Evolution of the Lower Permian Rochlitz volcanic system, Eastern Germany: reconstruction of an intra-continental supereruption

AbstractExtensional tectonics in the Late Paleozoic Central Europe was accompanied by rift magmatism that triggered voluminous intracontinental caldera-forming eruptions. Among these, the Lower Permian Rochlitz Volcanic System (RVS) in the North Saxon Volcanic Complex (Eastern Germany, Saxony) represents a supereruption (VEI 8, estimated volume of 1056 km3) of monotonous rhyolites followed by monotonous intermediates. Mapping, petrography, whole-rock geochemistry along with mineral chemistry and oxygen isotopes in zircon display its complex eruption history and magma evolution. Crystal-rich (> 35 vol%), rhyolitic Rochlitz-α Ignimbrite with strong to moderate welding compaction erupted in the climactic stage after reheating of the magma by basaltic injections. Due to magma mixing, low-volume trachydacitic-to-rhyolitic Rochlitz-β Ignimbrite succeeded, characterized by high Ti and Zr-values and zircon with mantle δ18O. Randomly oriented, sub-horizontally bedded fiamme, and NW–SE striking subvolcanic bodies and faults suggest pyroclastic fountaining along NW–SE-oriented fissures as the dominant eruption style. Intrusion of the Leisnig and the Grimma Laccoliths caused resurgence of the Rochlitz caldera forming several peripheral subbasins. In the post-climactic stage, these were filled with lava complexes, ignimbrites and alluvial to lacustrine sediments. Significant Nb and Ta anomalies and high Nb/Ta ratios (11.8–17.9) display a high degree of crustal contamination for the melts of the RVS. Based on homogenous petrographic and geochemical composition along with a narrow range of δ18O in zircon Rochlitz-α Ignimbrite were classified as monotonous rhyolites. For the Rochlitz-β Ignimbrites, underplating and mixing with basic melts are indicated by Mg-rich annite–siderophyllite and δ18O < 6.0 in zircon. The wide spectrum of δ18O on zircon suggests an incomplete mixing process during the formation of monotonous intermediates in the RVS.

Download Full-text

The Tertiary Kærven Syenite Complex, Kangerdlugssuaq, East Greenland: Mineral Chemistry and Geochemistry

Mineralogical Magazine ◽

10.1180/minmag.1988.052.367.02 ◽

1988 ◽

Vol 52 (367) ◽

pp. 435-450 ◽

Cited By ~ 8

Author(s):

Paul Martin Holm ◽

Niels-Ole Prægel

Keyword(s):

Magma Mixing ◽

Crustal Contamination ◽

Outer Part ◽

Alkali Feldspar ◽

Mineral Chemistry ◽

Crystal Fractionation ◽

Maximum Pressure ◽

General Sequence ◽

East Greenland ◽

Rock Suite

AbstractThe Kærven syenite complex, which reflects the hitherto earliest recorded stages in the Tertiary of East Greenland, outcrops in the middle reaches of the Kangerdlugssuaq Fjord as a peripheral intrusion to the Kangerdlugssuaq intrusion. The rocks of the Kærven complex range from syenite through alkali feldspar quartz-syenite to alkali feldspar granite. The general sequence of crystallization of the Kærven magmas was: alkali feldspar ± olivine(Fa96−99) ± plagioclase(An41−11), clinopyroxene (augite, ferrosalite, ferrohedenbergite), quartz and amphibole. Whole-rock major and trace-element data show coherent geochemical trends which suggest comagmatism. The data reveal that the Kærven rocks are distinct from the rocks from the adjacent Kangerdlugssuaq intrusion (e.g. higher TiO2, FeOT in low-SiO2 samples, lower Na2O, approx. constant Zr/Nb). The mineral chemistry supports this conclusion, as the Kærven samples typically have calcic amphiboles and clinopyroxenes with a very limited Na-enrichment in contrast to the sodic trends of the Kangerdlugssuaq intrusion. Normative feldspar compositions plot near to the Ab-Or cotectic in the Q-Ab-Or system and a maximum pressure of crystallization of 3–5 kbar with moderate to low PH2O is indicated.Trace elements preferently incorporated in plagioclase and alkali feldspar, i.e. Sr, Ba and Rb, show systematics which are not compatible with an evolution of the rock suite by crystal fractionation of these phases, though possibly alkali feldspar may be partially accumulated in a few very evolved rocks. Numerical calculations do not suggest a magmatic evolution by fractional crystallization of the observed phases. The variation of Sr, Ba and Rb as well as of the incompatible elements Nb, Zr and Th support a derivation of the rock suite mainly by mixing two components, a syenitic and a granitic end-member. It is concluded that magma mixing was the most significant process in the formation of the Kærven rock suite accompanied by some crystal fractionation. Evidence for crustal contamination is detected in a few samples from the outer part of the intrusion but has not affected the main suite of rocks.

