The Tynong pluton, its mafic synplutonic sheets and igneous microgranular enclaves: the nature of the mantle connection in I-type granitic magmas

Abstract

quartz dioritic sheets. Despite this evidence of direct mantle input into the Tynong magma system, the main granodioritic series do not appear to have been formed by magma mixing processes. Of any I-type granite in the region, the Tynong pluton has perhaps the most direct connection with mantle magmas. Nevertheless, the main mantle connection here is probably in the mantle-derived protolith for these crustal magmas and in the mantle thermal event that gave rise to melting of the deep crust in the Selwyn Block. This degree of mantle connectedness seems typical for I-type granitic rocks worldwide.

Transition From Low‐K to High‐K Calc‐Alkaline Magmatism at Approximately 84 Ma in the Eastern Pontides (NE Turkey): Magmatic Response to Slab Rollback of the Black Sea

“…Group II (< 84 Ma) As discussed above, the Group II samples are high-K calc-alkaline with higher K, Rb, Th, and Ba abundances, as well as elevated K 2 O/Na 2 O ratios relative to the Group I samples. These K-rich features can be attributed to (1) partial melting of the high-K basaltic or andesitic rocks derived from the metasomatic mantle wedge (e.g., Ancellin et al, 2017;Castro et al, 2010;Hildreth & Moorbath, 1988;Luhr, 1992;Wyllie, 1982), or (2) partial melting of sedimentary materials or preexisting amphibole-rich igneous rocks due to underplating of basaltic magmas (e.g., Chappell & White, 1992;Clemens et al, 2016;Collins & Vernon, 1992;Ducea & Barton, 2007;Roberts & Clemens, 1993;Whitney, 1988), and (3) phlogopite-, biotite-, or amphibole-dominated fractionation from high-K primitive melts (e.g., Bucholz et al, 2014;Fowler et al, 2001;Lobach-Zhuchenko et al, 2008).…”

Melt‐Fluxed Melting of the Heterogeneously Mixed Lower Arc Crust: A Case Study from the Qinling Orogenic Belt, Central China

“…Instead, the Tangzang adakitic pluton has slightly higher MgO (Mg # : 50-52) contents and is formed by melt-fluxed melting of the lower arc crust. In fact, granitoids, especially I-type granites, are very closely chemically related to mantle-derived mafic magmas (Clemens et al, 2016;Depaolo et al, 1992;Nandedkar et al, 2014). We, therefore, speculate that the andesitic continental crust may be also associated with aqueous melt-fluxed melting of the lower arc crust, especially those granodioritic intrusions with low magma temperature like the Tangzang pluton.…”

“…However, recent studies argued that freezing of mafic magmas would inhibit deformation of enclaves and further mechanical mixing (Farner et al, 2014;Paterson et al, 2004). Thus, magma mixing only occurs in a basalt-dominated system and magma interactions, in most cases, are in forms of mingling rather than mixing (Clemens et al, 2016;Farner et al, 2014). Material exchanges between the MMEs in the Tangzang diorites and felsic melts are evidenced by the following petrological observations: (1) the increasing proportion of hornblendes across the boundary between the host quartz diorite and the MMEs, and the occurrence of abundant biotite within the MMEs but only close to the boundary; (2) the existence stubby and acicular apatite close to boundary between the MMEs and the host rock.…”

“…Meanwhile, Kelemen et al (2014) proposed that delamination of dense cumulates cannot produce continental crust with Mg # of 50, because the typical arc section (Talkeetna) still has a basaltic bulk composition even after removing dense cumulates in the lower arc crust (Debari & Sleep, 1991;Greene et al, 2006). In fact, granitoids, especially I-type granites, are very closely chemically related to mantle-derived mafic magmas (Clemens et al, 2016;Depaolo et al, 1992;Nandedkar et al, 2014). However, partial melting of mafic lower arc crust alone cannot produce intermediate rocks with high MgO, Cr, and Ni contents (Figure 12), and mantle contributions are also required.…”

“…Mafic enclaves in granitic rocks can provide important petrogenetic information which is not available from their host rocks (Clemens et al, 2016;Maas et al, 1997;Yang et al, 2004). However, there are considerable discrepancies among models concerning the origin of the MMEs, chief among which are unmixed restites, inclusions of mantle-derived melts or lower crust materials (Chappell et al, 1987;Collins, 1998;Gray & Kemp, 2009).…”