南海北部—东海南部中生代盆地演化与油气资源潜力

目前的勘探成果表明,南海北部到东海南部的广阔海域普遍发育中生代地层,但是除了在台西南盆地发现工业油气藏之外,其他地区的中生界尚未有大的勘探突破。本次研究将中生代南海北部—东海南部作为一个整体,开展大地构造背景分析,厘清各构造时期盆地的性质及其形成演化机制,探讨油气资源潜力。结果表明:南海北部—东海南部从晚三叠世到白垩纪整体为一个大型盆地,盆地的演化受其周围板块相互运动所控制;晚三叠世(T₃)主要受特提斯构造域控制,发育被动陆缘边缘海沉积盆地;从早侏罗世(J₁)到早白垩世均受古太平洋板块(伊泽奈崎板块)向欧亚板块俯冲机制的控制,其中早—中侏罗世(J_1-2)发育弧前坳陷盆地,晚侏罗—早白垩世(J₃—K₁)盆地性质为弧后断陷盆地;晚白垩世(K₂)受太平洋板块、欧亚板块和印度板块的联合控制,性质依然为弧后断陷盆地,与前期相比,裂陷强度加大;海水由东南方向侵入,地层垂向上由海相向陆相逐渐过渡,由东南向西北和东北方向,水体逐渐变浅,亦由海相向陆相逐渐演变;中生界在南海北部潮汕坳陷等地区发育深海相和海湾相泥岩,在东海南部基隆坳陷也发育良好的海湾相泥岩,生烃潜力大,具有形成大型油气藏的物质基础和地质条件,勘探潜力巨大。本次研究结果可以为南海北部—东海南部中生界的油气资源勘探提供依据。     

“海南陆缘弧”体系的构建与“特提斯南海”的识别:一个关于“古南海”演化新模式的探讨

应用近期在琼南、广东、湘南和越南芽庄、大叻等地的研究成果,综合区域地质资料,从岩浆岩性质、组合与地化特征、沉积序列特征和碎屑岩组分、年代学和地层学等方面进行分析,构建起以海南岛中南部的岩浆-沉积组合为典型标志、以东西向延伸为基本特征、演化过程与浙闽活动陆缘带明显有别的海南陆缘弧体系。该陆缘弧晚中生代处于华南大陆的南端,在构造地理格局上从属于特提斯域。笔者主张向北俯冲于海南陆缘弧下的"古南海"应正名为"特提斯南海",它是特提斯多岛洋北部的边缘海,西段可能与缅、马等地的海域沟通,东段则与太平洋域相接。海南陆缘弧具有广阔的弧后区,各弧后盆地的演化进程可以对比。该弧最初似发育于晚侏罗世,早白垩世晚期和晚白垩世初期岩浆弧与俯冲造山活动达到高峰,晚白垩世发生弧后拉张,但近弧地带挤压条件下的岩浆-沉积作用一直延续至晚白垩世后期(约70 Ma)。海南陆缘弧的活动时间表实际上是特提斯南海消减过程的真实反映。由于消减过程及随后发生的中南半岛在早新生代的挤出逃逸运动和现代南海的扩张作用,特提斯南海的地质记录受到极其严重的破坏,恢复特提斯南海的原貌仍是一项有待开展的艰巨工作。     

东海到南海晚中生代岩浆弧及陆缘汇聚体制综述

晚中生代是古太平洋板块俯冲汇聚东亚大陆的重要时期,这一构造期促发了华南强烈的岩浆活动和陆内变形,相关俯冲杂岩残留在日本西南、中国台湾到婆罗洲一线。华南大陆特别是岩浆岩研究已取得了丰富的成果认识,但缺乏与典型岩浆弧相关的中性岩浆岩发现。位于海陆结合部的东海到南海区域,将是开展晚中生代岩浆弧和弧前盆地等研究的优选地区,目前已陆续发现了相关岩浆岩和沉积记录。开展东海到南海这一区域性的岩浆弧和弧前盆地等研究,同时结合东部俯冲杂岩和华南大陆岩浆岩等成果资料,将有助于形成和完善晚中生代古太平洋俯冲体制和东亚活动大陆边缘的演变模式,也是深化认识我国海域中生界沉积盆地性质及其油气潜力的重要环节。     

