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Magmas, ore deposits and geodynamic evolution at a convergent margin: the case of Ecuador

English title Magmas, ore deposits and geodynamic evolution at a convergent margin: the case of Ecuador
Applicant Chiaradia Massimo
Number 126896
Funding scheme Project funding
Research institution Département des sciences de la Terre Université de Genève
Institution of higher education University of Geneva - GE
Main discipline Geochemistry
Start/End 01.01.2010 - 31.12.2011
Approved amount 147'440.00
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Keywords (8)

magmatic processes; porphyry Cu; adakite; gold; Ecuador; radiogenic isotopes; geochronology; subduction

Lay Summary (English)

Lead
Lay summary
The petrogenetic and geodynamic significance of adakite-like magmas as well as their relationship with porphyry-type deposits is hotly debated. Adakite-like rocks are considered either the result of slab melting or of high-pressure fractional crystallization and crustal assimilation/melting at lower crustal levels. In the present project we want to address in detail the meaning of our finding from previous research that porphyry-type deposit formation occurs frequently during a transition in the magmatic rocks from normal to adakite-like signatures. In particular we will try to answer three specific questions: (1) Do adakite-like rocks evolve in large and long-lived lower to mid-crustal magmatic chambers? (2) Do adakite-like rocks indicate a structural regime in the continental crust that favors the formation of a major porphyry-type system? (3) Are adakite-like magmas enriched in metals and volatiles with respect to normal arc magmas? To answer these questions we will investigate the Apuela batholith (northern Ecuador) which displays a magmatic evolution through time (from about 19 to 6 Ma) characterized by a transition from normal to adakite-like rocks. The giant porphyry Cu-Mo of Junin (>9 Mt Cu) was formed towards the end of the magmatic cycle of the batholith in concomitance with the development of adakite-like signatures in porphyritic rocks crosscutting the main plutonic facies of the batholith.At the same time we will continue to investigate the petrogenesis of Quaternary adakite-like rocks of Ecuador and their relationship with the subduction of the aseismic Carnegie Ridge. In particular, after having investigated geochemical and isotopic changes of magmatism across-arc in previous research, we want now to address along-arc petrogenetic changes of volcanic rocks to better evaluate the impact that the Carnegie Ridge may have on variations of geochemistry and metallogenetic potential of the magmatism. In order to carry out this project we will use a range of methods including geochronology (U-Pb, Ar/Ar), geochemistry and radiogenic isotopes (Sr, Nd, Pb) of rocks and minerals (XRF, LA-ICP-MS, TIMS, microprobe).The outcome of this project will provide an improved understanding of the genesis of adakite-like rocks at convergent continental margins and of the meaning of their association with major porphyry-type deposits.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Challenges in dating magmatic-hydrothermal events of porphyry systems
Chiaradia Massimo, Schütte Philip (2011), Challenges in dating magmatic-hydrothermal events of porphyry systems.
High-pressure copper exsolution from andesite magma
Chiaradia Massimo, Ulianov Alexey (2011), High-pressure copper exsolution from andesite magma.
Temporal evolution of magmatic rocks at the Coroccohuayco Cu-skarn deposit, Tintaya cluster, Peru
Chelle-Michou Cyril, Chiaradia Massimo, Villon Gustavo (2011), Temporal evolution of magmatic rocks at the Coroccohuayco Cu-skarn deposit, Tintaya cluster, Peru.
Enriched basaltic andesites from mid-crustal fractional crystallization, recharge, and assimilation (Pilavo volcano, Western Cordillera of Ecuador)
Chiaradia Massimo, Müntener Othmar, Beate Bernardo (2011), Enriched basaltic andesites from mid-crustal fractional crystallization, recharge, and assimilation (Pilavo volcano, Western Cordillera of Ecuador), in Journal of Petrology, 52(6), 1107-1141.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Journée Lémanique 02.12.2011 Lausanne
11th Biennial SGA Meeting 26.09.2011 Antofagasta, Chile


Associated projects

Number Title Start Funding scheme
137663 Magmas, ore deposits and geodynamic evolution at a convergent margin: the case of Ecuador 01.01.2012 Project funding
117616 Magmas, ore deposits and geodynamic evolution at a convergent margin: the case of Ecuador 01.10.2007 Project funding
137663 Magmas, ore deposits and geodynamic evolution at a convergent margin: the case of Ecuador 01.01.2012 Project funding

