Recycling of orogenic arc crust triggers porphyry Cu mineralization in Kerman Cenozoic arc rocks,southeastern Iran

Pre-collisional Eocene–Oligocene arc diorites, quartzdiorites, granodiorites, and volcanic equivalents in the Kerman arc segment in central Iran lack porphyry Cu mineralization and ore deposits, whereas collisional middle-late Miocene adakite-like porphyritic granodiorites without volcanic equivalents host some of the world’s largest Cu ore deposits. Petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment. Ore-hosting Kuh Panj porphyry intrusions exhibit high Sr (>400 ppm), low Y (<12 ppm) contents, significant REE fractionation (La/Yb > 20), no negative Eu anomalies (Eu/Eu^* ≥ 1), and relatively non-radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr = 0.7042–0.7047), relative to Eocene–Oligocene granitoids (mainly Sr < 400 ppm; Y > 12; La/Yb < 15; Eu/Eu^* < 1; ⁸⁷Sr/⁸⁶Sr = 0.7053–0.7068). Trace element modeling indicates peridotite melting for the barren Eocene–Oligocene intrusions and a hydrous garnet-bearing amphibolite source for middle-late Miocene ore-hosting intrusions. The presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30–35 to 40–45 km or 12 kbar. The changes in residual mineralogy in the source of Eocene to Miocene rocks in the Kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel. Underplating of Cu and sulfur-rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust–mantle boundary, and dehydration melting under oxidizing conditions produced syn- and post-collisional ore-hosting intrusions, while the lack of post-collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur-rich and oxidized adakitic magmas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

冈底斯-喜马拉雅碰撞造山带前陆盆地系统及构造演化

碰撞带前陆盆地的建立是大陆碰撞的直接标志和随后造山带构造变形的忠实记录。本文对欧亚板块与印度板块碰撞前后发育在拉萨地块上的冈底斯弧背前陆盆地,同碰撞产生的雅鲁藏布江周缘前陆盆地,以及碰撞后陆内变形产生的喜马拉雅前陆盆地的沉积地层演化以及碎屑锆石物源特征等进行了系统分析,结合前人及我们近些年的研究成果,认为冈底斯岛弧北侧发育一个典型的弧背前陆盆地系统而不是以前普遍接受的伸展盆地。除传统认为的喜马拉雅前陆盆地系统外,在碰撞造山带中还发育一个雅鲁藏布江前陆盆地系统,它是欧亚板块与印度板块碰撞以后,欧亚板块加载到印度被动大陆边缘产生的典型周缘前陆盆地。上述2个造山带前陆盆地系统的识别,大大提高了对新特提斯洋俯冲、碰撞过程的认识。造山带前陆盆地证据指示,新特提斯洋至少于140 Ma以前就已开始俯冲, 110 Ma俯冲速度开始提高,在65 Ma前后印度大陆与欧亚大陆发生碰撞,喜马拉雅山于40 Ma开始隆升,其剥蚀物质大量堆积在喜马拉雅前陆盆地中。     

东南亚巽他群岛埃达克岩的分布及斑岩型铜(金)矿成矿预测的地质准则

东南亚巽他群岛是新生代埃达克岩、类埃达克岩极其发育的地区。这些中酸性岩浆岩广泛见于几内亚岛上的中央山脉、巴布亚新几内亚的欧文-斯坦利推覆带、俾斯麦岛弧、布干维尔岛-所罗门岛弧、印度尼西亚苏拉威西、加里曼丹中部、班达岛弧,零星见于苏门答腊、爪哇等地。根据微量元素特征及REE曲线类型的特点,本区埃达克岩可以明显地划分为2种类型：第一种埃达克岩类型属于拉斑/钙-碱性系列,具有大洋岛弧的REE曲线特征（相当于O型埃达克岩）;第二种埃达克岩属于高钾钙-碱性系列,归于大陆埃达克岩（相当于C型埃达克岩）,形成于弧-陆碰撞带或碰撞后造山带。埃达克岩与浅成热液金属矿床和斑岩矿床的成矿作用有密切的关系,是世界级浅成热液和斑岩铜-金矿的容矿岩石。     

