Eclogite origin and timings in the North Qinling terrane, and their bearing on the amalgamation of the South and North China Blocks

Abstract

The amalgamation of South (SCB) and North China Blocks (NCB) along the Qinling-Dabie orogenic belt involved several stages of high pressure (HP)-ultra high pressure (UHP) metamorphism. The new discovery of UHP metamorphic rocks in the North Qinling (NQ) terrane can provide valuable information on this process. However, no precise age for the UHP metamorphism in the NQ terrane has been documented yet, and thus hinders deciphering of the evolution of the whole Qinling-Dabie-Sulu orogenic belt. This article reports an integrated study of U-Pb age, trace element, mineral inclusion and Hf isotope composition of zircon from an eclogite, a quartz vein and a schist in the NQ terrane. The zircon cores in the eclogite are characterized by oscillatory zoning or weak zoning, high Th ⁄ U and 176 Lu ⁄ 177 Hf ratios, pronounced Eu anomalies and steep heavy rare earth element (HREE) patterns. The zircon cores yield an age of 796 ± 13 Ma, which is taken as the protolith formation age of the eclogite, and implies that the NQ terrane may belong to the SCB before it collided with the NCB. The e Hf (t) values vary from )11.3 to 3.2 and corresponding two-stage Hf model ages are 2402 to 1495 Ma, suggesting the protolith was derived from an enriched mantle. In contrast, the metamorphic zircon rims show no zoning or weak zoning, very low Th ⁄ U and 176 Lu ⁄ 177 Hf ratios, insignificant Eu anomalies and flat HREE patterns. They contain inclusions of garnet, omphacite and phengite, suggesting that the metamorphic zircon formed under eclogite facies metamorphic conditions, and their weighted mean 206 Pb ⁄ 238 U age of 485.9 ± 3.8 Ma was interpreted to date the timing of the eclogite facies metamorphism. Zircon in the quartz vein is characterized by perfect euhedral habit, some oscillatory zoning, low Th ⁄ U ratios and variable HREE contents. It yields a weighted mean U-Pb age of 480.5 ± 2.5 Ma, which registers the age of fluid activity during exhumation. Zircon in the schist is mostly detrital and U-Pb age peaks at c. 1950 to 1850, 1800 to 1600, 1560 to 1460 and 1400 to 1260 Ma with an oldest grain of 2517 Ma, also suggesting that the NQ terrane may have an affinity to the SCB. Accordingly, the amalgamation between the SCB and the NCB is a multistage process that spans c. 300 Myr, which includes: the formation of the Erlangping intra-oceanic arc zone onto the NCB before c. 490 Ma, the c. 485 Ma crustal subduction and UHP metamorphism of the NQ terrane, the c. 430 Ma arc-continent collision and granulite facies metamorphism, the 420 to 400 Ma extension and rifting in relation to the opening of the Palaeo-Tethyan ocean, the c. 310 Ma HP eclogite facies metamorphism of oceanic crust and associated continental basement, and the final 250 to 220 Ma continental subduction and HP-UHP metamorphism.

Granitic magmatism related to early Paleozoic continental collision in North Qinling

“…Several episodes of arc-continental collision might have taken place in the process of early Paleozoic convergence between the NCB and SCB. The Qinling oceanic crust was completely consumed alone the SDSZ in the Devonian [1, 13,25,32,33]. The HP-UHP metamorphism with the peak age of 500 Ma and two-phase retrogressive metamorphism of 450 Ma granulite-and 420 Ma amphibolitefacies, were distinguished in the NQB.…”

“…However, the early tectonic evolution of the Qinling orogen is poorly constrained, such as the timing of subduction of Paleozoic oceanic crust and subsequent collisional process for the closure of Paleotethys. Advances have been made in the understanding of time-space distribution and the nature of HP-UHP metamorphism in the NQB [4][5][6][7][8][9][10][11][12][13][14][15] after two-decade consistent studies, demonstrating that the early Paleozoic HP-UHP metamorphism was the consequence of northward continental deep-subduction along the SDSZ [16]. The new results concerning the early Paleozoic HP-UHP metamorphism shed some new light on the process and age of subduction of the oceanic crust as well as amalgamation among continental blocks during the early Paleozoic in the Qinling orogen.…”

Silurian high-pressure granulites from Central Qiangtang, Tibet: Constraints on early Paleozoic collision along the northeastern margin of Gondwana

“…Considering the paleogeographic framework of eastern Gondwana, early Paleozoic metamorphic rocks, especially the ultrahigh/high- Chen et al, 2007Chen et al, , 2009Zhang et al, 2008;Song et al, 2006;Yu et al, 2013), the South Altyn (501-485 Ma; Zhang et al, 2005;Liu et al, 2012;Cao et al, 2013), the North Qinling orogen (ca. 511-480 Ma, Liu et al, 2010;Zhang et al, 2011;Wang et al, 2011;Cheng et al, 2011Cheng et al, , 2012ca. 440-424 Ma, Zhang et al, 2011), Sibumasu (ca.…”

“…501-485 Ma; Zhang et al, 2005;Liu et al, 2012;Cao et al, 2013), the North Qinling orogen (ca. 511-480 Ma; Liu et al, 2010;Zhang et al, 2011;Cheng et al, 2011Cheng et al, , 2012Wang et al, 2011;ca. 440-424 Ma, Zhang et al, 2011), Sibumasu (ca.…”

Review on the Triassic Post-collisional Magmatism in the Qinling Collision Belt

“…그리고 북친링 소대륙판은 다시 북중국판과 430 Ma 경에 충돌이 완료되었고 400 Ma 경에는 남 친링 소대륙판이 북중국판의 일부가 된 북친링 소대 륙판과 충돌하였으며 이들 충돌 과정에서 샹단 전단 대를 형성되었다 (Dong et al, 2011). 하지만 북친링 소대륙판내에 나타나는 초고압 에클로자이트로가 형 성된 연령인 490-507 Ma (Wang et al, 2011;Cheng et al, 2012;Liu et al, 2013) (Sun et al, 2002;Chen et al, 2003;Yang et al, 2005Yang et al, , 2006. 그리고 충돌대의 동측인 한반도와 충돌대의 서 측인 친링지역에는 광역적인 트라이아스기 충돌 후 화성암이 관입을 하였다 Dong et al, 2011;Kim et al, 2011 Granite ( Pearce et al, 1984;Pearce, 1996), field are defined as follows: syn-COLG(syn-collisional granites), Post-COLG(post-collisional granites), WPG(within plate granite), ORG(ocean-ridge granite), VAG(volcanic-arc granite) and (b) the Rb-Hf-Ta discrimination diagrams (after Harris et al, 1986 Fig.…”