Early Paleozoic Island arc accretion to the North China craton and the Shang Dan fault zone: A major paleoplate boundary in eastern Asia
Early Paleozoic Island arc accretion to the North China craton and the Shang Dan fault zone: A major paleoplate boundary in eastern Asia
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DOI：
10.1029/95jb02508
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发表时间：
1996-08
影响因子：
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通讯作者：
M. Lerch;F. Xue;A. Kröner;W. Todt
中科院分区：
文献类型：
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作者：
M. Lerch;F. Xue;A. Kröner;W. Todt
根据野外填图、地球化学和年代学研究成果，重建了秦岭-大别-山东造山带部分地区早古生代的构造演化。秦岭造山带将太古宙-元古代的华北克拉通（NCC）与华南克拉通（SCC，也称扬子克拉通）分隔开来。研究区位于西安市西南约90公里处。可以区分出三个岩性不同的带，它们被断层带彼此分开。NCC（1区）的被动大陆边缘沉积物的eNd（t）值介于−6.16和−12.54之间，TDM年龄介于1.29和2.20 Ga之间。它们与早古生代岛弧序列（2带）被左行的陈车断裂分开。第1带南部的基性火山岩与晚元古代被动大陆边缘的发育有关。第2带的类似岩性具有洋岛弧的地球化学特征。早奥陶世至晚志留世期间，伴随着强烈的变形事件。第2带和第1带南部的岩浆侵入体与晚志留世至早泥盆世时期NCC改造大陆边缘上的北倾俯冲带上方发育的短命岩浆弧有关。第2带北方长英质侵入体的eNd（t）值沿北方方向从1.78降低到-1.05。在第2带南部的镁铁质到中等侵入体具有正的eNd（t）值从1.28到2.04，以及低的87 Sr/86 Sr（i）值在0.705到0.706之间，表明向南的地幔成分增加。浅变质泥质岩与第2带岛弧层序之间被一条宽不超过2km的商丹剪切带隔开。同位素研究表明，3区的花岗岩样品和SCC样品之间有很强的相似性。87 Sr/86 Sr（i）值从0.709增加到0.713，而eNd（t）值从-1.90减少到-5.34。将第2区与第3区分开的剪切带至关重要，它标志着NCC和SCC之间的边界。本文的研究结果证实了秦岭造山带早古生代的构造演化，并确定了亚洲东部古板块的基本边界之一。
The early Paleozoic tectonic evolution of part of the Qinling-Dabie-Shandong orogenic belt is reconstructed on the basis of the results of field mapping, geochemical, and geochronological studies. The Qinling orogenic belt separates the Archean-Proterozoic North China craton (NCC) from the South China craton (SCC, also Yangtze craton). The study area is located about 90 km southwest of the city of Xi'an. Three lithologically distinctive zones, separated from each other by fault zones, can be distinguished. Passive continental margin deposits of the NCC (zone 1) have eNd(t) values between −6.16 and −12.54 and TDM ages between 1.29 and 2.20 Ga. They are separated from an early Paleozoic island arc sequence (zone 2) by the sinistral Chenche fault. Mafic volcanic lithologies in the southern part of zone 1 are associated with the development of a passive continental margin in late Proterozoic time. Similiar lithologies of zone 2 have geochemical characteristics of an oceanic island arc. Accretion was accompanied by a strong deformation event between early Ordovician and late Silurian time. Magmatic intrusions in zone 2 and the southern part of zone 1 are associated with a short-lived magmatic arc that developed above a north dipping subduction zone on the modified continental margin of the NCC in late Silurian to early Devonian time. The eNd(t) values of felsic intrusions from the northern part of zone 2 decrease in a northern direction from 1.78 to −1.05. Mafic to intermediate intrusions in the southern part of zone 2 have positive eNd(t) values from 1.28 to 2.04 as well as low 87Sr/86Sr(i) values between 0.705 and 0.706 indicating an increasing mantle component toward the south. Low-grade metamorphic pelites are separated from the island arc sequence of zone 2 by a ≤2 km wide Shang Dan shear zone. Isotopic studies show strong similarities between a granite sample from zone 3 and samples from the SCC. 87Sr/86Sr(i) values increase from 0.709 to 0.713, whereas eNd(t) values decrease from −1.90 to −5.34 in a southern direction. The shear zone that separates zone 2 from 3 is of fundamental importance and marks the boundary between the NCC and the SCC. The results presented in this paper document a previously unknown early Paleozoic tectonic evolution of the Qinling orogenic belt and delineate one of the fundamental paleoplate boundaries in eastern Asia.