The Experts below are selected from a list of 3426 Experts worldwide ranked by ideXlab platform

Babita Rani Choudhary - One of the best experts on this subject based on the ideXlab platform.

  • melt inclusion evidence for mantle heterogeneity and magma degassing in the deccan large igneous province india
    Lithos, 2019
    Co-Authors: Babita Rani Choudhary, Gajananrao Jadhav, Benedetto De Vivo, Mysore Santosh, E V S S K Babu
    Abstract:

    Abstract Silicate melt inclusions (MI) trapped in minerals provide direct tools to evaluate source characteristics and magma evolution including magma chamber processes. Here we present results from the study of MIs in basalts from the Western Ghats region of the Deccan Large Igneous Province (LIP) in India. The MIs in plagioclase and clinopyroxene Phenocrysts were analyzed. The MIs exhibit post-entrapment modification by in situ crystal fractionation, chemical interaction with the host Phenocryst (plagioclase or clinopyroxene), degassing/decrepitation, and crystallization of daughter minerals during cooling. The MIs display variable silica (SiO2 41–68 wt%), low potassium, and high Fe Ti contents, corresponding to differentiation of basaltic to andesitic magma. Our data indicate H2O content of about 2 wt% which is consistent with recent evidence for elevated primary H2O content in the Deccan and other LIPs, corresponding to elevated H2O in the lithospheric mantle and plumes passing through the mid-mantle inheriting the hydrous nature.

Chusi Li - One of the best experts on this subject based on the ideXlab platform.

  • the magma plumbing system of the emeishan large igneous province and its role in basaltic magma differentiation in a continental setting
    American Mineralogist, 2015
    Co-Authors: Keith Putirka, Ruizhong Hu, Chusi Li
    Abstract:

    Magmatic activity of the Emeishan large igneous province (ELIP) of SW China is one of the most significant geological events of the late Paleozoic. The large volume flood basalts plus rare picrites were erupted in Late Permian. Previous studies indicate that the basalts are the derivatives of primary mantle-derived magma by fractional crystallization, but the depths at which this process took place remain unknown. To answer this question, we use Phenocryst compositions and mineral-liquid thermobarometers to determine the P-T conditions of the magma reservoirs where crystallization occurred, then use these data to reconstruct the magma plumbing system of the igneous province. Thermobarometric calculations show that most picrite-hosted clinopyroxene Phenocrysts crystallized at ~25 km and 1200–1280 °C, whereas most basalt-hosted clinopyroxene Phenocrysts crystallized at depths <20 km and temperatures <1200 °C. Some picrites containing primitive olivine with Fo up to Fo92 likely formed by eruption of the most primitive magma with composition similar to the primary magma from the deepest reservoir possibly at the Moho. Parental magmas yield mantle potential temperatures of 1740–1810 °C, which are the highest such temperatures yet recorded for terrestrial magmas of any age. Less primitive picrites containing both olivine and clinopyroxene Phenocrysts formed by eruption of moderately fractionated magma from a reservoir in the middle crust. Basalts and basaltic andesites formed by eruption of the most fractionated magmas from the reservoirs in the upper crust, coinciding with the depths of coeval sulfide ore-bearing and Fe-Ti-V oxide ore-bearing mafic-ultramafic intrusions. The reason that the Emeishan volcanic sequence is dominated by basalts is because most of the mantle-derived magma was trapped in the middle and upper crusts, undergoing variable degrees of crystal fractionation plus crustal contamination before eruption. Primitive picrites are rare because their eruption requires a trans-lithosphere conduit, which is difficult to create and maintain due to increasing lithospheric pressure with depth. The results from this study reveal that magma reservoirs at the crustal levels play a critical role in magma differentiation in a continental setting.

Scarlato Piergiorgio - One of the best experts on this subject based on the ideXlab platform.

