共和盆地东北部新生代沉积物源及其地质意义

共和盆地处于秦岭、祁连、昆仑造山系相互叠置的关键区域,盆地及周缘造山带记录的构造、岩浆、变质、沉积作用事件复杂多样,是研究青藏高原北部构造-沉积演化的关键位置。本文以多口钻井的岩心为基础,结合区域地质调查资料对共和盆地东北部进行了岩石组合、沉积类型和沉积相特征分析、碎屑锆石U-Pb年代学、砂岩组分和重矿物分析,明确了共和凹陷新生代的沉积特征、地层发育格架、沉积相类型、沉积物源及构造-沉积演化过程。碎屑锆石年代学分析结果揭示了共和凹陷新生代砂岩具有200~300Ma、400~500Ma、750~1000Ma、1800~2000Ma以及2400~2550Ma的年龄峰值,且主要集中在200~300Ma和400~500Ma,表明三叠纪的侵入岩及浅变质岩是其主要物源。砂岩组分和重矿物分析结果记录到共和盆地东北部在咸水河组和临夏组沉积之间发生过一次构造环境转变,其时共和凹陷的沉积物源发生变化,来自青海南山的物质供给增加。共和盆地东北部共和凹陷新生代沉积物在西宁组-咸水河组沉积时物源方向为NEE方向,而在临夏组沉积时物源方向为NNE方向。青海南山的隆起主要发生在晚中新世-上新世,分隔了青海湖盆地与共和盆地。

     

江汉盆地ZL钻孔微量元素含量的粒度效应与环境意义

江汉盆地是长江出三峡后第一个大型卸载区,近2.77 Ma以来堆积了近300m的碎屑沉积物,主要由河流相和湖沼相组成,形成了多个沉积旋回。选择江汉盆地中心位置的ZL钻孔,利用ICP-MS方法展开微量元素组成分析,细粒组分中微量元素含量与各粒组含量相关性并不明显,主要是5~7粒级组分表现出微弱的相关性.可见,粒度并非ZL钻孔微量元素丰度的主控因素。钻孔岩心中大部分亲石元素、亲硫元素相对上部陆壳均出现明显富集,亲铁元素总体低于上部陆壳,可能与江汉盆地总体上更多地接受了来自上游而非扬子古陆本地深源物质风化碎屑沉积有关。Sr、V/Ni和Sr/Ba值的变化则表明江汉盆地在2.6~2.43 Ma B.P.时可能有咸化湖的发育,而在2.1 Ma B.P.左右存在过一段大湖发育期。     

The Red River sediment budget in the Yinggehai and Qiongdongnan basins,northwestern South China Sea,and its tectonic implications

ABSTRACT

The rapid uplift of the Tibetan plateau, the intense movement of the Ailao Shan-Red River Shear Zone (ARSZ), and the related climate change during the Cenozoic Indo-Asian collision have been widely studied; however, their timings varied considerably due to different data and methods used. As these events have been documented in the Red River sediment that came from the eastern Tibetan plateau and the Red River region and eventually deposited in the offshore Yinggehai and Qiongdongnan basins, here these events can be explored by calculating and analysing the Red River sediment budget, especially in the Qiongdongnan basin based on dense seismic profiles and wells. Results show that the Red River sediment mainly accumulated in the Yinggehai basin and the west part of the Qiongdongnan basin, and there are three sedimentary accumulation peaks in the Red River sediment budget during ~29.5–21, ~15.5–10.5, and ~5.5–0 Ma. By further comparing with previous studies on the timings of these events, it is inferred that the first sedimentary peak, prior to the onset of the monsoon intensification (~22 Ma), was probably driven by an intense left-lateral movement of the ARSZ in ~29.5–21 Ma. The second peak (~15.5–10.5 Ma), however, reflects a rapid uplift of the Tibetan plateau after the cessation of the left-lateral strike slip of the ARSZ. The third peak (~5.5–0 Ma) is most likely linked with a right-lateral movement of the ARSZ and the related climate change. Overall, the Red River sediment budget from the offshore Yinggehai and Qiongdongnan basins provides an important constraint on the timings of these tectonic events as well as the related climate change during the Cenozoic Indo-Asian collision.     

