Mineralogy, geochemistry, and Sr–Nd isotopes of the Cretaceous leucogranite from Karamadazı (Kayseri), central Turkey: implications for their sources and geological setting

2008 ◽  
Vol 45 (8) ◽  
pp. 949-968 ◽  
Author(s):  
Kerim Kocak
Keyword(s):  
Mafic Magma ◽  
Mineral Chemistry ◽  
Major And Trace Elements ◽  
Quartz Diorite ◽  
Coarse Grained ◽  
Major Constituent ◽  
Geochemical Data ◽  
Nd Isotopes ◽  
Northern Margin ◽  
Central Turkey

The leucogranite is the major constituent of the bimodal Late Cretaceous Karamadazı granitoid, developed in relation with evolution of the Inner Tauride Ocean along the northern margin of the Taurides in central Turkey. New analyses of minerals major and trace elements (including rare-earth elements (REE)), and of Sr and Nd isotopes are performed to determine the origin and geochemical characteristics of the leucogranites. Medium-coarse-grained leucogranite contains normally zoned plagioclase (An12–20), mildly alkaline biotite, and xenocrystic magneziohornblende, actinolite, and ferrohornblende. It is characterized by concave-up REE patterns with respect to middle–heavy REE. Field relations, mineral chemistry, geochemical data, and isotopic data suggest that the leucogranite could have originated from an amphibole-bearing igneous source in lower to middle crust by low-rate partial melting (<40%) under low pressure and low H2O activity conditions, possibly coupled by mixing–mingling with mafic magma and high-level feldspar and minor biotite fractionation. In contrast, the quartz diorite and mafic microgranular enclave (MME) are probably developed from an enriched mantle, with possible mingling–mixing. MME, quartz diorite, and leucogranite may represent a magmatic suite, which formed in an extensional tectonic regime by bimodal magmatic activity probably because of lithospheric delamination or slab break off or after the Alpine thicken within the Gondwanan Tauride–Anatolide platform. Initial Sr data exhibit an age of 65 ± 13 Ma for the leucogranite, but it does not indicate a true intrusion age of the magma due to isotopic modification of the magma.

scholarly journals Distribution of elements among minerals of a single (muscovite-) biotite granite sample – an optimal approach and general implications

2014 ◽  
Vol 65 (4) ◽  
pp. 257-272i ◽  
Author(s):  
Vojtěch Janoušek ◽  
Tomáš Navrátil ◽  
Jakub Trubač ◽  
Ladislav Strnad ◽  
František Laufek ◽  
...  
Keyword(s):  
Mineral Chemistry ◽  
Major And Trace Elements ◽  
Biotite Granite ◽  
Coarse Grained ◽  
Granite Sample ◽  
Distribution Of Elements ◽  
Plutonic Complex ◽  
Supergene Processes ◽  
Optimal Approach

Abstract The petrography and mineral chemistry of the coarse-grained, weakly porphyritic (muscovite-) biotite Říčany granite (Variscan Central Bohemian Plutonic Complex, Bohemian Massif) were studied in order to assess the distribution of major and trace elements among its minerals, with consequences for granite petrogenesis and availability of geochemical species during supergene processes. It is demonstrated that chemistry-based approaches are the best suited for modal analyses of granites, especially methods taking into account compositions of whole-rock samples as well as their mineral constituents, such as constrained least-squares algorithm. They smooth out any local variations (mineral zoning, presence of phenocrysts, schlieren…) and are robust in respect to the presence of phenocrysts or fabrics. The study confirms the notion that the accessory phases play a key role in incorporation of many elements during crystallization of granitic magmas. Especially the REE seem of little value in petrogenetic modelling, unless the role of accessories is properly assessed and saturation models for apatite, zircon, monazite±rutile carefully considered. At the same time, the presence of several P-, Zr- and LREE-bearing phases may have some important consequences for saturation thermometry of apatite, zircon and monazite.

scholarly journals Porphyroclasts: Source and Sink of Major and Trace Elements During Deformation-Induced Metasomatism (Finero, Ivrea-Verbano Zone, Italy)

