三维古地貌重建技术在中生代羌塘地体古地理演化分析中的应用     

于淼  陈建平  严琼  武瞾  王春女  于萍萍 《地质通报》2011,30(5):694-701

近年来,从古地貌-沉积组合与油藏关系的角度进行油气远景评价成为研究热点。针对古地貌的复原研究,提出一种建立三维古地貌模型的方法,将二维平面古地理图通过对资料的整理、挖掘与转换,并结合GIS技术生成了三维立体模型,补充了区域地形地貌的相关信息。利用该方法,建立了青藏高原油气资源潜力最大的区域——羌塘地体在三叠纪和侏罗纪的一系列三维古地貌模型,进而对其古环境和演化过程进行分析,这对于该区域的沉积矿产资源的预测与评价有重要的参考价值。  相似文献   

Metamorphism of the Amdo metamorphic complex,Tibet: implications for the Jurassic tectonic evolution of the Bangong suture zone   总被引：5，自引：0，他引：5  

J. Guynn  P. Tropper  P. Kapp  G. E. Gehrels 《Journal of Metamorphic Geology》2013,31(7):705-727

Tibet consists of several terranes that progressively collided with the southern margin of Asia during the Mesozoic following the closure of intervening ocean basins. This Mesozoic amalgamation history, as well as the extent to which it may have contributed to crustal thickening prior to the Cenozoic Indo‐Asia collision, remains poorly constrained and strongly debated. Here, we present a metamorphic petrological and U‐Pb zircon geochronological study of the Amdo metamorphic complex, one of the few exposures of high‐grade metamorphic rocks in central Tibet, located along the Bangong suture between the Qiangtang terrane to the north and the Lhasa terrane to the south. U‐Pb ages of metamorphic zircon in gneiss constrain the timing of peak metamorphism at c. 178 Ma, prior to the Early Cretaceous collision between the two terranes. Peak P–T conditions of gneiss within the metamorphic complex are constrained by conventional as well as multi‐equilibrium (THERMOCALC v.3.21 and v.3.33) geothermobarometry of two samples of garnet‐amphibolite. Whereas THERMOCALC v.3.21 yields similar results as conventional geothermobarometry, THERMOCALC v. 3.33 yields dramatically lower pressures, mostly due to the change in the amphibole activity model used. Using THERMOCALC v.3.21, the two garnet‐amphibolite samples yield similar P–T conditions of 0.83 ± 0.06 GPa at 646 ± 33 °C and 0.97 ± 0.06 GPa at 704 ± 35 °C. Plagioclase coronas on the garnet‐amphibolite sample with lower peak P–T conditions indicate a period of isothermal decompression. Additional geothermometry on two garnet‐free amphibolites yielded similar temperatures of 700–750 °C and suggests similar P–T conditions across most of the complex. However, two exposures of garnet‐kyanite schist located along the southern edge of the metamorphic complex yielded slightly lower peak conditions of 0.75–0.85 GPa and 550–610 °C. Petrographic and field relations suggest the difference in metamorphic grade between the schist and gneiss is due to an intervening thrust fault. The existence of the thrust fault indicates that at least part of the exhumation of the complex was due to contractional deformation, possibly during the Lhasa‐Qiangtang collision. Our P–T–t results indicate the occurrence of a significant Early Jurassic tectonothermal event along the southern, active margin of the Qiangtang terrane that deeply buried the Amdo rocks. We suggest that the metamorphism is a result of arc‐related tectonism that may have been regionally extensive along the southern Qiangtang terrane; geological records of this tectonism may be rarely exposed along strike because of a lack of exhumation or subsequent depositional and structural burial.  相似文献   

西藏措勤晚白垩世英安岩的厘定与地球化学特征   总被引：1，自引：0，他引：1  

王伟  曾令森  刘静  肖萍  高利娥 《地质科学》2013,48(2):484-500

野外地质调查和SHRIMP锆石U/Pb地质年代学研究表明,拉萨地块中带措勤地区发育一套形成于晚白垩世中期的英安岩(88.5±1.2 Ma)。该套火山岩具有岛弧火山岩的地球化学特征,为地壳深部岩浆岩部分熔融形成的Ⅰ型岩浆岩,经历了明显的斜长石分离结晶作用。与同时代的侵入岩相比,该套火山岩为高度演化的岩浆,Rb/Sr比值较高,但Sr/Y比值较低。在拉萨地块内部,广泛发育的90～85 Ma的岩浆作用与新特提斯洋的北向俯冲作用相关。  相似文献   