Download Full-text

Chemistry and petrological evolution of the Lastarria volcanic complex in the north Chilean Andes

Geological Magazine ◽

10.1017/s0016756800008451 ◽

1992 ◽

Vol 129 (6) ◽

pp. 723-740 ◽

Cited By ~ 10

Author(s):

José A. Naranjo

Keyword(s):

Magma Mixing ◽

Crustal Contamination ◽

Volcanic Complex ◽

Magma Chambers ◽

The North ◽

Incomplete Mixing ◽

Major Controlling Factor ◽

Liquid Fractionation ◽

Storage Times ◽

Chemical Evidence

AbstractThe Lastarria volcanic complex, along the northern Chile–Argentina border, includes three morphostructural components: Southern Spur, Lastarria (the highest cone, 5697 m) and Negriales (a geographically associated lava field, 5.4 km3). Petrographically, the Lastarria complex consists of pyroxene andesites and pyroxene–amphibole dacites. The whole-rock geochemistry shows a bimodial silica variation between 57 and 68%, with peaks at 59–60% and 61.62% SiO2. Petrographie and chemical data indicate different magmatic sources for Lastarria and Negriales. Whole-rock geochemistry can be explained by crustal contamination and crystal–liquid fractionation, with differences in storage times in magma chambers being a major controlling factor. Strong textural, mineralogical and chemical evidence for magma mixing, shortly before explosive eruptions at Lastarria, suggests that this process may have triggered the violent eruptive volcanic activity which characterizes the latest stages of the main cone. Abundant bombs of banded clear pumice and dark scoria in pyroclastic flow deposits are the texturally heterogeneous products resulting from incomplete mixing homogenization.

Download Full-text

3-D Heterogeneous Elastic Crustal Structure for Deformation Models in the Hengill Area, SW Iceland

10.5194/egusphere-egu21-7553 ◽

2021 ◽

Author(s):

Cécile Ducrocq ◽

Halldór Geirsson ◽

Alex Hobé ◽

Gylfi Páll Hersir ◽

Thóra Árnadóttir ◽

...

Keyword(s):

Crustal Structure ◽

Power Plants ◽

Electrical Power ◽

Element Model ◽

Volcanic Complex ◽

Elastic Model ◽

Spatial Effects ◽

Volcanic System ◽

Shear Moduli ◽

Deformation Models

Crustal deformation in volcanic areas relates ground motions, measured by geodetic techniques, to physical (e.g. pressure or volumetric) changes of magmatic sources below the surface. These measurements contribute to studies of ongoing processes at the source of possible unrest, and are thus key for hazard assessment in active volcanic areas around the globe. However, such assessments often rely on geodetic-based models with quite simplistic assumptions of the physical structure of the volcanic complex. Particularly, constant values of elastic parameters (e.g. Poisson&#8217;s ratio and shear moduli) are commonly used for entire active volcanic areas, thus overlooking the spatial effects of lithological properties, depth-dependant compression and temperature variations on those parameters. These simplifications may lead to inaccurate interpretation of the location, shape, and volume change of deformation sources.&#160;In this study we ask how the 3-D heterogeneities of the elastic crustal structure beneath the Hengill volcanic system, SW Iceland, affects models of deformation sources in the area. The Hengill area hosts two active volcanic systems (Hengill and Hr&#243;mundartindur), and two high-enthalpy geothermal power plants (Nesjavellir and Hellishei&#240;i), which provide thermal and electrical power to Reykjav&#237;k, the capital of Iceland, only 30 km away. To retrieve information on the spatial heterogeneities in the shear moduli and Poisson&#8217;s ratio beneath the Hengill area, we first estimate the 3-D shallow density structure of the area using results from regional and local gravimetric surveys. We implement this structure, along with seismic tomographic studies of the SW Iceland, in a Finite Element Model to solve, using forward models, for the 3-D heterogeneities in the shear moduli and Poisson&#8217;s ratio beneath the Hengill area. Furthermore, we discuss the difference between static and kinematic elastic moduli, which is important when building deformation models from seismic tomography. The new 3-D inferred elastic model is then used to re-estimate parameters for different sources of deformation causing uplift and subsidence in the area in the past decades. This study shows the importance of accounting for heterogeneities in the crustal elastic structure to estimate with higher accuracy the sources of deformation in volcanic areas around the world.