南海北部古俯冲带的位置及其对南海扩张的控制

为了确定南海北部古俯冲带的具体位置,作者利用美国LCT综合反演软件对收集到的重磁数据进行处理解释,结果显示在南海北部从台湾西南部到一统暗沙隆起,即沿南海海盆北部陆坡为一条布格重力异常水平梯度峰值带,指示了古俯冲带的具体位置;其北部的高磁异常代表了与之对应的古火山弧。深反射地震资料也验证了南海北部陆坡位置存在古俯冲带,钻井资料显示俯冲带存在的时代为晚侏罗世到早白垩世。据此绘制了南海地区晚中生代到现今的构造古地理演化图,指出南海的扩张应与晚中生代俯冲带这个先存的软弱带有关,南海海盆正是从古俯冲带的位置开始扩张。     

西藏自治区革吉县米多南地区欧利组厘定的古生物证据及其意义

研究区位于羌塘地块与班公湖—怒江结合带交汇处,保存有一套晚侏罗世—早白垩世海相沉积记录,是研究晚侏罗世—早白垩世班公湖—怒江特提斯洋沉积环境演化及其沉积盆地类型的理想地区。通过对岩性组合、沉积环境、古生物化石等方面进行研究,厘定出欧利组,并探讨了欧利组时代归属及沉积盆地类型。根据欧利组中发现的小光星珊瑚、轮形异通珊瑚、米契林柱剑珊瑚、安多准柱剑珊瑚等化石,确定欧利组时代为晚侏罗世。初步分析沉积环境为局限台地-潮坪沉积,局部具潮汐水道沉积,沉积相分析表明研究区晚侏罗世—早白垩世沉积盆地类型为弧后前陆盆地。     

中国中生代沉积盆地演化

在综合分析中生代早-中三叠世、晚三叠世-早白垩世、晚白垩世-白垩纪3个时段中国沉积盆地分布、充填序列、岩相古地理和构造古地理的基础上, 建立了中国中生代沉积盆地的时空演化, 并探讨了中国中生代沉积盆地的时空演化与中生代构造运动的响应关系, 认为: (1)随着亚洲洋俯冲消亡及天山-兴蒙造山系形成, 中国北方地区总体处于古亚洲洋消亡以后, 陆块汇聚碰撞背景, 西北地区盆山格局基本定型, 南部古特提斯洋的双向俯冲消减, 在北羌塘-三江多岛弧盆系中的一系列弧后洋盆相继俯冲消亡; (2)晚三叠世的"印支运动"使古亚洲陆最终固结并向外增生, 中国己经基本形成了南海北陆的分布格局, 绝大部分地区进入陆内演化阶段.印支期以后, 华南中部上隆, 隔开了西部的古地中海域和东部的古太平洋海域; (3)中侏罗世以来, 在古太平洋板块向欧亚大陆俯冲的影响下, 整个中国东部卷入滨太平洋构造域, 西太平洋型活动大陆边缘形成.中国东北大部分地区为弧内裂陷(火山沉积)盆地; 华北-阿拉善陆块东西分化, 中西部主要发育压陷盆地或断陷盆地或坳陷盆地, 东部则形成与古太平洋板块俯冲有关的陆缘岩浆弧弧内裂陷盆地; 华南则以雪峰山为界, 东部广泛发育与陆缘岩浆弧演化相关的弧内裂陷盆地, 西侧则发育陆内大型压陷盆地、断陷盆地或断坳盆地.中国西南则仍然为多岛洋弧盆系格局.      

南海北部白垩纪—渐新世早期沉积环境演变及构造控制*

南海北部珠江口—琼东南盆地白垩系—下渐新统记录了华南大陆边缘从主动陆缘向被动陆缘的转换过程。基于盆地构造-地层、单井相、地震相等特征的综合分析,结合南海中南部的沉积环境和区域构造演化,探讨南海北部白垩纪—渐新世早期的沉积环境演变及构造控制背景。研究发现: (1)南海北部白垩系广泛分布,古新统分布极为有限; 始新世早-中期,琼东南盆地只在部分凹陷深部发育了小规模的滨浅湖相和扇三角洲相沉积,珠江口盆地白云凹陷以大规模发育的湖泊相为特征; 始新世晚期—渐新世早期,琼东南盆地和珠江口盆地白云凹陷都受到海侵作用的影响,以海岸平原相和滨浅海相为主。 (2)构造演变包括5期:包括白垩纪安第斯型大陆边缘的“弧—盆”体系发育期,古新世区域隆升剥蚀山间盆地发育期,始新世早-中期裂陷发育,始新世晚期—渐新世早期陆缘破裂期,渐新世晚期东部海盆稳定扩张期。最后,探讨了南海盆地中生代末/新生代初的动力学转换过程及特征。     

