolerites and camptonites chemically overlap, their mineralogical contrasts resulting from differential loss of an H2O, CO2-rich fluid phase during ascent. By contrast most monchiquites have high Mg-values and are relatively primitive compositions, some being near-primary magmas which have risen rapidly from mantle levels with little chemical modification.HREE-buffered incompatible element profiles imply a garnet–lherzolite source, which must underlie the lithospheric mantle region represented by spinel lherzolite xenoliths found in some monchiquites. C. 0·5–2·0% partial melting can account for the gross incompatible element variation in the suite, but relative fluctuations in K, Ba, Rb, Sr, P and Zr imply chemical heterogeneity controlled either by refractory mantle accessory phases or by modification of magmas during ascent through variably metasomatised lithospheric mantle.

Evolution of lithospheric mantle beneath mobile belt between two cratons: An example from the Oku Massif, Cameroon Volcanic Line (W Africa)

2021 ◽  
Author(s):  
Jacek Puziewicz ◽  
Sylvin S. T. Tedonkenfack ◽  
Sonja Aulbach ◽  
Theodoros Ntaflos ◽  
Mary-Alix Kaczmarek ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Mantle Peridotite ◽  
Mobile Belt ◽  
Constant Composition ◽  
Cameroon Volcanic Line ◽  
Western Africa ◽  
Equatorial Africa ◽  
Cenozoic Volcanism ◽  
Continental Part ◽  
Ree Patterns

<p>Cameroon Volcanic Line (CVL) is located in the western part of equatorial Africa and consists of volcanoes which were active from Eocene to recent, stretching ca. 1700 km from the Atlantic in the SW into the African continent in the NE. The continental part of the CVL is located on the Neoproterozoic Central African Orogenic Belt and is situated between the Congo craton and Sahara/Western Africa craton. Mantle peridotite xenoliths which occur locally in lavas of the CVL come from the spinel facies only, suggesting a relatively shallow lithosphere-asthenosphere boundary (LAB). This is supported by seismic studies, showing the LAB at 90-100 km.</p><p>In order to understand better the evolution of the lithospheric mantle beneath the CVL, we studied xenolith suite (16 xenoliths) from Befang in the Oku Massif (Tedonkenfack et al., submitted). The Befang xenoliths are almost entirely lherzolites which have cataclastic to weakly porphyroclastic texture. Harzburgites and websterites occur subordinately. Spinel is interstitial and has amoeboidal shape. The studied peridotites (14 lherzolites, 1 harzburgite) consist of minerals with almost constant composition (olivine Fo<sub>88.7-90.3</sub>, orthopyroxene Al 0.17-0.19 atoms per formula unit (a pfu), clinopyroxene Al 0.28-0.30 a pfu, spinel Cr# dominantly 0.09-0.11). Spinel of Cr# 0.15 occurs in one of the lherzolites, whereas that occurring in harzburgite has Cr# 0.19. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the EBSD-studied subset of 8 samples (one harzburgite and 7 lherzolites). Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of the fabric of host rock.</p><p>These data, thermometry, phase relationships and phase equilibria diagrams suggest that the Befang mantle section was refertilised by MORB-like melt at pressures 1.0-1.4 GPa and temperatures slightly above 1200 – 1275 ºC. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the fabric of protolith. On the other hand, the LREE-depleted clinopyroxene shows discordant orientation relative to olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the melt. The major element and REEs composition of pyroxenes occurring in the Befang peridotites indicate chemical reequilibration at temperatures 930 – 1000 ºC. Trace element modeling shows that websterites can be linked to Cenozoic volcanism. We speculate that they form veins in the lithospheric mantle. Our study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process, which contrasts with the incompatible element-enriched melts typically invoked in within-plate settings.</p><p>This study originated thanks to the project of Polish National Centre of Research NCN 2017/27/B/ST10/00365 to JP. The bilateral Austrian-Polish project WTZ PL 08/2018 enabled extensive microprobe work.</p><p>References:</p><p>Tedonkenfack SST, Puziewicz J, Aulbach S, Ntaflos T., Kaczmarek M-A, Matusiak-Małek M, Kukuła A, Ziobro M: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Submitted.</p>

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