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1.
新元古代江南造山带远离晚中生代活动大陆边缘,是研究华南地区新元古代至早中生代多期造山作用的理想对象。文章通过对江南造山带东段沉积建造、岩浆活动、构造变形以及同位素年代学数据的综合分析,总结了其晋宁期、广西期以及印支期造山作用的特征。江南造山带东段在晋宁期经历了南北两侧大洋俯冲和两期碰撞造山作用。新元古代早期(880~860 Ma)双溪坞岛弧与扬子陆块东南缘发生弧-陆碰撞作用,形成淡色花岗岩、高压蓝片岩、NNE向褶皱-逆冲构造以及弧后前陆盆地。新元古代中期(约850 Ma),扬子陆块北缘开始发育由北向南的大洋俯冲。随着俯冲作用的进行,弧后盆地发生关闭,扬子陆块与华夏陆块发生陆-陆碰撞并形成新元古代(820~810Ma)江南造山带,导致近E-W走向褶皱-逆冲构造、韧性变形以及过铝质花岗岩的发育。江南造山带东段在约810Ma开始发生后造山垮塌和裂谷作用,以发育南华纪早期(805~750 Ma)花岗岩、中酸性火山岩、基性岩以及裂谷盆地为特征。江南造山带东段万载—南昌—景德镇—歙县断裂带以南地区卷入了华南广西期造山作用,发育近E-W走向由南向北的逆冲构造(465~450 Ma)、NNE向正花状构造(449~430 Ma)以及后造山近E-W走向韧性走滑剪切带(429~380 Ma)。印支期造山作用导致了NNE向褶皱-逆冲构造和花岗岩的发育,并奠定了江南造山带东段的基本构造面貌。 相似文献
2.
江南造山带是否格林威尔期造山带?——关于华南前寒武纪地质的几个问题 总被引：16，自引：0，他引：16
本世纪初这几年利用SHRIMP和La-ICP-MS锆石U-Pb法及其他新的定年方法已获得的定年结果表明,扬子与华夏板块的拼合发生在870～820Ma之间,形成格林威尔造山带的"陆-陆碰撞"发生在1190～980Ma期间,江南造山带的碰撞事件要滞后320～160Ma。江南造山带形成过程中普遍发生绿片岩相的区域变质作用,未找到格林威尔造山带中广泛存在的麻粒岩相的高级变质记录。根据这两点,目前无法确认江南造山带是格林威尔期造山带。江南造山带可能是Rodinia向Gondwana超级大陆过渡过程中两相邻陆块拼合的产物。在江南造山带西段,作为基底出露的四堡群、梵净山群、冷家溪群等曾被认为是中元古代地层,这些地层中砂岩的碎屑锆石定年表明,这些基底地层的最大沉积年龄为870～860Ma,属于新元古代。沿着江南造山带分布的S-型花岗岩可作为板块间碰撞、造山事件的岩石学记录,并非地幔柱岩浆作用的产物。江南造山带西段～760Ma的部分基性火山-侵入岩、扬子地块周边及华夏地块某些新元古代"双峰式火山岩"(803～818Ma)中的基性火山岩具OIB的地球化学特征,它们的规模很小,是造山后伸展阶段、软流圈局部上侵形成的,不能作为Rodinia裂解的岩石学证据。 相似文献
3.
湘中地区冷家溪群和板溪群锆石U-Pb年龄、Hf同位素特征及对华南新元古代构造演化的意义 总被引：7，自引：4，他引：3
通过对江南造山带中段冷家溪群和板溪群凝灰岩及碎屑岩锆石U-Pb定年及系统的Hf同位素分析表明,冷家溪群沉积时代大致在860～820 Ma,不整合在其上的板溪群沉积下限在820 Ma左右,这表明在江南造山带,晋宁造山运动之后,很快进入伸展裂解阶段。锆石的Hf同位素组成显示,在850～800 Ma之间,锆石Hf初始值表现出快速上升趋势,表明这一时期有显著的地幔物质加入。造成这一现象的原因,一方面是早期的岛弧岩浆岩(850～820 Ma,尤其是I型花岗岩)是碎屑物的主要来源,另一方面造山后快速裂解形成的壳幔混合岩浆物质(如凝灰岩)形成板溪群部分物质来源。结合本研究和前人的研究成果,表明新元古代板块俯冲、拼合以及拼合后由于板片的拆沉引起的快速裂解(plate-rift model)是江南造山带形成的比较合理的地球动力学模型。 相似文献
4.
