Petrogenesis of mid-Neoproterozoic low-δ ¹⁸ O and high Ba-Sr granitoids in the western margin of the South China Block

Middle Neoproterozoic granitoids from the western margin of the Yangtze Block provide critical insights into crust-mantle interaction and crustal growth processes of the South China Block during Rodinia supercontinental cycles. Zircon U-Pb dating reveals that the Datian diorite and granite were emplaced contemporaneously at ca. 760–770 Ma. The Datian diorites exhibit variable SiO 2 (56.60–67.03%), high Mg # (49.32–55.18), medium Na 2 O+K 2 O (5.02–6.46), A/CNK (1.02–1.16) shows aluminum, and high Cr and Ni concentrations, while the granites show high SiO 2 (70.91–80.73%) and low MgO (0.11–0.67%), Na 2 O+K 2 O (4.72–8.52) shows a subalkaline series, A/CNK (0.86–1.22) indicates metaluminous to peraluminous. Both the diorite and granite are enriched in LILEs but depleted in HFSEs, resembling that of typical arc affinities. The diorites display moderate positive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ε</mml:mi> </mml:math> Hf (t) (+2.3 to +6.6) and mantle-like <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 18 O (4.95–6.30 ‰), while the granites exhibit similar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>ε</mml:mi> </mml:math> Hf (t) compositions (+1.83 to +7.15) but low- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 18 O (0.59–5.90‰) values. More importantly, the diorites display high Ba-Sr (Ba + Sr = 898 – 1720 ppm) signatures and characterized by amphibole-rich lithologies. These geochemical and isotopic signatures suggest that the parental magmas of the diorites were most likely generated by partial melting of the mantle wedge metasomatized by the subducted oceanic slab during the early stage, and subsequently the high Ba-Sr melts differentiate to generate the Datian diorite in a continental arc setting. The low- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> ¹⁸O granites were formed through partial melting of juvenile lower gabbroic crust that had been interpointed by high-temperature hydrothermal alteration. The high Ba-Sr granitoids share geochemical affinity with Archean sanukitoids, forming via amphibole-dominated fractional crystallization of fluid-metasomatized mantle. The development of mid-Neoproterozoic continental arcs along the margin of the Yangtze Block suggests that South China occupied a peripheral location in Rodinia.