Timing of formation and geological setting of low-sulphidation epithermal gold deposits in the continental margin of NE China     

《International Geology Review》2012,54(5):608-632

The margin of NE China, a part of the West Pacific metallogenic belt, contains innumerable low-sulphidation mineral deposits. Gold deposits in this region can be classified into three distinct types based on geology and ore mineral paragenesis: (1) low-sulphidation epithermal silver–gold deposits, (2) low-sulphidation tellurium–gold deposits, and (3) low-sulphidation epithermal tellurium–gold deposits. Ores formed during the late Early Cretaceous and the early Late Cretaceous reflect three distinct metallogenic periods: the Fuxin Stage at 115.98 ± 0.89 Ma, the Quantou Stage at 107.2 ± 0.6 Ma or <103 Ma, and the Qingshankou or Yaojiajie Stage at < 97 Ma and 88.2 ± 1.4 Ma. The Fuxin Stage is dominated by trachyandesitic magmatism, with magmas emplaced at hypabyssal depths. In comparison, the Quantou Stage is characterized by high-K calc-alkaline, calc-alkaline, and sodic andesitic, dacitic, and rhyolitic magmatism of three different suites. The first of these is a high-K calc-alkaline andesitic magmatic suite that was accompanied by the emplacement of a calc-alkaline sodic dacite during the formation of the Ciweigou and Wufeng ore deposits. The second suite is dominated by calc-alkaline sodic rhyolite and high-K calc-alkaline sodic dacite magmatism associated with the formation of the Sipingshan ore deposit. The third suite is typified by high-K calc-alkaline andesitic magmatism associated with the emplacement of calc-alkaline hypabyssal granitoid complexes accompanying the formation of the Dong'an and Tuanjiegou ore deposits. The Qingshankou or Yaojia Stage is characterized by calc-alkaline sodic dacite magmatism associated with the formation of the Wuxing ore deposit. Metallogenesis during the Fuxin Stage characterized by trachytic magmatism is closely related to the formation of a deep-seated fault within a magmatic arc or the back-arc region of an immature continental margin and is associated with the Early Cretaceous subduction of the Pacific plate beneath Eurasia. Ore deposits that formed during the Fuxin Stage were generally related to magmato-hydrothermal fluids associated with mantle-derived magmas. In contrast, metallogenesis during the Quantou and Qingshankou or Yaojiajie stages was closely related to the formation of a mature high-K calc-alkaline magmatic arc within a continental margin setting again associated with the westward subduction of the Pacific plate. This metallogenic event was a product of magmato-hydrothermal systems derived from crust–mantle interaction and mixing of magmas derived from partial melting of different sections of the continental crust.  相似文献   

Formation of the world's largest molybdenum metallogenic belt: a plate-tectonic perspective on the Qinling molybdenum deposits     

《International Geology Review》2012,54(9):1093-1112

Qinling ore belt is the largest known molybdenum belt in the world with a total reserve of >5 Mt of Mo metal. Based on the geochemical behaviour of Mo, the structural settings of the Qinling orogenic belt, and geological events in eastern China, we propose that tectonic settings are of critical importance to the formation of these ore deposits. Molybdenum is very rare in the earth with an abundance of ～0.8 ppm in the continental crust. Both surface- and magmatic-hydrothermal enrichment processes are required for Mo mineralization. It can be easily oxidized to form water-soluble MoO₄ ^– in the surface environment, especially in the Phanaerozoic, and then precipitated under anoxic conditions. Therefore, closed or semi-closed water bodies with large catchment areas and high chemical erosion rates are the most favourable locations for Mo-enriched sediments. The Qinling orogenic belt was located in the tropics during crustal collisions, such that the chemical erosion was presumably intense, whereas the Erlangping back-arc basin was probably a closed or semi-closed water body as a result of plate convergence. More than 90% of the Mo reserves so far discovered in the Qinling molybdenum belt are associated with the Palaeozoic Erlangping back-arc basin. Compiled Re–Os isotopic ages for porphyry deposits (including several carbonate vein deposits) that have been dated show peaks during 220 million years (>0.32 Mt), 145 million years (>?3.5 Mt), and 115 million years (>?0.84 Mt), which correlate well with the three major episodes of granitoid magmatism since the Triassic. The ～220 million year episode of mineralization, represented by the Huanglongpu carbonate vein-type deposit and the Wenquan porphyry deposit, coincided with the formation of the South Qinling syn-orogenic granites as well as the Dabie ultrahigh-pressure metamorphic rocks, suggests a genetic relationship with the collision between South and North China Blocks. The ～145 Ma porphyry Mo deposits, representing the main mineralization, are attributed to reactivation by ridge subduction along the lower Yangtze River belt to the east of the Qinling orogen ～150–140 Ma. The ～115 Ma Mo deposits likely reflect slab rollback of the northwestwards subducting Pacific plate ～125–110 Ma.  相似文献   