江南造山带位于华夏与扬子地块之间,发育大量新元古代火成岩,是研究地球早期壳幔相互作用、板块构造演化的理想对象。江南造山带东段新元古代板块演化研究已初具雏形,但对其西南段构造演化还争议不断,主要问题在于没有构建与区域地质特点吻合的岩浆活动年代学格架。本文以江南造山带西南段梵净山为研究区,基于详细的区域地质填图结果,针对侵入于梵净山群(沉积时代850~830 Ma)中的基性-超基性岩样品开展原位锆石年代学研究。新的年代学数据表明,侵入于梵净山群的3个辉长岩体结晶年龄分别为813 Ma、804 Ma、748 Ma。结合前人发表数据,提出梵净山地区岩浆活动可划分为两个阶段:晋宁Ⅰ期(850~825 Ma)、晋宁Ⅱ期(820~750 Ma),分别对应于梵净山期、下江期盆地演化。该岩浆岩年代学格架与区域地层年代格架吻合,形成了完整的新元古代沉积-岩浆活动记录。这套沉积-岩浆组合的大地构造背景尚不明确,需要通过大地构造相分析予以确定。 相似文献
5.
大别山沙村中生代A型花岗岩和基性岩的源区演化关系 总被引：4，自引：5，他引：4
A型花岗岩的成因虽存在不同的认识模式,但对大别山沙村A型花岗岩的岩石化学和地球化学研究结果表明,其物质源自大陆岩石圈地幔的部分熔融,含有古老地壳信息。结合被侵入基性岩的地球化学和年代学资料,推测大别造山带中生代岩石圈地幔的地球化学性质与下扬子地幔相似。花岗岩中锆石SHRIMP法U-Pb年龄为119.0±3.2Ma,说明其岩浆侵位于早白垩世,与邻近的基性岩侵位时间相近但稍晚。在三叠纪因大陆俯冲碰撞增厚的岩石圈在早白垩世被拉张减薄,含有古老地壳成分的扬子陆下岩石圈地幔及其上覆下地壳发生部分熔融,形成了不同成分的碰撞后岩浆岩。其中部分基性岩浆分异结晶成为辉长岩,而A型花岗岩可能是同一地幔源区物质小比例部分熔融后分异结晶的产物。 相似文献
6.
近年来在下扬子西缘地区厘定的一系列新元古代火成岩,为认识该区扬子板块新元古代岩浆活动历史与规律提供了窗口。结合本次与前人锆石U-Pb年代学数据,指示下扬子地区张八岭群、肥东杂岩与董岭杂岩内变火成岩的原岩时限分别为767~748 Ma、812~745 Ma和829~754 Ma。这些新元古代火成岩分别是峰期为750 Ma、800 Ma和825 Ma岩浆活动的产物。下扬子地区峰期为825 Ma的岩浆活动只出现在靠近江南造山带的南部。锆石年代学信息显示,下扬子地区还发生过峰期为840 Ma、2010 Ma和2454 Ma岩浆活动,但缺失1000~860 Ma的岩浆活动。通过区域对比表明,攀西—汉南弧没有延入下扬子地区。下扬子地区南部受到峰期为840 Ma的弧岩浆活动的影响。扬子板块上峰期为825 Ma的岩浆活动及早阶段的南华裂谷应是江南造山带后造山伸展的产物;而峰期为800 Ma和750 Ma的岩浆活动与相应的南华裂谷扩展,代表了Rodinia超大陆裂解的全面影响。 相似文献
7.
湖南城步火成岩锆石SHRIMP U-Pb年龄及其对江南造山带新元古代构造演化的约束 总被引：10，自引：1，他引：9
目前对新元古代中期江南造山带构造演化及钦杭结合带南西段构造性质存在不同认识。本文对湘西南城步地区新元古代火山岩和花岗岩进行了锆石SHRIMPU-Pb年龄测定并厘定其构造环境,从而为区域构造演化提供了约束。城步新元古代花岗岩侵入于云场里组变质火山-沉积地层中。云场里组变质火山岩与花岗岩的锆石SHRIMPU-Pb年龄分别为828±10Ma和805.7±9.2Ma。构造环境的地球化学判别图解表明花岗岩形成于岛弧环境;区域地质背景指示云场里组可能形成于活动陆缘弧前盆地。以城步火山岩和花岗岩研究为基础,结合区域地质资料,提出新元古代中期江南造山带西段构造演化过程:872～835Ma期间为陆缘盆地;835～820Ma期间俯冲造山,江南造山带形成基性—超基性岩和早阶段岛弧花岗闪长岩,东侧的城步地区为弧前盆地;820～810Ma期间江南造山带发生弧-陆碰撞;810～800Ma期间江南造山带进入后碰撞环境并形成晚阶段强过铝(黑云母)花岗岩,东侧城步地区因华南洋洋壳俯冲而形成新的岛弧;800Ma后华南进入伸展裂陷盆地演化阶段。上述认识揭示出扬子陆块东南缘的连续岛弧增生过程,同时为钦杭结合带南西段雪峰期"残留洋盆"属性提供了新证据。 相似文献
8.
