Genesis of the Archean–Paleoproterozoic Tabletop Domain,Rudall Province,and its endemic relationship to the West Australian Craton

The Tabletop Domain of the Rudall Province has been long thought an exotic entity to the West Australian Craton. Recent re-evaluation of this interpretation suggests otherwise, but is founded on limited data. This study presents the first comprehensive, integrated U–Pb geochronology and Hf-isotope analysis of igneous and metasedimentary rocks from the Tabletop Domain of the eastern Rudall Province. Field observations, geochronology and isotope results confirm an endemic relationship between the Tabletop Domain and the West Australian Craton (WAC), and show that the Tabletop Domain underwent a similar Archean–Paleoproterozoic history to the western Rudall Province. The central Tabletop Domain comprises Archean–Paleoproterozoic gneissic rocks with three main age components. Paleo–Neoarchean (ca 3400–2800 Ma) detritus is observed in metasedimentary rocks and was likely sourced from the East Pilbara Craton. Protoliths to mafic gneiss and metasedimentary rocks are interpreted to have been emplaced and deposited during the early Paleoproterozoic (ca 2400–2300 Ma), and exhibit age and isotopic affinities to the Capricorn Orogen basement (Glenburgh Terrane). Mid–late Paleoproterozoic mafic and felsic magmatism (ca 1880–1750 Ma) is assigned to the Kalkan Supersuite, which is exposed in the western Rudall Province. The Kalkan Supersuite provided the main source of detritus for mid–late Paleoproterozoic metasedimentary rocks in the Tabletop Domain. Similarities in the age and Hf-isotope compositions of detrital zircon from these metasedimentary rocks and Capricorn Orogeny basin sediments suggests that a regionally extensive, linked basin system may have spanned the northern WAC at this time. The Tabletop Domain records evidence for two metamorphic events. Mid–late Paleoproterozoic deformation (ca 1770–1750 Ma) was high-grade, regional and involved the development of gneissic fabrics. In contrast, early Mesoproterozoic (ca 1580 Ma) high-grade deformation was localised and associated with more widespread, late-stage, greenschist facies alteration. These new findings highlight that the Tabletop Domain experienced a much higher grade of deformation than previously assumed, with a Paleoproterozoic metamorphic history similar to that of the western Rudall Province.     

Early Carboniferous anorogenic magmatism in the Levant: implications for rifting in northern Gondwana

The Variscan orogenesis in Europe peaked during the Late Devonian–Early Carboniferous times when Gondwanan terranes collided with Laurasia. Hitherto it has been thought that Carboniferous tectonics in northern Arabia and the adjacent parts of NE Africa were broad swells (‘arches’) and depressions (‘basins’) that formed as a far-field contractional effect of the Variscan compression. The discovery of a 351 ± 3 Ma (U–Pb in zircon) within-plate felsic volcanism in the Helez borehole, southern coastal Israel, suggests that the Levant Arch is, instead, extensional in origin. Felsic volcanism was associated with gabbro underplating of the crust, an extreme (~50°C/km) crustal thermal gradient, major uplift, and truncation of the ≥2.5 km section. Taken together with the recent discovery of the ~340 Ma oceanic crust in the Eastern Mediterranean, the Levant Arch is interpreted as an uplifted shoulder of a rift, preceding ocean spreading.     

中天山造山作用的同位素年代分期

我们把近年来所获得的一些年龄数据以及前人已有的年龄数据与区域地层接触关系作了对比,发现二者有意想不到的一致性,据此将中天山造山作用划分为5期,年龄分别大约为452—439Ma,412—402Ma,355—345Ma,334—327Ma和315—289Ma。中生代还可能有3期构造热事件,年龄大约为226—200Ma,165—160Ma和83Ma,代表了中天山的后期演化。上述年龄数据主要是从中天山南缘断裂带构造岩中获得的,它与区域年龄一致,这说明沿中天山两条边界断裂的逆冲推覆可能是导致中天山造山带变形的基本方式和原因。     