Download Full-text

Relative roles of source composition, fractional crystallization and crustal contamination in the petrogenesis of Andean volcanic rocks

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1984.0014 ◽

1984 ◽

Vol 310 (1514) ◽

pp. 675-692 ◽

Cited By ~ 114

Keyword(s):

Subduction Zone ◽

Continental Crust ◽

Fractional Crystallization ◽

Magma Mixing ◽

Volcanic Rocks ◽

Crustal Contamination ◽

Oceanic Lithosphere ◽

Alkaline Basalt ◽

Complex Process ◽

Heterogeneous Mantle

There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt—andesite-dacite-rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt-trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of ‘within-plate’ character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust.

Download Full-text

Mineral Chemistry Studies and Evidences For Magma Mixing of Bala Zard Basic- Intermediate Volcanic Rocks, Lut Block, Iran

Current World Environment ◽

10.12944/cwe.10.special-issue1.140 ◽

2015 ◽

Vol 10 (Special-Issue1) ◽

pp. 1194-1205 ◽

Cited By ~ 1

Author(s):

Omid Namin ◽

Afshin Ardalan ◽

Mohammad Razavi ◽

Arash Gourabjeripour ◽

Abdollah Yazdi

Keyword(s):

Magma Mixing ◽

Volcanic Rocks ◽

Mineral Chemistry ◽

Lut Block

Download Full-text

A 3-D genetic approach to high-resolution geological modelling of the volcanic infill of a paleovalley system. Application to the Volvic catchment (Chaîne des Puys, France)

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.183.5.395 ◽

2012 ◽

Vol 183 (5) ◽

pp. 395-407 ◽

Cited By ~ 2

Author(s):

Simon Rouquet ◽

Pierre Boivin ◽

Patrick Lachassagne ◽

Emmanuel Ledoux

Keyword(s):

Lava Flow ◽

Lava Flows ◽

Genetic Approach ◽

Hydrogeological Model ◽

Volcanic System ◽

Geochemical Composition ◽

Crystalline Bedrock ◽

Volcanic Events ◽

Aa Lava ◽

Scoria Cones

Abstract The Volvic natural mineral water is catched in a complex volcanic aquifer located in the northern part of the “Chaîne des Puys” volcanic system (Auvergne, France). In the watershed, water transits through scoria cones and basaltic to trachybasaltic lava flows. These aa lava flows, emitted by strombolian cones between 75,000 and 10,000 years ago, are emplaced in deep paleovalleys incised within the variscan crystalline bedrock. The volcanic infill is highly heterogeneous. In order to build a hydrogeological model of the watershed, a simple but robust methodology was developed to reconstruct the bedrock morphology and the volcanic infill in this paleovalley context. This methodology, based on the combination of genetic and geometric approaches, appears to be rather efficient to define both the substratum and the lava flows geometry. A 3D geological model is then proposed. It synthesizes the data from 99 boreholes logs, 2D geoelectric profiles, morphologic clues, datings and petrographic data. A genetic approach, integrating aa lava flow morphology and emplacement behaviour, was used to reconstruct the chronology of the volcanic events and lava flow emplacement from the upper part of the Dômes plateau to the Limagne plain. The precision of the volcanic reconstruction is discussed: the main limitation of the methodology are related to the homogeneity of the petrographic and geochemical composition of the lava flows succession (except for the trachyandesitic Nugere lava), the spatially variable borehole density, the lack of a real petrographical and geological description on most of the available geological logs. Nevertheless, the developed methodology combining spatial and genetic approaches appears to be well adapted to constrain complex lava flow infill geometries in paleovalley context.

Download Full-text

Petrology, mineral chemistry, and geochemistry of Late Triassic Ni–Cu ore-bearing mafic–ultramafic intrusions, Hongqiling, northeastern China: petrogenesis and tectonic implications

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0014 ◽

2019 ◽

Vol 56 (2) ◽

pp. 111-128

Author(s):

Ai Li ◽

Jian Wang ◽

Yue Song

Keyword(s):