Arc magmatism in the Delhi Fold Belt: SHRIMP U–Pb zircon ages of granitoids and implications for Neoproterozoic convergent margin tectonics in NW India     

《Journal of Asian Earth Sciences》2013

The northwestern region of Peninsular India preserves important records of Precambrian plate tectonics and the role of Indian continent within Proterozoic supercontinents. In this study, we report precise SHRIMP zircon U–Pb ages from granitoids from the Sirohi terrane located along the western fringe of the Delhi Fold Belt in Rajasthan, NW India. The data reveal a range of Neoproterozoic ages from plagiogranite of Peshua, foliated granite of Devala, and porphyritic granite of Sai with zircon crystallization from magmas at 1015 ± 4.4 Ma, 966.5 ± 3.5 and 808 ± 3.1 respectively. The plagiogranite shows high SiO₂, Na₂O and extremely low K₂O, Rb, Ba, comparable with typical oceanic plagiogranites. These rocks possess low LREE and HREE concentrations and a relatively flat LREE–HREE slope, a well-developed negative Eu-anomaly and conspicuous Nb and Ti anomalies. Compared to the plagiogranite, the foliated Devala granite shows higher SiO₂ and moderate Na₂O, together with high K₂O and comparatively higher Rb, Ba, Sr and REE, with steep REE profiles and a weak positive Eu anomaly. In contrast to the plagiogranite and foliated granite, the porphrytic Sai granite has comparatively lower SiO₂ moderately higher Na₂O, extremely high Y, Zr, Nb and elevated REE. The geochemical features of the granitoids [HFSE depletion and LILE enrichment, Nb- and Ta-negative anomalies], and their plots in the fields of Volcanic Arc Granites and those from active continental margins in tectonic discrimination diagrams suggest widespread Neoproterozoic arc magmatism with changing magma chemistry in a protracted subduction realm. Our results offer important insights into a long-lived active continental margin in NW India during early and mid Neoproterozoic, consistent with recent similar observations on Cryogenian magmatic arcs widely distributed along the margins of the East African Orogen, and challenge some of the alternate models which link the magmatism to extensional tectonics associated with Rodinia supercontinent breakup.  相似文献   

滇西保山地块东缘晚三叠世何珠次英安斑岩的发现 及其地质意义     

廖世勇  尹福光  孙志明  王冬兵  唐渊  孙洁 《地质通报》2013,32(7):1006-1013

在野外地质调查和岩相学观察的基础上,对保山地块东缘何珠次英安斑岩进行了LA-ICP-MS锆石原位U-Th-Pb同位素测定,得到16个测定点的206Pb/238U年龄加权平均值为216.8Ma±2.2Ma。该年龄值反映了岩体的侵位时间,表明其属于晚三叠世,而非前人认为的新生代。结合岩相学和前人地球化学研究资料分析认为,岩体具有I型和S型花岗岩的特征,反映了其在矿物和地球化学组成上的不平衡,应为幔源高温基性岩浆与壳源岩浆混合形成的,且前者占主导地位。这是昌宁-孟连结合带西侧首次报道幔源物质对晚三叠世岩浆活动的参与,表明保山地块在碰撞后地壳熔融过程中伴随地幔物质的上涌。研究表明,以何珠岩体为代表的次英安斑岩并非前人认为的新生代,保山地块南端前人划分的新生代岩体群的分布范围和规模可能需要重估。  相似文献   