秦岭造山带及相邻地块元古代基性岩墙群研究综述及相关问题探讨 总被引：32，自引：7，他引：25
基性岩墙群是重建古陆块聚合、伸展乃至裂解的关键标志之一。通过对秦岭造山带及相邻的华北地块、扬子地块元古代基性岩墙群的时空对比综
合分析表明,华北地块区发育2300Ma±和1700～1200Ma的两期基性岩墙群,分别代表了新太
古代和古元古代华北古陆块的聚合、伸展过程;扬子地块区发育800～620Ma的基性岩墙群,
反映了新元古代扬子古陆块的聚合、伸展过程。认为前震旦纪华北地块和扬子地块可能是独
立古陆块或不同古陆块的组成部分。晋宁造山作用(1100～850Ma)和澄江伸展、裂解作用(800Ma±)是可与新元古代Rodinia超大陆聚合、裂解过程进行对比、研究的重要时期。 相似文献
9.
华南大陆历经长期复杂的构造演化,其浅部复杂而多样的构造形态与深部壳幔结构及其动力学机制有着密切联系,但当前的深部探测资料有限,深部构造并不明确。为了研究华南的深部岩石圈结构状态,布设了多条宽频长周期大地电磁联合探测剖面。通过对景德镇-温州剖面的数据处理,获得了该剖面的岩石圈电性结构模型。分析表明:华夏地块与扬子地块东部的江南造山带以江绍断裂为界;华夏地块整体呈现高阻特征,可能具有深部岩石圈背景的上虞-政和-大浦断裂将其分为华夏褶皱带与东南沿海岩浆岩带;扬子地块东部的江南造山带整体电阻率较低,结构更破碎,受到深部改造明显,岩石圈底界约为110 km;剖面发现3处低阻带通道,可能与软流圈上涌相关;江绍断裂呈喇叭状向深部张开,华夏地块与扬子地块的裂解拼合可能与断裂深部的高导体活动有关。华夏地块与扬子地块的接触状态呈现为双向汇聚,华夏地块在上地幔挤入扬子地块,深部接触边界可能越过江绍断裂带。 相似文献
10.
扬子板块西北缘碧口微地块红岩沟地区碧口群火山岩系之上发育有南华—震旦纪沉积盖层,但南华系的沉积时代尚缺乏依据,其物源及构造背景也仍无定论。本文采用LA-ICP-MS锆石U-Pb测年方法,对南华系上部含砾岩系中的长石砂岩进行了碎屑锆石测年研究,结果表明碎屑锆石的年龄可以分为两组:(1)新元古代晚期年龄组(750~800Ma),峰值年龄为795Ma;(2)新元古代早中期年龄组(820~920Ma),该组有明显峰值,峰值年龄为850Ma。碎屑锆石最小年龄组平均年龄为750Ma,即南华系上部含砾岩系沉积时代不老于750Ma,结合地层序列中的层位关系,认为该地层的沉积时代可能为晚南华世。综合研究认为,南华系上部含砾岩系物源具多源性,主要来自扬子板块西北缘碧口微地块内部和南侧后龙门山构造带、汉南-米仓山微地块的新元古代中酸性岩浆岩,北侧勉略构造带出露的岩浆岩可能也为该地层提供了少量的物源,其沉积事件对应于新元古代中晚期(~810Ma)碧口微地块及扬子板块西北缘后碰撞-裂解阶段。 相似文献
11.