宜昌第四纪砾石层钾长石主、微量元素物源研究及其地质意义

位于长江三峡出口的宜昌地区分布着一套第四纪砂砾石层,详细记录了区域内古环境变迁以及长江的形成与演化,但这些砾石层何时与长江上游物质建立物源关系一直存在较大争议。而钾长石是河流沉积物中常见的矿物,其地球化学元素组成在不同区域内存在显著差异,是进行河流物源对比研究的理想矿物。基于此,利用激光剥蚀电感耦合等离子质谱仪（LA-ICP-MS）对宜昌第四纪砾石层和宜昌以上长江流域开展碎屑钾长石原位主微量元素和主成分（PCA）分析,结合砾石层已发表的地层沉积年龄,综合区域内已发表的研究结果,系统对比分析宜昌砾石层与长江上游物质建立物源联系的时间,结果表明在1.15 Ma时宜昌砾石层和长江流域存在物源关系;在0.75 Ma时随着长江上游水系的拓展与调整,有新物源区的物质进入长江。这些物源变化现象,主要体现了1.2~0.7 Ma期间长江流域受东亚和南亚夏季风的气候影响出现的沉积过程。      

Geochemical and Nd isotope composition of detrital sediments on the north margin of the South China Sea: provenance and tectonic implications

A major re‐organization of regional drainages in eastern Tibet and south‐western China took place in the Cenozoic as deformation from the growing Himalayas and Tibetan Plateau affected an increasingly wider area. The effects of these changes on the regional sediment routing systems is not well constrained. This study examines the geochemical and Nd signatures of sedimentary rocks from the Ying‐Qiong and Nanxiong basins on the northern margin of the South China Sea to constrain and identify any significant changes in sediment source. Upper Cretaceous to Lower Eocene sedimentary rocks in the Nanxiong Basin show higher Th/Sc, La/Sc, Th/Cr and Th/Co ratios and lower Eu/Eu* ratios than PAAS (post‐Archaean Australian Shale), which indicates that Palaeozoic sedimentary rocks of the South China Block were the main basin sediment source. In contrast, Oligocene to Pleistocene sedimentary rocks of the Ying‐Qiong Basin show an abrupt change in these trace‐element ratios between 16·3 and 10·4 Ma, indicating a mid‐Miocene shift in provenance. ɛ_Nd values from the Ying‐Qiong Basin (range = −11·1 to −2·1) reinforce this, with pre‐13·8 Ma sedimentary rocks having average ɛ_Nd of −5·6 (range = −2·1 to −7·4), and post‐13·8 Ma sedimentary rocks having average ɛ_Nd of −9·3 (range = −8·7 to −11·1). During the Oligocene, the centre of rifting transferred south and basins on the north margin of the South China Sea experienced rapid subsidence. Further uplift and erosion then exposed Mesozoic and Cenozoic granites that supplied large amounts of granitic detritus, especially to the Ying‐Qiong Basin. Then a change occurred at ca 13 Ma resulting in less input from local sources (i.e. the fault blocks formed by Mesozoic‐Cenozoic tectonics and magmatism) to an increasing contribution of older continental material, mostly from Indochina to the west of the South China Sea.     