苏鲁超高压地体部分熔融时间的厘定：荣成花岗质片麻岩中浅色条带的锆石U-Pb定年、微量元素和Lu-Hf同位素证据   总被引：2，自引：1，他引：1  

续海金  宋衍茹  叶凯 《岩石学报》2013,29(5):1594-1606

威海-荣成地区混合岩化花岗质片麻岩为研究超高压地体折返过程中的部分熔融提供了理想的窗口。本文通过对荣成地区鲍村花岗质片麻岩中浅色条带野外观察、岩相学以及锆石的CL图像、U-Pb定年、微量元素和Lu-Hf同位素的系统研究表明,鲍村花岗质片麻岩中的浅色条带为部分熔融的产物,其主要矿物组成为石英+斜长石+钾长石+黑云母。锆石CL图像显示清楚的核-边结构:继承岩浆核和新生岩浆边。继承核的206Pb/238U协和年龄为620±8～784±7Ma(Mean=701±33Ma);具有典型的岩浆锆石的微量元素特征,如重稀土(HREE)和Y富集,强烈的正Ce异常和负Eu异常,以及极低的(Gd/Lu)N和Hf/Y比值;εHf(t=700Ma)值为-13.0～-8.0(Mean=-10.9±0.8),相应的tDM2为2120～2429Ma(Mean=2303±51Ma)。新生边的206Pb/238U协和年龄为211±6～244±5Ma(226±10Ma);虽然微量元素的整体含量低于继承核,但也具有岩浆锆石的微量元素特征,如稀土元素配分模式显示HREE明显上翘的特征,正Ce异常和负Eu异常,以及极低的(Gd/Lu)N比值;εHf(t=225Ma)值为-17.3～-14.2(Mean=-15.2±0.6),相应的tDM2为2152～2347Ma(Mean=2214±33Ma)。上述特征表明,部分熔融的原岩是由古元古代(2.2～2.3Ga)的地壳物质在新元古代(701±33Ma)重熔而成,部分熔融可能发生在超高压地体折返早期的热折返阶段(榴辉岩相-高压麻粒岩相条件下),时代应为226±10Ma。威海-荣成混合岩化片麻岩内广泛发育的富含钾长石和石英的酸性岩脉(约220～210Ma),可能为折返晚期的角闪岩相冷凝阶段,部分熔融形成的熔体经历了结晶分异作用的产物。  相似文献   

拉萨地体东南缘始新世早期变质作用及其构造意义   总被引：1，自引：1，他引：0  

林彦蒿  张泽明  董昕 《岩石学报》2013,29(6):1962-1976

本文对位于青藏高原拉萨地体东南缘林芝杂岩中的片麻岩进行了岩石学和锆石U-Pb年代学研究.所研究的样品包括正片麻岩和副片麻岩,它们经历了中压角闪岩相变质作用.岩石地球化学分析结果表明,所研究的正片麻岩的原岩具有钙碱性岛弧岩浆岩的特征.锆石U-Pb年代学分析结果表明,副片麻岩中的碎屑锆石核部为岩浆成因,它们给出的206Pb/238U年龄范围为3012～ 522Ma,其锆石的增生边给出了～51Ma的变质年龄.在正片麻岩中,黑云母片麻岩给出了～67Ma的原岩结晶年龄和～ 55 Ma的变质年龄;石榴石角闪黑云斜长片麻岩给出了～58Ma的原岩结晶年龄和～54Ma的变质年龄.因此,所研究的林芝杂岩并不能代表拉萨地体中的前寒武纪变质基底,而是古生代的沉积岩和晚白垩纪至早新生代的岩浆岩在始新世早期变质而成.这一时期,表壳岩和侵入岩一起经历的中压角闪岩相变质作用很可能跟新特提斯洋俯冲导致的地壳增生、加厚有关.  相似文献   

苏鲁-大别超高压岩石中锆石SHRIMP U-Pb定年研究——综述和最新进展   总被引：6，自引：9，他引：6  

刘福来  薛怀民 《岩石学报》2007,23(11):2737-2756

如何建立苏鲁-大别超高压岩石深俯冲-超高压-快速折返过程连续而完整的P-T-t轨迹及精细的年代谱系,是目前地学界研究的热点。而变质锆石是否记录深俯冲石英榴辉岩相进变质阶段的年代学信息和超高压峰期变质时代的准确归属,是目前苏鲁-大别超高压变质带需要深入研究的核心问题。本文在对前人同位素年代学方面所取得的成果进行系统总结的基础上。采用锆石中矿物包体激光拉曼和电子探针测试、锆石阴极发光图像成因分析以及SHRIMP U-Pb定年等综合研究手段,确定苏鲁-大别地体榴辉岩及其强退变质围岩在深俯冲-构造折返过程中主要经历了四个阶段的变质演化:深俯冲石英榴辉岩相进变质(Ⅰ)、超高压峰期变质(Ⅱ)、构造折返初期石英榴辉岩相退变质(Ⅲ)和构造折返晚期角闪岩相退变质(Ⅳ)。研究发现,扬子板块(中)新元古代巨量的陆壳物质在早三叠纪(246～244Ma)俯冲到华北板块之下约65km的深处。发生了石英榴辉岩相进变质,相应的变质温压条件为T=542～693℃,P=1.7～2.02GPa。这些高压石英榴辉岩相岩石在中-新三叠纪继续向下俯冲,在235～225Ma期间,俯冲的深度至少达到了170km的地幔深处,并发生了峰期柯石英榴辉岩相超高压变质,相应的变质温压条件为T=722～866℃,P>5.5GPa。苏鲁-大别超高压地体自石英榴辉岩相进变质阶段到超高压峰期变质阶段的俯冲速率为7.0km/Myr。这些超高压岩石在219～216Ma期间,发生了第一次构造抬升至75km的深处,并经历了石英榴辉岩相退变质作用的改造,退变质温压条件为T=730～780℃,P=1.7～2.6GPa。这些退变质岩石在212～205Ma期间,又经历了第二次抬升至25km中-下地壳深处,并叠加了角闪岩相退变质作用,该阶段变质温压条件为T=610～710℃,P=0.7～1.2GPa。苏鲁-大别超高压地体两次构造抬升的速率大致相同,为5.6km/Myr。该项成果不仅确定了苏鲁-大别榴辉岩及其强退变质岩石深俯冲过程石英榴辉岩相进变质-超高压峰期变质、构造折返过程石英榴辉岩相-角闪岩相退变质连续而完整的变质演化P-T-t轨迹及精细的年代谱系,而且对于重新建立苏鲁-大别巨量陆壳物质快速超深俯冲-快速折返的动力学模式有着重要的科学意义。  相似文献   