《International Geology Review》2012,54(4):383-403
ABSTRACTThe Neoproterozoic tectonic evolution of the Jiangnan Orogen is controversial, with one of the issues being whether the ca. 850–820-Ma granitoids were generated by mantle plumes or the collision between the Yangtze and Cathaysia blocks. This paper tackles this problem by examining the age and petrogenesis of one of the granitoids, the Getengling pluton in the central Jiangnan Orogen, and through comparison with a regional geochronological–geochemical database compiled from previous studies. The Getengling pluton is characterized by high A/CNK values (~1.5), slight negative whole-rock εNd(t) values (?2.8 to ?3.4), and positive zircon εHf(t) values (0.7 ± 1.1), suggesting S-type granite affinities with juvenile contributions. Rb/Sr, Rb/Ba, and high CaO/Na2O ratios indicate psammitic sources with both clay-rich and clay-poor characters. These geochemical characteristics are distinct from those of the granitoids (typically of A type) associated with mantle plumes. The zircon laser ablation-inductively coupled plasma-mass spectrometry U–Pb age of 845 ± 4 Ma obtained in this study, together with other ca. 835–820 Ma ages of S-type granites in the Jiangnan Orogen, indicates that the felsic magmatism in the Jiangnan Orogen lasted for ca. 25 Ma, which is longer than typical plume-related felsic magmatism. In addition, the mafic rocks in the Jiangnan Orogen and elsewhere in the South China Block are geochemically distinct from the coeval mantle plume-related ones in Australia and west Laurentia. In geochemical diagrams diagnostic of tectonic settings, the Getengling pluton and other ca. 850–820 Ma intrusions plot in the syn- and post-collisional fields, whereas the pre-850 and post-820-Ma igneous rocks plot in the arc and within-plate settings, respectively. This sequential tectonic evolution from plate subduction through collision to within-plate environments further supports the hypothesis that the ca. 850–820-Ma granitoids in the Jiangnan Orogen resulted from the Yangtze–Cathaysia collision rather than from mantle pluming. 相似文献
12.
Jinbao Su Shuwen Dong Yueqiao Zhang Licheng Ma Xuanhua Chen Yong Li 《International Geology Review》2018,60(3):365-381
The mid-Neoproterozoic tectonic setting of the Jiangnan Orogen (JO) is uncertain due to the ongoing debate regarding the history of interactions between the Yangtze and Cathaysia Blocks. Extensive magmatic rocks with ages >830 Ma are observed in the eastern JO and are reported to indicate their formation conditions; however, such magmatic rocks are rare in the western JO. This paper presents data from samples collected from two ultramafic intrusions in northern Guangxi province that yield SHRIMP U–Pb ages of 848 ± 7 and 836 ± 5 Ma. These two intrusions have similar geochemical compositions; are enriched in LILE (Rb, Ba, Th, and Pb) relative to HFSE (Hf, Zr, Nb, Ta, and Y), reflecting an arc-like signature; and are derived from the same source. The intrusions have positive εNd(t) and εHf(t) values, implying a depleted mantle source. Comparing the Neoproterozoic mafic–ultramafic rocks of the JO, differences exist between the rocks that formed at 860–830, 830–800, and 800–740 Ma in terms of their mantle sources and formation conditions. Considering the geochemical composition and ages of formation of the strata and the deep structure of the western JO, we speculate that the western JO was a back-arc foreland basin, which experienced shallow subduction-related and arc-like magmatism during the period between 860 and 830 million years. In contrast to the western JO, the eastern JO may have been a back-arc basin with oceanic crustal basement during that time. The JO formed between 830 and 800 million years in association with subduction-related collisional magmatism due to the amalgamation of the Yangtze and Cathaysia Blocks. Subsequently, magmatism occurred in the JO that resulted from the post-orogenic extension. 相似文献
13.
“江南造山带”变质基底形成的构造环境及演化特征 总被引：11，自引：0，他引：11
"江南造山带"变质基底的形成和演化长期存在不同认识。本文试图通过区域地层对比、火山—沉积组合、构造变形特征,大量新的测年数据以及淡色花岗岩(MPG)和含堇青石花岗闪长岩(CPG)等岩体的分布及产出的构造环境分析,再次探讨"江南造山带"变质基底的构造环境和演化特征。笔者等认为"江南造山带"变质基底的形成和演化与1.1～0.9Ga的"格林威尔运动"无关,它是Rodinia超大陆裂解后的不同陆块(如扬子陆块、华夏陆块等)的大陆边缘沉积,经830～780Ma之晋宁运动期碰撞造山,进而构成新元古代中—晚期扬子古陆新的増生大陆边缘。晋宁期碰撞造山的特征是:在时间演化方面经历了早期初始强烈碰撞、挤压变形—松弛拉张接受不同规模裂陷盆地或裂谷火山—碎屑沉积—终期再碰撞演化过程;在空间变化方面则显示为构造环境的多样性。以湘、赣边界剪切断裂带和鄱阳湖—赣江剪切断裂带为界,形成三种不同的构造环境。湘黔桂代表的西部区段和赣西北代表的中部区段均为被动大陆边缘的陆—陆对接碰撞构造环境。但二者在挤压和拉张强度和规模的差别,导致两区段构造形态的不同。赣皖浙东部区段为活动大陆边缘具多列岛弧及弧后盆地的洋—陆俯冲—碰撞构造环境。 相似文献
14.
