Hi Leonid Shumlyanskyy,

What about the low degree partial melting of a metasomatic enriched mantle lithosphere?

Thanks.

Lu

Leonid,

In many orogenic belts, andesites, basaltic andesites and diorites are common, in some cases outspacing basalt and gabbro. Do you mean to say that all these andesites are derivitives of basaltic magmas? 

In the Cretaceous Kohistan magmatic arc in the Himalaya of Pakistan, the huge Chilas complex is essentially composed of gabbronorites. Average rock would be the equivalent of basaltic andesite in chemical composition. We consider that this was the composition of the magma that did not undergo much fractionatiion.

Most of andesitic melts are produced from enriched mantle lithosphere.

YES, read the following paper: 

Melting experiments on lherzolite KLB-1 under hydrous conditions

and generation of high-magnesian andesitic melts

Kei Hirose Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo 152, Japan

Geology; January 1997; v. 25; no. 1; p. 42–44;

To best of my knowledge, this melting generated Lunar anorthosite

Hydrous melting of mantle is perhaps one of the best explanation to generate Lunar anorthosites. The water for this melting came from inherited meteoritic water which the Moon acquired from its precursor chondritic meteorite.  

Hi Leonid Shumlyanskyy,

I will.

Although it is a hotly debated issue, I prefer to agree with the pointveiw that the partial melting of mantle lithosphere can produce directly andesitic melts. Certainly, whether it happens to a great extent depends on  some specific melting conditioons, such as tempertaure, pressure and water-activity, and composion of mantle lithosphere source (depleted or enriched). I'm now searching for more convincing evidences to support this seemingly eccentric  view.

Thanks everybody for paticipating this discussion. This discussion wlcome more  specialists to provide brilliant views.

Thanks.

Lu

Partial melting of mantle lithosphere can directly produce andesitic melts, which has been documented by geochemical studies of Mesozoic andesitic rocks in eastern China (Chen et al., 2014, 2016). In this case, peridotite cannot serve as the lithology of mantle sources for andesitic magmatism. Instead, the partially melted are mafic lithologies such as garnet pyroxenite and hornblendite rather than ultramafic ones such as pyroxenite and hornblendite.

Chen, L., Zhao, Z.-F. & Zheng, Y.-F. (2014). Origin of andesitic rocks: geochemical constraints from Mesozoic volcanics in the Luzong basin, South China. Lithos 190, 220–239.

Chen, L., Zhao, Z.-F. & Zheng, Y.-F. (2016). Geochemical constraints on the origin of Late Mesozoic andesitic volcanics from the Ningwu basin in the Middle-Lower Yangtze Valley, South China. Lithos 254–255, 94–117.

Because of the incongruent melting of source rocks, the majority of felsic to mafic melts produced by partial melting of crustal or mantle lithologies are generally not in equilibrium with their residues. Although the melts of andesitic composition can be produced by partial melting of subducting mafic oceanic crust (eclogite), the oceanic-type eclogite is generally characterized by depletion in both melt-mobile incompartible trace elements such as LILE and LREE and their pertinent radiogenic isotopes. In comparison, the adakites of andesitic composition commonly show arc-style trace element signatures, precluding their derivation from partial melting of the subducting oceanic slab itself.