Geosciences ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 196
Author(s):  
Stefania Corvò ◽  
Antonio Langone ◽  
José Alberto Padrón-Navarta ◽  
Andrea Tommasi ◽  
Alberto Zanetti
Keyword(s):  
Trace Elements ◽  
Shear Zone ◽  
Major And Trace Elements ◽  
Trace Element Composition ◽  
Lower Jurassic ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Fine Grained ◽  
Mantle Peridotites ◽  
Scale Shear

Petrographic and geochemical data for mylonites from a metric-scale shear zone in mantle peridotites from the Finero massif (Southern Alps) record large mineralogical and geochemical modifications compared to surrounding coarse-grained ultramafic rocks, which were pervasively deformed in presence of hydrous melts. The mylonites are composed by olivine and orthopyroxene and, less frequently, clinopyroxene, phlogopite, and pargasite porphyroclasts enclosed in a fine-grained matrix of phlogopite and olivine, with subordinate amounts of orthopyroxene, clinopyroxene, pargasite, and chromite. P-T estimates indicate that deformation occurred under granulite- to upper-amphibolite facies conditions. Field relationships and U-Pb dating indicate that the shear zone was active during Lower Jurassic and/or later, in an extensional setting at the western margin of the Adria plate, which led to the opening of the Alpine Tethys. The major and trace element composition of the porphyroclasts in the mylonites significantly differ from those in the hosting coarse-grained ultramafics. Porphyroclasts were chemically active during deformation acting as source (diffusion-out) or sink (diffusion-in) for some trace elements. The chemical modifications were promoted by the interaction with aqueous fluids and the composition varied from mantle- (enriched in Ni, Co, Li, Na, REE, Y, and Sr) to crustal-derived (enriched in Zn, K, Al, Ti, and Fe).

The petrology, geochemistry, and economic potential of the Musquodoboit batholith, Nova Scotia

1985 ◽  
Vol 22 (11) ◽  
pp. 1633-1642 ◽  
Author(s):  
M. A. MacDonald ◽  
D. B. Clarke
Keyword(s):  
Nova Scotia ◽  
Alkali Feldspar ◽  
Coarse Grained ◽  
Major Constituent ◽  
Geochemical Data ◽  
Economic Potential ◽  
Magmatic Differentiation ◽  
Metasedimentary Rocks ◽  
South Mountain Batholith ◽  
Rock Types

The Musquodoboit batholith of southwestern Nova Scotia is a massive, post-tectonic granitoid intrusion that was emplaced into the regionally deformed and metamorphosed Meguma Group metasedimentary rocks. The batholith is composed primarily of medium- to coarse-grained monzogranites into which two small (≈1 km2) porphyries and numerous dykes have been injected. All rocks contain quartz, alkali feldspar, plagioclase, muscovite, and biotite (with the exception of some leucocratic dykes). Cordierite is a major constituent in most monzogranitic rocks and also occurs in some leucocratic dykes. Andalusite and garnet 0are also present as accessory phases in some rocks.Major-element chemical analyses indicate that all rock types in the Musquodoboit batholith are peraluminous. Compositions resemble those of the eastern part South Mountain batholith; however, slightly higher concentrations of Al2O3 and P2O5 distinguish the Musquodoboit batholith from the central part of the South Mountain batholith. Major- and trace-element data indicate that magmatic differentiation has operated; however, the decrease in Σ 8 REE's, Th/U, and K/Rb from monzogranite to dyke rocks suggests that stripping by hydrothermal fluids has also occurred.Various field, petrographic, and geochemical data yield equivocal estimates of the economic potential of the Musquodoboit batholith.

scholarly journals Crystallization and Segregation of Syenite in Shallow Mafic Sills: Insights from the San Rafael Subvolcanic Field, Utah

2020 ◽  
Author(s):  
Aurelie Germa ◽  
Danielle Koebli ◽  
Paul Wetmore ◽  
Zachary Atlas ◽  
Austin Arias ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Mafic Magma ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Fine Grained ◽  
Mantle Sources ◽  
Plumbing Systems ◽  
Order Of Magnitude ◽  
Magma Compositions ◽  
San Rafael

