Magnetite/Ilmenite–series Classification and Magnetic Susceptibility of the Mesozoic‐Cenozoic Batholiths in Peru

Abstract

: Plutonic rocks of the Coastal Batholith of Peru were evaluated in terms of the granitoid‐series classification using the bulk ferric/ferrous ratio from the literature and new measurements of magnetic susceptibility. The batholith is largely composed of magnetite‐series plutonic rocks; the magnetite series make up 85% by number of chemical analyses (n=130) and 80% by measurement of magnetic susceptibility (n=210). The ilmenite‐series rocks are mostly found in the felsic facies of the batholith. Asymmetrical distribution of magnetic susceptibility is not clear as in the Japanese Islands and Peninsular Range Batholith, but the magnetic susceptibility may decreases continentward (i. e., Peninsular Range type). The Cordillera Blanca Batholith and stocks are also composed of mainly magnetite series plutonic rocks, but ilmenite‐series rocks may be more predominant than in the Coastal Batholith, which is also indicated by the presence of Sn and W mineralizations.

Occurrence and origin of soils with andic properties in Calabria (southern Italy)

“…As a whole, the comparison of soil and bedrock data revealed soil χ lf values that were significantly higher (24.1-1193 × 10 −8 m 3 kg −1 ) than those for bedrock (b0.1-18.5 × 10 −8 m 3 kg −1 ). Magnetic χ lf values of the granitic-like bedrocks ranged from 5.33 to 18.5 × 10 −8 m 3 kg −1 , so reflecting data reported in literature for the leucocratic ilmenite series (I-granite), the least magnetic granites (Ishihara, 1977(Ishihara, , 1979Ishihara et al, 2000). In the cases of SPI and SSB, soil χ lf values were enriched vs. bedrock by around 2 orders of magnitude (701-813 vs. 11.9 × 10 −8 m 3 kg −1 and 149-247 vs. 6.28 × 10 −8 m 3 kg −1 ), respectively, while, for CAS, they were generally around 1 order higher (52.6-95.0, solum 1 and 2 respectively, vs. 7.75 × 10 −8 m 3 kg −1 ).…”

A Late Variscan tin province associated to the ilmenite-series granites of the Sardinian Batholith (Italy): The Sn and Mo mineralisation around the Monte Linas ferroan granite

“…8 Frost, 2011) as they have FeO tot /(FeO tot + MgO) values of >0.90 and ilmenite-series granites as their magnetic susceptibility values are < 3  -3 SI units (Ishihara et al, 2000) in good agreement with the lack of primary magnetite. Indeed, the magnetic susceptibility values for the pluton range from 20 to 60  10 -6 SI units (Cifelli, pers.…”

Autochthonous v. accreted terrane development of continental margins: a revised in situ tectonic history of the Antarctic Peninsula

“…This distribution is at odds with a tectonic model involving a palaeo-subduction zone along the line of the Eastern Palmer Land Shear Zone as this would produce suprasubduction extension and dominantly magnetite-series plutons in the overriding Eastern Domain as well as the volcanic arc of the Central Domain. Instead, the evidence for decreasing fO 2 from west to east supports a simpler model of a single subduction zone west of the Peninsula, placing the magnetite-series granitoids of the Central Domain closer to the convergent margin and the Eastern Domain plutonic rocks farther landward, as seen in North and South America (Ishihara et al 2000;Hart et al 2004). This interpretation of crustal assimilation as the dominant control on magnetic susceptibility is supported by the εNd i data (see above), which show decreased crustal assimilation during formation of the Early Cretaceous extensional magnetite-series intrusions of the Central Domain.…”

“…The distribution of magnetite-series (high fO 2 ) and ilmenite-series (low fO 2 ) granitoids on the East Pacific margin (Ishihara et al 2000;Hart et al 2004) has shown a tectonic control on oxidation state, with dominantly magnetite-series intrusions occurring closest to the convergent margin where crustal extension reduced the degree of crustal contamination and consequent reduction in oxidation state. In contrast, ilmenite-series granitoids dominantly crop out further inland where crustal contamination of the intruding melts was increased by crustal thickening.…”