Experimental and geochemical evidence for derivation of the El Capitan Granite, California, by partial melting of hydrous gabbroic lower crust

2005 ◽  
Vol 149 (6) ◽  
pp. 713-734 ◽  
Author(s):  
Kent Ratajeski ◽  
Thomas W. Sisson ◽  
Allen F. Glazner
Author(s):  
Jia Chang ◽  
Andreas Audétat ◽  
Jian-Wei Li

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.


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

Lithos ◽  
2018 ◽  
Vol 302-303 ◽  
pp. 312-328 ◽  
Author(s):  
Orhan Karsli ◽  
Faruk Aydin ◽  
Ibrahim Uysal ◽  
Abdurrahman Dokuz ◽  
Mustafa Kumral ◽  
...  

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jia Liu ◽  
Naoto Hirano ◽  
Shiki Machida ◽  
Qunke Xia ◽  
Chunhui Tao ◽  
...  

AbstractA discontinuity in the seismic velocity associated with the lithosphere-asthenosphere interface, known as the Gutenberg discontinuity, is enigmatic in its origin. While partial mantle melts are frequently suggested to explain this discontinuity, it is not well known which factors critically regulate the melt production. Here, we report geochemical evidence showing that the melt fractions in the lithosphere-asthenosphere boundary were enhanced not only by accumulation of compacted carbonated melts related to recycled ancient marine sediments, but also by partial melting of a pyroxene-rich mantle domain related to the recycled oceanic eclogite/pyroxenites. This conclusion is derived from the first set of Mg isotope data for a suite of young petit-spot basalts erupted on the northwest Pacific plate, where a clearly defined Gutenberg discontinuity exists. Our results reveal a specific linkage between the Gutenberg discontinuity beneath the normal oceanic regions and the recycling of ancient subducted crust and carbonate through the deep Earth.


1969 ◽  
Vol 6 (3) ◽  
pp. 427-440 ◽  
Author(s):  
Trevor H. Green

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.


2007 ◽  
Vol 48 (9) ◽  
pp. 1761-1791 ◽  
Author(s):  
Satoshi Saito ◽  
Makoto Arima ◽  
Takashi Nakajima ◽  
Keiji Misawa ◽  
Jun-Ichi Kimura

Lithos ◽  
2009 ◽  
Vol 113 (3-4) ◽  
pp. 347-368 ◽  
Author(s):  
Shao-Bing Zhang ◽  
Yong-Fei Zheng ◽  
Zi-Fu Zhao ◽  
Yuan-Bao Wu ◽  
Honglin Yuan ◽  
...  

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