Origin of two contrasting latest Permian-Triassic volcanic rock suites in the northern North China Craton: implications for early Mesozoic lithosphere thinning
Origin of two contrasting latest Permian-Triassic volcanic rock suites in the northern North China Craton: implications for early Mesozoic lithosphere thinning
复制标题
华北克拉通北部两个截然不同的最新二叠纪-三叠纪火山岩组的成因：对早中生代岩石圈减薄的影响
DOI：
10.1080/00206814.2014.951979
复制
发表时间：
2014
影响因子：
2.6
通讯作者：
Zhao Yue
中科院分区：
文献类型：
--
作者：
Ye Hao;Zhang Shuan-Hong;Zhao Yue
对华北北方早中生代沉积岩中的火山岩和卵石进行了新的地质、年代学和地球化学研究，确定了两套截然不同的二叠纪-三叠纪火山岩。早二叠世-早三叠世爆发的早期岩套约为早侏罗世以前，北CC北方广泛分布。它由流纹质熔结凝灰岩、流纹岩和凝灰质砂岩组成，具有SiO2和K2 O含量高，初始87 Sr/86 Sr中等，εNd（t）和εHf（t）负值低，Nd-Hf同位素模式年龄老的特点。它可能是由下地壳衍生的岩浆分离结晶，由于底侵岩石圈幔源岩浆壳幔边界附近的同碰撞后碰撞/后造山构造环境。晚三叠世晚期岩套，喷发于中-晚三叠世，约1000年。238-228 Ma，显示埃达克质的地球化学特征，由中间火山岩，如安山岩，粗安岩，自碎粗安岩角砾岩，少量长英质岩石。该套岩石具有高Al_2 O_3、MgO、Sr、Ba、Cr、V和Ni含量，高Mg#值，低Y和Yb含量及高Sr/Y比值，低初始~（87）Sr/~（86）Sr，高负εNd（t）和εHf（t）值，年轻Nd-Hf同位素模式年龄等特征。年轻的套房是由混合的岩浆来自熔融的软流圈上涌，与熔融的古下地壳引起的玄武岩浆底侵在板内伸展设置。软流圈地幔的强烈上涌和软流圈地幔物质的显著卷入表明，北方华北克拉通岩石圈地幔在中晚三叠世发生了部分拆沉，代表了北方华北克拉通岩石圈的初始破坏和减薄。岩石圈减薄和拆沉作用可能是北克拉通北方三叠纪构造转换、岩浆活动和变形方式变化的重要原因。
New geological, geochronological, and geochemical results on volcanic rocks and cobbles from early Mesozoic sedimentary rocks identify two contrasting latest Permian–Triassic volcanic rock suites in the northern North China Craton (NCC). The early rock suite erupted during the latest Permian–Early Triassic at ca. 255–245 Ma and was probably widely distributed in the northern NCC prior to the Early Jurassic. It comprises rhyolitic welded tuff, rhyolite, and tuffaceous sandstone and is characterized by high contents of SiO2and K2O, moderate initial87Sr/86Sr, low negativeεNd(t) andεHf(t) values, and old Nd-Hf isotopic model ages. It was likely produced by fractional crystallization of lower crustal-derived magmas due to underplating by lithospheric mantle-derived magmas near the crust–mantle boundary in syncollisional to post-collisional/post-orogenic tectonic settings. The late rock suite, erupted during the Middle–Late Triassic at ca. 238–228 Ma, displays adakitic geochemical signatures and consists of intermediate volcanic rocks such as andesite, trachyandesite, and autoclastic trachyandesite breccia, with minor felsic rocks. This suite is characterized by high Al2O3, MgO, Sr, Ba, Cr, V, and Ni concentrations; high Mg# values; low Y and Yb concentrations and high Sr/Y ratios; low initial87Sr/86Sr; high negativeεNd(t) andεHf(t) values; and young Nd-Hf isotopic model ages. The younger suite was generated by mixing of magmas derived from melting of upwelling asthenosphere, with melts of ancient lower crust induced by underplating of basaltic magmas in an intraplate extensional setting. Strong upwelling of asthenospheric mantle and significant involvement of the asthenospheric mantle materials indicate that the lithospheric mantle beneath the northern NCC was partially delaminated during Middle–Late Triassic time, representing the initial destruction and lithospheric thinning of the northern NCC. Lithospheric thinning and delamination are likely the most important reasons for the Triassic tectonic transition and change of magmatism and deformation patterns in the northern NCC.