Morphology and geochemistry of zircons from late Mesozoic igneous complexes in coastal SE China: implications for petrogenesis

Abstract

The Pingtan and Tonglu igneous complexes in SE China are typical of the calc-alkaline series developed at active continental margins. These two complexes are dominated by felsic rocks, temporally and spatially associated with minor mafic rocks. Morphological and trace-element studies of zircon populations in rocks from each of these complexes show that the zircon populations may be divided into 3–4 distinct growth stages, characterized by different distributions of morphological indices (Ipr, Ipy and Iel), and different contents of the substituting elements (Hf, U, Th, Y and P). The four growth stages recognized in the zircons are believed to have formed successively in the magma chamber, during the emplacement, and in the early and later stages of magma consolidation, respectively. All four stages are recognized in the plutonic Pingtan complex, whereas the stages 3 and 4 are less developed in the volcanic/subvolcanic Tonglu complex. Based on the chemistry and morphology of the different zircon populations of the Pingtan and Tonglu complexes, it is suggested that basaltic magmas underplating at the boundary between crust and mantle caused partial melting of the mid–lower crust and produced granitoid magmas. Subsequently, mixing between magmas was important.

Behavior and Impact of Zirconium in the Soil–Plant System: Plant Uptake and Phytotoxicity

“…Tejan-Kella et al ( 1991 ) recorded etch-pitted zircon grains only in soils that were 100,000 years old. The chemical composition of zircon mineral is used to elaborate many magmatic processes, including the interaction with hydrothermal fl uids (Thomas et al 2002 ;Hoskin 2005 ) , crystal fractionation (Pettke et al 2005 ;Lowery Claiborne et al 2006 ) , and/or magma mixing (Wang et al 2002 ;Belousova et al 2006 ) , as well as being a potential source indicator (Aja et al 1995 ;Belousova et al 2002 ;Gagnevin et al 2009 ) .…”

Relict Proterozoic basement in the Nanling Mountains (SE China) and its tectonothermal overprinting

“…During this step, we selected a representative number of each morphological population recognized (including variations in elongation, color and crystal face development) [Wang et al, 2002]. More than 30 grains from most of the samples were mounted in epoxy blocks and polished for analysis.…”

The Composition of Zircon and Igneous and Metamorphic Petrogenesis

“…Although this scheme was initially widely accepted and is still used (e.g., Dabard et al 1996), three subsequent and ongoing observations have seen it rarely used: (1) zircon from a single rock and single age population can have widely varying morphologies; (2) zircon from widely different rock-types can have similar to identical morphologies with no systematic measurable differences despite claims to the contrary (see Fig. 9a of Wang et al 2002); and (3) the external morphology of a single crystal can change a number of times during a single growth event (Fig. 2a) as a result of kinetic factors, such as diffusion rates and adsorption, which effect the growthrates of crystal faces and therefore control the morphology of a growing crystal (Dowty 1980, Vavra 1990.…”