Chronology of subduction and collision along the İzmir-Ankara suture in Western Anatolia: records from the Central Sakarya Basin

ABSTRACT

Western Anatolia is a complex assemblage of terranes, including the Sakarya Terrane and the Tauride-Anatolide Platform that collided during the late Cretaceous and Palaeogene (80–25 Ma) after the closure of the Izmir-Ankara Ocean. Determining the precise timing at which this ocean closed is particularly important to test kinematic reconstructions and geodynamic models of the Mediterranean region, and the chronology of suturing and its mechanisms remain controversial. Here, we document the Cretaceous-Eocene sedimentary history of the Central Sakarya Basin, along the northern margin of the Neotethys Ocean, via various approaches including biostratigraphy, geochronology, and sedimentology. Two high-resolution sections from the Central Sakarya Basin show that pelagic carbonate sedimentation shifted to rapid siliciclastic deposition in the early Campanian (~ 79.6 Ma), interpreted to be a result of the build-up of the accretionary prism at the southern margin of the Sakarya Terrane. Rapid onset of deltaic progradation and an increase in accumulation rates in the late Danian (~ 61 Ma), as well as a local angular unconformity are attributed to the onset of collision between the Sakarya Terrane and the Tauride-Anatolide Platform. Thus, our results indicate that though deformation of the subduction margin in Western Anatolia started as early as the Campanian, the closure of the ?zmir-Ankara Ocean was only achieved by the early Palaeocene.     

Provenance of Permian Delaware Mountain Group,central and southern Delaware Basin,and implications of sediment dispersal pathway near the southwestern terminus of Pangea

ABSTRACT

The Delaware Basin is located near the southwestern end of the Alleghanian–Ouachita–Marathon orogenic belt. The basin is mostly filled by Permian clastic rocks of the Delaware Mountain Group with ramp- to shelf-carbonate rimming basin edges. The Delaware Mountain Group has been well-documented as a deep-water clastic reservoir unit in the prolific Permian Basin, but its sources and related sediment dispersal pathways remain inconclusive. In this study, a total of 55 samples of the Delaware Mountain Group were collected from whole core and sidewall core from the central and southern Delaware Basin, and sandstone modal analyses and U-Pb detrital zircon geochronology were applied to constrain their potential sources. Sandstone modal analyses show that the majority of samples fall within the transitional continental source field. Age spectra of detrital zircon from five selected samples include a prominent middle Palaeozoic age cluster (~490–275 Ma), a major Neoproterozoic to early Palaeozoic age cluster (~790–510 Ma), and a series of minor age clusters of the middle to late Mesoproterozoic (~1300–920 Ma), early Mesoproterozoic (~1600–1300 Ma), late Palaeoproterozoic (~1825–1600 Ma), and Archaean and Palaeoproterozoic (> ~1825 Ma). Integrating detrital zircon data from all potential sources and coeval sandstones from the northern Delaware Basin suggests that the majority of sediment was derived from the Appalachian foreland, the Ouachita orogenic system, and the peri-Gondwanan terranes. Variation in the abundance of the different age groups reveals a provenance shift between deposition of the Brushy Canyon Formation and the Cherry and Bell Canyon Formations. To accommodate the composition, and the stratigraphic and spatial age spectral variations, we proposed that the sediment dispersal pathway includes a transcontinental fluvial system from the Appalachian orogenic belt to the east, a regional scale fluvial system from the Ouachita orogenic belt to the north and northeast, and a local, proximal fluvial system from the peri-Gondwanan terranes to the south and southeast.     

柴达木路乐河地区新生代碎屑组分变化及其对构造隆升的指示

碎屑组分变化是反映盆地物源演化历程的重要物质表现。路乐河地区作为柴达木盆地的重要组成部分,沉积地层记载着印度-欧亚板块碰撞以来青藏高原北缘造山带的构造隆升过程。高长石组分含量、物源方向及毗邻山脉岩性对比揭示,路乐河物源主要受南祁连和赛什腾山控制,其碎屑组分变化对毗邻造山带构造活动具有很好的耦合性。新生代53.5~2.9Ma期间,路乐河地区存在3次物源转换事件,发生时间依次同印度-欧亚板块碰撞及高原内部构造隆升事件相吻合。其中早期50.1~46.6Ma,南祁连山的快速抬升是对大陆初始碰撞的远程响应;44.5Ma,高原以垂向增生和推覆构造发育为特点,赛北断裂高速剥露,致使路乐河地区物源发生转变;渐新世末期(22.6Ma),青藏高原准同时整体隆升,赛什腾山和南祁连山协同为路乐河地区供给沉积物。所获认识为深入了解高原隆升演化和板块碰撞远程效应提供新的沉积依据。     