塔里木盆地晚志留世-石炭纪伸展构造的发现及其地质意义

通过精细的地震资料解释,在塔里木盆地中部的满西地区发现晚志留世-石炭纪伸展构造。伸展构造由一系列规模不大的正断层组成,平面上组成两条北东-南西向的左行雁列状正断层带,剖面上构成负花状构造和堑垒构造。根据生长系数计算结果,正断层形成于晚志留世,在泥盆纪和石炭纪持续活动,于石炭纪末停止活动。正断层活动的高峰期为晚志留世。该期伸展构造在塔中和塔北地区也有发育,反映当时塔里木盆地处于区域性伸展构造背景。塔里木盆地晚志留世-石炭纪的伸展构造,是昆仑早古生代晚期（晚奥陶世-中志留世）碰撞造山后构造应力松弛作用的产物。     

印支期龙门山造山楔推进作用与前陆型礁滩迁移过程研究

马鞍塘期龙门山前陆盆地是印支期造山楔加载于扬子地台西缘而形成的挠曲前陆盆地。根据地表露头、钻孔剖面和地震反射剖面资料,本文通过分析前陆盆地早期前陆缓坡型鲕粒滩-硅质海绵礁组合在时间和空间上的迁移规律,标定了卡尼期龙门山造山楔的推进速率。结果表明:卡尼期马鞍塘组是分布于底部不整合面之上的第一套地层单元,在垂向上前陆型鲕粒滩-硅质海绵礁组合显示为鲕粒灰岩滩-生物碎屑滩-硅质海绵礁灰岩-泥页岩的向上变细的沉积序列,记录了前缘隆起边缘碳酸盐缓坡和海绵礁的构建和淹没过程,反映了在相对海平面的持续上升中鲕粒滩-硅质海绵礁被淹没致死的过程。在横向上,盆地结构显示为西厚东薄,并向西倾斜的不对称盆地,由西向东依次分布了深水盆地、碳酸盐缓坡和海绵礁和浅水滨岸带等沉积物类型,显示了从龙门山造山楔向前陆一侧具有泥页岩向鲕粒滩-硅质海绵礁的变化特征。其中鲕粒滩-硅质海绵礁丘组合发育于15～30m深度的前陆同斜缓坡上,呈面向西的条带状展布,其走向线与龙门山冲断带的走向大致平行。并可将其划分为7个鲕粒滩-硅质海绵礁相带,表明卡尼期硅质海绵礁丘和滩沿底部不整合面向南东方向的前陆缓坡超覆,其超覆线和相带的走向与龙门山冲断带的走向平行,显示了7条硅质海绵礁丘和滩是随着相对海平上升过程而向南东方向的前陆缓坡超覆过程中逐次形成的。卡尼期硅质海绵礁迁移速率为18mm·yr-1,其与龙门山造山楔推进速率(15mm·yr-1)基本一致,表明印支期龙门山逆冲楔推进速率与前陆鲕粒滩-硅质海绵礁丘迁移速率具有明显的耦合关系。据此,本次提出了龙门山前陆盆地早期前陆型碳酸盐缓坡和硅质海绵礁的迁移模式,其形成的过程为:龙门山造山楔于卡尼期初始构造负载于扬子板块西缘,导致了前陆地区的挠曲沉降,形成了前陆盆地,驱动了相对海平面的持续上升,前陆盆地处于欠补偿状态,当相对海平面上升速率与硅质海绵礁生长速率相同时,在15～30m深度的前陆同斜缓坡上发育了鲕粒滩-硅质海绵礁丘组合,随着龙门山造山楔不断地的向前陆地区推进,前陆盆地内相对海平面持续上升,逐次在前陆缓坡上15～30m深度的的位置开启了新的硅质海绵礁群的生长窗,形成了本区卡尼期7条带状展布的鲕粒滩-硅质海绵礁丘组合。因此,硅质海绵礁的淹没过程和迁移过程是龙门山造山楔向扬子克拉通推进过程的沉积响应,显示了在卡尼期-诺利期松潘-甘孜残留洋盆的迅速闭合和逆冲楔构造负载向扬子板块推进的动力学过程。     

The Grenvillian orogeny in the Altun–Qilian–North Qaidam mountain belts of northern Tibet Plateau: Constraints from geochemical and zircon U–Pb age and Hf isotopic study of magmatic rocks