The South China Block was built up by the assembly of the Yangtze and Cathaysia blocks along the Neoproterozoic Jiangnan Orogenic Belt. The timing of the Jiangnan Orogeny remains controversial. The widespread orogeny–related Neoproterozoic angular unconformity that separates the underlying folded Sibao (ca.1000–820 Ma) and overlying Danzhou (ca.800–720 Ma) Groups was investigated. Six sedimentary samples, below and above the unconformity in three distal localities (Fanjingshan, Madiyi, and Sibao) yield detrital zircon with UPb ages ranging from 779 ± 16 Ma to 3006 ± 36 Ma, with a prominent peak at ca. 852 Ma. The youngest ages of 832 ± 11 Ma and 779 ± 16 Ma are revealed for the underlying Sibao and overlying Danzhou Groups, respectively. The detrital zircon UPb age relative probability plot of the Jiangnan Orogen matches well with those of the Yangtze and Cathaysia blocks since ca. 865 Ma. Integrating geological, geochemical and geochronological results, we suggest that the Paleo–South China Ocean began to subduct under the Yangtze block at ca. 1000 Ma, and was partly closed at ca. 865 Ma. Afterwards, the Yangtze and Cathaysia blocks initially collide at 865 Ma, forming the Jiangnan Orogen. This collision resulted in not only the folding of the Sibao Group, but also sediment deposition in a syn-collisional setting, which makes the upper part of the Sibao Group. The youngest S-type granite dated at ca. 820 Ma that intruded in the Sibao Group marks the late stage of the Jiangnan Orogeny. 相似文献
15.
The Jiangnan Orogen, the eastern part of which comprises the oceanic Huaiyu terrane to the northeast and the continental Jiuling terrane to the southwest, marks the collision zone of the Yangtze and the Cathaysia Blocks in South China. Here, zircon U–Pb geochronological and Lu–Hf isotopic results from typical basement and cover meta-sedimentary/sedimentary rock units in the eastern Jiangnan Orogen are presented. The basement sequences in southwestern Huaiyu terrane are mainly composed of marine volcaniclastic turbidite, ophiolite suite and tuffaceous phyllite, whereas those in the northeastern Huaiyu consist of littoral face pebbly feldspathic sandstones and greywacke interbedded with intermediate-basic volcanic rocks. Combined with previous studies, the present data show that the basement sequences exhibit arc affinities. Zircons from the basement phyllite in the southwestern margin of the Huaiyu terrane, representing a Neoproterozoic back-arc basin, yield a single age population of 800–900 Ma. The basement greywacke from northeastern Huaiyu terrane, representing fore-arc basin, is also characterized by zircons that preserve a single tectono-thermal event during 800–940 Ma. However, the late Neoproterozoic cover sequence preserves zircons from multiple sources with age populations of 750–890 Ma, 1670–2070 Ma and 2385–2550 Ma. Moreover, Hf isotopic data further reveal that most detrital zircons from the basement sequences yield positive εHf(t) values and late Mesoproterozoic model ages, while those of the cover sequence mostly show negative εHf(t) values. The Hf isotopic data therefore suggest that the basement sequences are soured from a Neoproterozoic arc produced by reworking of subducted late Mesoproterozoic materials. The geochronological and Hf isotopic data presented in this study suggest ca. 800 Ma for the assembly of the Huaiyu and Jiuling terranes, implying that the amalgamation of the Yangtze and Cathaysia Blocks in the eastern part occurred at ca. 800 Ma. 相似文献
16.