刚果盆地西南缘Inkisi组碎屑锆石U-Pb年代学: 对地层时代及物源的约束

Inkisi组是泛非运动之后刚果盆地最早的沉积地层之一。确定Inkisi组地层时代、物源及恢复构造演化过程,对研究刚果盆地的演化具有重要地质意义。本文通过对Inkisi组碎屑锆石进行U-Pb年代学研究,深入探讨了其形成时代,对泛非运动进行了约束,并进一步探讨了其物源。研究发现,Inkisi组下段与上段碎屑锆石最小年龄分别为526±6 Ma和534±14 Ma,最年轻的4颗锆石的加权平均年龄为532±9.4 Ma,由此限定了Inkisi组的最大沉积时代。因此将其时代划归早寒武世,并将其从新元古界Xisto-Gresoso群解体。另外,Inkisi组岩石并未发生变质变形,也说明其形成于泛非运动之后。碎屑锆石年龄谱结果显示,Inkisi组碎屑锆石的年龄变化范围较广,整体呈现五个年龄峰值：＞2800 Ma、2800~2400 Ma、2100~1750 Ma、1500~900 Ma、850~500 Ma。通过将年龄峰值及周围地质体进行对比,认为西刚果造山带、卡赛克拉通、安哥拉克拉通是其主要的物源,卢弗里安构造带等是其次要物源。     

阿尔金断裂带年代学和阿尔金山隆升

对阿尔金山断裂带内变形的中生代剪切带中眼球状片麻岩、糜棱岩化花岗片麻岩和新生代剪切带中强变形绿片岩系列样品中同构造新生云母矿物的40Ar-39Ar法定年,获得了164.3~178.4Ma和26.3~36.4Ma两组年龄。结合阿尔金走滑断裂水平错距的研究,认为164.3~178.4Ma的年龄代表阿尔金走滑断裂带的起始活动时间(早侏罗世末—中侏罗世),尔后分别在距今100~85Ma,40~25Ma和10~8Ma发生多次脉冲式走滑活动。新生代沉积物研究表明上干柴沟组和下干柴沟组砂岩骨架矿物成份含量明显不同,随时间变化,石英含量减少,岩屑组份和不稳定矿物含量增加,分选性逐渐变差。这表明阿尔金山在渐新世(下干柴沟组时期)开始发生明显的隆升。地震和柴达木—塔里木盆地沉积速率资料显示在晚中新世山体也发生了一次强烈的隆升。七个泉组(上新世末—早更新世初)和下伏沉积物(上新世中期)之间的角度不整合反映了最后一次强烈隆升事件发生在晚上新世。多数隆升事件和阿尔金断裂带新生代脉冲式活动的同位素年龄完全一致,表明阿尔金山的隆升和断裂带的活动具有密切的成因联系。     

http://www.sciencedirect.com/science/article/pii/S1674987114000693

The Yangtze River is one of the most important components of the East Asia river system.In this study,sediments in the Jianghan Basin,middle Yangtze River,were selected for trace element and rare earth element(REE)measurements,in order to decipher information on the change of sediment provenance and evolution of the Yangtze River.According to the elemental variations,the late Cenozoic sediments of the Jianghan Basin could be divided into four parts.During 2.68e2.28 Ma and 1.25e0 Ma,provenance of the sediments was consistent,whereas sediments were derived from variable sources during2.28e1.25 Ma.Comparison of the elemental compositions between the Pliocene and Quaternary sediments revealed a change in sediment source from a more felsic source area to a more basic source area around the PlioceneeQuaternary boundary.Input from the Emeishan LIP should account for this provenance change.Based on the provenance analysis of sediments in the Jianghan Basin,we infer that the Yangtze River developed into a large river with its drainage basin extended to the Emeishan LIP no later than the PlioceneeQuaternary boundary.     

