The JTGM is essentially composed of harzburgite and dunite, but lherzolite
has also been reported from the lowermost part of the massif (Mahmood et al., 1995).
The residual character of the harzburgitic mantle xenoliths (believed tobe consistent with melting and basalt-component removal) is also indicated by the decrease in the cpx/opx modal ratio with decreasing modal cpx, which fits the model variation trend induced by partial melting of lherzolite
Real in-situ measurement and rock sampling for laboratory measurement were carried out in the southern part of Balmuccia massif at a flat outcrop of the lherzolite
in the Sesia River Valley, between Balmuccia and Isola villages (Fig.
The relationship between these rocks and the adjacent units is tectonic, having been overthrusted on the Eocene flysch and Miocene marl and sandstone.Inside the serpentinites still traces of Pridotites of Harzburgite and sometimes Lherzolite
combination is observed in the form of floating pieces.
The Sabalan lavas are relatively similar to Salmas Quaternary basalts, characterized by low degree of partial melting (<0.1%) of a mantle source containing clinopyroxene-garnet lherzolites
The foliated peridotite is mainly harzburgite with minor dunite and lherzolite
. The dunite present is either interlayered with harzburgite or occurs as envelopes around harzburgite containing mostly podiform chromite deposits.
The second type recognized in the mafic-ultramafic bodies is dominated by variably metamorphosed ultramafic rocks (lherzolite
, harzburgite, wehrlite, dunite, and pyroxenite; Fig.
Xenoliths of eclogite and lherzolite
suggest a mantle origin; isotopic studies indicate an emplacement age around 35.6 to 70.5 million years.
This feature emphasizes their primitive source (garnet lherzolite
origin) and the absence of plagioclase in the early crystallization process.
Arc-related calc-alkalic and tholeiitic basalts typically show moderate degrees of light rare-earth-element (LREE) enrichment, and flat heavy rare-earth-element (HREE) profiles, indicating an origin in a shallow (spinel lherzolite
Although debated, primary magmas are thought to have Mg# values of about 0.72 as a result of equilibration with [Fo.sub.92] olivine that is found in most mantle lherzolite
xenoliths (Roeder and Emslie, 1970).