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Interaction between mafic magmas and crustal metamorphic rocks at mid-crustal levels causes modification of mafic magma composition by assimilation or reaction with crustal materials. This petrologic process is studied at the Suya Taco... more
Interaction between mafic magmas and crustal metamorphic rocks at mid-crustal levels causes modification of mafic magma composition by assimilation or reaction with crustal materials. This petrologic process is studied at the Suya Taco Complex where a suite of mafic magmas interacted with metamorphic rocks at 6.6±1 kbar. The Suya Taco Complex consists of close-spaced bodies of biotite-bearing gabbronorites. These magmas intruded into a supracrustal sequence consisting of amphibolite– to granulite–facies gneisses and migmatites. The peak-metamorphic mineral assemblage Bt+Qtz+Pl(An30)+Grt+Kfs±Crd±Sil of supracrustal rocks crystallised before igneous mafic magmatism. Interaction between mafic magmas and metamorphic rocks produces two major hybrid lithologies: diorites made up of Opx+Bt+Pl (An38–50)+Ilm±Cpx±Qtz; and garnet- and orthopyroxene-bearing rocks characterised by the coexistence of Bt+Pl (An30–45)+Grt+Opx+Qtz+Ilm±Spl±Kfs. The latter lithology may locally appear as a quartz-absent and high-aluminous mineral assemblage. The two hybrid rocks occur interlayered at the contact zone between igneous mafic rocks and high-grade gneisses. Individual layers range from centimeter to meter scales; moreover, dioritic and orthopyroxene- and garnet-bearing layers present a spectrum of mineral assemblages and mineral chemistry that spread among those that appear in igneous mafic and metamorphic rocks. The work shows that the changes of mineral assemblages and variations of mineral chemistry in the hybrid diorites and orthopyroxene- and garnet-bearing rocks are the result of interaction processes between mafic magmas and regional metamorphic rocks. Field relationships, petrographic features, mineral compositional changes and qualitative analyses of phase relations suggest that rocks formed by interaction between mafic magmas and metamorphic rocks results from: (1) assimilation of metamorphic rocks by mafic magmas at variable degrees and (2) ion diffusion among mineral assemblages of contrasting composition. The implication of these processes is that Ca is transferred from mafic magmas to metamorphic rocks, which forces the breakdown of garnet and quartz, and induces the crystallisation of plagioclase and orthopyroxene in the resulting hybrid rocks.
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Zircon LA-ICP-MS and CA-TIMS and molybdenite Re-Os geochronology for the El Abra porphyry copper deposit (Chile) document a ~8.6 Ma protracted magmatic-hydrothermal history. Initial magmatic events occurred at ~45 Ma, and continued to ~36... more
Zircon LA-ICP-MS and CA-TIMS and molybdenite Re-Os geochronology for the El Abra porphyry copper deposit (Chile) document a ~8.6 Ma protracted magmatic-hydrothermal history. Initial magmatic events occurred at ~45 Ma, and continued to ~36 Ma. An ~1.8 m.y. magmatic lull is recorded in the early stages of magmatism, which is characterized by equigranular rocks from the Pajonal suite. Magmatism from ~41 to ~36 Ma, corresponding to the El Abra Granodiorite Complex, is more recurrent, ending in a ~1.4 m.y. period of porphyritic intrusions, which are coeval with Cu-Mo mineralization. Late porphyritic units reveal subtle zircon inheritance likely associated with early magmatic pulses. The young stages of magmatism indicate system reju-venation based on plagioclase phenocryst compositions, suggesting that the porphyry system is ultimately linked to a less evolved magma. Although there are multiple porphyry and veining events, molybdenite Re-Os ages define a focused mineralization episode from 36.34 to 36.18 Ma. Molybdenite Re-Os ages from nearby related prospects belonging to the El Abra cluster expand the mineralization period in the district up to ~1.0 m.y., suggesting a multistage, long-lived hydrothermal system. Integration of the molybdenite Re-Os dates and those from previous works at the El Abra and Toki clusters, accompanied by available tectonic reconstruction along the Domeyko fault system suggest the development, by late Eocene times, of a single, large (~30 km across) porphyry copper cluster, which was subsequently separated by an offset of ~35 km along the West fault.
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The Paleogene Farallon-Aluk divergent ridge collision with the South American plate evolved into a transform margin along the SAM western coast, with the detachment and sinking of the Aluk plate and the development of a large slab... more
The Paleogene Farallon-Aluk divergent ridge collision with the South American plate evolved into a transform margin along the SAM western coast, with the detachment and sinking of the Aluk plate and the development of a large slab window. This collision promoted a magmatic hiatus at the former arc axis, with the tectono-magmatic scenario changed to postorogenic synextensional volcanism that spread to the former fore-arc (basalt, andesite, rhyolite) and to the former back-arc (bimodal ignimbrite flare-up, basalt). Geochemistry of this slab window synextensional volcanism shows more MORB-like basalts towards the former fore-arc, and MORB-OIB like basalts towards the former back-arc.
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... Fernando Barra Osvaldo M. Rabbia Guillermo Alfaro. ... Las serpentinitas del área de La Cabañaforman parte de la Serie Occidental del Basamento Metamórfico de la Cordillera de la Costa de la IX Región y corresponden a dunitas de grano... more
... Fernando Barra Osvaldo M. Rabbia Guillermo Alfaro. ... Las serpentinitas del área de La Cabañaforman parte de la Serie Occidental del Basamento Metamórfico de la Cordillera de la Costa de la IX Región y corresponden a dunitas de grano grueso parcial a totalmente ...
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One of the most striking features of these samples is a correlation between geochemistry and geography. SiO 2 contents in domes progressively decrease towards the south. Fe 2 O 3 , MgO, CaO, Ni, Cr, and Co increase from N to S, while... more
One of the most striking features of these samples is a correlation between geochemistry and geography. SiO 2 contents in domes progressively decrease towards the south. Fe 2 O 3 , MgO, CaO, Ni, Cr, and Co increase from N to S, while alkalis and incompatible elements ...
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Page 1. DISCUSSION Osvaldo M. Rabbia Æ Laura B. Herna´ndez Robert W. King Æ Leopoldo Lo´pez-Escobar ... Keywords Andes Æ Adakite Æ Flat slab Æ Lower crust Æ Porphyry copper In a recent thought-provoking article, Oyarzun et al. ...