Subduction and collision processes between the North China and South China blocks constrained by the geochronology and geochemistry of the Wuguan Complex in the Qinling orogen,China

ABSTRACT

The Qinling orogen is a key area for understanding the processes of subduction and collision between the South China Block (SCB) and North China Block (NCB). The Wuguan Complex, distributed along the southern margin of the Shangdan suture zone, can provide important constraints on the age of collision between NCB and SCB and the tectonic evolution of the Qinling orogen in Late Paleozoic. Detrital zircons from meta-sedimentary rocks of the Wuguan Complex in the Danfeng-Shangnan area have an age spectrum with two main peaks at ~448 Ma and ~819 Ma, and two subordinate peaks at ~938 and ~1440 Ma, respectively, and are interpreted to have been derived from the North Qinling terrane (NQT). The petrographic and geochemical characteristics of the meta-sedimentary rocks indicate that they were deposited in a fore-arc basin along the southern margin of the NQT. The youngest detrital zircons yield a weighted mean age of 378 ± 3 Ma, indicating that the fore-arc deposition was continuing at least to this time, which implies that the Paleo-Qinling Ocean between the NCB and SCB was not finally closed until at least the late Devonian. In combination with regional data, we propose that sedimentary rocks of the Wuguan Complex might once have been a sequence of late Ordovician to late Devonian strata with intercalated mafic rocks, which has been dismembered by the later tectonic activity. It was metamorphosed during northward subduction of the Paleo-Qinling Ocean at ca. 320 Ma, and slowly cooled through ca. 350°C at ca. 247 Ma (muscovite ⁴⁰Ar/³⁹Ar age). It has recorded the detailed processes of subduction and collision between the NCB and SCB.     

柴西红沟子地区晚新生代沉积特征及其对阿尔金山隆升的约束

柴达木盆地是青藏高原东北缘的一个山间盆地,发育了巨厚的中-新生代地层,详细记录了盆地及周缘山地的构造活动历史。本文通过对柴达木盆地西北部厚约1040m并具有精确古地磁年代控制的红沟子剖面（包括下油砂山组、上油砂山组、狮子沟组和七个泉组）开展精细沉积学研究,包括岩性特征与沉积相、砾岩与砂岩含量变化、剖面沉积速率变化特征以及沉积区物源分析等,结果表明：1）红沟子剖面晚新生代沉积相经历了下油砂山组（>17.0Ma） 的冲积扇或扇三角洲平原相到上油砂山组（17.0~9.8Ma）扇三角洲前缘-半深湖-扇三角洲前缘相,再到狮子沟组（9.8~5.0Ma）扇三角洲前缘相,最后转为七个泉组（16.5Ma、9.8Ma以及16.5~5.0Ma）沉积物可能主要来自北部的阿尔金山地区。基于上述认识,将红沟子剖面晚新生代沉积划分为5个演化阶段：1）>16.5Ma 主要以粗颗粒砾岩为主的冲-洪积相沉积;2）16.5~9.8Ma 沉积环境主要为半深湖或前扇三角洲,以泥岩或泥灰岩等细颗粒为主,沉积速率较低;3）9.80~8.53Ma 沉积环境为扇三角洲前缘,岩性变粗且有大套砾岩堆积,沉积速率达到剖面最高值,并在9.8Ma存在不整合面;4）8.53~7.48Ma沉积环境基本与上一阶段类似,砾岩含量减少,砂岩沉积相对增加,沉积速率呈现低值特征;5）7.48~5.00Ma 主要是扇三角洲前缘沉积环境,砂岩含量较高,沉积速率较高。因此,进而分析指出构造活动是影响研究区沉积特征演化的主要因素,并建立了研究区及周缘新生代构造与沉积特征演化模式图。综合对比前人资料,发现红沟子剖面沉积特征在9.8Ma的变化,特别是沉积速率的陡增在阿尔金山具有普遍性,与前人不同方法捕获的晚新生代阿尔金山乃至整个高原东北部地区的构造隆升时间基本一致,认为红沟子剖面沉积特征在9.8Ma的突变可能是对阿尔金山乃至青藏高原东北缘约10Ma一次大范围隆升事件的响应。     

