Heterogeneous magmas of the Quaternary Sierra Chichinautzin volcanic field (central Mexico): the role of an amphibole-bearing mantle and magmatic evolution processes

the quaternary sierra chichinautzin volcanic field (scvf) is located at the volcanic front of the trans-mexican volcanic belt (tmvb), 350 km from the middle american trench where the cocos plate subducts beneath the north american plate. the scvf is characterized by more than 200 monogenetic centers, ranging in composition from rare basalts to dacites. less evolved terms have aphyric to porphyritic textures with phenocrysts of euhedral olivine (± cr-spinels inclusions) + cpx, -whereas evolved terms have porphyritic textures with phenocrysts of pyroxene (cpx>opx), xenocrysts of corroded quartz, and sieve-textured plagioclase from the local basement. regardless of the degree of magmatic evolution, plagioclase occurs as microphenocrysts or in the groundmass. new geochemical and isotopic data presented in this work are in good agreement with previous analyses; however, a new division for the scvf mafic rocks (mgo >6.0 wt.%) is proposed. in fact, although concentrations of large ion lithophile elements (lile) and light to medium rare earth elements (ree) are roughly constant in mafic rocks, tio2 and other high field strength elements (hfse) such as nb are scattered and vary from 0.8 to 1.8 wt.% and from 5 to 30ppm, respectively. these characteristics allow grouping the scvf rocks in two main magmatic series with different tio2-hfse enrichment: high(h)-tio2 and low(l)-tio2, with subordinate transitional samples. additionally, a cinder cone with shoshonitic affinity and extremely high lile/hfse ratio is reported for the first time in central mexico. compositional variability is also observed among the mineral phases of these mafic rocks (e.g., the cr# of spinel hosted in olivine phenocrysts), and the 87sr/86sr ratios that progressively increase from the h-tio2series (0.70307-0.70425) to the l-tio2 series (0.70365-0.70434), up to the shoshonitic scoria (0.70456). the calc-alkaline affinity, lile, and pb positive anomalies of the magmas confirm the occurrence of a subduction