Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/12585
Authors: Tecchiato, Vanni* 
Gaeta, Mario* 
Mollo, Silvio* 
Bachmann, Olivier* 
von Quadt, Albrecht* 
Scarlato, Piergiorgio* 
Title: Snapshots of primitive arc magma evolution recorded by clinopyroxene textural and compositional variations: The case of hybrid crystal-rich enclaves from Capo Marargiu Volcanic District (Sardinia, Italy)
Journal: American Mineralogist 
Series/Report no.: /103 (2018)
Issue Date: 2018
DOI: 10.2138/am-2018-6446
Abstract: Capo Marargiu Volcanic District (CMVD) is an Oligo-Miocene calc-alkaline complex located in north-western Sardinia (Italy) and characterized by the widespread occurrence of basaltic to andesitic domes. One of these domes hosts abundant crystal-rich enclaves with millimeter-to-centimeter-sized clinopyroxenes showing intriguing textural features as a result of complex magma dynamics. To better understand the mechanisms governing the early evolution of the CMVD magmatic system, such clinopyroxene phenocrysts have been investigated in terms of their major, trace element and isotopic compositions. Three distinct clinopyroxene populations have been identified, i.e., Type 1, Type 2, and Type 3. Type 1 appears as the sub-rounded cores of diopsidic clinopyroxenes with overgrowth textures corresponding to Type 2 and Type 3. These latter populations may also occur as single isolated crystals. Type 2 diopsidic pyroxene exhibits oscillatory zoning and spongy cellular textures with Type 3 overgrowths, whereas Type 3 are polycrystalline augitic glomerocrysts with occasional Type 2 overgrowths. The crystal overgrowths are striking evidence of magma recharge dynamics. Type 1 (cpxMg#83-92), Type 2 (cpxMg#75-82) and Type 3 (cpxMg#72-79) are, respectively, in equilibrium with Sardinian mantle-derived high-Mg basalts (HMB with meltMg#56-73), least differentiated basaltic andesites (BA with meltMg#45-56) and evolved basaltic andesites (EBA with meltMg#41-50). Type 1 and Type 2 are diopsidic phenocrysts which have evolved along a similar geochemical path (i.e., linear increase of Al, Ti, La, and Hf contents, as well as negligible Eu-anomaly) controlled by olivine + clinopyroxene + amphibole fractionation. This differentiation path is related to phenocryst crystallization from hydrous HMB and BA magmas stalling at moderate crustal pressures. The occurrence of globular sulfides within Type 1 suggests saturation of the HMB magma with a sulfide liquid under relatively low redox conditions. Moreover, Type 1 clinopyroxenes show variable 87Sr/86Sr ratios ascribable either to assimilation of crustal material by HMB magma or a mantle source variably contaminated by crustal components. In contrast, Type 3 augitic phenocrysts recorded the effect of plagioclase and titanomagnetite fractionation (i.e., low Al and Ti contents associated with high La and Hf concentrations, as well as important Eu-anomaly) from more degassed EBA magmas ponding at shallow depths. Rare titanite associated to Type 3 and titanomagnetite crystals point to high oxidizing conditions for EBA magmas. The 87Sr/86Sr ratios of both Type 2 and Type 3 are almost constant, suggesting a limited interaction of BA and EBA magmas with the country rock. The overall textural and compositional features of Type 1, Type 2 and Type 3 clinopyroxene phenocrysts lead to the conclusion that CMVD was characterized by a polybaric plumbing system where geochemically distinct magmas crystallized and mixed under variable environmental conditions
Appears in Collections:Article published / in press

Files in This Item:
File Description SizeFormat Existing users please Login
00_Tecchiato et al._2018_American Mineralogist_103_899-910.pdf5.67 MBAdobe PDF
Show full item record

WEB OF SCIENCETM
Citations 5

6
checked on Feb 10, 2021

Page view(s)

52
checked on Mar 27, 2024

Download(s)

1
checked on Mar 27, 2024

Google ScholarTM

Check

Altmetric