“三江”云龙锡(钨)成矿带晚白垩世二云母花岗岩LA-ICP-MS锆石U-Pb定年及其地质意义   总被引：6，自引：0，他引：6  

廖世勇  王冬兵  唐渊  尹福光  孙志明  孙洁 《岩石矿物学杂志》2013,32(4):450-462

云龙成矿带位于西南“三江”中段,是该区重要的锡(钨)矿集区.本文利用LA-ICP-MS锆石U-Pb定年方法,对带内与成矿相关的二云母花岗岩进行了年龄测试,获得成岩年龄为72.2±0.8 Ma(MSWD=1.9),属晚白垩世.这是在保山地块首次发现确凿的晚白垩世岩浆岩,表明保山地块经受了该时期构造-岩浆活动的影响.通过锆石微量元素和主微量地球化学特征分析,认为其应属S型花岗岩.结合区域地质背景,认为云龙成矿带该期花岗岩可能与腾冲地块晚白垩世S型花岗岩形成于一致的动力学背景,为新特提斯东向俯冲过程中内陆增厚地壳熔融的产物.本次报道的晚白垩世S型花岗岩与成矿带内一期重要成矿期次时代一致.结合前人研究资料认为,云龙成矿带内三期主要的成矿事件均有同期构造-岩浆事件对应,其中早、晚白垩世成矿活动与同期花岗岩体侵入紧密相关,而新生代成矿活动则与崇山剪切带走滑活动关系密切.这表明本区锡(钨)矿床经历了多期成矿过程,岩浆侵入活动和构造相关混合岩化对矿床形成均有贡献,单一的成因机制(花岗岩相关或混合岩化)可能无法合理解释本区矿床的成因.  相似文献   

从单晶褶皱看斜方辉石流变学的特征     

嵇少丞 《大地构造与成矿学》2013,37(2)

迄今为止,上地幔流变学的研究主要集中于橄榄石单晶与多晶集合体的实验和野外观察,但对辉石的流变学特征知之甚少,虽然辉石亦是上地幔岩石的主要组成矿物.因此,查清斜方辉石的流变学行为、塑性变形机制、重结晶作用以及与其共生的橄榄石之间的流变强度差等,现已成为国际地学界研究的新的热点课题.新疆中天山南缘库米什地区的榆树沟高压变质地体中出现地幔超糜棱岩,其中带状拉伸的斜方辉石(En90)碎斑晶发生了强烈地弯滑褶皱,周围橄榄石(Fo90)重结晶成细粒(～10 μm)多晶基质.显微构造研究表明,单晶斜方辉石的褶皱主要通过单一的(100)[001]滑移进行的,而细粒重结晶橄榄石基质的变形机制则最可能以超塑性(颗粒边界滑移与扩散)为主.单晶斜方辉石发生弯滑褶皱,而不形成常见的膝折(Kinks),说明所处物理化学条件下斜方辉石晶体位错攀移与原子扩散并不足够活跃.此外,即使其晶格发生高达140.的旋转,斜方辉石依然没有发生光学显微镜下足以识别的重结晶结构,说明启动重结晶作用的临界剪切应变应不少于5.5.根据现有的层状材料的褶皱理论,推测榆树沟高压变质地体中地幔岩发生塑性变形时位错蠕变的斜方辉石的流动强度至少比相同条件下超塑性变形的细粒橄榄石多晶基质高近2个数量级.  相似文献