Low-δ18O and negative-Δ199Hg felsic igneous rocks in NE China: Implications for Early Cretaceous orogenic thinning

Abstract

<p>Magmatic rocks carry key information to understand the processes of material cycling in the Earth's interior and record crucial clues to reconstruct the important <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/tectonic-evolution" title="Learn more about tectonic evolution from ScienceDirect's AI-generated Topic Pages">tectonic evolution</a> of the Earth. Therefore, it is of great importance to constrain the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/magma" title="Learn more about magma from ScienceDirect's AI-generated Topic Pages">magma</a> source (such as origin from crust or mantle, <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/oceanic-crust" title="Learn more about oceanic crust from ScienceDirect's AI-generated Topic Pages">oceanic crust</a> or <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/continental-crust" title="Learn more about continental crust from ScienceDirect's AI-generated Topic Pages">continental crust</a>, lower or upper continental crust) accurately, which however remains to be unraveled because of the variety magmatic sources and complex magmatic processes. High-precision stable isotopic analyses provide new tools to decipher the genesis of igneous rocks and to reconstruct their associated <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/tectonic-setting" title="Learn more about tectonic settings from ScienceDirect's AI-generated Topic Pages">tectonic settings</a>. Here, we report a pioneering work using integrated O-Hg-Hf-Nd isotopes to understand the genesis of the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/early-cretaceous" title="Learn more about Early Cretaceous from ScienceDirect's AI-generated Topic Pages">Early Cretaceous</a> A-type granites and <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/rhyolite" title="Learn more about rhyolites from ScienceDirect's AI-generated Topic Pages">rhyolites</a> from the Paleozoic-Mesozoic accretionary orogen in NE China. Low δ¹⁸O <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/zircon" title="Learn more about zircon from ScienceDirect's AI-generated Topic Pages">zircon</a> values (3.2–5.7‰) of the A-type rocks reveal a <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/magma" title="Learn more about magma from ScienceDirect's AI-generated Topic Pages">magma</a> source affected by meteoric fluids. Their whole-rock negative Δ¹⁹⁹Hg values (−0.24 to −0.01‰), which are similar with the terrestrial systems but clearly different from the marine systems, indicate that <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/hydrothermal-alteration" title="Learn more about hydrothermal alteration from ScienceDirect's AI-generated Topic Pages">hydrothermal alteration</a> took place in the continental setting. Positive <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/zircon" title="Learn more about zircon from ScienceDirect's AI-generated Topic Pages">zircon</a> <em>ε</em>_Hf(<em>t</em>) (4.2–10.7) and mainly positive whole-rock <em>ε</em>_Nd(<em>t</em>) (−0.5 to 2.4, mean = 1.2 ± 1.0, 1SD) values indicate that the magma source was dominated by juvenile crustal materials. This study suggests an elevated <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/geothermal-gradient" title="Learn more about geothermal gradient from ScienceDirect's AI-generated Topic Pages">geothermal gradient</a> due to the lithospheric thinning triggered by rollback and foundering of a Paleo-oceanic slab. The specific <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/temperature-anomaly" title="Learn more about thermal anomaly from ScienceDirect's AI-generated Topic Pages">thermal anomaly</a> caused the remelting of the altered upper <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/continental-crust" title="Learn more about continental crust from ScienceDirect's AI-generated Topic Pages">continental crust</a>, resulting in the formation of the A-type granites and <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/rhyolite" title="Learn more about rhyolites from ScienceDirect's AI-generated Topic Pages">rhyolites</a>, with the characters of low-δ¹⁸O and negative-Δ¹⁹⁹Hg values. Our study shows that Hg isotope, coupled with O and Nd<img src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/55/entities/sbnd.gif" alt="single bond">Hf isotopes, is a promising tool for petrogenetic studies.</p>