赣东北樟树墩早侏罗世水北组碎屑锆石研究及其地质意义

赣东北樟树墩地区早侏罗世盆地处于江南造山带东南缘,揭示盆地沉积物质来源对于认识和探讨周缘早中生代造山事件和古地理格局具有重要意义。对樟树墩早侏罗世盆地开展了岩相学、碎屑锆石U-Pb年代学和Lu-Hf同位素研究。结果表明: 盆地为类磨拉石建造与内陆湖沼含煤建造,碎屑锆石年龄跨度大(2 431~263 Ma),未出现同沉积或准同沉积的碎屑锆石; 碎屑锆石年龄呈现极强的早古生代峰值(420~380 Ma,ε_Hf(t)为-10.7~-3.0, T_DM^C为2.08~1.58 Ga)、弱的新元古代峰值(858~663 Ma,ε_Hf(t)为-18.8~-6.7, T_DM^C为2.79~2.09 Ga)和晚古生代峰值(370~355 Ma),另有少量早中生代((263±5) Ma)、中—古元古代(2 431~1 224 Ma)碎屑锆石记录。碎屑锆石年龄和Hf同位素组成与华夏地块西北武夷山地区所出露地质体组成相似,而与扬子东南缘地质体组成存在显著差异,其碎屑物质主要来自陆内西北武夷山地区前寒武纪基底和古生代地质体,少量碎屑物质可能来源于浙西北地区,具有被动型大陆边缘盆地沉积特征。综合区域上早中生代盆地研究成果,认为江南造山带东段景德镇—黄山东南在早—中侏罗世并未整体隆升剥蚀,华南内陆中生代的构造-岩浆活动是其周缘多板块俯冲汇聚的构造响应,晚三叠世—早侏罗世古太平洋板块向东亚大陆的俯冲造成华南东南部隆升,使其开始为内陆盆地提供物源,至早—中侏罗世之交构造体制转换为古太平洋板块的俯冲消减。     

南海北部陆缘盆地形成的构造动力学背景

摘要：南海北部陆缘盆地处于印度板块与太平洋及菲律宾海板块之间,但三大板块对南海北部陆缘盆地的影响是不同的。通过对三大板块及古南海演化的研究,可知南海北部陆缘地区应力环境于晚白垩世发生改变。早白垩世处于挤压环境,晚白垩世以来转变为伸展环境并且不同时期的成因不同。晚白垩世-始新世,华南陆缘早期造山带的应力松弛、古南海向南俯冲及太平洋俯冲板块的滚动后退导致其处于张应力环境。始新世时南海北部陆缘裂陷盆地开始产生,伸展环境没有变,但因其是由太平洋板块向西俯冲速率的持续降低及古南海向南俯冲引起的,南海北部陆缘盆地继续裂陷。渐新世-早中新世,地幔物质向南运动及古南海向南俯冲导致南海北部陆缘地区处于持续的张应力环境;渐新世早期南海海底扩张;中中新世开始,三大板块开始共同影响着南海北部陆缘盆地的发展演化。     

东地中海原型盆地演化

东地中海经历了伸展-聚敛的构造演化旋回,聚集了丰富的油气资源。基于2D地震、ODP Leg160、IHS及Tellus商业数据库和公开发表的文献资料,本文在建立东地中海及周缘构造-地层格架的基础上,恢复了东地中海12个关键地质历史时期的原型盆地,并以板块构造为切入点探讨了盆地演化机制。东地中海及周缘上三叠统以来地层可划分为新特提斯被动大陆边缘陆地及浅水区、新特提斯被动大陆边缘深水区和塞浦路斯弧前褶皱区3个地层分区,前两个地层分区均发育一套裂谷-被动大陆边缘层系,但是二者的岩相特征和不整合发育有明显的差异,而塞浦路斯弧前褶皱区发育一套大洋盆地-弧前盆地层系。研究认为东地中海经历了二叠纪—早侏罗世裂解期、中侏罗世巴柔期—晚白垩世土伦期漂移期和晚白垩世森诺期以来的汇聚改造期3个原型阶段,其中汇聚改造期又可细分为晚白垩世森诺期“双俯冲带”消减期、古近纪北部俯冲-碰撞期、中新世塞浦路斯岛弧带南侧俯冲-碰撞与黎凡特边缘活化期和中新世梅西期以来“弧-山碰撞”与“走滑逃逸”期4个阶段。东地中海盆地演化受控于图哈罗德-安纳托利亚板块以及凯里尼亚、特罗多斯和埃拉托色尼等微板块与冈瓦纳大陆北缘的分离、向北的漂移和与欧亚大陆汇聚拼贴的板块构造活动。     