断层与幔源二氧化碳气藏的形成和分布——以渤海湾盆地济阳坳陷为例

幔源CO_2气的形成和分布与不同级别断层早白垩世以来的活动密切相关。郯庐断裂带是研究区最主要的成气断层,拆离断层和变换断层这些地壳断层是次要的成气断层,二者于早白垩世143Ma、124Ma、新生代~43Ma、~24Ma和~8Ma的走滑或伸展活动,以及与之准同时的新生代碱性玄武岩浆活动,控制了幔源CO_2气的分散和聚集。它们与基底断裂、盖层断裂共同组成运移通道,其中拆离滑脱处的低速带和盖层断裂中的顺层断层是重要的水平运移通道。早白垩世古太平洋板块俯冲脱水脱气,产生的幔源CO_2气沿着郯庐断裂带向上分散聚集;新生代以来受控于太平洋板块俯冲方向和速度的改变以及印欧板块碰撞的远程效应,形成幔源CO_2气。与此同时郯庐断裂带切割深度亦逐渐加大,~43Ma碱性岩浆活动亦开始形成幔源CO_2气并主要位于断裂带,24Ma和8Ma(5Ma)为新近纪碱性岩浆活动脱气两个主要形成时期。郯庐断裂带的活动使地幔脱气形成的CO_2沿断层走向向上运移,并在作为重要横向运移通道的拆离断层拆离滑脱处,与因岩浆脱气形成的CO_2汇合,再通过陡倾斜、缓倾斜基底断层、盖层断层的接力传递在浅部聚集成藏。预测郯庐断裂带附近是无机成因油气重要的聚集分布区带。     

青藏高原东北缘龙首山晚新生代多阶段构造隆升的盆地记录

龙首山地区位于青藏高原与阿拉善地块的结合部位,其盆山演化过程和断裂带扩展模式的恢复对揭示青藏高原新生代北东向生长具有重要意义。本文基于龙首山南北两麓3个新近系沉积剖面的构造特征和5个砂岩样品的碎屑锆石U-Pb同位素LA-ICP-MS年龄结果,重建了青藏高原东北缘龙首山地区晚新生代的盆山演化过程。研究结果显示,龙首山地区晚新生代沉积-构造演化经历了3个主要阶段：（1）~14Ma,龙首山南缘断裂带活化,阿拉善地块南缘沿此断裂逆冲于张掖盆地之上,张掖盆地开始接收阿拉善地块的物源;（2）~5Ma,龙首山南缘断裂带的次级断裂开始发育,使龙首山南侧山麓白垩系开始剥露并为张掖盆地提供物源,同时,龙首山北缘断裂带活化并导致潮水盆地发生挠曲沉降,接收龙首山的物源;（3）5~2.5Ma,龙首山北缘断裂带的次级断裂开始发育,导致龙首山北麓白垩系开始剥露并为潮水盆地提供物源。通过对龙首山周缘盆地沉积相和物源开展分析,本研究反演了龙首山地区中新世以来的断裂带活动和山体隆升过程,表明在14~2.5Ma,随着龙首山南缘断裂、北缘断裂的活化和次级断裂的发育,龙首山经历了3次强烈的隆升,这对揭示青藏高原北东向的扩展过程具有重要的指示意义。

     

Provenance of the Langjiexue Group to the south of the Yarlung-Tsangpo Suture Zone in southeastern Tibet: Insights on the evolution of the Neo-Tethys Ocean in the Late Triassic