Abstract

The present proposal is for a 2-years continuation of the SNF project N. 200020-117616 “Magmas, ore deposits and geodynamic evolution at a convergent margin: the case of Ecuador”. Funds are asked for a PhD student salary, fieldwork of and attendance to conferences by the PhD student and the applicant, as well as for analytical work for a period of 24 months.In the past years we have investigated the link between changes in magma chemistry and geodynamic setting at convergent continental margins in Ecuador and Peru, and how these could influence the formation of porphyry-type deposits. In particular we have investigated the petrogenetic and geodynamic meaning of a type of subduction-related magmas, so called adakite-like, and their relationship with porphyry-type deposits, since this type of rocks has been found by various studies to be associated with major porphyry-type mineralization throughout the world. A hot debate has developed around the petrogenetic significance of adakite-like rocks, which has propagated into their potential association with porphyry-type deposits. Adakite-like rocks are considered either the result of slab melting or of magmatic evolution processes at lower crustal levels characterized by high pressure fractional crystallization and crustal assimilation.The main results of our investigation so far are the following: (i) in all cases investigated adakite-like rocks are formed by magmatic evolution at deep crustal levels and not by slab melting; (ii) porphyry-type deposits form in association with adakite-like rocks during a few (1-3) My towards the end of a several (6-15) My long transition from normal to adakite-like magmatism; (iii) increased compression is held responsible to have caused a shift of the locus of magmatic evolution from shallow crustal levels (normal arc rocks) to deeper ones (adakite-like signatures); (iv) increased compression might be related to subduction of aseismic ridges and/or any other topographic high (e.g., oceanic plateau) which increase the coupling between subducting and overriding plates, although other changes at the subduction zone (e.g., subduction obliquity, plate relative velocity) may also play a role.In the present project we want to address in detail the meaning of our finding that porphyry-type deposit formation, at least in most of the cases investigated (but in many others documented in the literature as well), occurs during a transition from normal to adakite-like signatures. In particular we will try to answer three specific questions, which are strictly related to the association of porphyry-type deposits with adakite-like rocks: (1) do adakite-like rocks evolve in large and long-lived lower crustal magmatic chambers that are big enough to supply the amount of metals and volatiles required to form a giant porphyry-type deposit? (2) Do adakite-like rocks indicate a structural regime in the continental crust that favors focusing and increased frequency of magmatic pulses in a restricted volume of the upper crust thus creating a thermal, fluid and metal anomaly that will lead to the formation of a major porphyry-type system? (3) Are adakite-like magmas enriched in metals and volatiles with respect to normal arc magmas?To answer these questions we will investigate the Apuela batholith which displays a magmatic evolution through time (from about 19 to 6 Ma) characterized by a transition from normal to adakite-like rocks. The giant porphyry Cu-Mo of Junin (>9 Mt Cu) was formed towards the end of the magmatic cycle of the batholith in concomitance with the development of adakite-like signatures in porphyritic rocks crosscutting the main plutonic facies of the batholith. This magmatic system therefore is a suitable case study to try to answer the above questions.At the same time we will continue to investigate the petrogenesis of Quaternary adakite-like rocks of Ecuador and their relationship with the subduction of the aseismic Carnegie Ridge. In particular, after having investigated geochemical and isotopic changes of magmatism across-arc in the previous years of the project, we want now to address petrogenetic changes of volcanic rocks of an along-arc transect to better evaluate the impact that the Carnegie Ridge may have on changes of geochemistry and metallogenetic potential of magmatism.In order to carry out this project we will use a range of methods including geochronology (U-(Th-)Pb dating of zircon by TIMS and MC-LA-ICPMS, 40Ar/39Ar dating, Re-Os dating), geochemistry and isotope (Sr, Nd, Pb) geochemistry of rocks and minerals (XRF, LA-ICP-MS, TIMS, microprobe).The project will be divided into two subprojects. Subproject A (Geochronologic and petrologic evolution of the Apuela batholith and the formation of a giant porphyry Cu-Mo, Junin, northern Ecuador) dealing with the study of the magmatic evolution of the Apuela batholith and associated porphyry Cu-Mo of Junin will be carried out by a PhD student as the main investigator. Subproject B (Subduction of the aseismic Carnegie ridge and its effects on geochemistry and metallogenic potential of Quaternary magmatism in Ecuador: study of a longitudinal transect of Quaternary volcanic centers between 1°N and 1°S) will deal with the study of the Quaternary adakite-like rocks of Ecuador and will be carried out by the applicant as the main investigator. The outcome of this project will provide an improved understanding of the genesis of adakite-like rocks at convergent continental margins and of the meaning of their association with major porphyry-type deposits.
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