Late Mesozoic Convergent Continental Margin with Magmatic Arc from East to South China Seas: A Review

The Late Mesozoic is an important tectonic period for subduction of Paleo-Pacific slab beneath East Asia continent. It intensely led to Jurassic to Cretaceous magmatism associated with intracontinental deformation in South China. Subduction-related accretionary complexes remained regionally from SW Japan, E Taiwan to the W Philippines and Borneo. Studies on geology in South China, especially in magmatism, have been performed with good data, results, and sufficient understandings; whereas those arc-related intermediate igneous rocks have been less found. The areas from East to South China Seas which are located at the junction between sea and land will be the preferred areas for the study of the Late Mesozoic magmatic arc and the forearc basin. The relevant arc-related magmatic rocks and forearc sedimentary records have been increasingly discovered. Studies of magmatic arc and forearc basin combined with subdction complex will be essential to the reconstruction of the convergent continental margin in South China. Analyses of magmatic arc identification from South to East China Seas, arc to forearc relationship, and assembly between arc and regional faults will become necessary to improve the knowledge of the model of East Asia convergent continental margin, and as well help to develop the understanding of Late Mesozoic forearc basin and resource potentials in the southeast sea areas.     

Arc accretion to the early Paleozoic Antarctic margin of Gondwana in Victoria Land

The Antarctic Ross Orogen was built up during the early Paleozoic in the framework of the convergence between the Paleo-Pacific oceanic plate and the Gondwana continental margin. Models for the Ross Orogen in northern Victoria Land are based on terranes having a variable provenance with respect to the margin. However, recent studies provide evidence for the occurrence of different pieces of the lithospheric puzzle: (i) the Wilson continental magmatic arc, representing the main part of the active Gondwana margin, (ii) the Bowers arc–backarc system, (iii) the Admiralty crustal ribbon including continental material of the Wilson forearc, and (iv) the newly discovered, Cambrian oceanic magmatic Tiger arc, along the Ross Sea coast. An updated model is presented in which, after the Early Cambrian magmatic activity of the Wilson arc, a retreat of the subduction zone in the Early–Middle Cambrian gave way to boudinage of the Wilson forearc, trenchward arc migration, opening of the Bowers backarc basin and inception of the outboard Tiger subduction zone. Renewed convergence resulted in the development of the Middle Cambrian Bowers arc, closure of the backarc and deep underthrusting of portions of it at the Middle–Late Cambrian. Finally, in the latest Cambrian to earliest Ordovician, fast exhumation was coupled in the north with erosion and sediment shed to the northeast, and with extension and potassic magmatism in central and southern Victoria Land.     

Sedimentary basins of Yemen: their tectonic development and lithostratigraphic cover