Numerous Neoproterozoic magmatic and metamorphic events in the Altun–Qilian–North Qaidam (AQNQ) region record Grenvillian orogenesis and amalgamation of the supercontinent Rodinia. However, the tectonothermal regimes responsible for these Neoproterozoic events and the assumed position of the AQNQ in Rodinia remain controversial. Zircon U–Pb age data show that the orthogneiss and paragneiss/schist of the AQNQ experienced concurrent magmatism and metamorphism at 895–925 Ma. Zircon Lu–Hf isotopic data indicate that the gneisses in the AQNQ have ε_Hf (0.9 Ga) values and t_DM2 (Hf) model ages ranging from −5.6 to +3.9 and 1.4 to 1.9 Ga. These data suggest that the early Neoproterozoic magma in the AQNQ was predominately derived from a late Paleoproterozoic–early Mesoproterozoic crustal source between 1.4 and 1.9 Ga, marking an important episode of crustal growth in the AQNQ. The Neoproterozoic magmatism is geochemically characterized by (1) high SiO₂, K₂O, and low P₂O₅; (2) A/CNK ratios >1.0, ranging from 1.03 to 1.09; (3) enrichment in Rb, Th and U, and depletion in Ba, Nb, Ta, Sr, Ti, and Eu. Based on the geochemical resemblance to high-K calc-alkaline I-type granite and zircon Lu–Hf isotope signatures, the Neoproterozoic magmatism in the AQNQ was probably derived from ancient mafic-intermediate igneous rocks in an active continental margin. The Neoproterozoic tectono-magmatic–metamorphic history of the AQNQ, directly associated with the South China block (SCB) and the Tarim block (TB), indicates that the AQNQ and the TB coexisted as a single block in the early Neoproterozoic, which was temporarily connected to the SCB to the north or west in Rodinia during the late stages of the Grenvillian orogeny (950–900 Ma).     

柴北缘前寒武纪岩体（地层）变质年龄 及其对早古生代造山作用的指示

柴北缘前寒武纪岩体（地层）分布广泛。为确定柴北缘地区前寒武纪岩体（地层）受早古生代碰撞造山作用的影响,采用LA-ICP-MS技术,对大柴旦地区前寒武纪黑云斜长片麻岩、斜长角闪岩及石榴子石斜长角闪岩中的锆石进行了U-Pb同位素定年。黑云斜长片麻岩获得479~472Ma的变质年龄,斜长角闪岩获得440Ma和470Ma 2个变质年龄,石榴子石斜长角闪岩获得418.8Ma±3.0Ma的变质年龄。初步确定,柴北缘早古生代造山作用对前寒武纪岩体构成了3次强度不等的变质作用叠加,分别为大洋俯冲末期阶段(495~467Ma)岛弧花岗岩弱热烘烤变质作用、大陆碰撞造山阶段(467~423Ma)区域变质作用、S型花岗岩热动力变质作用和大陆后碰撞造山阶段(423~371Ma) I型花岗岩强烈接触热变质作用。     

Stratigraphy and tectonic evolution of the Kazdağı Massif (NW Anatolia) based on field studies and radiometric ages

The Kazda?? Massif was previously considered as the metamorphic basement of the Sakarya Zone, a microcontinental fragment in NW Anatolia. Our new field mapping, geochemical investigations, and radiometric dating lead to a re-evaluation of previous suggested models of the massif. The Kazda?? metamorphic succession is subdivided into two major units separated by a pronounced unconformity. The lower unit (the Tozlu metaophiolite) is a typical oceanic crust assemblage consisting of ultramafic rocks and cumulate gabbros. It is unconformably overlain by a thick platform sequence of the upper group (the Sar?k?z unit). The basement ophiolites and overlying platform strata were subjected to a single stage of high-temperature metamorphism under progressive compression during the Alpine orogeny, accompanied by migmatitic metagranite emplacement. Radiometric age data obtained from the Kazda?? metamorphic succession reveal a wide range of ages. Metagranites of the Kazda?? metamorphic succession define a U–Pb discordia upper intercept age of ca. 230 Ma and a lower intercept age of 24.8 ± 4.6 Ma. This younger age agrees with ²⁰⁷Pb/²⁰⁶Pb single-zircon evaporation ages of 28.2 ± 4.1 to 26 ± 5.6 Ma. Moreover, a lower intercept age of 28 ± 10 Ma from a leucocratic metagranite supports the Alpine ages of the massif within error limits. Reconnaissance detrital zircon ages constrain a wide range of possible transport and deposition ages of the metasediments in the Sar?k?z unit from ca. 120 to 420 Ma. Following high-temperature metamorphism and metagranite emplacement, the Kazda?? sequence was internally imbricated by Alpine compression, and the lowermost Tozlu ophiolite thrust southward onto the Sar?k?z unit. Field mapping, internal stratigraphy, and new radiometric age data show that the Sar?k?z unit is the metamorphic equivalent of the Mesozoic platform succession of the Sakarya Zone. The underlying metaophiolites are remnants of the Palaeo tethys Ocean, which closed during the early Alpine orogeny. After strong deformation attending nappe emplacement, the unmetamorphosed Miocene Evciler and Kavlaklar granites intruded the tectonic packages of the Kazda?? Massif. During Pleistocene time, the Kazda?? Massif was elevated by EW trending high-angle normal faults dipping to Edremit Gulf, and attained its present structural and topographic position. Tectonic imbrication, erosion and younger E–W-trending faulting were the main cause of the exhumation of the massif.     

