Beginning of melting and composition of first melts in the system Qz-Ab-Or-H2O-CO2

Ebadi, A.; Johannes, Wilhelm

doi:10.1007/bf00324558

Cited by 259 publications

(124 citation statements)

References 33 publications

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“…Similarly the solidus of a eutectic granite may vary from ~900ºC for an anhydrous granite to ~650ºC for a water-saturated one (Ebadi and Johannes, 1991;Holtz and Johannes, 1994). In general, mineral-melt fractionations will be larger at lower temperatures (Fig.…”

Section: Modeling Results Compared To Datamentioning

confidence: 99%

“…Water contents of granitic melts may also be determined using experimentally determined plagioclase-liquid hygrometers (Lange et al, 2009) which can then help to constrain magmatic temperatures when used in conjunction with the T-H 2 O relationships for granitic melts (Ebadi and Johannes, 1991;Holtz and Johannes, 1994). …”

Section: Modeling Results Compared To Datamentioning

confidence: 99%

“…3-11). This ternary system is well constrained over a range of pressures (0.05-1.0 GPa) and from dry to water-saturated conditions (Ebadi and Johannes 1991;Holtz et al 1989;Luth et al 1964;Tuttle and Bowen 1958). Notably, the Or/(Ab+Or) ratio of the minimum or eutectic melt increases markedly with decreasing water activity, whereas the normative Qz content remains almost invariant.…”

Section: Comparison Of Hydrous Basalt Llds To Quartz-albite-orthoclasmentioning

confidence: 99%

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Chemical, isotopic, and temporal variations during crustal differentiation : insights from the Dariv Igneous Complex, Western Mongolia

Bucholz¹

2016

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Fractional crystallization of mantle-derived basaltic melts is a critical process in producing a compositionally stratified continental crust characterized by a silicic upper crust and a mafic lower crust. This thesis explores outstanding questions associated with fractional crystallization through detailed field, petrological, and geochemical studies of the Dariv Igneous Complex in Western Mongolia. The Dariv Igneous Complex records the crystallization of a high-K primitive arc melt at shallow crustal levels, preserving both biotite-bearing ultramafic and mafic cumulates, as well as liquid-like evolved plutonics, such as (quartz-)monzonites. Chapter 2 presents comprehensive field and petrographic descriptions of the complex and establishes the petrogenetic groundwork to understand the conditions under which it formed. Results of this study indicate that the observed lithologies formed through the fractional crystallization of a high-K hydrous basalt, typical of alkali-rich basalts found in subduction zone settings, at 0.2-0.5 GPa and elevated oxygen fugacities. Chapter 3 presents a quantitatively modeled liquid line of descent (LLD) for the complex based on whole rock geochemical analyses, which is able to explain the trends observed in the monzonitic plutonic series observed in continental arcs. The oxygen isotope trajectory of fractionally crystallizing melts is rigorously constrained through modeling and mineral analyses in Chapter 4. This study indicates that large (1 to 1.8‰) increases in δ 18 O as a melt evolves from basaltic to granitic in composition due to the fractionation of low δ 18 O minerals. As such, the majority of δ 18 O values of upper crustal silicic plutonics can be explained through fractional crystallization of primitive arc basalts alone without needing to invoke assimilation of high δ 18 O crustal material. Finally, Chapter 5 explores the timescales associated with fractional crystallization through high precision U-Pb geochronology of zircon from the Dariv Igneous Complex. Evolution from a basaltic melt to a silica-rich monzonitic melt in the Dariv Igneous Complex occurred in <300 ka. If rates of fractional crystallization are primarily a function of cooling, this study provides an end-member constraint for fractional crystallization of a basaltic melt at relatively cool, shallow crustal levels. Together, these studies advance our understanding of the compositional, isotopic, and temporal variations associated with the formation of the continental crust.

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Section: Modeling Results Compared To Datamentioning

confidence: 99%

Section: Modeling Results Compared To Datamentioning

confidence: 99%

Section: Comparison Of Hydrous Basalt Llds To Quartz-albite-orthoclasmentioning

confidence: 99%

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Chemical, isotopic, and temporal variations during crustal differentiation : insights from the Dariv Igneous Complex, Western Mongolia

Bucholz¹

2016

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“…3), this sets an upper bound for the temperature conditions during syn-kinematic migmatization at ∼750-800°C (e.g., Thompson, 1982;Gardien et al, 1995;Patiño Douce and Harris, 1998;White et al, 2001). A lower temperature bound is provided by the end-member hypothesis of water-saturated melting of granitic parent rocks, such as those met in A, which yields ∼615-635°C at 10 kbar (e.g., Wyllie, 1983;Ebadi and Johannes, 1991). The obtained range of possible temperatures of migmatization during top-to-SW shearing, between ∼625°C and ∼750-800°C, agrees with the estimates of 650-750°C (Turpaud, 2006) and 600-750°C (Schmidt et al, 2010) for the development of this shear fabric within the garnet-kyanite micaschists.…”

Section: Field Observations and Samplingmentioning

confidence: 99%

Polycyclic alpine orogeny in the Rhodope metamorphic complex: the record in migmatites from the Nestos shear zone (N. Greece)

Gautier

Bosse

Cherneva

et al. 2017

Bull. Soc. géol. Fr.