This paper describes the updated stratigraphy, structural framework and evolution, and hydrocarbon prospectivity of the Paleozoic, Mesozoic and Cenozoic basins of Yemen, depicted also on regional stratigraphic charts. The Paleozoic basins include (1) the Rub’ Al-Khali basin (southern flanks), bounded to the south by the Hadramawt arch (oriented approximately W–E) towards which the Paleozoic and Mesozoic sediments pinch out; (2) the San’a basin, encompassing Paleozoic through Upper Jurassic sediments; and (3) the southern offshore Suqatra (island) basin filled with Permo-Triassic sediments correlatable with that of the Karoo rift in Africa. The Mesozoic rift basins formed due to the breakup of Gondwana and separation of India/Madagascar from Africa–Arabia during the Late Jurassic/Early Cretaceous. The five Mesozoic sedimentary rift basins reflect in their orientation an inheritance from deep-seated, reactivated NW–SE trending Infracambrian Najd fault system. These basins formed sequentially from west to east–southeast, sub-parallel with rift orientations—NNW–SSE for the Siham-Ad-Dali’ basin in the west, NW–SE for the Sab’atayn and Balhaf basins and WNW–ESE for the Say’un-Masilah basin in the centre, and almost E–W for the Jiza’–Qamar basin located in the east of Yemen. The Sab’atayn and Say’un–Masilah basins are the only ones producing oil and gas so far. Petroleum reservoirs in both basins have been charged from Upper Jurassic Madbi shale. The main reservoirs in the Sab’atayn basin include sandstone units in the Sab’atayn Formation (Tithonian), the turbiditic sandstones of the Lam Member (Tithonian) and the Proterozoic fractured basement (upthrown fault block), while the main reservoirs in the Say’un–Masilah basin are sandstones of the Qishn Clastics Member (Hauterivian/Barremian) and the Ghayl Member (Berriasian/Valanginian), and Proterozoic fractured basement. The Cenozoic rift basins are related to the separation of Arabia from Africa by the opening of the Red Sea to the west and the Gulf of Aden to the south of Yemen during the Oligocene-Recent. These basins are filled with up to 3,000 m of sediments showing both lateral and vertical facies changes. The Cenozoic rift basins along the Gulf of Aden include the Mukalla–Sayhut, the Hawrah–Ahwar and the Aden–Abyan basins (all trending ENE–WSW), and have both offshore and onshore sectors as extensional faulting and regional subsidence affected the southern margin of Yemen episodically. Seafloor spreading in the Gulf of Aden dates back to the Early Miocene. Many of the offshore wells drilled in the Mukalla–Sayhut basin have encountered oil shows in the Cretaceous through Neogene layers. Sub-commercial discovery was identified in Sharmah-1 well in the fractured Middle Eocene limestone of the Habshiyah Formation. The Tihamah basin along the NNW–SSE trending Red Sea commenced in Late Oligocene, with oceanic crust formation in the earliest Pliocene. The Late Miocene stratigraphy of the Red Sea offshore Yemen is dominated by salt deformation. Oil and gas seeps are found in the Tihamah basin including the As-Salif peninsula and the onshore Tihamah plain; and oil and gas shows encountered in several onshore and offshore wells indicate the presence of proven source rocks in this basin.     

Tectonic evolution of the southern margin of Laurasia in the Black Sea region

The Black Sea region comprises Gondwana-derived continental blocks and oceanic subduction complexes accreted to Laurasia. The core of Laurasia is made up of an Archaean–Palaeoproterozoic shield, whereas the Gondwana-derived blocks are characterized by a Neoproterozoic basement. In the early Palaeozoic, a Pontide terrane collided and amalgamated to the core of Laurasia, as part of the Avalonia–Laurasia collision. From the Silurian to Carboniferous, the southern margin of Laurasia was a passive margin. In the late Carboniferous, a magmatic arc, represented by part of the Pontides and the Caucasus, collided with this passive margin with the Carboniferous eclogites marking the zone of collision. This Variscan orogeny was followed by uplift and erosion during the Permian and subsequently by Early Triassic rifting. Northward subduction under Laurussia during the Late Triassic resulted in the accretion of an oceanic plateau, whose remnants are preserved in the Pontides and include Upper Triassic eclogites. The Cimmeride orogeny ended in the Early Jurassic, and in the Middle Jurassic the subduction jumped south of the accreted complexes, and a magmatic arc was established along the southern margin of Laurasia. There is little evidence for subduction during the latest Jurassic–Early Cretaceous in the eastern part of the Black Sea region, which was an area of carbonate sedimentation. In contrast, in the Balkans there was continental collision during this period. Subduction erosion in the Early Cretaceous removed a large crustal slice south of the Jurassic magmatic arc. Subduction in the second half of the Early Cretaceous is evidenced by eclogites and blueschists in the Central Pontides and by a now buried magmatic arc. A continuous extensional arc was established only in the Late Cretaceous, coeval with the opening of the Black Sea as a back-arc basin.     

珠江口盆地构造演化旋回及其新生代沉积环境变迁

目前对珠江口盆地中生代以来的演化过程及其与沉积环境演变的响应关系尚缺乏系统性认识.基于珠江口盆地中-新生代岩浆活动、断陷结构样式及其改造、典型构造变形样式、沉积中心的转换等特征的对比分析,将盆地中-新生代的构造演化划分为4个阶段、7个期次:（1）中侏罗世-晚白垩世早期（~170~90 Ma）为古太平洋板块俯冲主控的陆缘岩浆弧-弧前盆地演化阶段;（2）晚白垩世-始新世中期（~90~43 Ma）为太平洋板块俯冲后撤背景下弧后周缘前陆/造山后塌陷-主动裂谷演化阶段;（3）始新世中期-中中新世（~43~10 Ma）为华南挤出-古南海俯冲拖曳主导的被动陆缘演化阶段;（4）晚中新世以来（~10~0 Ma）为菲律宾板块NWW向仰冲主导的挤压张扭演化阶段.~90 Ma、~43 Ma、~10 Ma分别实现了由安第斯型俯冲向西太平洋型俯冲、由主动裂谷向被动陆缘伸展、由被动陆缘伸展向挤压张扭的转换.在此过程中,伴随着古南海和南海的发育-消亡,新生代裂陷期沉积环境由东向西、由南向北逐渐海侵,裂后期由南向北阶段性差异沉降,由陆架浅水向陆坡深水转换,这使得珠一/三、珠二、珠四坳陷的石油地质条件具有显著的分带差异性.      

