Zircon trace element characteristics and ages in granulite xenoliths: a key to understanding the age and origin of the lower crust, Arkhangelsk kimberlite province, Russia

Thermodynamic constraints on the composition of orogenically thickened lower crust

“…A histogram shows the compositional ranges of X Fe3+ [ = Fe 3+ /∑Fe], X Mg [ = MgO/(MgO + FeO t )], X Al [ = Al 2 O 3 /(Al 2 O 3 + MgO + FeO t )], and X Ca [ = CaO/(CaO + MgO + FeO t + Na 2 O)] in the mafic lower crustal xenoliths. Source data are collected from Huang et al (2013), Liu et al (2013), Koreshkova et al (2014), Mansur et al (2014), Ping et al (2015), and Moyen et al (2017)…”

“…, and X Ca [ = CaO/(CaO + MgO + FeO t + Na 2 O)] in the mafic lower crustal xenoliths. Source data are collected from Huang et al (2013), Liu et al (2013), Koreshkova et al (2014), Mansur et al (2014), Ping et al (2015), and Moyen et al (2017) the P-X diagrams are considered here to represent the reasonable conditions of thickened continental crust. Our new results provide insightful constraints on the potential factors controlling the stability of doubly thickened mafic lower crust.…”

“…a) and X Mg -X Ca -SiO 2 (b) plots of bulk-rock compositions of global mafic granulite facies xenoliths (Huang et al, 2013, and reference therein;Liu et al, 2013;Koreshkova et al, 2014;Mansur et al, 2014;Ping et al, 2015;Moyen et al, 2017). The shaded field represents the lower crustal compositions that are gravitationally stable at 70 km F I G U R E 1 1 Cartoon showing the thickness and composition of thickened lower crust under various Moho temperatures.…”

Origin of coarse-granular and equigranular eclogites from V. Grib kimberlite pipe, Arkhangelsk region, NW Russia

“…The main subduction event and eclogite-facies metamorphism of the Salma association occurred within the time interval from ~2.87 to ~2.82 Ga (Mints et al, 2014). Late Archean age (2.7 Ga) was also obtained from the V.Grib pipe granulitic zircons that corresponds to major events recorded in upper-crustal rocks of the north-eastern Baltic Shield (Koreshkova et al, 2014). Nevertheless, three of V. Grib pipe CG eclogites samples have Proterozoic Sm/Nd DM model ages of 2.0, 1.8 and 1.2 Ga that correspond to the age of the most of V. Grib pipe EG eclogites zircons.…”

“…And, the 1.7 Ga is regarded as the time of exhumation of the Belomorian province eclogite assemblage to mid-to-lower crust under the erosion or younger thermal event (Mints et al, 2014). The Proterozoic ages were also established for the tonalite-trondhjemite-granodiorite (TTG) orthogneiss and granitoids (1.8-2.0 Ga) representing the lower crust in the area of V. Grib kimberlite pipe (Samsonov et al, 2009) as well as for some granulitic zircons from V. Grib pipe (1.8 -1.9 Ga; Koreshkova et al, 2014). The age range of 1.8 -1.9 Ga corresponds to the period of the formation of the orogenic zones upon collision in many cratons worldwide (e.g.…”