新疆东天山大黑山地区眼球状花岗片麻岩成因及形成环境

文章对东天山大黑山地区眼球状花岗质片麻岩的特征及其成因进行探讨。通过野外地质调查和岩石学、矿物学、地球化学的研究,认为区内岩体为岛弧钙碱性火山-沉积岩系原地重熔改造的产物,这种原地花岗片麻岩的成岩过程主要为深源熔体和流体与原岩的相互作用,使原岩发生不同程度的部分熔融,因而其地球化学特征同时受到原岩和外来熔体-流体的控制。锆石U-Pb年龄为1 141 Ma,代表了重熔事件的时间。根据岩石地球化学及构造环境判别图解认为该岩体为碰撞造山后期-期后的产物。     

冈底斯中段林子宗火山岩~(40)Ar-~(39)Ar年龄及其意义

广泛分布在冈底斯岩浆岩带上的林子宗火山岩及与下伏地层间的区域不整合提供了印度-亚洲大陆碰撞的重要证据.本文对冈底斯中段谢通门地区林子宗火山岩年波组下段玄武安山岩中斜长石进行了40Ar-39Ar测年分析.结果表明,年波组火山岩形成于51.67±0.29 Ma,与林周地区年波组火山岩年龄基本一致,均为始新世.结合该区林子宗火山岩岩石学及岩石地球化学特征,指出谢通门地区林子宗火山岩形成于印度-亚洲大陆碰撞过程中.     

Paleoproterozoic Granitoids on Liaodong Peninsula,North China Craton

Paleoproterozoic granitoids are an important constituent of the Jiao–Liao–Ji Belt(JLJB). The spatial-temporal distribution and types of Paleoproterozoic granitoids are closely related to the evolution of the JLJB. In this paper, we review the field occurrence, petrography, geochronology, and geochemistry of Paleoproterozoic granitoids on Liaodong Peninsula, northeast China. The Paleoproterozoic granitoids can be divided into pre-tectonic(～2.15 Ga; peak age=2.18 Ga) and post-tectonic(～1.85 Ga) granitoids. The pre-tectonic granitoids are magnetite and hornblende–biotite monzogranites and granodiorites. Pre-tectonic monzogranites are widespread in the JLJB and have A_2-type affinities. In contrast, pretectonic granodiorites are only present in the Simenzi area and have adakitic affinities. The post-tectonic granitoids consist of porphyritic monzogranite, syenite, diorite, granodiorite, quartz monzonite, monzogranite, and granitic pegmatite, which are adakitic rocks and I-, S-, and A_2-type granitoids. The assemblage of pre-tectonic A_2-type granitoids and adakitic rocks indicates the initial tectonic setting of the JLJB was a continental back-arc basin. The assemblage of post-tectonic adakitic rocks and I-, S-, and A_2-type granitoids indicates a post-collisional setting. The 2.20–2.15 Ga A_2-type granitoids and adakitic rocks were associated with the initial stage of back-arc extension, and the peak of back-arc extension is inferred from the subsequent(2.15–2.10 Ga) mafic intrusive activity. The ～1.90 Ga adakitic rocks mark the beginning of the postcollisional stage, which was followed by the intrusion of low-temperature S-and I-type granitoids. High-to low-pressure granitoids(S-type) were generated during the peak of post-collisional lithospheric delamination and asthenospheric upwelling. The emplacement of later granitic pegmatites occurred during the waning of the orogeny.     

内蒙古狼山地区晚志留世石英闪长岩的发现及其地质意义

内蒙古狼山山脉西侧分布零星的早古生代岩浆岩,晚志留世石英闪长岩主要出露于哈日音熬瑞一带。该岩体岩性为石英闪长岩,块状构造,LA-ICP-MS锆石U-Pb年龄显示,其~(206)Pb/~(238)U年龄加权平均值为419.0±4.0~413.3±1.8Ma。岩石暗色矿物为黑云母,富铁(4.27%~4.65%)、富钠(4.17%~4.45%),富集大离子亲石元素Sr、K、Pb,不同程度亏损高场强元素P、Ti、Nb,轻稀土元素富集,重稀土元素亏损,弱负Eu异常,这些特征与弧岩浆岩的地球化学特征相似;La/Ba-La/Nb图解显示俯冲交代地幔的源区特点;岩石负的ε_(Hf)(t)值(-12.1~-8.8)及较大的T_(DM2)值(1981~2362Ma)反映了古元古代古老地壳熔融的特点。花岗岩类构造判别图解及区域地质资料显示岩体形成于弧陆拼贴的构造背景。对比白乃庙地区新发现的晚志留世弧陆拼贴的石英闪长岩,两者的岩石地球化学特征及同位素特征基本一致,因此,华北地块北缘晚志留世弧陆拼贴作用向西延伸至狼山地区。     