ABSTRACT

The Upper Triassic Langjiexue Group, which lies immediately south of the Yarlung-Tsangpo Suture Zone in the Shannan area of southeastern Tibet, represents an important part of the Tethyan Himalayan Sequence (THS). Its provenance and palaeogeography have been the subject of debate. We present new data on petrographic composition, whole-rock geochemistry, and detrital zircon U–Pb geochronology to constrain the provenance of the Langjiexue Group. The dominance of quartz grains and felsic volcanic lithic fragments suggests that the sandstones are litho-quartzose. The trace element geochemical signatures (V–Ni–Th*10, Co/Th–La/Sc, Eu/Eu*–Th/Sc) suggest derivation from felsic igneous sources. The detrital zircon age spectra display three major peaks: a Meso-to-Neoproterozoic peak (1200–900 Ma, 7–18%), a Neoproterozoic-to-Late Cambrian peak (750–500 Ma, 32–65%), and a Late Carboniferous-to-Late Triassic peak (300–200 Ma, 11–33%). The maximum depositional age of early Carnian (236–235 Ma) is obtained by calculating weighted average ages of the youngest zircons (≤250 Ma). The youngest age cluster (300–200 Ma) is incompatible with sources from neighbouring terranes, including the South Qiangtang terrane, Lhasa terrane, THS, and Higher Himalayan Crystalline. Correlations of the Permian–Triassic zircons with those of time-equivalent strata in northwest Australia, west Burma, and the Banda Arc unveil a potential connection to the Tasmanides along the convergent margin of eastern Australia. The New England Orogen (300–230 Ma) could have supplied the Langjiexue Group with magmatic materials via continent-scale drainage systems or a submarine fan complex. This scenario provides a new perspective into the transport of detritus from distal orogens to sedimentary basins thousands of kilometres away.     

Geologic evolution of a Cretaceous tectonometamorphic unit in the Franciscan Complex,western California

ABSTRACT

The Franciscan Yolla Bolly terrane of the NE California Coast Ranges consists mainly of quartzose metagreywackes containing sparse high-pressure/low-temperature (HP/LT) neoblastic minerals, including ubiquitous lawsonite. Some Yolla Bolly rocks also contain one or more of the newly grown phases, pumpellyite, aragonite, glaucophane, and/or jadeitic pyroxene. These blueschist-facies metasandstones recrystallized under physical conditions of ~200–300°C and ~8 kbar at subduction-zone depths approaching 30 km. Petrologically similar Franciscan metaclastic-rich map units – Yolla Bolly terrane-like rocks, here designated the ‘YB’ unit – crop out in the central and southern California Coast Ranges. Recently published detrital zircon U?Pb SIMS and LA-ICPMS data for 19 ‘YB’ metagreywackes indicate maximum ages of formation as follows: ~110–115 Ma (8) in the NE California Coast Ranges; ~95–107 Ma (7) in the San Francisco Bay area + Diablo Range; and ~85–92 Ma (4) in the dextrally offset Nacimiento Block. These fault-bounded ‘YB’ strata do not constitute coeval parts of a single tectonostratigraphic unit. Instead the term tectonometamorphic is proposed for such time-transgressive map units. Based on the current and likely Cretaceous 30° angular divergence between NS-palaeomagnetic stripes of the Farallon oceanic plate and the NNW-trending California convergent margin, I infer that arrival at the arc margin and underflow of a relatively thick segment of oceanic crust and its largely clastic sedimentary blanket may have resulted in progressive southeastward migration of an accreted, subducted, then exhumed HP/LT metagreywacke section. During the ~30 million year interval, ~115–85 Ma, the locus of ‘YB’ accretion, underflow, and tectonic regurgitation evidently moved SE along an ~1000 km stretch of the accretionary margin of western California.     