  • Snapshots of primitive arc magma evolution recorded by clinopyroxene textural and compositional variations: The case of hybrid crystal-rich enclaves from Capo Marargiu Volcanic District (Sardinia, Italy)
    'Mineralogical Society of America', 2018
    Co-Authors: Tecchiato Vanni, Mollo Silvio, Von Quadt Albrecht, Gaeta Mario, Bachmann Olivier, Scarlato Piergiorgio
    Abstract:

    Capo Marargiu Volcanic District (CMVD) is an Oligo-Miocene calc-alkaline complex located in north-western Sardinia (Italy) and characterized by the widespread occurrence of basaltic to andesitic domes. One of these domes hosts abundant crystal-rich enclaves with millimeter-to-centimeter-sized clinopyroxenes showing intriguing textural features as a result of complex magma dynamics. To better understand the mechanisms governing the early evolution of the CMVD magmatic system, such clinopyroxene Phenocrysts have been investigated in terms of their major, trace element and isotopic compositions. Three distinct clinopyroxene populations have been identified, i.e., Type 1, Type 2, and Type 3. Type 1 appears as the sub-rounded cores of diopsidic clinopyroxenes with overgrowth textures corresponding to Type 2 and Type 3. These latter populations may also occur as single isolated crystals. Type 2 diopsidic pyroxene exhibits oscillatory zoning and spongy cellular textures with Type 3 overgrowths, whereas Type 3 are polycrystalline augitic glomerocrysts with occasional Type 2 overgrowths. The crystal overgrowths are striking evidence of magma recharge dynamics. Type 1 (cpxMg#83-92), Type 2 (cpxMg#75-82) and Type 3 (cpxMg#72-79) are, respectively, in equilibrium with Sardinian mantle-derived high-Mg basalts (HMB with meltMg#56-73), least differentiated basaltic andesites (BA with meltMg#45-56) and evolved basaltic andesites (EBA with meltMg#41-50). Type 1 and Type 2 are diopsidic Phenocrysts which have evolved along a similar geochemical path (i.e., linear increase of Al, Ti, La, and Hf contents, as well as negligible Eu-anomaly) controlled by olivine + clinopyroxene + amphibole fractionation. This differentiation path is related to Phenocryst crystallization from hydrous HMB and BA magmas stalling at moderate crustal pressures. The occurrence of globular sulfides within Type 1 suggests saturation of the HMB magma with a sulfide liquid under relatively low redox conditions. Moreover, Type 1 clinopyroxenes show variable 87Sr/86Sr ratios ascribable either to assimilation of crustal material by HMB magma or a mantle source variably contaminated by crustal components. In contrast, Type 3 augitic Phenocrysts recorded the effect of plagioclase and titanomagnetite fractionation (i.e., low Al and Ti contents associated with high La and Hf concentrations, as well as important Eu-anomaly) from more degassed EBA magmas ponding at shallow depths. Rare titanite associated to Type 3 and titanomagnetite crystals point to high oxidizing conditions for EBA magmas. The 87Sr/86Sr ratios of both Type 2 and Type 3 are almost constant, suggesting a limited interaction of BA and EBA magmas with the country rock. The overall textural and compositional features of Type 1, Type 2 and Type 3 clinopyroxene Phenocrysts lead to the conclusion that CMVD was characterized by a polybaric plumbing system where geochemically distinct magmas crystallized and mixed under variable environmental conditionsPublished899–9103V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcaniciJCR Journa

  • Snapshots of primitive arc magma evolution recorded by clinopyroxene textural and compositional variations. The case of hybrid crystal-rich enclaves from Capo Marargiu Volcanic District (Sardinia, Italy)
    'Mineralogical Society of America', 2018
    Co-Authors: Tecchiato Vanni, Mollo Silvio, Von Quadt Albrecht, Gaeta Mario, Bachmann Olivier, Scarlato Piergiorgio
    Abstract:

