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1.
环东冈瓦纳大陆周缘的古生代造山作用:东喜马拉雅构造结南迦巴瓦岩群的岩石学和年代学证据 总被引：25，自引：15，他引：10
喜马拉雅造山带东端的南迦巴瓦岩群是高喜马拉雅结晶岩系的一部分,主要由麻粒岩相和角闪岩相变质的片麻岩、斜长角闪岩、片岩和钙硅酸盐岩组成.长英质片麻岩主要由斜长石、钾长石、石英、石榴石、黑云母和褐帘石组成.片麻岩中的锆石具有核一边结构,由一个大的继承岩浆核和一个窄的变质生长边组成.锆石岩浆核具同心韵律环带.其REE配分模式以HREE富集和负Eu异常为特征,并具有高的Th/U比值.锆石U-Pb年代分析表明,这种继承岩浆锆石给出的加权平均年龄为490～500Ma.地球化学特征表明,这些片麻岩的原岩是花岗岩和花岗闪长岩,形成在俯冲带的岩浆弧构造环境.钙硅酸盐岩中的锆石具有高级变质岩中变质生长锆石的典型特征,即具有相对较低的REE含量,不明显的负Eu异常和较低的Th/U比值.变质锆石所获得的U-Pb加权平均年龄为505Ma.本文和现有的研究结果表明,喜马拉雅造山带是一个复合造山带,它经历了古生代的原始造山作用,在新生代印度与欧亚板块的碰撞过程中发生了再造山作用.喜马拉的古生代造山带作用是原特提斯洋向冈瓦纳大陆北缘俯冲和亚洲微陆块(包括拉萨和羌塘地块)增生的结果,是在冈瓦纳大陆拼合之后其边缘发生的安底斯型造山作用,因此,它并不属于在冈瓦纳超大陆聚合过程中陆-陆碰撞形成的泛非造山带. 相似文献
2.
喜马拉雅早古生代造山作用:来自尼泊尔帕朗花岗质片麻岩锆石U-Pb年代学和Hf同位素证据 总被引：1，自引：0，他引：1
《地学前缘》2016,(2):190-205
尼泊尔帕朗花岗质片麻岩是加德满都逆冲席体的一部分,其主要矿物组成为石英、斜长石、钾长石、微斜长石和白云母。片麻岩中的锆石发育核-边结构,由继承碎屑锆石核和韵律环带的岩浆锆石边组成。LAICP-MS U-Pb定年结果显示,边部岩浆锆石的加权平均年龄为(485.5±1.4)Ma和(455.1±3.1)Ma,指示片麻岩原岩为早古生代早期的花岗岩,并记录了两期岩浆作用。锆石边部εHf(t)值变化范围为-8.7~-3.5,Hf同位素两阶段模式年龄TCDM为2.01~1.69Ga,结合岩石学特征并对比大喜马拉雅和小喜马拉雅变质沉积岩的Hf同位素成分,认为原岩花岗岩来自大喜马拉雅变泥质岩的部分熔融。帕朗花岗质片麻岩的研究结果和现有的年代学数据表明,喜马拉雅地区存在早古生代造山事件,这一事件可与相邻的拉萨地体、羌塘地体以及青藏高原东南缘的保山-腾冲地体内同一时代的构造事件对比,是早古生代早期原特提斯洋岩石圈沿冈瓦纳大陆北缘俯冲的安第斯型造山作用的产物,而与冈瓦纳大陆内部块体聚合过程中陆-陆碰撞的泛非造山作用无关。 相似文献
3.
青藏高原东南缘滇西早古生代早期造山事件 总被引：22，自引：10，他引：12
野外观察、LA-ICP-MS锆石U-Pb测年和Hf同位素分析结果表明:青藏高原东南缘滇西芒市地区存在奥陶系底砾岩与前寒武-寒武系之间的地层不整合;龙江眼球状片麻岩锆石边部U-Pb年龄约为502 ～ 518Ma,代表原岩花岗岩结晶时代;继承性锆石核部具有与拉萨地体相似的年龄谱,说明早古生代早期腾冲地体与拉萨地体属于统一陆块;锆石边部具有负的、变化范围较大的εHf(t)值(-15.7 ～-2.0),结合眼球状片麻岩野外、岩相学特征及区域构造背景说明原岩花岗岩来源于古老地壳部分熔融,并伴随不同程度幔源物质的注入,可能为岩浆弧的一部分.综合野外观察及锆石同位素研究结果,明确了青藏高原东南缘存在早古生代早期造山事件.与喜马拉雅、拉萨、羌塘等地体的同一时代构造事件对比,认为青藏高原东南缘滇西地区早古生代早期造山带为形成在冈瓦纳大陆北缘的安第斯型造山带的一部分,为认识冈瓦纳大陆北缘早古生代演化提供新的证据. 相似文献
4.