Crustal Contamination ◽

Parental Magma ◽

Mineral Chemistry ◽

Late Triassic ◽

Sulfide Deposit ◽

Chemical Compositions ◽

Tholeiitic Magma ◽

Average Value ◽

Central Asian ◽

History Of

The Hongqiling magmatic Ni–Cu sulfide deposit, situated on the southern margin of the eastern Central Asian Orogenic Belt (CAOB), is composed of over 30 mafic–ultramafic intrusions. These ore-bearing intrusions are composed mainly of harzburgite, lherzolite, websterite, orthopyroxenite, and norite (gabbro). The constituent minerals are olivine, diopside, bronzite, calcic-hornblende, plagioclase, and spinel with orthopyroxene as a dominant mineral in these intrusions. These ore-bearing intrusions are not Alaskan-type complexes. Spinel and clinopyroxene both exhibit different chemical compositions from those in the Alaskan-type complexes. The rocks that make up the intrusions have high contents of MgO (average value = 25.20 wt.%) and low TiO2 (average value = 0.58 wt.%). The high MgO contents of the minerals and the high Mg# (71) of the calculated melt in equilibrium with olivine demonstrate that the parental magma of the Hongqiling mafic–ultramafic intrusions was a high-Mg tholeiitic magma. The Hongqiling ore-bearing mafic–ultramafic intrusions and the calculated “trapped liquids” for the olivine-orthopyroxene cumulate rocks are all enriched in large-ion lithophile elements and depleted in high field strength elements. The Ce/Pb, Ta/La, Th/Yb, and (La/Sm)PM values and the depletion of Nb and Ta suggest that the magma experienced crustal contamination. The Hongqiling ore-bearing intrusions display many similarities with mafic–ultramafic intrusions that formed in a post-collisional extensional environment in the western CAOB (e.g., Huangshanxi). Common features include their whole-rock compositions and mineral chemistry. Combined with the evolutionary history of the eastern segment of the CAOB, we believe that the Late Triassic Hongqiling mafic–ultramafic intrusions formed in a post-collisional extensional environment.

Download Full-text

Mafic and ultramafic amphibolites from the northwestern Pontiac Subprovince: chemical characterization and implications for tectonic setting

Canadian Journal of Earth Sciences ◽

10.1139/e93-094 ◽

1993 ◽

Vol 30 (6) ◽

pp. 1110-1122 ◽

Cited By ~ 14

Author(s):

G. E. Camiré ◽

J. N. Ludden ◽

M. R. La Flèche ◽

J. -P. Burg

Keyword(s):

Magma Mixing ◽

Tectonic Setting ◽

Crustal Contamination ◽

Chemical Characterization ◽

Mantle Metasomatism ◽

Primitive Mantle ◽

Mafic Dykes ◽

Metavolcanic Rocks ◽

Source Mantle ◽

Ree Patterns

In the northwestern Pontiac Subprovince, metavolcanic rocks are exposed within a metagraywacke sequence that is intruded by metamorphosed mafic dykes. The metavolcanics are Al-undepleted komatiites ([La/Sm]N = 0.3, [Tb/Yb]N = 0.9) and tholeiitic Fe-basalts ([La/Sm]N = 0.8 and [Tb/Yb]N = 0.8). The nearly flat chondrite-normalized distributions of high field strength elements (HFSE), Ti and P, the constant Zr/Y, Nb/Th, Ti/Zr, and Ti/P ratios, and the lack of depletion of HFSE relative to rare-earth elements (REE) in both ultramafic and mafic metavolcanics, imply that crustal assimilation and magma mixing with crustal melts were not significant during differentiation and argue against the presence of subduction-related magmatic components. Contemporaneous volcanism and sedimentation in the northwestern Pontiac Subprovince are unlikely. The metavolcanics do not show any evidence of crustal contamination and likely represent a structurally emplaced, disrupted assemblage, chemically similar to early volcanics of the adjacent southern Abitibi Subprovince.Metamorphosed mafic dykes intruding the metagraywackes are not genetically related to the metavolcanics. The dykes have high CaO, P2O5, K2O, Ba, Rb, and Sr, intermediate Cr and Ni contents, and strongly fractionated REE patterns ([La/Yb]N = 10.8). Normalized to the primitive mantle, they display pronounced negative Nb, Ta, Ti, Zr, and Hf anomalies. These amphibolites are metamorphosed equivalents of Mg-rich calc-alkaline lamprophyre dykes, most likely derived from a hybridized mantle source. Mantle metasomatism was probably related to a subduction event prior to the peak of compressional Kenoran deformation in the Pontiac Subprovince.