    Capo Marargiu Volcanic District (CMVD) is an Oligo-Miocene calc-alkaline complex located in northwestern Sardinia (Italy) and characterized by the widespread occurrence of basaltic to andesitic domes. One of these domes hosts abundant crystal-rich enclaves with millimeter-to-centimeter sized clinopyroxenes showing intriguing textural features as a result of complex magma dynamics. To better understand the mechanisms governing the early evolution of the CMVD magmatic system, such clinopyroxene Phenocrysts have been investigated in terms of their major, trace element, and isotopic compositions. Three distinct clinopyroxene populations have been identified, i.e., Type 1, Type 2, and Type 3. Type 1 appears as the sub-rounded cores of diopsidic clinopyroxenes with overgrowth textures corresponding to Type 2 and Type 3. These latter populations may also occur as single isolated crystals. Type 2 diopsidic pyroxene exhibits oscillatory zoning and spongy cellular textures with Type 3 overgrowths, whereas Type 3 are polycrystalline augitic glomerocrysts with occasional Type 2 overgrowths. The crystal overgrowths are striking evidence of magma recharge dynamics. Type 1 (CpxMg#83–92), Type 2 (CpxMg#75–82), and Type 3 (CpxMg#72–79) are, respectively, in equilibrium with Sardinian mantle-derived high-Mg basalts (HMB with meltMg#56–73), least differentiated basaltic andesites (BA with meltMg#45–56) and evolved basaltic andesites (EBA with meltMg#41–50). Type 1 and Type 2 are diopsidic Phenocrysts that have evolved along a similar geochemical path (i.e., linear increase of Al, Ti, La, and Hf contents, as well as negligible Eu-anomaly) controlled by olivine + clinopyroxene + amphibole fractionation. This differentiation path is related to Phenocryst crystallization from hydrous HMB and BA magmas stalling at moderate crustal pressures. The occurrence of globular sulfides within Type 1 suggests saturation of the HMB magma with a sulfide liquid under relatively low redox conditions. Moreover, Type 1 clinopyroxenes show variable 87Sr/86Sr ratios ascribable either to assimilation of crustal material by HMB magma or a mantle source variably contaminated by crustal components. In contrast, Type 3 augitic Phenocrysts recorded the effect of plagioclase and titanomagnetite fractionation (i.e., low Al and Ti contents associated with high La and Hf concentrations, as well as important Eu-anomaly) from more degassed EBA magmas ponding at shallow depths. Rare titanite associated to Type 3 and titanomagnetite crystals point to high oxidizing conditions for EBA magmas. The 87Sr/86Sr ratios of both Type 2 and Type 3 are almost constant, suggesting a limited interaction of BA and EBA magmas with the country rock. The overall textural and compositional features of Type 1, Type 2, and Type 3 clinopyroxene Phenocrysts lead to the conclusion that CMVD was characterized by a polybaric plumbing system where geochemically distinct magmas crystallized and mixed under variable environmental conditions

  • The 2013 eruption of Chaparrastique volcano (El Salvador). Effects of magma storage, mixing, and decompression
    'Elsevier BV', 2017
    Co-Authors: Scarlato Piergiorgio, Mollo Silvio, Del Bello Elisabetta, Von Quadt Albrecht, Brown, Richard J., Gutierrez Eduardo, Martinez Hackert Bettina, Papale Paolo
    Abstract:

    On December 29, 2013, an isolated vulcanian-type eruption occurred at Chaparrastique volcano (El Salvador) after 12 years of inactivity. The eruption was classified as VEI 2 and produced an ash plume with a maximum height of ~9 km. Textural and compositional data from Phenocrysts from the erupted products have been integrated with geochemical and isotopic information from bulk rocks to elucidate the magmatic processes responsible for the reawakening of volcanic activity. Phenocrysts consist of Fo-rich poikilitic olivines hosting high-Mg titanomagnetites, and Fo-poor olivines coexisting with low-Mg titanomagnetites. Mineral-melt equilibria suggest an origin for the distinct Phenocryst populations by mixing between a high-T (~1130–1150 °C), basaltic magma with fO2 (NNO buffer) typical of the lower crust in arc systems and a low-T (~1060–1080 °C), basaltic andesitic magma with fO2 (NNO + 1 buffer) commonly encountered in shallower, more oxidized crustal reservoirs. Thermobarometry based on Fe-Mg exchange between orthopyroxene and clinopyroxene constrains the crystallization before eruption at relative low-P (~150–250 MPa) and low-T (~1000–1050 °C). Mixing between two chemically distinct magmas is also evidenced by the occurrence of reverse zoned plagioclase Phenocrysts with resorbed sodic cores and re-growth of sieve-textured calcic mantles. Conversely, plagioclase rims exhibit disequilibrium compositions addressed to decompression kinetics (~10−3 MPa/s) driven by rapid magma ascent to the surface (~0.03 m/s). Major and trace element modelling excludes fractional crystallization as the primary mechanism controlling the bulk rock variability, whereas geochemical data align along a mixing trend between two end-members representative of the primitive basalt and the differentiated basaltic andesite. Trace element and isotope data indicate that the primary source of magmatism is an enriched MORB-like mantle with the contribution of fluxes of metasomatic fluids and/or melts produced by the subducted slab. The role played by slab-fluid inputs of carbonate origin and slab-melts from the hemipelagic sediments seems to be minimal. Assimilation/contamination processes of magmas by crustal rocks are also negligible. In contrast, the geochemical signature of magmas is greatly influenced by slab-derived aqueous fluids produced prevalently by progressive dehydration of marine sediments and altered basaltic crust

