scholarly journals Pyroxenite as a Product of Mafic-Carbonate Melt Interaction (Tazheran Massif, West Baikal Area, Russia)

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 654
Author(s):  
Eugene V. Sklyarov ◽  
Andrey V. Lavrenchuk ◽  
Anna G. Doroshkevich ◽  
Anastasia E. Starikova ◽  
Sergei V. Kanakin
Keyword(s):  
Partial Melting ◽  
Lake Baikal ◽  
Lower Crust ◽  
Silicate Melts ◽  
Magmatic System ◽  
Crystallization Point ◽  
Carbonate Material ◽  
Silicate Carbonate ◽  
Carbonate Melt

Pyroxenite and nepheline-pyroxene rocks coexist with dolomite-bearing calcite marbles in Tazheran Massif in the area of Lake Baikal, Siberia, Russia. Pyroxenites occur in a continuous elongate zone between marbles and beerbachites (metamorphosed gabbro dolerites) and in 5 cm to 20 m fragments among the marbles. Pyroxene in pyroxenite is rich in calcium and alumina (5–12 wt% Al2O3) and has a fassaite composition. The Tazheran pyroxenite may originate from a mafic subvolcanic source indicated by the presence of remnant dolerite found in one pyroxenite body. This origin can be explained in terms of interaction between mafic and crust-derived carbonatitic melts, judging by the mineralogy of pyroxenite bodies and their geological relations with marbles. According to this model, the intrusion of mantle mafic melts into thick lower crust saturated with fluids caused partial melting of silicate-carbonate material and produced carbonate and carbonate-silicate melts. The fassaite-bearing pyroxenite crystallized from a silicate-carbonate melt mixture which was produced by roughly synchronous injections of mafic, pyroxenitic, and carbonate melt batches. The ascending hydrous carbonate melts entrained fragments of pyroxenite that crystallized previously at a temperature exceeding the crystallization point of carbonates. Subsequently, while the whole magmatic system was cooling down, pyroxenite became metasomatized by circulating fluids, which led to the formation of assemblages with garnet, melilite, and scapolite.

In-situ reaction-replacement origin of hornblendites in the Early Cretaceous Laiyuan complex, North China Craton, and implications for its tectono-magmatic evolution

2021 ◽  
Author(s):  
Jia Chang ◽  
Andreas Audétat ◽  
Jian-Wei Li
Keyword(s):  
Partial Melting ◽  
North China Craton ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
North China ◽  
Ultramafic Rocks ◽  
Magmatic Evolution ◽  
Mafic Magmas ◽  
Felsic Rocks

Abstract Two suites of amphibole-rich mafic‒ultramafic rocks associated with the voluminous intermediate to felsic rocks in the Early Cretaceous Laiyuan intrusive-volcanic complex (North China Craton) are studied here by detailed petrography, mineral- and melt inclusion chemistry, and thermobarometry to demonstrate an in-situ reaction-replacement origin of the hornblendites. Moreover, a large set of compiled and newly obtained geochronological and whole-rock elemental and Sr-Nd isotopic data are used to constrain the tectono-magmatic evolution of the Laiyuan complex. Early mafic‒ultramafic rocks occur mainly as amphibole-rich mafic‒ultramafic intrusions situated at the edge of the Laiyuan complex. These intrusions comprise complex lithologies of olivine-, pyroxene- and phlogopite-bearing hornblendites and various types of gabbroic rocks, which largely formed by in-situ crystallization of hydrous mafic magmas that experienced gravitational settling of early-crystallized olivine and clinopyroxene at low pressures of 0.10‒0.20 GPa (∼4‒8 km crustal depth); the hornblendites formed in cumulate zones by cooling-driven crystallization of 55‒75 vol% hornblende, 10‒20 vol% orthopyroxene and 3‒10 vol% phlogopite at the expense of olivine and clinopyroxene. A later suite of mafic rocks occurs as mafic lamprophyre dikes throughout the Laiyuan complex. These dikes occasionally contain some pure hornblendite xenoliths, which formed by reaction-replacement of clinopyroxene at high pressures of up to 0.97‒1.25 GPa (∼37‒47 km crustal depth). Mass balance calculations suggest that the olivine-, pyroxene- and phlogopite-bearing hornblendites in the early mafic‒ultramafic intrusions formed almost without melt extraction, whereas the pure hornblendites brought up by lamprophyre dikes required extraction of ≥ 20‒30 wt% residual andesitic to dacitic melts. The latter suggests that fractionation of amphibole in the middle to lower crust through the formation of reaction-replacement hornblendites is a viable way to produce adakite-like magmas. New age constraints suggest that the early mafic-ultramafic intrusions formed during ∼132‒138 Ma, which overlaps with the timespan of ∼126‒145 Ma recorded by the much more voluminous intermediate to felsic rocks of the Laiyuan complex. By contrast, the late mafic and intermediate lamprophyre dikes were emplaced during ∼110‒125 Ma. Therefore, the voluminous early magmatism in the Laiyuan complex was likely triggered by the retreat of the flat-subducting Paleo-Pacific slab, whereas the minor later, mafic to intermediate magmas may have formed in response to further slab sinking-induced mantle thermal perturbations. Whole-rock geochemical data suggest that the early mafic magmas formed by partial melting of subduction-related metasomatized lithospheric mantle, and that the early intermediate to felsic magmas with adakite-like signatures formed from mafic magmas through strong amphibole fractionation without plagioclase in the lower crust. The late mafic magmas seem to be derived from a slightly different metasomatized lithospheric mantle by lower degrees of partial melting.