Continental flood basalts of the Huashan Group,northern margin of the Yangtze block – implications for the breakup of Rodinia     

《International Geology Review》2012,54(15):1865-1884

It is generally accepted that Neoproterozoic extension and dispersal of the supercontinent Rodinia was associated with mantle plume or superplume activities. However, plume-generated contemporaneous continental flood basalts (CFBs) have rarely been identified. In this study, we present geochronological and geochemical evidence for the basalts from the Liufangzui Formation of the Huashan Group in the Dahongshan region of east-central China. A representative sample yields a SHRIMP U–Pb zircon age of 824 ± 9 Ma, interpreted as the crystallization age of the rocks. Geochemically, these basalts belong to the subalkaline tholeiite series and display slight enrichments in light rare earth elements (LREE) and varying degrees of deficiency of high field strength elements (HFSE) such as Nb, Ta, and Ti. This pattern is very similar to that of CFBs from the Bikou Group and Tiechuanshan Formation in the northwestern Yangtze block in China and Siberia in Russia. The basaltic magmas underwent partially-fractional crystallization during ascent, but were not intensely influenced by crustal contamination. The characteristic element ratios and negative Hf isotopic analyses (?_Hf(t) = ?6.6–2.6) in zircons indicate that the parental magmas of the basalts might have been derived from an enriched lithospheric mantle rather than from the depleted mantle such as normal mid-ocean ridge basalts (N-MORBs). The geochemical signatures and regional geological characteristics show that these basalts were formed along intraplate continental rifts rather than in island arcs or ocean basins. Considering the coeval basic volcanic rocks in South China, we propose that these Huashan Group basalts represent the remnants of plume-generated CFBs and have close spatiotemporal ties with a coeval basic igneous province in Australia. Our results support the Neoproterozoic location of the South China block adjacent to southeastern Australia in the reconstruction model of the supercontinent Rodinia.  相似文献   

Age and nature of 560–520 Ma calc-alkaline granitoids of Biarjmand,northeast Iran: insights into Cadomian arc magmatism in northern Gondwana     

《International Geology Review》2012,54(12):1492-1509

ABSTRACT

The Biarjmand granitoids and granitic gneisses in northeast Iran are part of the Torud–Biarjmand metamorphic complex, where previous zircon U–Pb geochronology show ages of ca. 554–530 Ma for orthogneissic rocks. Our new U–Pb zircon ages confirm a Cadomian age and show that the granitic gneiss is ~30 million years older (561.3 ± 4.7 Ma) than intruding granitoids (522.3 ± 4.2 Ma; 537.7 ± 4.7 Ma). Cadomian magmatism in Iran was part of an approximately 100-million-year-long episode of subduction-related arc and back-arc magmatism, which dominated the whole northern Gondwana margin, from Iberia to Turkey and Iran. Major REE and trace element data show that these granitoids have calc-alkaline signatures. Their zircon O (δ¹⁸O = 6.2–8.9‰) and Hf (–7.9 to +5.5; one point with εHf ~ –17.4) as well as bulk rock Nd isotopes (εNd(t) = –3 to –6.2) show that these magmas were generated via mixing of juvenile magmas with an older crust and/or melting of middle continental crust. Whole-rock Nd and zircon Hf model ages (1.3–1.6 Ga) suggest that this older continental crust was likely to have been Mesoproterozoic or even older. Our results, including variable zircon εHf(t) values, inheritance of old zircons and lack of evidence for juvenile Cadomian igneous rocks anywhere in Iran, suggest that the geotectonic setting during late Ediacaran and early Cambrian time was a continental magmatic arc rather than back-arc for the evolution of northeast Iran Cadomian igneous rocks.  相似文献   

