40 Ar/ 39 Ar Geochronology and stable isotope geochemistry of Late-Hercynian intrusions from north-eastern Iberia with implications for argon loss in K-feldspar

Abstract

The cooling history of Hercynian calc-alkalic, post-kinematic plutonic intrusions of the Montnegre massif (NE Spain) has been determined by 40 Ar/ 39 Ar analysis of two hornblendes, four biotites and eight K-feldspars (Kfs). The hornblendes have 40 Ar/ 39 Ar total fusion ages of 291±3 Ma and define the magmatic cooling of the basic and oldest structural intrusions. The biotites from the acid and intermediate rocks have 40 Ar/ 39 Ar plateau ages of 285±3 Ma, which date cooling of the intrusions through argon closure in biotite. The 40 Ar/ 39 Ar ages of the K-feldspars vary widely, ranging from 276-191 Ma. A correlation between K-feldspar 40 Ar/ 39 Ar total fusion age and several other features such as structural state, microstructures indicated by obliquity and, to some degree, optically visible perthites, is consistent with post-crystallisation partial argon loss in the K-feldspars. The δD values of the biotites also correlate with age and chlorite contents, but this is not so for the δ 18 O values of either feldspar or quartz. We infer that most microtextural changes occurred during cooling of the batholith, but a possibly Mesozoic, late disturbing hydrothermal event of weak intensity and with only minor fluid circulation must have occurred. This event provoked significant argon loss in the most structurally complex K-feldspars and is recorded in the hydrogen, but not oxygen, isotope data.

A multiscale analysis of a fracture pattern in granite: A case study of the Tamariu granite, Catalunya, Spain

“…3b). It is chiefly a M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 7 biotite granodiorite with K-feldspar megacrysts dated from 288.4 ±2 Ma (Ferrés-Hernàndez, 124 1998), with some Permian spessartite dykes that intrude the granitic body (Solé et al, 2002). (Roca et al, 1999;Le Garzic, 2010).…”

Polyphasic hydrothermal and meteoric fluid regimes during the growth of a segmented fault involving crystalline and carbonate rocks (Barcelona Plain, NE Spain)

“…Isotopic studies of the late Hercynian intrusive rocks of the Montnegre Horst (CCR) show δ 18 O values up to +6.1‰ SMOW and δD values up to −35‰ SMOW, suggesting the hydrothermal alteration of the rock by a δ 18 O‐depleted fluid with a low water/rock ratio (Solé et al . ). The δ 18 O‐depleted fluid could have got different origins as its signal has been completely buffered by the granitic host rock.…”

Leveling vs. InSAR in urban underground construction monitoring: Pros and cons. Case of la sagrera railway station (Barcelona, Spain)

“…1). Geologically, this area is formed by a coastal plain (The Barcelona Coastal Plain) (Vázquez-Suñé et al, 2016) bounded by two Quaternary deltaic formations (corresponding to the Besòs -Velasco et al, 2012a -and Llobregat rivers - Gámez et al, 2009) and an elevated area, the Catalan Coastal Ranges (mainly Paleozoic rocks composed by granodiorite materials) (Sanz, 1988;Banda and Santanach, 1992;Roca and Guimerà, 1992;Solé et al, 2002). More concretely, the study site is located in an actual plain, which consists of Quaternary formations that overlie a substrate mainly consisting of Pliocene series and is mainly composed of marine blue marls, sandy marls, and Paleozoic granite.…”