Characteristics of tectonic deformation of the melange zone in the Lachlan Orogen along eastern coast of Australia

The Narooma-Batemans Bay (NBB) area along the southeast coast of Australia is a part of the eastern zone of the Early Paleozoic Lachlan Orogen. In the NBB, a set of rock association consisting of turbidites, siliceous rock, basic lava, and argillaceous melange zone is mainly developed. According to systematic field geological survey, the deformation of 3 stages (D1, D2, and D3) was identified in the NBB. At stage D1, with the original bedding S0 in a nearly east-west trending as the deformation plane, tight folds, isoclinal folds, and other structures formed in the NBB accompanied by structural transposition. As a result, crenulation cleavage developed along the axial plane of the folds and schistosity S1 formed. At stage D2, with north-south-trending schistosity S1 as the deformation plane, a large number of asymmetrical folds and rotated porphyroclasts formed owing to thrusting and shear. At stage D3, left-lateral strike-slip occurred along the main north-south-trending schistosity. Based on the analysis of the characteristics of tectonic deformation in the NBB and summary of previous research results, it is determined that the early-stage (D1) deformation is related to Ordovician Macquarie arc-continent collision and the deformation at stages D2 and D3 is the result of the westward subduction of Paleo-Pacific Plate. That is, it is not the continuous westward subduction of the Paleo-Pacific Plate that constitutes the evolution model of the NBB as previously considered.     

The Cansiwang Melange of Southeast Bohol (Central Philippines): Origin and tectonic implications

Abstract The Cansiwang Melange underlies the Southeast Bohol Ophiolite Complex (SEBOC) and is composed mainly of sheared ophiolite-derived blocks such as harzburgites, microgabbros, basalts and cherts in a pervasive serpentinite matrix. Available field, as well as geophysical evidence show that this melange unit is not diapiric, nor does it have a sedimentary origin considering that it lacks slump and flow structures. A tectonic origin for the Cansiwang Melange is favored in view of the numerous thrust faults, which cut across the exposures, as well as the tectonic contacts that the melange has with the overlying and underlying formations. The presence of the Cansiwang Melange in between the SEBOC and the Alicia Schist provides evidence that the amphibolite of the Alicia Schist do not correspond to the metamorphic sole of SEBOC. Similar to what is recognized in the Josephine Ophiolite, this suggests a 'cold' emplacement of the ophiolite over the Alicia Schist. The Cansiwang Melange represents an accretionary prism product which marks the location of an ancient subduction zone in what is now Central Philippines.     

Crustal deformation due to Alaska–Yakutat collision

The region of Alaska and adjacent northwest Canada is tectonically active and is subjected to multiple tectonic processes including plate subduction and terrane accretion. These tectonic processes and the forces originating thereof are responsible for high seismicity in the region and deformation of the crust. In the present-day tectonic setting, the Yakutat terrane is obliquely colliding with Alaska along the Aleutian Trench. Also, flat subduction due to under thrusting of a thickened crust, probably of oceanic affinity, is contributing to the tectonic evolution of this region in a basal traction collision style. This study uses the 2D, planform, thin-viscous-sheet model to investigate the effect of the Yakutat terrane colliding with Alaska and adjacent northwest Canada. Along with the obliquity and velocity of convergence, the lateral strength heterogeneities in the crust are considered in this investigation. The results of the numerical model are constrained with the observed topography and stress orientation in Alaska. It is shown that the Alaska–Yakutat collision is producing asymmetric deformation of the crust with respect to the normal to the collision boundary and that lateral strength heterogeneities contribute significantly to the deformation of the crust. Also, the influence of this collision can be observed up to a distance of 700 km inland from the collision boundary.