Relationship of the Tarim Craton to the Central Asian Orogenic Belt: insights from Devonian intrusions in the northern margin of Tarim Craton,China     

《International Geology Review》2012,54(16):2007-2028

ABSTRACT

The boundary and relation of the Tarim Craton to the Central Asian Orogenic Belt (CAOB) and its role in the formation history of the CAOB remain controversial. This article presents ages and Hf-in-zircon isotopic and geochemical results for gabbroic, dioritic, and granitic plutons from the northern margin of Tarim Craton (NMTC), and discusses their petrogenesis and tectonic regimes as well as the boundary between the CAOB and the Tarim Craton. These plutons yield zircon ages of 424–385 Ma. In the Quruqtagh zone south of the Xinger Fault, the gabbroic pluton shows enrichment in LREEs and LILEs, depletion in HFSEs and positive ε_Hf(t) values (+4.0 to +11.4), suggesting that parental magmas of gabbros were likely derived by partial melting of a depleted mantle wedge previously metasomatized by slab-derived aqueous fluids. In the Hulashan Zone north of the Xinger Fault, the studied rocks include one dioritic pluton and three granitic plutons. The geochemical characteristics and petrogenesis of the dioritic pluton are similar to those of the studied gabbroic with positive ε_Hf(t) values (+3.0 to +9.4). The three granitic plutons display relative depletion in HFSEs and enrichment in LILEs. Their variable ε_Hf(t) values range from ?2.1 to +8.9, with T_DM2 ages of 858–1503 Ma, suggesting complex crustal sources with different proportions of juvenile and ancient materials. This article confirms and evidences an Andean-style active continental margin of the Tarim Craton due to southward subduction of the South Tianshan Ocean. Furthermore, our Hf isotopic data, together with regional data from the literature, show that the Hulashan zone to the north to the Xinger Fault has younger continental materials in deep than these of NMTC south of the fault, and is similar to microcontinental fragments in the CAOB. This suggests that the Xinger fault may be the boundary between the Tarim Craton and Tianshan orogen.  相似文献   

Partial melting of subducted Southern Qiangtang crust in northern Tibet: evidence from the geochemistry and geochronology of the Riwanchaka granodiorite porphyry in Central Qiangtang     

《International Geology Review》2012,54(6):738-753

ABSTRACT

This article presents new zircon U–Pb geochronology, Hf isotopic, and whole-rock major- and trace-element geochemical data that provide insights into the petrogenesis and tectonic history of the Riwanchaka granodiorite porphyries of Central Qiangtang, Tibet. Zircon U–Pb ages of 236–230 Ma indicate an early Late Triassic age of emplacement of the porphyries, and zircon Hf isotopic data yield εHf(t) values of – 7.0 to – 1.5 and ancient zircon Hf crustal model ages (T_DM^C) of 1524–1220 Ma. The granodiorite porphyries are characterized by low K₂O contents, high Mg# values, and relatively high Cr and Ni contents. They are classified as I-type calc-alkaline granite and are considered to have formed through the anatexis of ancient mafic crustal rocks with contributions from mantle-derived components. The geochemistry and isotopic compositions of all samples are similar to those of magmatic rocks that originated in the South Qiangtang crust. However, field observations indicate that the pluton intrudes the North Qiangtang crust, and we propose that the granodiorite porphyries were derived by partial melting of subducted continental crust of the South Qiangtang terrane. These new data have been integrated with data from previous studies to construct a new model of slab rollback during northward subduction of the Southern Qiangtang continental crust at ca. 245–226 Ma, thereby improving our understanding of magmatic processes involved in continental subduction in collision settings.  相似文献   