Sedimentary provenance of the Hengyang and Mayang basins,SE China,and implications for the Mesozoic topographic change in South China Craton: Evidence from detrital zircon geochronology

Detrital zircon U–Pb data from sedimentary rocks in the Hengyang and Mayang basins, SE China reveal a change in basin provenance during or after Early Cretaceous. The results imply a provenance of the sediment from the North China Craton and Dabie Orogen for the Upper Triassic to Middle Jurassic sandstones and from the Indosinian granitic plutons in the South China Craton for the Lower Cretaceous sandstones. The 90–120 Ma age group in the Upper Cretaceous sandstones in the Hengyang Basin is correlated with Cretaceous volcanism along the southeastern margin of South China, suggesting a coastal mountain belt have existed during the Late Cretaceous. The sediment provenance of the basins and topographic evolution revealed by the geochronological data in this study are consistent with a Mesozoic tectonic setting from Early Mesozoic intra-continental compression through late Mesozoic Pacific Plate subduction in SE China.     

班公湖-怒江结合带西段多岛弧盆系时空结构初步分析

笔者依据班公湖地区1：25万喀纳幅、日土县幅、羌多幅地质填图和专题研究工作取得的阶段性成果,将班公湖带的多岛弧盆系时空结构厘定为3条蛇绿混杂岩亚带。该3条亚带为盆地所隔,从北而南依次为班公湖带北亚带、班摩掌侏罗纪弧间盆地、班公湖带中亚带、日土-巴尔穷侏罗纪—早白垩世复合弧后盆地和班公湖带南亚带等。初步认为班公湖-怒江特提斯洋经历了晚三叠—早侏罗世往北俯冲、中晚侏罗世早期向北、往南双向俯冲、早白垩世往南俯冲等3次俯冲消亡阶段;同时,讨论了在班公湖带研究中存在的问题及其在反演班公湖-怒江结合带西段构造演化和在找矿方面的意义,以及进一步研究方向。     

Evolution of the Pacific margin of the northern Antarctic Peninsula: an overview

The sector of the northern Antarctic Peninsula between the Tula and Shackleton Fracture Zones provides evidence for the subduction of south-east Pacific oceanic crust under Antarctic continental crust during Late Mesozoic through Miocene times. The pre-subduction depositional history of this sector includes the formation of a marine siliciclastic turbidite wedge (?Permian-Triassic) deposited in a marginal basin setting. It was folded and thrust retroarc before the Middle Jurassic to form the Trinity accretion foldbelt, which extended for several hundred kilometres along the Pacific margin of Gondwanaland. The foldbelt was deeply eroded and levelled under subaerial conditions, then unconformably covered either by Middle-Upper Jurassic alluvial to lacustrine deposits (in the north) or by Early Cretaceous basic lavas (in the south). The subduction-related magmatism, in the form of acidic effusions and intrusions, began in the northern Antarctic Peninsula during Middle Jurassic times and continued as predominantly basic lavas and agglomerates intruded by basic, intermediate and acidic plutons, and by a succession of dykes, during the Early to Late Cretaceous. Thus the inner magmatic are of the northern Antarctic Peninsula (northern Graham Land-Trinity Peninsula) was formed. An outward (north-westerly) migration of centres of magmatic activity with time (Cretaceous-Tertiary) towards the subduction trench, coupled with a northeastward shift of these centres along the Arc's length due to the counterclockwise rotation of Antarctica, produced the outer magmatic arc of the South Shetland Islands. Slight folding of Late Mesozoic and Tertiary magmatic suites occurred at several stages of subduction. Stronger folding and retroarc thrusting appeared locally as a result of the collision of the Aluk Ridge-Antarctic Peninsula during the Mid-Miocene. The latest plate tectonic event was the opening of the Bransfield Rift (Oligocene-Recent) as a spreading back-arc basin, associated with terrestrial and submarine volcanic activity.