Abstract Exposed plumbing systems provide important insight into crystallization and differentiation in shallow sills beneath volcanic fields. We use whole rock major element, trace element and radiogenic isotopic compositions, along with mineral geochemical data on 125 samples to examine the conditions of melt differentiation in shallow sills from the exposed 4-Ma-old San Rafael subvolcanic field (SRVF), Utah. The field consists of ∼2000 dikes, 12 sills and 63 well preserved volcanic conduits. Intrusive rocks consist of mainly fine-grained trachybasalts and coarse-grained syenites, which are alkaline, comagmatic and enriched in Ba, Sr and LREE. Within sills, syenite is found as veins, lenses, and sheets totally enveloped by the basalt. The SRVF intrusions have geochemical signatures of both enriched sub-continental lithospheric and asthenospheric mantle sources. We estimate partial melting occurred between 1·2 and 1·9 GPa (50–70 km), with mantle potential temperatures in the range 1260–1326 ± 25°C, consistent with those estimated for volcanic rocks erupted on the Colorado Plateau. Geobarometry results based on clinopyroxene chemistry indicate that (1) basalt crystallized during ascent from at least 40 km deep with limited lithospheric storage, and (2) syenites crystallized only in the sills, ∼1 km below the surface. San Rafael mafic magma was emplaced in sills and started to crystallize inward from the sill margins. Densities of basalt and syenite at solidus temperatures are 2·6 and 2·4 g/cc, respectively, with similar viscosities of ∼150 Pa s. Petrographic observations and physical properties suggest that syenite can be physically separated from basalt by crystal compaction and segregation of the tephrophonolitic residual liquid out of the basaltic crystal mush after reaching 30–45% of crystallization. Each individual sill is 10–50 m thick and would have solidified fairly rapidly (1–30 years), the same order of magnitude as the duration of common monogenetic eruptions. Our estimates imply that differentiation in individual shallow sills may occur during the course of an eruption whose style may vary from effusive to explosive by tapping different magma compositions. Our study shows that basaltic magmas have the potential to differentiate to volatile-rich magma in shallow intrusive systems, which may increase explosivity.

Generation of the Giant Porphyry Cu-Au Deposit by Repeated Recharge of Mafic Magmas at Pulang in Eastern Tibet

2021 ◽  
Author(s):  
Kang Cao ◽  
Zhi-Ming Yang ◽  
Noel C. White ◽  
Zeng-Qian Hou
Keyword(s):  
Mafic Magma ◽  
Magma Reservoir ◽  
Quartz Diorite ◽  
Coarse Grained ◽  
Fine Grained ◽  
Porphyry Cu ◽  
Eastern Tibet ◽  
Quartz Monzonite ◽  
Magma Recharge ◽  
Diorite Porphyry

