Formation of the trachybasalt–trachyte bimodal series of the Malo-Khamardaban volcanotectonic complex, southwestern Transbaikalia: Role of fractional crystallization and magma mixing

Petrology ◽  
2015 ◽  
Vol 23 (5) ◽  
pp. 451-479 ◽  
Author(s):  
V. B. Khubanov ◽  
T. T. Vrublevskaya ◽  
B. Ts. Tsyrenov ◽  
A. A. Tsygankov
Keyword(s):  
Fractional Crystallization ◽  
Magma Mixing

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

1984 ◽  
Vol 310 (1514) ◽  
pp. 675-692 ◽  
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.

Role of viscous folding in magma mixing

2018 ◽  
Vol 501 ◽  
pp. 26-34 ◽  
Author(s):  
Bibhuti Gogoi ◽  
Ashima Saikia
Keyword(s):  
Magma Mixing

Field, geochemical, and isotopic evidence for magma mixing and assimilation and fractional crystallization processes in the Quottoon Igneous Complex, northwestern British Columbia and southeastern Alaska

1999 ◽  
Vol 36 (5) ◽  
pp. 819-831 ◽  
Author(s):  
J B Thomas ◽  
A K Sinha
Keyword(s):  
British Columbia ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Parental Magma ◽  
Geochemical Data ◽  
Igneous Complex ◽  
Source Regions ◽  
Magmatic Body ◽  
Color Indices ◽  
Lower Crustal

The quartz dioritic Quottoon Igneous Complex (QIC) is a major Paleogene (65-56 Ma) magmatic body in northwestern British Columbia and southeastern Alaska that was emplaced along the Coast shear zone. The QIC contains two different igneous suites that provide information about source regions and magmatic processes. Heterogeneous suite I rocks (e.g., along Steamer Passage) have a pervasive solid-state fabric, abundant mafic enclaves and late-stage dikes, metasedimentary screens, and variable color indices (25-50). The homogeneous suite II rocks (e.g., along Quottoon Inlet) have a weak fabric developed in the magmatic state (aligned feldspars, melt-filled shears) and more uniform color indices (24-34) than in suite I. Suite I rocks have Sr concentrations <750 ppm, average LaN/YbN = 10.4, and initial 87Sr/86Sr ratios that range from 0.70513 to 0.70717. The suite II rocks have Sr concentrations >750 ppm, average LaN/YbN = 23, and initial 87Sr/86Sr ratios that range from 0.70617 to 0.70686. This study suggests that the parental QIC magma (initial 87Sr/86Sr approximately 0.706) can be derived by partial melting of an amphibolitic source reservoir at lower crustal conditions. Geochemical data (Rb, Sr, Ba, and LaN/YbN) and initial 87Sr/86Sr ratios preclude linkages between the two suites by fractional crystallization or assimilation and fractional crystallization processes. The suite I rocks are interpreted to be the result of magma mixing between the QIC parental magma and a mantle-derived magma. The suite II rocks are a result of assimilation and fractional crystallization processes.

The role of fractional crystallization and late-stage peralkaline melt segregation in the mineralogical evolution of Cenozoic nephelinites/phonolites from Saghro (SE Morocco)

2009 ◽  
Vol 73 (1) ◽  
pp. 59-82 ◽  
Author(s):  
J. Berger ◽  
N. Ennih ◽  
J.-C. C. Mercier ◽  
J.-P. LiéGeois ◽  
D. Demaiffe
Keyword(s):  
Fractional Crystallization ◽  
Late Stage ◽  
Nepheline Syenite ◽  
Major Element ◽  
Eudialyte Group ◽  
Intermediate Composition ◽  
Group Mineral ◽  
Melt Segregation ◽  
Evolution Trend

The Saghro Cenozoic lavas form a bimodal suite of nephelinites (with carbonatite xenoliths) and phonolites emplaced in the Anti-Atlas belt of Morocco. Despite the paucity of samples with intermediate composition between the two main types of lava (only one phonotephrite flow is reported in this area), whole-rock major element modelling shows that the two main lithologies can be linked by fractional crystallization. The most primitive modelled cumulates are calcite-bearing olivine clinopyroxenites, whereas the final stages of differentiation are characterized by the formation of nepheline-syenite cumulates. This evolution trend is classically observed in plutonic alkaline massifs associated with carbonatites. Late-stage evolution is responsible for the crystallization of hainite- and delhayelite-bearing microdomains, for the transformation of aegirine-augite into aegirine (or augite into aegirine-augite), and for the crystallization of lorenzenite and a eudialyte-group mineral as replacement products of titanite. These phases were probably formed, either by crystallization from late residual peralkaline melts, or by reaction of pre-existing minerals with such melt, or hydrothermal peralkaline fluid.

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