Garnet variety and zircon ages in UHP meta-sedimentary rocks from the Jubrique zone (Alpujárride Complex,Betic Cordillera,Spain): evidence for a pre-Alpine emplacement of the Ronda peridotite

The Ronda peridotite is a group of lherzolite slabs (1.5 to 2 km thick) in southern Spain. Despite clear evidence that pre-Alpine events affected pre-Permo-Triassic units from the Alborán domain (internal zone of the Betic-Rif Cordillera, Spain, and Morocco), numerous papers continue to emphasize Alpine metamorphic and structural evolution. Here, we evaluate the pre-Cenozoic evolution of the Ronda peridotite by reporting new petrographic and U–Pb SHRIMP zircon dating of meta-sedimentary rocks from the Jubrique zone (Alpujárride Complex, Betic Cordillera, Spain) directly overlying the Ronda peridotite. Field inspection and petrographical study revealed generalized migmatitic textures and a gradual transition mainly defined by garnet content (from ~30 to <3 wt.%) and size (from 1.5 cm to <0.5 mm) in the overlying granulite-gneiss sequence, suggesting that most garnet grew as a consequence of the peridotite emplacement. Garnet shows notable variations in composition and inclusion types, which are interpreted as reflecting different stages of garnet growth. Diamond-bearing garnets are only well-preserved in gneisses from the uppermost part of the sequence, whereas the large garnets from rocks overlying the peridotite mainly record later thermal events. SHRIMP zircon dating indicates two age peaks at 330 ± 9 and 265 ± 4 Ma. The oldest age characterizes rims overgrowing detrital cores and reflects an early Hercynian metamorphism; the younger age characterizes zircon with magmatic oscillatory zoning, reflecting anatexis. On the basis of these data and of previous dating of monazite included in the large garnets, we conclude that the peridotite was emplaced either shortly before or during early Hercynian times, ~330 Ma.     

内蒙古东七一山花岗岩地球化学、锆石SHRIMP U-Pb年龄及岩体形成环境探讨

古生代时期, 北山地区的地壳活动非常强烈, 主要表现为: 早古生代初期大陆的裂解, 一直到中奥陶世广阔大洋盆的发育。志留纪末, 洋盆在自南向北的俯冲中封闭, 使北侧的哈萨克斯坦板块和南侧的塔里木板块拼贴, 并在碰撞造山过程中又构成了一个相对统一的陆块。在晚古生代, 北山地区地壳又在另外一种形式中异常强烈活动, 特别是自石炭纪到二叠纪, 大规模的中酸性岩浆侵入活动构成本区重要的地质事件, 其出露的花岗岩类占到了全区总面积的近1/3, 但泥盆纪时期的地壳活动, 特别是花岗岩浆的侵入活动常被人们忽视, 笔者据泥盆纪时期的沉积-火山作用及挤压构造活动也较发育认为, 海西早期也应有较强的花岗岩浆侵入活动。本文有针对性地对北山地区, 原定为海西中期的东七一山花岗岩岩基, 在岩石学和地球化学等方面研究基础上, 对3处岩石中锆石首次进行了SHRIMP U-Pb年龄测定, 其结果分别是(355±4) Ma、 (359±4) Ma、(355±5) Ma, 这表明东七一山花岗岩形成于泥盆纪晚期, 从而确定了北山晚古生代早期也有花岗岩浆的强烈活动, 这对深化北山古生代地壳演化过程有积极意义。