Abstract The giant Pulang porphyry Cu-Au district (446.8 Mt at 0.52% Cu and 0.18 g/t Au) is located in the Yidun arc, eastern Tibet. The district is hosted in an intrusive complex comprising, in order of emplacement, premineralization fine-grained quartz diorite and coarse-grained quartz diorite, intermineralization quartz monzonite, and late-mineralization diorite porphyry, which were all emplaced at ca. 216 ± 2 Ma. Mafic magmatic enclaves are found in both the coarse-grained quartz diorite and quartz monzonite. The well-preserved primary mineral crystals in such a systematic magma series (including contemporaneous relatively mafic intrusions) with well-defined timing provide an excellent opportunity to investigate upper crustal magma reservoir processes, particularly to test the role of mafic magma recharge in porphyry Cu formation. Two groups of amphibole crystals, with different aluminum contents, are observed in these four rocks. Low-Al amphibole crystals (Аl2О3 = 6.2–7.6 wt %) with crystallization temperatures of ~780°C mainly occur in the coarse-grained quartz diorite and quartz monzonite, whereas high-Al amphibole crystals (Al2O3 = 8.0–13.3 wt %) with crystallization temperatures of ~900°C mainly occur in the fine-grained quartz diorite and diorite porphyry. These characteristics, together with detailed petrographic observations and mineral chemistry studies, indicate that the coarse-grained quartz diorite and quartz monzonite probably formed by crystal fractionation in the same felsic magma reservoir, whereas the fine-grained quartz diorite and diorite porphyry formed from relatively mafic magmas sourced from different magma reservoirs. The occurrence of mafic magmatic enclaves, disequilibrium phenocryst textures, and cumulate clots indicates that the coarse-grained quartz diorite and quartz monzonite evolved in an open crustal magma storage system through a combination of crystal fractionation and repeated mafic magma recharge. Mixing with incoming batches of hotter mafic magma is indicated by the appearance of abundant microtextures, such as reverse zoning (Na andesine core with Ca-rich andesine or labradorite rim overgrowth), sharp zoning (Ca-rich andesine or labradorite core with abrupt rimward anorthite decrease) and patchy core (Ca-rich andesine or labradorite and Na andesine patches) textured plagioclase, zoned amphibole, high-Al amphibole clots, skeletal biotite, and quartz ocelli (mantled quartz xenocrysts). Using available partitioning models for apatite crystals from the coarse-grained quartz diorite, quartz monzonite, and diorite porphyry, we estimated absolute magmatic S contents to be 20–100, 25–130, and &gt;650 ppm, respectively. Estimates of absolute magmatic Cl contents for these three rocks are 1,000 ± 600, 1,800 ± 1,100, and 1,300 ± 1,000 ppm, respectively. The slight increase in both magmatic S and Cl contents from the premineralization coarse-grained quartz diorite magma to intermineralization quartz monzonite magma was probably due to repeated recharge of the relatively mafic diorite porphyry magma with higher S but similar Cl contents. Mass balance constraints on Cu, S, and Cl were used to estimate the minimum volume of magma required to form the Pulang porphyry Cu-Au deposit. Magma volume calculated using Cu mass balance constraints implies that a minimum of 21–36 km3 (median of 27 km3) of magma was required to provide the total of 2.3 Mt of Cu at Pulang. This magma volume can explain the Cl endowment of the deposit but is unlikely to supply the sulfur required. Recharge of 5–11 km3 of diorite porphyry magma to the felsic magma reservoir is adequate to account for the additional 6.5–15 Mt of S required at Pulang. Repeated diorite porphyry magma recharge may have supplied significant amounts of S and some Cl and rejuvenated the porphyry system, thus aiding formation of the large, long-lived magma reservoir that produced the porphyry Cu-Au deposit at Pulang.

Mineral chemistry, petrogenesis, and tectonic setting of the Wateranga layered intrusion, southeast Queensland, Australia

2005 ◽  
Vol 42 (11) ◽  
pp. 1967-1985 ◽  
Author(s):  
Reddy VR Talusani ◽  
Warwick J Sivell ◽  
Paul M Ashley
Keyword(s):  
Tectonic Setting ◽  
Parental Magma ◽  
Layered Intrusion ◽  
Mafic Magma ◽  
Mineral Chemistry ◽  
Geochemical Data ◽  
Magma Source ◽  
Olivine Gabbro ◽  
Layered Mafic Intrusion ◽  
Southeast Queensland

The Wateranga layered mafic intrusion (28 km2 in area, > 500 m thick) is a tholeiitic, undeformed, unmetamorphosed, Permo-Triassic layered gabbroic pluton intruded into the late Carboniferous Goodnight beds of the Goodnight Block in southeast Queensland. The intrusion mainly consists of gabbro and norite, associated with subordinate amounts of troctolite, anorthosite, and orthopyroxenite, and rare picrite. Olivine gabbro is the dominant rock type of the intrusion. Fractionation followed a tholeiitic trend with iron enrichment in the liquid. Petrographic, mineral chemical, and whole-rock geochemical data have been used to divide the intrusion into Lower, Middle, and Upper zones, which are interpreted as reflecting magma chamber replenishment. The observed changes in the crystallization order between the zones reveal that a single parental magma is inadequate to explain the data. The common differentiation indices, such as An content of plagioclase, Mg#s of olivine, clinopyroxene, orthopyroxene and whole-rocks, and the whole-rock concentrations of various incompatible trace elements (Zr, Y, Nb, La Ba, Rb, Sr, and Nd), all vary widely with stratigraphic depth and display abrupt shifts at the zone boundaries, indicating open system addition of new mafic magma. Temperatures estimated from two-pyroxene geothermometer vary from 1057 to 927 °C. During the course of crystallization, pressure probably was > 2 and < 4 kbar (1 kbar = 100 MPa). The variation trend of anorthite content of plagioclase versus the forsterite content of olivine precludes an arc-related magma source. The composition and geological setting of the intrusion are consistent with emplacement in a post-subduction extensional tectonic environment.

