Genesis of highly fractionated I-type granites from Fengshun complex: Implications to tectonic evolutions of South China

Abstract

The South China Block is characterized by the large-scale emplacement of felsic magmas and giant ore deposits during the Yanshanian. We present zircon Hf isotopic compositions, whole-rock major and trace element compositions of the Fengshun complex, located in eastern Guangdong Province, South China. The Fengshun complex is a multi-stage magmatic intrusion. It is composed of two main units, i.e., the Mantoushan (MTS) syeno-monzogranites, alkali feldspar granites and the Hulutian (HLT) alkali feldspar granites. LA-ICPMS zircon dating shows that the complex emplaced in 166-161 and 139±2 Ma, respectively. Geochemically, the MTS granites show relatively various geochemical compositions with low REE contents (87.76×10 -6 -249.71×10 -6 ), Rb/Sr ratios (1.19-58.93), pronounced Eu negative anomaly (0.01-0.37) and low Nb/Ta ratios (2.40-6.82). In contrast, the HLT granites exhibit relatively stable geochemical characteristics with high REE contents (147.35×10 -6 -282.17×10 -6 ), Rb/Sr ratios (2.05-10.30) and relatively high Nb/Ta ratios (4.45-13.00). The isotopic data of the MTS granites display relatively enriched values, with I Sr varying from 0.708 2 to 0.709 7, ε Nd (t) from -7.8 to -6.9 and ε Hf (t) from -7.4 to -3.2, in comparison with those of the HLT which are I Sr =0.703 05-0.704 77, ε Nd (t)=-5--3.4 and ε Hf (t)=-0.7-1.8). The two-stage model ages of the MTS granites (T 2DM (Nd)=1.51-1.59 Ga and T 2DM (Hf)=1.26-1.48 Ga) are also higher than those of the HLT granites (T 2DM (Nd)=1.21-1.34 Ga and T 2DM (Hf)=0.96-1.10 Ga). Thus the MTS and HLT granites might originate from different sources. The former is more likely derived from partial melting of Meso-Proterozoic basement triggered by upwelling of asthenosphere and/or underplate of the basaltic magma and then extensive fractional crystallisation, similar to the genesis of Early Yanshanian granitoids of the EW-trending tectono-magmatism belt in the Nanling range. In comparison, the latter might have involved with asthenosphere component, similar to the Early Cretaceous granitoids of NE-NNE-trending granitoid-volcanic belt in coastal region, southeastern China. We propose that the MTS granites were mainly formed in Paleo-Tethyan post-orogenic extensional tectonic setting whereas the HLT granites were formed in the back-arc extensional tectonic setting. The period at 139 Ma represents the initial time of roll-back of the paleo-Pacific Plate in SE-trending.

Origin of Late Jurassichigh‐Kfelsic volcanic rocks and related Au mineralization in the Dongyang deposit, central‐eastern Fujian,SEChina, and its tectonic implications

“…The zircons in the rhyolites have negative ε Hf( t ) values ranging from −9.7 to −6.3 and yield two‐stage Hf model ages of 1,054–1,202 and 2,527–2,205 Ma. These Hf isotope characteristics are similar to those of Late Jurassic (164–145 Ma) magmatic rocks and felsic volcanic rocks in central‐eastern Fujian and eastern Guangdong (Figure 8 and Table 5; Guo et al, 2012; Liang et al, 2013; Liu et al, 2015; Qiu, Li, et al, 2017; Qiu, Yan, et al, 2017; Ye et al, 2014; Zhou et al, 2016). Furthermore, the Hf isotope data plot beneath or slightly above the chondrite line and above the domain of Cathaysia crustal basement rocks (Figure 8a), suggesting that the magma was derived from a crustal source.…”

“…The Dongyang dacitic crystal tuff has negative ε Hf( t ) values (−11.2 to −5.3) and two‐stage model ages of 2,650–2,121 Ma, which are similar to those of the Late Jurassic magmatic rocks in the surrounding areas and eastern Guangdong. Most of the data points are located close to the chondritic line and within or above the field of Cathaysia basement rocks, suggesting partial melting of crustal sources (Figure 8a; Table 5; Guo et al, 2012; Liang et al, 2013; Liu et al, 2015; Zhang et al, 2015; Zhou et al, 2015, 2016). Since the Dongyang dacitic crystal tuff lava is strongly peraluminous (Figure 6c), Palaeoproterozoic felsic rocks (meta‐igneous or metasedimentary rocks; Figures 3 and 4g) are possible magma sources.…”

Insights into deep metallogenic setting inSEChina based on geophysical data

“…It stimulated regional extrusion orogeny, with substantial crustal thickening and crustal temperature growth. However, as the subduction angle of the Palaeo‐Pacific Plate increased (Zhou et al, 2016), the lithosphere was fully extended and thinned. Mid‐crustal materials form acidic magma under conditions of decompression and melting.…”

“…The understanding of the deep dynamics, magmatism and metallogenic mechanism in South China mostly came from petrology and geochemistry (Chen & Xing, 2013; Hu & Zhou, 2012; Mao et al, 2014; Meng et al, 2012; Wang et al, 2011; Zhou et al, 2016). It is also of great significance to understand the deep metallogenic background by using geophysical techniques to image the deep structure of ore‐forming element‐rich areas at multiple scales and deducing the major geological events in the past in combination with geological chronology.…”

Post‐rift Tectonic History of the Songliao Basin, NE China: Cooling Events and Post‐rift Unconformities Driven by Orogenic Pulses From Plate Boundaries

“…Afterward, we place identified uplift and exhumation events in the context of regional tectonics (Braun, ), thus deciphering the major orogenic pulses in the northeastern Chinese section of the Asian continental margin. Recent tectonic studies of different plate regions have shown that plate boundary stresses exerted a primary control upon coeval deformation and exhumation in intraplate settings (Allen & Davies, ; Echaurren et al, ; Fairhead et al, ; Gleadow et al, ; Holford et al, ; Lin et al, ; Shi et al, ; X. Zhang et al, ; Zhou et al, ). Therefore, in the final step of this study, we correlate the timing of orogenic and exhumation pulses in the Songliao Block and adjacent areas with major subduction and collision events along the Pacific and Neo‐Tethys (India‐Asia) plate boundaries of the continent.…”