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-The Rhodope Metamorphic Complex (RMC) is a high-grade crystalline massif located at the northern margin of the Aegean region. Numerous scenarios have been proposed for the evolution of the RMC during Alpine times. A debated issue is whether there has been a single protracted orogenic cycle since around the mid-Mesozoic or whether Alpine orogeny involved distinct episodes of subduction and crustal accretion. We describe a key outcrop located on the Nestos Shear Zone (NSZ), a major NNE-dipping top-to-SW shear zone characterized by an inverted metamorphic sequence. Structural and petrological data document the existence of two anatectic events. The first event, best preserved in decametric structural lenses, is pre-kinematic with respect to top-to-SW shearing and involved high-temperature "dry" melting. Zircon and monazite LA-ICPMS U-Th-Pb data indicate that this event occurred at ∼140 Ma. The second event is syn-kinematic with respect to top-to-SW shearing and involved lower-temperature water-assisted melting. Zircon and rutile LA-ICPMS U-Pb data indicate that this second event occurred at ∼40 Ma. During ongoing top-to-SW shearing and as late as ∼36 Ma, the rocks from the outcrop were at higher temperatures than the peak temperatures experienced by lower levels of the NSZ. This confirms the existence of the inverted metamorphic sequence and demonstrates that the NSZ was a major thrust at 36-40 Ma. The ∼100 Myr time laps between the two anatectic events encompasses the period from ∼115 to ∼70 Ma characterized by a gap in the geochronological record on the scale of the RMC (the Eastern Rhodope excluded). This ∼45 Myr gap likely reflects a period of tectonic quiescence between the mid-Mesozoic orogen and the Cenozoic one, attesting for polycyclic Alpine orogeny in the RMC. Unlike assumed in several geodynamic scenarios, the Alpine evolution of the RMC did not consist of a single orogenic cycle of Mesozoic age followed by Cenozoic crustal-scale extension triggered by mantle delamination. Polycyclic orogeny has resulted in a two-loop P-T-t path for the hangingwall unit of the NSZ. The Cenozoic P-T paths of this unit and the footwall unit merged while both units were being exhumed, a feature attributed to synthrusting extensional spreading of the main mass of the hangingwall unit above the NSZ.Keywords: Aegean / syn-deformation migmatization / U-Pb dating / LA-ICPMS / inverted metamorphism / synmetamorphic thrusting Résumé -Orogenèse alpine polycyclique dans le complexe métamorphique du Rhodope : enregistrement dans les migmatites de la zone de cisaillement du Nestos (Grèce). Le Rhodope est un complexe métamorphique de haut grade situé à la frange Nord de la région égéenne. De nombreux scénarios ont été proposés pour son évolution durant la période alpine. Une question débattue est de déterminer s'il n'y a eu qu'un seul cycle orogénique de longue durée depuis le milieu du Mésozoïque ou bien si l'orogenèse alpine a impliqué des épisodes distincts de subduction-accrétion crustale. Nous décrivons un affleurement-...

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“…Instead, they form a spread of compositions with a trend defined by variable quartz/orthoclase and orthoclase/albite ratios. Experimental work by Johannes and Holtz (1990) orthoclase/albite ratios of granite minimum-melt compositions are greatly increased at decreased water activities (Ebadi and Johannes, 1991). Experimental studies on crystallization of leucogranite magmas (Scaillet and others, 1995) suggest that two-mica granites and tourmaline granites can be generated at low (between 5 and 7.5 wt %) and high (>7 wt.…”

Section: State Of the Tibetan Lithospherementioning

confidence: 99%

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

Leech¹,

Klemperer²,

Mooney³

2010

Open-File Report

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Beginning of melting and composition of first melts in the system Qz-Ab-Or-H2O-CO2

Cited by 259 publications

References 33 publications

Chemical, isotopic, and temporal variations during crustal differentiation : insights from the Dariv Igneous Complex, Western Mongolia

Chemical, isotopic, and temporal variations during crustal differentiation : insights from the Dariv Igneous Complex, Western Mongolia

Polycyclic alpine orogeny in the Rhodope metamorphic complex: the record in migmatites from the Nestos shear zone (N. Greece)

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

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