  • The 2013 eruption of Chaparrastique volcano (El Salvador): Effects of magma storage, mixing, and decompression
    'Elsevier BV', 2017
    Co-Authors: Scarlato Piergiorgio, Mollo Silvio, Del Bello Elisabetta, Von Quadt Albrecht, Brown, Richard J., Gutierrez Eduardo, Martinez Hackert Bettina, Papale Paolo
    Abstract:

    On December 29, 2013, an isolated vulcanian-type eruption occurred at Chaparrastique volcano (El Salvador) after 12 years of inactivity. The eruption was classified as VEI 2 and produced an ash plume with a maximum height of ~9 km. Textural and compositional data fromPhenocrysts fromthe erupted products have been inte- grated with geochemical and isotopic information frombulk rocks to elucidate the magmatic processes respon- sible for the reawakening of volcanic activity. Phenocrysts consist of Fo-rich poikilitic olivines hosting high-Mg titanomagnetites, and Fo-poor olivines coexisting with low-Mg titanomagnetites.Mineral-melt equilibria suggest an origin for the distinct Phenocryst populations by mixing between a high-T (~1130–1150 °C), basaltic magma with fO2 (NNO buffer) typical of the lower crust inarc systems and a low-T (~1060–1080 °C), basaltic andesiticmagma with fO2 (NNO+1 buffer) commonly encountered in shallower, more oxidized crustal reservoirs. Thermobarometry based on Fe-Mg ex- change between orthopyroxene and clinopyroxene constrains the crystallization before eruption at relative low-P (~150–250MPa) and low-T (~1000–1050 °C).Mixing between twochemically distinctmagmas is also ev- idenced by the occurrence of reverse zoned plagioclase Phenocrysts with resorbed sodic cores and re-growth of sieve-textured calcicmantles. Conversely, plagioclase rims exhibit disequilibriumcompositions addressed to de- compression kinetics (~10−3 MPa/s) driven by rapidmagma ascent to the surface (~0.03 m/s). Major and trace element modelling excludes fractional crystallization as the primarymechanismcontrolling the bulk rock variability,whereas geochemical data align along amixing trend between two end-members represen- tative of the primitive basalt and the differentiated basaltic andesite. Trace element and isotope data indicate that the primary source of magmatism is an enriched MORB-like mantle with the contribution of fluxes ofmetaso- matic fluids and/ormelts produced by the subducted slab. The roleplayed by slab-fluid inputs of carbonate origin and slab-melts fromthe hemipelagic sediments seems to beminimal. Assimilation/contamination processes of magmas by crustal rocks are also negligible. In contrast, the geochemical signature of magmas is greatly influ- enced by slab-derived aqueous fluids produced prevalently by progressive dehydration of marine sediments and altered basaltic crustPublished110-1223V. Proprietà dei magmi e dei prodotti vulcanici4V. Dinamica dei processi pre-eruttivi5V. Dinamica dei processi eruttivi e post-eruttiviJCR Journa

Kathy Cashman - One of the best experts on this subject based on the ideXlab platform.

  • rapid decompression driven crystallization recorded by melt inclusions from mount st helens volcano
    Geology, 2005
    Co-Authors: Jon D Blundy, Kathy Cashman
    Abstract:

    Crystals in hydrous magmas can form in response to falling temperature (magma cooling) or degassing (magma decompression). It remains unclear which process dominates beneath explosive silicic volcanoes. Because decompression and cooling operate on very different time scales, resolving the driving force behind crystallization is of fundamental importance for determining magma dynamics and eruption hazard. Here we use ion-microprobe measurements of dissolved H 2 O in Phenocryst-hosted melt inclusions from pumices erupted between May and October 1980 at Mount St. Helens volcano to show that all microlites and a significant proportion of Phenocrysts were formed by near isothermal decompression. Magmas erupted after 18 May show evidence for subsequent crystallization of both Phenocrysts and microlites, indicating that the time scales of crystal nucleation and growth are on the order of months or less.