祁连山北缘酒西盆地新生代沉积通量变化对周缘山体构造隆升-风化剥蚀历史的响应

酒西盆地是青藏高原东北缘的一个内陆沉积盆地,发育了巨厚且连续的中-新生代地层,详细记录了盆地及周缘山地的构造、环境演变历史。本文在利用平衡剖面法恢复不同时期酒西盆地原始盆地边界基础上,通过盆地天然露头控制剖面和钻井资料的地层厚度,恢复了酒西盆地新生代各组沉积等厚图。根据不同时期盆地大小和沉积等厚图的计算,获得了酒西盆地新生代不同时期的沉积通量。结合前人对该区构造与古气候研究成果,认为古近纪持续干旱的气候条件下从火烧沟组(40.2~33.4 Ma)到白杨河组(30.9~23.8 Ma)盆地沉积通量增加主要由青藏高原持续挤压使祁连山快速构造隆升导致风化剥蚀量增加所致;中新世早期(疏勒河组弓形山段,23~14 Ma)虽然气候相对温暖,但此时祁连山构造带相对稳定,控制了物源区祁连山风化剥蚀量相对前期减小,使盆地沉积通量相对减小;中新世中期(疏勒河组胳塘沟段,14~8.3 Ma)盆地沉积通量增大可能是气候和构造共同作用的结果;中新世晚期以来(<8.3 Ma,疏勒河组牛胳套段-玉门组)盆地沉积通量呈阶段性大幅陡增,主要由祁连山晚新生代以来阶段性急剧构造隆升导致风化剥蚀量猛增所致。     

Age,petrologic significance and provenance analysis of the Hamedan low-pressure migmatites; Sanandaj-Sirjan Zone,west Iran

ABSTRACT

Meta-pelitic rocks with interlayers of meta-psammites within the inner thermal aureole of the Alvand plutonic complex (Sanandaj-Sirjan Zone (SaSZ), western Iran) underwent partial melting; generating various types of migmatites. The mesosome of the Hamedan migmatites is classified into two groups: (1) cordierite-rich and Al-silicate-poor mesosomes and (2) cordierite-poor, Al-silicate-rich groups. Leucosomes are also variable, ranging from plagioclase-rich to K-feldspar-rich leucosomes. Mineral-chemical studies and thermobarometric estimations indicate temperature and pressure of 640–700°C and 3–5 kbar, respectively, for the formation of mesosomes. U–Pb zircon geochronology on 214 grains from the mesosome of migmatites indicates ages of 160–180 Ma (ca ~170 Ma) for zircon metamorphic rims and variable ages of 190–2590 Ma for the inherited detrital zircon cores. Inherited core ages show various age populations, but age populations at 200–600 Ma are more frequent. The age populations of the detrital zircons clarify that the provenance of the younger zircon grains (200–500 Ma) was more likely the Iranian plate, whereas the older grains (600 Ma to >2.5 Ga) may be sourced from both northern Gondwana (such as Arabian-Nubian Shield) and the neighbouring, old cratons like as Africa. We suggest that magmatic activities, especially mafic plutonism at ~167 Ma, are the main triggers for the heat source of metamorphism, partial melting, and migmatization. In contrast to a presumed idea for a Cretaceous regional metamorphic event in the NW parts of the SaSZ, this study attests that the metamorphism should be older and can be associated with Jurassic magmatic pulses.     

柴达木盆地新生界碎屑锆石FT年龄对蚀源区的约束

柴达木盆地新生界碎屑锆石裂变径迹年龄的研究表明, 沉积物主要蚀源区是遭受海西-印支运动影响的盆地周缘山地, 燕山运动仅在柴西阿尔金山有所表现。揭示出蚀源区发生过多次的(热) 构造运动, 在柴北缘有5次( ～284.5 Ma、～263.6 Ma、～243.6 Ma、～221.6 Ma和～199.8 Ma) , 而在柴西则有6次( ～344.2 Ma、～275.2 Ma、～244.9 - 246.8 Ma、～210 - 220.3 Ma、～186.9 - 195.7 Ma和～162.9 Ma) , 说明青藏高原北部在前新生代具有多阶段、同步整体隆升特点。进入新生代, 柴达木盆地及其周缘山带构造活动具有强-弱-强的特征。