The significance of microgranular enclaves in assessing the magmatic evolution of a high-level composite batholith: A case on the Los Pedroches Batholith, Iberian Massif, Spain

Abstract

are partly a consequence of the heterogeneities of the Earth's crust, in most cases requiring a case-by-case study of granitoid genesis. In other instances, however, uncertainties are a consequence of an insufficient integration of geochemical information with other geological data (field, petrographic, geophysical, etc.), either by scarcity or ambiguousness.We present here the case of the Los Pedroches batholith (LPB), one of the largest Variscan batholiths in Spain, as an example in which a number of the usual uncertainties in granite genesis can be overcome by a careful integration of geochemical and isotopic data with field and petrographic evidence.There are several reasons making the LPB of particular interest. The geological setting is very well constrained, as there is both compelling evidence and a wide consensus on its intrusion age, its emplacement style, and its main subdivision in two plutonic suites (Larrea et al., 2004). Also, the LPB is very suitable for a mineralogical and geochemical study, as all of the LPB units contain very fresh rocks. In addition, the LPB rocks are remarkably homogeneous at a large scale, particularly in the case of the granodioritic rocks (LPG). For these reasons, we consider the LPB as a good target to build up a model, which could be of major interest, not only at a regional scale, but also with regard to the general role of microgranular enclaves as indicators of magma genesis (Received May 15, 2007; Accepted October 6, 2007) To evaluate the origin and significance of microgranular enclaves hosted by granites, we present new data on two granitoid series belonging to the Los Pedroches Batholith (LPB), SW Iberian Massif, Spain. The two series in the LPB show a distinct contrast in terms of field, petrographic, mineralogical and geochemical data. This contrast also extends to the enclaves, differing in abundance and other features in each of the series considered. Isotopic measurements, however, including 87 Sr/ 86 Sr, ε Nd and δ 18 O data, show no significant, inter-or intra-series contrast throughout the LPB. These data lend additional support to an origin of all the granitoid rocks in the LPB from a single, isotopically homogeneous, lower crustal source. We also suggest that differences between microgranular enclaves in the two LPB granitoid series cannot be related to a different degree of participation of mafic rocks in the genesis of the respective groups: in both cases, microgranular enclaves are better interpreted as autoliths.

Overlapping Sr–Nd–Hf–O isotopic compositions in Permian mafic enclaves and host granitoids in Alxa Block, NW China: Evidence for crust–mantle interaction and implications for the generation of silicic igneous provinces

“…The cumulate model has been criticized because it would not be compatible with the small grain size and the fine-grained margins of many enclaves (Donaire et al, 2005;Esna-Ashari et al, 2011). In the chilled margin scenario, microgranular enclaves have high SiO 2 contents (commonly N58 wt.%) (Donaire et al, 2005;Esna-Ashari et al, 2011;Pascual et al, 2008), can be classified as intermediate-felsic microgranular enclaves (Didier and Barbarin, 1991) and the major mafic mineral is biotite (Donaire et al, 2005;Esna-Ashari et al, 2011;Pascual et al, 2008). These characteristics are not observed in the studied MMEs.…”

“…The similar mineral assemblages and isotopic compositions of the MMEs and host granitoids in both plutons, which are considered further in Section 6.2, are commonly used to indicate that the microgranular enclaves crystallized from coeval, cognate host magmas via accumulation (Dahlquist, 2002;Dodge and Kistler, 1990) or chilled margins processes (Donaire et al, 2005;Esna-Ashari et al, 2011;Pascual et al, 2008). The cumulate model has been criticized because it would not be compatible with the small grain size and the fine-grained margins of many enclaves (Donaire et al, 2005;Esna-Ashari et al, 2011).…”

Lanthanides in granulometric fractions of Mediterranean soils. Can they be used as fingerprints of provenance?

“…Chondrite‐normalized concentrations of lanthanides (logarithmic scale) in: (a) the soil fine sand fraction (50–250 μm) (all horizons; this study), (b) the soil clay fraction (< 2 μm) (mean profile, this study), (c) free forms from the soil clay fraction (mean profile, this study) extracted with citrate‐dithionite‐bicarbonate (FF clay‐CDB ), (d) free forms from the soil clay fraction (mean profile, this study) extracted with oxalate (FF clay‐Ox ), (e) acid igneous and magmatic‐like rocks from the Guadalquivir catchment (Larrea et al ., , , ; Carracedo et al ., ; Pascual et al ., ), (f) alkaline igneous rocks from the Guadalquivir catchment (Larrea et al ., ; Pin et al ., ), (g) sedimentary rocks from the Guadalquivir catchment (Martínez‐Ruiz, ; Jiménez‐Espinosa et al ., ), (h) metasedimentary rocks from the Guadalquivir catchment (Torres‐Ruiz et al ., ) and (i) Sahara–Sahel materials (Moreno et al ., ) and Spanish topsoil (Locutura et al ., ). The shaded area (b to i) and the area with horizontal lines (c to i) enclose the upper and lower margins of the mean values per profile of the fine sand and clays (a and b).…”

“…Plot of La N /Yb N against Σ(La, Ce, Nd, Sm, Eu, Yb, Lu) for soil fine sand and soil clay fractions (mean profile values) and all values for rocks from the Guadalquivir catchment (igneous, sedimentary and metasedimentary rocks; Larrea et al ., , , ; Martínez‐Ruiz, ; Carracedo et al ., ; Pin et al ., ; Pascual et al ., ; Jiménez‐Espinosa et al ., ), Sahara–Sahel materials (Moreno et al ., ) and Spanish topsoil (Locutura et al ., ). Symbols used are the same as in Figure ; the numbers in the circles correspond to soil profile number and P to point bar sediment (PM).…”

“…The linear functions fitted to these families of points suggest a lithological relation. Furthermore, the family of points for fine Larrea et al, 1992Larrea et al, , 1994Larrea et al, , 1995Martínez-Ruiz, 1994;Carracedo et al, 1997;Pin et al, 2002;Pascual et al, 2008;Jiménez-Espinosa et al, 2016). Symbols used are the same as in Figure 5; the numbers in the circles correspond to soil profile numbers, and P corresponds to point bar sediment (PM).…”