  • ascent driven crystallisation of dacite magmas at mount st helens 1980 1986
    Contributions to Mineralogy and Petrology, 2001
    Co-Authors: Jon D Blundy, Kathy Cashman
    Abstract:

    We introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system Qz–Ab–Or–H2O in order to relate variations in volcanic glass chemistry to changing pressure (P) and temperature (T) conditions in the sub-volcanic magma system. By this means an important distinction can be made between ascent-driven and cooling-driven crystallisation under water-saturated or undersaturated conditions. In samples containing feldspar and a silica phase (quartz or tridymite), quantitative P–T estimates of the conditions of last equilibrium between crystals and melt can be made. Formation of highly silicic melts (i.e. >77 wt% SiO2) is a simple consequence of the contraction of the silica phase volume with decreasing pressure, such that high silica glasses can only form by crystallisation at low pressure. Resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation. Groundmass and inclusion glasses in dacites from the 1980–1986 eruption of Mount St Helens volcano (WA) span a wide range in SiO2 (68–80 wt%, anhydrous). The compositions of the least evolved (SiO2-poor) inclusions in amphibole Phenocrysts record entrapment of silicic liquids with ≤5.4 wt% water, corresponding to a water saturation pressure of ~200 MPa at 900 °C. The compositions of more evolved (higher SiO2) plagioclase-hosted inclusions and groundmass glasses are consistent with extensive ascent-driven fractional crystallisation of plagioclase, oxide and orthopyroxene Phenocrysts and microlites to low pressures. During this polybaric crystallisation, plagioclase Phenocrysts trapped melts with a wide range of dissolved water contents (3.5–5.7 wt%). Magmas erupted during the Plinian phase of the 18 May 1980 eruption were derived from a large reservoir at depths of ≥6 km. Subsequent magmas ascended to varying depths within the sub-volcanic system prior to extraction. From glass chemistry and groundmass texture two arrest levels have been identified, at depths of 0.5–1 and 2–4 km. A single dome sample from February 1983 contains groundmass plagioclase, tridymite and quartz, testifying to temperatures of at least 885 °C at 11 MPa. These shallow storage conditions are comparable to those in the cryptodome formed during spring 1980. The corresponding thermal gradient, ≤0.2 °C MPa–1, is consistent with near-adiabatic magma ascent from ~8 km. We argue that the crystallisation history of Mount St Helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation. This challenges the conventional view that Phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980–1986 eruption. Because the crystallisation process is both polybaric and fractional, it cannot be simulated directly using isobaric equilibrium crystallisation experiments. However, calculation of the phase proportions in water-saturated 910±15 °C experiments by Rutherford et al. (1985) over the pressure range 220–125 MPa reproduces the crystallisation sequence and Phenocryst modes of Mount St Helens dacites from 18 May 1980. By allowing for the effects of fractional versus equilibrium crystallisation, entrained residual source material, and small temperature differences between nature and experiment, phase compositions can also be matched to the natural samples. We conclude that decompression of water-saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres.

E V S S K Babu - One of the best experts on this subject based on the ideXlab platform.

  • melt inclusion evidence for mantle heterogeneity and magma degassing in the deccan large igneous province india
    Lithos, 2019
    Co-Authors: Babita Rani Choudhary, Gajananrao Jadhav, Benedetto De Vivo, Mysore Santosh, E V S S K Babu
    Abstract:

    Abstract Silicate melt inclusions (MI) trapped in minerals provide direct tools to evaluate source characteristics and magma evolution including magma chamber processes. Here we present results from the study of MIs in basalts from the Western Ghats region of the Deccan Large Igneous Province (LIP) in India. The MIs in plagioclase and clinopyroxene Phenocrysts were analyzed. The MIs exhibit post-entrapment modification by in situ crystal fractionation, chemical interaction with the host Phenocryst (plagioclase or clinopyroxene), degassing/decrepitation, and crystallization of daughter minerals during cooling. The MIs display variable silica (SiO2 41–68 wt%), low potassium, and high Fe Ti contents, corresponding to differentiation of basaltic to andesitic magma. Our data indicate H2O content of about 2 wt% which is consistent with recent evidence for elevated primary H2O content in the Deccan and other LIPs, corresponding to elevated H2O in the lithospheric mantle and plumes passing through the mid-mantle inheriting the hydrous nature.