《地球科学进展》2016,(4)
喜马拉雅造山带中段的吉隆和聂拉木地区出露一套眼球状片麻岩,其矿物组成为石英、钾长石、斜长石、黑云母和少量的白云母。片麻岩中锆石发育典型的岩浆韵律环带,LA-ICP-MS锆石U-Pb测年显示,2件样品中岩浆锆石的加权平均年龄分别为(488.5±1.1)Ma,(475.1±0.7)Ma和(468.1±2.5)Ma,代表研究区早古生代早期的岩浆作用。现有的早古生代地质记录表明,喜马拉雅地体存在早古生代造山事件,这一事件可与青藏高原南部和东南部的拉萨、羌塘、保山和腾冲地体内同一时代的构造热事件对比,指示区域早古生代造山作用。早古生代早期的造山作用是冈瓦纳大陆聚合之后,原特提斯洋岩石圈沿冈瓦纳大陆北缘俯冲调整的安第斯型造山作用的产物,而非超大陆内部块体拼合过程中陆—陆碰撞为主要特征的泛非造山作用。 相似文献
5.
错那洞穹隆是藏南特提斯喜马拉雅地区新发现的一个片麻岩穹隆构造。穹隆核部发育一套早古生代眼球状片麻岩。本文在野外地质调查的基础上,利用LA-(MC)-ICP-MS对花岗质片麻岩2个样品的锆石开展U-Pb年代学和Lu-Hf同位素分析。片麻岩中的锆石发育核-幔-边结构,核部为具溶蚀港湾结构的继承锆石,幔部为具韵律(震荡)环带的岩浆锆石,边部(增生边)为重熔变质成因的黑锆石。岩浆锆石幔部的~(206)Pb/~(238)U年龄加权平均值为(500.6±2.6)Ma～(501.1±2.5)Ma,代表该片麻岩的早古生代岩浆结晶年龄。边部变质锆石的新生代重熔年龄为(37.7±0.5)Ma,可能代表藏南拆离系的启动时间。早古生代岩浆锆石幔部的ε_(Hf)(t)值为-2.1-+5.3 (平均值为+2.2),Hf同位素两阶段模式年龄(TDM2)为1.1～1.6 Ga(平均值为1.3 Ga),表明其源岩起源于高喜马拉雅元古宙地层的部分熔融。结合区域内早古生代岩浆活动和新生代穹隆构造变质事件,本文认为错那洞花岗质片麻岩的形成受控于早古生代原特提斯洋壳板片向冈瓦纳大陆下俯冲的造山作用,同时记录了新生代印度一欧亚大陆碰撞造山后的变质和深熔事件。 相似文献
6.
喜马拉雅造山带东构造结拉布拉多期和格林威尔期造山作用的记录 总被引：6，自引：6，他引：0
位于喜马拉雅东构造结西北部的南迦巴瓦复合体,是构造应力最强、隆升和剥蚀最快、新生代变质和深熔作用最强的地区。为厘定该地区早期的变质岩浆作用,本文对南迦巴瓦复合体北部的花岗片麻岩和混合岩进行了岩石学和年代学研究。花岗片麻岩原岩为富钾的偏铝质花岗岩,具有岩浆弧花岗岩的成分特征。花岗片麻岩中的锆石具有岩浆锆石的环带结构,记录了487.9±1.6Ma的一期构造岩浆事件;混合岩的锆石具有明显的核-边结构,核部和边部的不协和线交点年龄分别为1559±13Ma、1154±12Ma。对比印度大陆东部的西隆高原、东高止造山带,发现三者都经历了拉布拉多期、格林威尔期以及泛非期的造山作用。因此,我们认为喜马拉雅东构造结与这两个地区密切相关,可能是他们向北的延伸,这三者可能组成统一的印度大陆东部造山带,一起经历了哥伦比亚超大陆、Rodinia和冈瓦纳超大陆的聚合与裂解过程。 相似文献
7.
喜马拉雅造山带东部错那县麻玛沟地区发育多种类型的花岗片麻岩和淡色花岗岩。锆石SHRIMP U-Pb地质年代学研究结果表明：花岗片麻岩（MM15）原岩结晶年龄为500.7±4.5Ma，含石榴子石淡色花岗岩中携带的继承性核部锆石年龄为498.6±3.4Ma，表明该地区经历了早古生代的岩浆作用事件。淡色花岗岩的结晶年龄区间为15.7~25.1Ma之间，为白云母脱水熔融的产物，可能是晚元古代-早古生代花岗质岩石发生低程度部分熔融的结果。锆石形态学表明该区的花岗片麻岩和淡色花岗岩均为过铝质花岗岩，并相对富集Cs、Rb、U、Pb，亏损Zr、Hf和低Nb/Ta比值，属于造山型花岗岩，支持该区域古生代岩浆作用事件与俯冲-碰撞造山作用相关，不是被动大陆边缘构造背景。结合前人数据推断：（1）从晚元古代末期开始，原特提斯洋向印度大陆的初始俯冲为自东向西的俯冲扩展模式；和（2）喜马拉雅造山带中新世淡色花岗岩为白云母脱水熔融和水致白云母熔融共同作用的结果，岩浆活动至少存在五个相。 相似文献
8.