多岛弧盆系构造模式:认识大陆地质的关键   总被引：8，自引：4，他引：4       下载免费PDF全文

潘桂棠  王立全  李荣社  尹福光  朱弟成 《沉积与特提斯地质》2012,(3):1-20

本文在对以青藏高原为主体的东特提斯30多年来的地质调查和研究实践基础上,通过与现今西南太平洋区域弧盆构造体系的对比研究,提出了适合于板块构造登陆的现实主义替代模型-多岛弧盆系构造模式。大洋岩石圈与大陆岩石圈之间的多岛弧盆系构造模式是板块构造登陆的入门向导,是认识大陆地质演化的关键。基于该模式研究认为,特提斯大洋最初开始于Rodinia超大陆解体的晚前寒武纪晚期,比太平洋体系更老。青藏高原形成受控于不同时期大陆边缘多岛弧盆系构造演化,一系列弧后或弧间盆地消亡、弧-弧或弧-陆碰撞的岛弧造山作用实现大陆边缘增生。该现实主义模式即可成功地解释青藏高原的形成演化过程,亦可为现在和将来特提斯构造域与亚洲大陆的地质工作所检验。多岛弧盆系构造的识别与深入研究不仅在造山带具有强大的生命力,能够全面解剖造山带的物质组成、结构构造与演化历史,而且对于分析前寒武纪大陆克拉通基底的形成也具有重要启示。  相似文献   

青海省同仁地区早白垩世大陆裂谷环境火山岩的确定及意义     

祁生胜  邓晋福  陈健  付军  史连昌 《西北地质》2012,45(1):20-32

西秦岭西端在同仁地区沿近南北向断裂分布一套典型的灰紫色陆相火山岩,岩性组合为灰紫色块层状-杏仁状橄榄玄武岩、安山玄武岩、火山角砾岩夹灰紫色厚层状复成分砾岩、灰紫色—青灰色中厚层状含砾粗砂岩和灰紫色薄层状泥岩,火山岩以碱性系列为主,其形成时代为早白垩世。其地球化学显示轻稀土富集,Eu具轻度正异常,不相容元素富集,岩石具有较高的87Sr/86Sr、143Nd/144Nd、εNd和206Pb/204Pb特点。岩石的εNd均值为7.69,εSr均值为-10.7,其物源与典型的EM或HIMU型洋岛玄武岩明显不同,物源受部分大陆壳的混染,岩浆源成分属于EM与HIMU幔源间混合成因。综合分析其为大陆板块内部拉张环境下的岩浆活动产物,是形成于伸展构造背景下类似于大陆裂谷环境的火山岩。  相似文献   

柴达木盆地北缘全吉地块东端变基性岩体LA-ICP-MS锆石U-Pb年龄:中元古代陆块裂解的证据     

廖梵汐  龚松林  董彦君  王勤燕  张璐  陈能松 《地质通报》2012,31(8):1279-1286

全吉地块东端古元古代二长花岗片麻岩中普遍发育变质的基性岩体,它们的形成时代、变质作用时代和对地块基底构造演化的指示意义尚不清楚。应用LA-ICP-MS技术测定其中的一个变基性岩体的锆石U-Pb年龄,获得的10个测点数据显示,锆石受到热事件的强烈改造而发生严重铅丢失,但拟合的不一致线仍给出相关性较好的上交点年龄1712Ma±47Ma和下交点年龄472Ma±29Ma,MSWD=1.4。这表明,变质基性岩的原岩形成于中元古代早期,是全吉地块在古元古代末期汇入Columbia超大陆之后于中元古代早期初始裂解而侵位的基性岩体。这些基性岩体在早古生代卷入了柴北缘碰撞带而发生角闪岩相变质作用,并受到构造肢解。  相似文献   

大陆下地壳和岩石圈地幔含水性的差异——山东莒南玄武岩中深源包体的初步观察   总被引：1，自引：0，他引：1  

杨贵才  杨晓志  郝艳涛  夏群科 《岩石矿物学杂志》2012,31(5):691-700

对产于莒南晚中生代玄武岩中的镁铁质麻粒岩和橄榄岩包体矿物进行了傅里叶变换红外光谱(FTIR)分析.结果显示,麻粒岩矿物和全岩中水含量分别为:单斜辉石300×10-6～1 180×10-6,斜方辉石80×10-6～169×10-6,斜长石717×10-6～1 239×10-6,全岩525×10-6～855×10-6;橄榄岩矿物和全岩中水含量分别为:单斜辉石466×10- 6～746×10-6,斜方辉石187×10-6～304×10-6,橄榄石6×10-6～15×10-6,全岩81×10-6～245×10-6.从单矿物看,麻粒岩和橄榄岩之间水含量的差距不是很明显,但麻粒岩的全岩水含量明显高于橄榄岩,表明大陆深部岩石圈的水含量在垂向上具有不均一性.  相似文献