Synchronous late Neoarchean Na- and K-rich granitoid magmatism at an active continental margin in the Eastern Liaoning Province of North China Craton
Synchronous late Neoarchean Na- and K-rich granitoid magmatism at an active continental margin in the Eastern Liaoning Province of North China Craton
复制标题
华北克拉通辽东活动大陆边缘新太古代晚期同步富钠、富钾花岗岩岩浆作用
DOI：
10.1016/j.lithos.2020.105770
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发表时间：
2020
期刊：
影响因子：
3.5
通讯作者：
Wang Wei
中科院分区：
文献类型：
--
作者：
Liu Heng;Wang Wei
晚太古代大量富钾花岗岩的出现标志着大陆地壳的逐渐成熟和稳定。富钾花岗岩类岩浆活动大多发生在TTG岩浆活动之后，但有时是同步发生的，这种关系对认识晚太古代大陆地壳演化及其地球动力学背景具有重要意义。本研究在华北克拉通辽东抚顺南部地区发现了一系列~2.57 ~ 2.52 Ga的花岗岩类岩石，包括石英闪长岩、花岗闪长岩至二长/正长岩片麻岩。~2.57 Ga石英闪长质片麻岩MgO中等（≤3.96 wt.%）， Mg#中~高（37.3 ~ 75.5）。地球化学模拟、轻度分馏的REE模式、负Eu异常和贫化锆石ƐHf(t2)（+2.1−+7.4）表明，它们是由一个由板源流体交代的贫化地幔源分化而成的。较年轻的长闪质片麻岩（~2.55 ~ 2.52 Ga）分为两个亚群，即较老的亚群（~2547 ~ 2540 Ma）以轻度REE分异模式和负Eu异常为特征，较年轻的亚群（~2533 ~ 2517 Ma）以强烈REE分异模式和正Eu异常为特征。长闪片麻岩缺乏证据证明。岩浆分异，推测它们是由不同地壳水平的角闪岩/灰岩改造形成的，早期亚群中有地幔物质的输入。同时期~2550 ~ 2529 Ma花岗闪长岩和二长/同长花岗质片麻岩具有高K2O/Na2O(0.67 ~ 2.45)，低MgO和Mg#（分别<2 wt.%和< 50）的特征。地球化学模拟数据表明，花岗闪长质片麻岩分异程度较低，可能与高钾基性岩石（如区域性晚新太古代钙碱性变质玄武岩）的部分熔融有关，A/CNK（1.00 ~ 1.14）和锆石ƐHf(t2)（+2.0 ~ +9.3）的恒定值进一步支持了这一特征。二长/正长片麻岩A/CNK值为0.78 ~ 1.32，锆石ƐHf（t2）值为−2.4 ~ +7.8。它们是由高钾基性岩和沉积岩混合源部分熔融形成的，原生岩浆表现出斜长石和磷灰石分选作用。综合来看，上述花岗质岩石锆石ƐHf（t2）值逐渐减小，地壳厚度逐渐增大。综合岩石成因资料、区域地质资料和部分~3.45 ~ 2.70 Ga地壳物质的存在，认为抚顺南部新太古代晚期花岗岩类岩浆活动可能是在活动大陆边缘复杂的壳幔相互作用过程中产生的。太古宙活动大陆边缘是地壳初始成熟的关键场所，这一构造情景是花岗岩类多样化的触发因素。
The appearance of voluminous K-rich granitoid rocks during Late Archean marks gradual maturation and stabilization of the continental crust. While most K-rich granitoid magmatism followed TTG magmatism, they occursynchronously sometimes, and this relationship is crucial for our understanding of the evolution of late Archean continental crust and its geodynamic setting. In this study, a series of ~2.57–2.52 Ga coeval and diverse granitoid rocks, including quartz dioritic-trondhjemitic and granodioritic to monzo-/syenogranitic gneisses, were identified in the southern Fushun area of Eastern Liaoning Province, North China Craton. The ~2.57 Ga quartz dioritic gneisses show moderate MgO (≤ 3.96 wt.%) and moderate to high Mg# (37.3–75.5). Geochemical modeling, together with mildly fractionated REE patterns and negative Eu anomalies and depleted zircon ƐHf(t2) (+2.1 − +7.4), suggest that they were differentiated from a depleted mantle source that was metasomatized by slab-derived fluids. The younger trondhjemitic gneisses (~2.55–2.52 Ga) are divided into two subgroups, i.e., an older subgroup (~2547–2540 Ma) characterized by mildly fractionated REE patterns and negative Eu anomalies, and a younger subgroup (~2533–2517 Ma) with strongly fractionated REE patterns and positive Eu anomalies. The trondhjemitic gneisses lack evidence for.magma differentiation, and they are inferred to have been formed by reworking of amphibolites/greywackes at diverse crustal levels, with some inputs of mantle materials in the earlier subgroup. The coeval ~2550–2529 Ma granodioritic and monzo-/syenogranitic gneisses are characterized by high K2O/Na2O.(0.67–2.45) but low MgO and Mg# (mostly <2 wt.% and < 50, respectively). Geochemical modeling data indicate that the granodioritic gneisses are less differentiated, which could have been derived from the partial melting of high-K mafic rocks (e.g., regional late Neoarchean calc-alkaline meta-basaltic rocks), as further supported by the constant A/CNK (1.00–1.14) and zircon ƐHf(t2) (+2.0 − +9.3) values. In comparison, the monzo-/syenogranitic gneisses show variable A/CNK (0.78–1.32) and zircon ƐHf(t2) (−2.4 − +7.8) values. They are explained to be formed by the partial melting of mixed sources of high-K mafic and sedimentary rocks, with the primary magmas showing plagioclase and apatite fractionation.Taken together, the above granitoid rocks record gradually decreasing zircon ƐHf(t2) values and increasing crustal thickness. Considering the petrogenetic information, regional geological data and the presence of some ~3.45–2.70 Ga crustal materials, the late Neoarchean granitoid magmatism of southern Fushun were likely generated via complex crust-mantle interaction processes at an active continental margin. It is further emphasized that Archean active continental margins are key sites for the initial maturation of the crust, and this tectonic scenario acted as a trigger for granitoid diversification.