The South China Block (SCB) consists of the Yangtze and Cathaysia Blocks which, in the northeast, are separated from each other by the Jiangnan Orogen. The southward continuation of the Jiangnan Orogen into the Youjiang Basin remains much debated. Here, we present detailed petrological, chemical and isotope evidence from the Late Jurassic (~159 Ma) Yangtun and Liuliang high-Mg andesites (HMA), eastern Youjiang Basin, to place important constraints on an ancient subduction event. These HMA are enriched in large ion lithophile elements and depleted in Nb-Ta-Ti, with negative whole-rock εNd(t) and zircon εHf(t) values, similar to Neoproterozoic high-Mg rocks that occur in the eastern Yangtze Block. Considering the distance of our study areas to penecontemporaneous Pacific or Tethyan trenches, we infer that these HMA derived from a metasomatised lithospheric mantle preserved beneath the eastern Yangtze Block, which was associated with a Neoproterozoic subduction event. The Late Jurassic HMA in the eastern Youjiang Basin provide potential clues for the southward continuation of the Jiangnan Orogen into the basin. 相似文献
17.
江南造山带西段岩浆作用特性 总被引：12，自引：1，他引：11
在湖南浏阳南桥的中元古代冷家溪地层中发现了一种高度亏损、具N—MORB属性的玄武岩一辉绿岩。这种玄武岩的K2O特低,不相容的高场强元素,如Nb,Zr,Hf,Ti等和稀土元素的丰度都低于（少数元素接近）N-MORB的丰度,εNd（1271Ma）为6．86～8、98。在俯冲带附近N—MORB的发现为“九岭古岛弧”的存在提供了新的证据。湘西黔阳、古丈新元古代玄武岩-辉绿岩属碱性玄武岩．其微量元素特征近似于OIB,它的规模值得进一步调查。广西北部丹洲群中基性-超基性岩的TiO2,Ta及Nb的含量低,Hf／Th,Ti／Y和Ti／Zr等的比值也低,La/Ta和Th／Yb等的比值高,具有“弧玄武岩”特性。它们不具有CFB及OIB的地球化学特征,在构造环境判别图解上的标绘点集中在“火山弧玄武岩区”,少数样品位于“弧后盆地玄武岩区”。至今未发现具高温特征的高镁熔岩,也未见大规模放射性岩墙群。这些基性岩的规模极小（约100km^2）,不具有地幔柱来源的镁铁质岩浆的特性。桂北及湘东北的新元古代强过铝（SP）花岗岩体与江西九岭和安敞许村、休宁、歙县等岩体具有相似的特征,它们沿江南造山带呈带状分布,其形成与华夏和扬子板块之间的碰撞事件有关。在全球不同时代的造山带中都有S-型花岗岩出露;地幔柱岩浆作用形成的“镁铁质大火成岩省”中,出现的少量花岗岩是非造山、板内或A-型花岗岩,而不会是S-型花岗岩。不能把S-型花岗岩作为地幔柱岩浆作用的证据。这些都说明“江南造山带”的厘定有充分的岩石学证据。 相似文献
18.
The Fuchuan ophiolite belt in the eastern Jiangnan Orogen of South China provides important constraints on the tectonic setting and evolution of the Neoproterozoic suture zone between the Yangtze and Cathaysia blocks. Combined UPbHf isotopic and REE analysis of zircon from gabbroic and dioritic samples of the Shexian complex, located 10 km southwest of the main Fuchuan ophiolite body, indicate that the complex crystallized at ca. 870–860 Ma with a large variation of zircon εHf(t) values from − 4.80 to + 13.30. Whole-rock geochemistry reveals that the magma mainly experienced fractionation of olivine, clinopyroxene and plagioclase and was partly affected by crustal contamination, which resulted in elevated Th/Nb, Th/La and La/Sm ratios, as well as the scattered εHf(t) values. The most mafic and least contaminated sample shows MORB affinity and was probably formed by partial melting of a depleted subduction-metasomatized mantle wedge. Other samples exhibit arc-like signatures and were probably modified by both melt- and fluid-related subduction metasomatism. The emplacement of the Shexian complex corresponds to the time that subduction switched from a ca. 1000–880 Ma intra-oceanic island arc to a 870–830 Ma continental arc along the southeastern Yangtze Block. The sequence of igneous rocks associated with this continental arc resemble those preserved in forearc Tethyan ophiolites, with magma evolving from ca. 870–860 Ma MORB to ca. 860–850 Ma arc tholeiite and ca. 830 Ma boninite. Arc magmatism concluded with the final assembly of the Yangtze and Cathaysia blocks at 830–800 Ma. 相似文献