Download Full-text

Mineral chemistry and geothermobarometry of the Balıkesir Volcanites (NW Anatolia, Turkey)

10.5194/egusphere-egu21-12060 ◽

2021 ◽

Author(s):

Alp Ünal ◽

Şafak Altunkaynak

Keyword(s):

Mineral Composition ◽

Magma Chamber ◽

Magma Mixing ◽

Textural Properties ◽

Mineral Chemistry ◽

Oscillatory Zoning ◽

Magma Chamber Processes ◽

Crystallization Conditions ◽

Compositional Variations ◽

Opaque Minerals

Bal&#305;kesir Volcanites (BV) are included into the Bal&#305;kesir Volcanic Province and contain various products of Oligo-Miocene volcanic activity in NW Anatolia. BV are formed from trachyandesite, andesite and dacite lavas with associated pyroclastic rocks. In this study, we report the petrographical investigations, mineral chemistry results and geothermobarometry calculations of the Bal&#305;kesir Volcanites in order to deduce the magma chamber processes and crystallization conditions. Andesites present a mineral composition of plagioclase (An35&#8211;50) + amphibole (edenitic hornblende) +biotite &#177; quartz and opaque minerals. The major phenocryst phases in dacite lavas are plagioclase (An39&#8211;53), quartz, amphibole (magnesio-hornblende), biotite, sanidine and opaque minerals. The mineral composition of the trachyandesites, on the other hand, is represented by plagioclase (An38&#8211;57) + amphibole (pargasitic hornblende) + biotite + clinopyroxene (endiopside- augite) &#177; sanidine &#177; quartz &#177; opaque minerals. Bal&#305;kesir Volcanites present distinct textural properties such as rounded plagioclase phenocrysts with reaction rims, oscillatory zoning, honeycomb and sieve textures in plagioclase, reverse mantled biotite and hornblende crystals. The plagioclase- amphibole geothermobarometry calculations of Bal&#305;kesir volcanites indicate that, andesite and dacite lavas present similar crystallization temperature and pressures conditions of 798- 813&#176;C and 1,98- 2.17 kbar. Oppositely, trachyandesites were crystallized under 857&#176;C and 3,72 kbar temperature and pressure conditions. These results show that the andesite and dacite lavas were originated from the same magma chamber with the depth of 7km whereas trachyandesites were evolved in a deeper magma chamber with 13 km depth. Combined mineral chemistry, petrography and geothermobarometry studies indicate that the open system processes such as magma mixing/mingling and/or assimilation fractional crystallization (AFC) were responsible for the textural and compositional variations of the Bal&#305;kesir Volcanites.

Download Full-text

Distribution of gallium between phenocrysts and melt in peralkaline salic volcanic rocks, Kenya Rift Valley

Mineralogical Magazine ◽

10.1180/minmag.2010.074.2.351 ◽

2010 ◽

Vol 74 (2) ◽

pp. 351-363 ◽

Cited By ~ 6

Author(s):

R. Macdonald ◽

N. W. Rogers ◽

B. Bagiński ◽

P. Dzierżanowski

Keyword(s):

Rift Valley ◽

Inductively Coupled Plasma ◽

Magma Mixing ◽

Volcanic Rocks ◽

Alkali Feldspar ◽

Volcanic Complex ◽

Kenya Rift ◽

Inductively Coupled ◽

Plasma Mass Spectrometry ◽

Kenya Rift Valley

AbstractGallium abundances, determined by laser ablation-inductively coupled plasma-mass spectrometry, are presented for phenocrysts and glassy matrices from a metaluminous trachyte and five peralkaline rhyolites from the Greater Olkaria Volcanic Complex, Kenya Rift Valley. Abundances in the glasses range from 28.9 to 33.3 ppm, comparable with peralkaline rhyolites elsewhere. Phenocryst Ga abundances (in ppm) are: sanidine 31.5–45.3; fayalite 0.02–0.22; hedenbergite 3.3–6.3; amphibole 12; biotite 72; ilmenite 0.56–0.72; titanomagnetite 32; chevkinite-(Ce) 364. The mafic phases and chevkinite-(Ce) are enriched in Ga relative to Al, whereas Ga/Al ratios in sanidine are smaller than in coexisting glass. Apparent partition coefficients range from <0.01 in fayalite to 12 in chevkinite-(Ce). Coefficients for hedenbergite, ilmenite and titanomagnetite decrease as melts become peralkaline. The sharp increase in Ga/Al in the more fractionated members of alkaline magmatic suites probably results from alkali feldspar-dominated fractionation. Case studies are presented to show that the Ga/Al ratio may be a sensitive indicator of such petrogenetic processes as magma mixing, interaction of melts with F-rich volatile phases, mineral accumulation and volatile-induced crustal anatexis.

Download Full-text