scholarly journals Mineralogy, mineral chemistry and thermobarometry of post-mineralization dykes of the Sungun Cu–Mo porphyry deposit (Northwest Iran)

2020 ◽  
Vol 12 (1) ◽  
pp. 764-790
Author(s):  
Amin Allah Kamali ◽  
Mohsen Moayyed ◽  
Nasir Amel ◽  
Fadaeian Mohammad ◽  
Marco Brenna ◽  
...  
Keyword(s):  
Active Continental Margin ◽  
Mineral Chemistry ◽  
Quartz Diorite ◽  
Alkaline Magmatism ◽  
Porphyry Deposit ◽  
Average Percentage ◽  
The North ◽  
Northwestern Iran ◽  
Subduction System ◽  
Late Stages

AbstractThe Sungun copper–molybdenum porphyry deposit is located in the north of Varzaghan, northwestern Iran. The Sungun quartz-monzonite is the oldest mineralized intrusive body in the region and was emplaced during the Early Miocene. Eight categories of the late and unmineralized dykes, which include quartz diorite, gabbrodiorite, diorite, dacite, microdiorite and lamprophyre (LAM), intrude the ore deposit. The main mineral phases in the dykes include plagioclase, amphibole and biotite, with minor quartz and apatite and secondary chlorite, epidote, muscovite and sericite. The composition of plagioclase in the quartz diorite dykes (DK1a, DK1b and DK1c) varies from albite-oligoclase to andesine and oligoclase to andesine; in the diorite, it varies from andesine to labradorite; in the LAM, from albite to oligoclase; and in the microdiorite (MDI), it occurs as albite. Amphibole compositions are consistent with classification as hornblende or calcic amphibole. Based on their AlIV value (less than 1.5), amphibole compositions are consistent with an active continental margin affinity. The average percentage of pistacite (Ps) in epidotes formed from alteration of plagioclase and ferromagnesian minerals is 27–23% and 25–30%, respectively. Thermobarometric studies based on amphibole and biotite indicate approximate dyke crystallization temperature of 850–750℃, pressure of 231–336 MPa and high fO2 (>nickel-nickel-oxide buffer). The range of mineral compositions in the postmineralization dyke suite is consistent with a genetic relationship with the subduction of the Neotethys oceanic crust beneath the continental crust of the northwest part of the Central Iranian Structural Zone. Despite the change from calc-alkaline to alkaline magmatism, the dykes are likely related to the late stages of magmatic activity in the subduction system that also generated the porphyry deposit.

scholarly journals Extreme isotopic heterogeneity in Samoan clinopyroxenes constrains sediment recycling

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jenna V. Adams ◽  
Matthew G. Jackson ◽  
Frank J. Spera ◽  
Allison A. Price ◽  
Benjamin L. Byerly ◽  
...  
Keyword(s):  
Mantle Source ◽  
Magma Mixing ◽  
Major And Trace Elements ◽  
Mantle Heterogeneity ◽  
Isotopic Data ◽  
Nd Isotopes ◽  
Isotopic Heterogeneity ◽  
Total Variability ◽  
High Silica ◽  
Insight Into

AbstractLavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87Sr/86Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87Sr/86Sr lava from Savai’i Island, Samoa for detailed analyses of 87Sr/86Sr and 143Nd/144Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87Sr/86Sr—including the highest observed in an oceanic hotspot lava—encompassing ~30% of the oceanic mantle’s total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene 87Sr/86Sr variability resulting from magma mixing between a high silica, high 87Sr/86Sr (up to 0.7316) magma, and a low silica, low 87Sr/86Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth’s mantle.

A new record of the Toarcian oceanic anoxic event from Scotland (UK) and environmental responses

2021 ◽  
Author(s):  
Wenhan Chen ◽  
David Bryan Kemp ◽  
Tianchen He ◽  
Chunju Huang
Keyword(s):  
Chemical Weathering ◽  
Coarse Grained ◽  
Global Ocean ◽  
Geochemical Data ◽  
Oceanic Anoxic Event ◽  
Organic Carbon Isotope ◽  
Anoxic Event ◽  
Geographic Differences ◽  
Environmental Responses ◽  
Global Carbon