Early sulfide saturation is not detrimental to porphyry Cu-Au formation

Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 519-524 ◽  
Author(s):  
Jingguo Du ◽  
Andreas Audétat
Keyword(s):  
Lower Crust ◽  
Silicate Melts ◽  
Mining District ◽  
Sulfide Saturation ◽  
Southeastern China ◽  
Porphyry Cu ◽  
Magmatic Sulfides ◽  
The Common ◽  
Common Association ◽  
Amphibole Fractionation

Abstract Ore-forming magmas are commonly considered to have been unusually metal rich. Because Cu and Au are strongly chalcophile, early sulfide saturation has been regarded as detrimental to porphyry Cu-Au mineralization. Here we demonstrate, based on amphibole-rich cumulate xenoliths and amphibole megacrysts from the Tongling porphyry(-skarn) Cu-Au mining district in southeastern China, that this view is not necessarily correct. Age data combined with petrological and geochemical evidence suggest that the mineralizing magmas at Tongling underwent significant fractional crystallization of amphibole, clinopyroxene, and magmatic sulfides in the middle to lower crust. The fact that the silicate melts nevertheless were able to produce substantial porphyry(-skarn) Cu-Au deposits implies that the formation of metal-rich cumulates at depth was not detrimental to their fertility. On the contrary, the common association of porphyry Cu (Au, Mo) deposits with high-Sr/Y magmas suggests that amphibole fractionation at depth even promotes the mineralization potential, despite the likely loss of metals.

Granulites, partial melting and the rheology of the lower crust

2011 ◽  
Vol 29 (1) ◽  
pp. 1-6 ◽  
Author(s):  
M. BROWN ◽  
K. SCHULMANN ◽  
R. W. WHITE
Keyword(s):  
Partial Melting ◽  
Lower Crust

Latest Cretaceous “A2-type” granites in the Sakarya Zone, NE Turkey: Partial melting of mafic lower crust in response to roll-back of Neo-Tethyan oceanic lithosphere

Lithos ◽  
2018 ◽  
Vol 302-303 ◽  
pp. 312-328 ◽  
Author(s):  
Orhan Karsli ◽  
Faruk Aydin ◽  
Ibrahim Uysal ◽  
Abdurrahman Dokuz ◽  
Mustafa Kumral ◽  
...  
Keyword(s):  
Partial Melting ◽  
Lower Crust ◽  
Oceanic Lithosphere ◽  
Sakarya Zone ◽  
Roll Back ◽  
Mafic Lower Crust

High-pressure experimental studies on the origin of anorthosite

1969 ◽  
Vol 6 (3) ◽  
pp. 427-440 ◽  
Author(s):  
Trevor H. Green
Keyword(s):  
High Pressure ◽  
Partial Melting ◽  
Lower Crust ◽  
Experimental Studies ◽  
Quartz Diorite ◽  
Main Phase ◽  
Large Field ◽  
High Alumina ◽  
High Alumina Basalt ◽  
Rock Types

Experimental crystallization of anhydrous synthetic quartz diorite (≈andesite), gabbroic anorthosite, and high-alumina basalt has been conducted in their respective partial melting fields at high pressure. The quartz diorite composition shows a large field of crystallization of plagioclase from 0–13.5 kb, together with subordinate amounts of orthopyroxene and clinopyroxene and minor opaque minerals. In the gabbroic anorthosite, plagioclase is the main phase crystallizing from 0–22.5 kb, but at higher pressure it is replaced by aluminous clinopyroxene. Aluminous clinopyroxene is the main phase crystallizing from the high-alumina basalt from 9–18 kb and is joined by plagioclase at lower temperatures. At higher pressure it is joined by garnet. The albite content of the liquidus and near-liquidus plagioclase increases markedly with increasing pressure in each of the three compositions.The results for the high-alumina basalt and gabbroic anorthosite compositions preclude any major trends towards alumina enrichment and derivation of anorthositic plutons at crustal or upper mantle depths under anhydrous conditions. However, the results for the quartz diorite suggest that anorthositic complexes may form as a crystalline residuum from the partial melting of a lower crust of overall andesitic composition or from fractional crystallization of an andesitic magma. In either case a large separation of plagioclase crystals occurs (andesine – acid labradorite composition at lower crustal pressures), together with subordinate pyroxenes and ore minerals. Under appropriate temperature conditions separation of crystals and liquid by a filter-pressing mechanism during deformation may result in the genesis of igneous complexes containing rock types ranging in composition from gabbro through gabbroic anorthosite to anorthosite, together with associated acid rocks. The acid rocks need not necessarily remain spatially associated with the refractory gabbroic anorthosite and anorthosite. Where these processes have operated in the crust, anorthositic rocks may be left as the main component of the lower crust, while the low melting acidic fraction has intruded to higher levels.

scholarly journals Formation of Distinct Granitic Magma Batches by Partial Melting of Hybrid Lower Crust in the Izu Arc Collision Zone, Central Japan

2007 ◽  
Vol 48 (9) ◽  
pp. 1761-1791 ◽  
Author(s):  
Satoshi Saito ◽  
Makoto Arima ◽  
Takashi Nakajima ◽  
Keiji Misawa ◽  
Jun-Ichi Kimura
Keyword(s):  
Partial Melting ◽  
Lower Crust ◽  
Granitic Magma ◽  
Central Japan ◽  
Collision Zone
Sign in / Sign up

Export Citation Format

Share Document