Late Paleozoic to Early Mesozoic mafic–ultramafic complexes from the northern North China Block: Constraints on the composition and evolution of the lithospheric mantle
Late Paleozoic to Early Mesozoic mafic–ultramafic complexes from the northern North China Block: Constraints on the composition and evolution of the lithospheric mantle
复制标题
DOI：
10.1016/j.lithos.2009.01.008
复制
发表时间：
2009-06
期刊：
影响因子：
3.5
通讯作者：
Shuan‐Hong Zhang;Yue Zhao;Xiaochun Liu;Dunyi Liu;Fukun Chen;Liewen Xie;Haijiao Chen
中科院分区：
文献类型：
--
作者：
Shuan‐Hong Zhang;Yue Zhao;Xiaochun Liu;Dunyi Liu;Fukun Chen;Liewen Xie;Haijiao Chen
利用华北地块北部晚古生代至早中生代基性-超基性杂岩来约束晚中生代岩石圈破坏开始前不同构造阶段地幔储层的同位素组成和演化。锆石U-Pb年龄表明，基性-超基性杂岩体的侵位至少发生在中泥盆世（约395 Ma）、晚石炭世-早二叠世（308-276 Ma）和三叠纪（250-220 Ma）三个阶段。大部分中泥盆统杂岩的初始87sr /86Sr比值较低，为0.70467 ~ 0.70492,εNd(t)值为- 6.3 ~ - 1.5,εHf(t)值为- 11.5 ~ 5.5，锆石εHf(t)值为弱负~弱正，表明母岩浆来源于微富集的岩石圈地幔。晚石炭世—早二叠世杂岩的初始87sr /86Sr比值较低，为0.70521 ~ 0.70604,εNd(t)值为- 14.1 ~ - 9.3，锆石εHf(t)值为- 17.0 ~ - 10.5，可能来源于交代岩石圈地幔。早三叠世杂岩的初始87sr /86Sr比值为0.70656 ~ 0.70825,εNd(t)值为- 17.1 ~ - 8.2，表明它们来源于富集的岩石圈地幔。晚三叠世基性-超基性杂岩的εNd(t)值为- 4.4 ~ 0.5，锆石的εHf(t)值为- 2.9 ~ 1.7，表明岩浆来源可能是贫软流圈地幔与富岩石圈地幔的混合作用。锆石年龄、地球化学和Sr-Nd-Hf同位素研究表明，北北岩石圈地幔在中泥盆世具有轻微的富集特征，但在晚石炭世至早二叠世期间，由于古亚洲大洋板块向南俯冲过程中岩石圈地幔的交代作用，岩石圈地幔开始明显富集。在二叠世晚期至三叠世早期，古亚洲洋最终闭合，蒙古弧地体与北陆块体合并后，早三叠世北陆块体下方仍存在丰富的岩石圈地幔。然而，在晚三叠世，由于软流圈地幔的强烈上升流和早-晚三叠世碰撞后岩石圈的拆沉作用，软流圈地幔的参与变得明显。这些结果表明，北北岩石圈下的克拉通岩石圈地幔在破坏和变薄之前经历了多阶段的改造。NCB北部岩石圈破坏和减薄可能发生在早-晚三叠世，远早于NCB其他地区的晚中生代。由于碰撞后岩石圈的分层作用，岩石圈的破坏和NCB的减薄最初可能始于克拉通的北部和东部边缘，然后扩散到克拉通的内部。
The Late Paleozoic to Early Mesozoic mafic–ultramafic complexes from the northern North China Block (NCB) are used to constrain the isotopic composition and evolution of mantle reservoirs during different tectonic stages prior to the initiation of lithosphere destruction in the Late Mesozoic. Zircon U–Pb ages show that emplacement of the mafic–ultramafic complexes occurred in at least three stages: Middle Devonian (ca. 395 Ma), Late Carboniferous–Early Permian (308–276 Ma) and Triassic (250–220 Ma). Most of the Middle Devonian complexes display low initial87Sr/86Sr ratios of 0.70467–0.70492, weak to moderate negative εNd(t) values from −6.3 to −1.5 and weakly negative to weakly positive zircon εHf(t) values from −11.5 to 5.5, indicating that the parent magma was derived from slightly enriched lithospheric mantle. The Late Carboniferous–Early Permian complexes are characterized by low initial87Sr/86Sr ratios of 0.70521–0.70604, significant negative εNd(t) values from −14.1 to −9.3 and zircon εHf(t) values from −17.0 to −10.5, and were probably derived from metasomatized lithospheric mantle. The Early Triassic complexes exhibit initial87Sr/86Sr ratios of 0.70656–0.70825 and significant negative εNd(t) values from −17.1 to −8.2, indicating their derivation from enriched lithospheric mantle. However, the Late Triassic mafic–ultramafic complexes display weakly negative to weakly positive εNd(t) values of −4.4 to 0.5 and zircon εHf(t) values from −2.9 to 1.7, indicating that magma sources likely resulted from mixing of depleted asthenospheric mantle and enriched lithospheric mantle. Zircon ages, geochemistry and Sr–Nd–Hf isotopic studies suggest that the lithospheric mantle beneath the northern NCB had a slightly enriched signature during the Middle Devonian, but it became significantly enriched during the Late Carboniferous to Early Permian due to metasomatism of lithospheric mantle during the southward subduction of the Paleo-Asian oceanic plate. After final closure of the Paleo-Asian Ocean and amalgamation of the Mongolian arc terranes with the northern NCB in the latest Permian to earliest Triassic, enriched lithospheric mantle still existed beneath the northern NCB during the Early Triassic. However, in the Late Triassic involvement of asthenospheric mantle became significant, owing to strong upwelling of asthenospheric mantle and post-collisional lithospheric delamination in the Early–Late Triassic. These results suggest that the cratonic lithospheric mantle beneath the northern NCB underwent multiple stages of modification prior to its destruction and thinning. Initiation of lithospheric destruction and thinning in the northern NCB likely occurred during the Early–Late Triassic, which is much earlier than in other parts of the NCB, where it occurred in the Late Mesozoic. It appears likely that lithospheric destruction and thinning of the NCB initially started at the northern and eastern margins of the craton as a result of post-collisional lithospheric delamination, and then spread to the interior of the craton.