&lt;p&gt;The early Toarcian oceanic anoxic event (T-OAE, ~183 Ma) was characterized by a prominent environmental perturbation, likely associated with a large amount of &lt;sup&gt;12&lt;/sup&gt;C-enriched carbon released into the global ocean-atmosphere system. This effusion caused a marked disruption to the global carbon cycle and propagated a series of remarkable changes in ocean chemistry and climate. Although the T-OAE has been recognized worldwide, clear geographic differences in the character of the event and its environmental effects have been recognized. Here, we present new geochemical data from a lower Toarcian succession on the Isle of Raasay, NE Scotland (Hebrides Basin, Northwest European Shelf). Organic carbon isotope data through the Raasay section reveal a pronounced negative excursion, similar to that recognised globally. The excursion interval is enriched in organic matter, and redox sensitive element data suggest that suboxic bottom water conditions contemporaneously occurred, likely interspersed with anoxic episodes. Our findings contrast with evidence of more pervasive anoxia/euxinia in nearby basins, and emphasize how deoxygenation was spatially variable within the T-OAE. Inorganic geochemical data and sedimentological observations suggest a significant enhancement in chemical weathering and coarse-grained detrital flux during the T-OAE on Raasay. These findings support evidence from other localities for a strengthening of hydrological cycling in response to global warming during the T-OAE.&lt;/p&gt;

scholarly journals Building Arc Crust: Plutonic to Volcanic Connections in an Extensional Oceanic Arc, the Southern Alisitos Arc, Baja California

2019 ◽  
Vol 60 (6) ◽  
pp. 1195-1228 ◽  
Author(s):  
Rebecca A Morris ◽  
Susan M DeBari ◽  
Cathy Busby ◽  
Sarah Medynski ◽  
Brian R Jicha
Keyword(s):  
Reference Model ◽  
Volcanic Rocks ◽  
Three Dimensional ◽  
Mineral Chemistry ◽  
Major And Trace Elements ◽  
Low Velocity ◽  
Fractionation Process ◽  
Process Step ◽  
Rock Types ◽  
Plutonic Rocks

Abstract The ∼50 km long Rosario segment of the Cretaceous Alisitos oceanic arc terrane provides undeformed three-dimensional exposures of the upper 7 km of an oceanic extensional arc, where crustal generation processes are recorded in both the volcanic and underlying plutonic rocks. These exceptional exposures allow for the study of the physical and chemical links between the rock units and help constrain the differentiation processes active during the growth and evolution of arc crust. This study focuses on the southern third of the Rosario segment, previously referred to as the southern volcano-bounded basin, and its plutonic underpinnings. Upper crustal rocks in the Rosario segment consist of a 3–5 km thick volcanic–volcaniclastic section with hypabyssal intrusions. Plutons intrude these units at various levels along-strike, but at each intrusive contact the transition is complete over a distance of <150 m, where stoped volcanic blocks are present. There is striking compositional overlap in whole-rock and mineral chemistry between the plutonic and volcanic units, suggesting a comagmatic source. Whole-rock geochemistry shows coherent trends in major and trace elements in mafic to intermediate compositions, but less coherent trends above 63 wt % SiO2. Units are predominantly low-K with flat rare earth element patterns, and show large ion lithophile element enrichment and high field strength element depletion. Initial Nd and Pb isotope ratios overlap for all units and imply no cratonic continental involvement. This agrees with low Sr/Y ratios of all rock types, indicative of thin, immature oceanic arc crust. Modeling results show that closed-system fractional crystallization drove crustal differentiation from mafic to intermediate compositions, but open-system processes likely occurred to produce some of the felsic compositions. Differentiation occurred in a two-step fractionation process. Step 1, from basaltic andesite to andesite, fractionated an anhydrous gabbroic cumulate (∼40% crystallization). Step 2, from andesite to rhyolite, fractionated a hydrous amphibole cumulate (∼65% crystallization, total), which is similar to what fluid dynamical models suggest for production of rhyolite (between 50–70% crystallization). Our results can be used as a reference model for differentiation processes relating to the growth of the middle and upper crust within active extensional arc systems. The Rosario segment plutonic rocks may be analogous to the low-velocity zone (Vp = 6·0–6·5 km s–1) imaged within the extensional Izu–Bonin arc. The chemistry of the plutonic and volcanic rocks is most similar to those of volcanic rocks in the Izu–Bonin active rift.

Sign in / Sign up

Export Citation Format

Share Document