喜马拉雅造山带东构造结南迦巴瓦岩群地质年代学和前寒武纪构造演化 总被引：16，自引：10，他引：6
位于喜马拉雅造山带东构造结,印度-雅鲁藏布江缝合带以南的南迦巴瓦岩群经历了高压变质作用和强烈的部分熔融与混合岩化作用.本文选择广泛分布的长英质片麻岩进行了岩石学和年代学研究.除个别岩石保存了由石榴石 蓝晶石 三元长石 石英组成的高压泥质麻粒岩相变质矿物组合以外,大多数片麻岩具有角闪岩相变质矿物组合,它们的原岩包括闪长岩和花岗闪长岩,并具有岩浆弧花岗岩的化学成分特征.片麻岩中的锆石普遍具有核-边结构.SARIMP和LA-ICP-MS原位分析表明,锆石的边缘给出了古生代至新生代的多期变质和岩浆事件年龄(500～10Ma),而锆石的核部给出了前寒武纪年龄,但主要集中在～2500Ma,～1800Ma,～1600Ma和～1000Ma.所分析的锆石区域具有明显的岩浆结晶环带和高的Th/U比值,表明它们所指示的是多期岩浆活动事件年代.这些年代峰值与整个高喜马拉雅结晶杂岩及印度陆块所获得的前寒武纪构造热事件年龄及分布特征基本上可以对比.因此,我们认为南迦巴瓦岩群及高喜马拉雅结晶杂岩的原岩是由新太古代至新元古代形成的多期岩浆岩组成,并作为印度陆块的一部分经历了Columbia、Rodinia和Gondwana超大陆的形成与裂解过程,以及喜马拉雅期的区域变质与岩浆作用再造. 相似文献
9.
喜马拉雅造山带亚东地区多期构造热事件——锆石和独居石U-Th-Pb年代学证据 总被引：1，自引：0，他引：1
喜马拉雅造山带是研究板块构造的天然实验室,位于造山带核心部位的大喜马拉雅岩系是揭示碰撞造山过程和造山带演化的关键。本文主要对亚东地区大喜马拉雅岩系中的花岗质片麻岩进行了岩相学、锆石和独居石UTh-Pb年代学以及全岩主微量地球化学研究。野外和显微结构特征观察表明,花岗质片麻岩的矿物组合为斜长石+钾长石+石英+黑云母+石榴石,岩石发生了部分熔融,经历了高角闪岩相至麻粒岩相的变质作用。年代学和全岩地球化学研究表明,花岗质片麻岩的原岩包括新元古代(～800 Ma)的花岗闪长岩和志留纪(～440 Ma)的花岗岩,二者均在中新世(～16 Ma)发生了变质作用。新元古代花岗闪长岩具有负的εHf(t)值(-16. 4～-12. 2),地壳Hf模式年龄为3. 11～2. 79 Ga,说明其起源于古老下地壳物质的部分熔融。新元古代花岗闪长岩和志留纪花岗岩具有相似的弧花岗质岩石地球化学特征,即具有高场强元素Nb、Ta、P和Ti的负异常。本次研究表明大喜马拉雅岩系经历了多期构造热事件,其不仅记录了新生代的碰撞造山作用,还记录了与新元古代与罗迪尼亚超大陆演化相关的岩浆热事件以及古生代冈瓦纳大陆拼合后的周缘安第斯型造山作用。 相似文献
10.
北山造山带南部早古生代构造演化：来自花岗岩的约束 总被引：3，自引：1，他引：2
北山造山带是中亚造山带的重要组成部分,处于天山造山带和索仑缝合带之间的关键构造位置,对认识中亚造山带的构造演化和古亚洲洋的最终闭合具有重要意义。本文选择北山造山带南部早古生代桥湾糜棱岩化花岗岩和金塔钾长花岗岩进行了LA-ICP-MS锆石U-Pb年代学、LA-MC-ICP-MS锆石Hf同位素和地球化学研究。结果表明,桥湾糜棱岩化花岗岩和金塔钾长花岗岩均形成于~430Ma,岩浆结晶锆石的二阶段Hf模式年龄分别为2.14~2.37Ga和1.32~1.72Ga。样品中含有少量继承锆石,继承锆石的Hf同位素特征与北山南部新元古代花岗质片麻岩类似。在地球化学组成上,两者均具有高的SiO2含量(73.18%~75.00%),弱过铝质,富集Rb、U、K等元素,亏损Ba、Nb、Ta、和Sr、P、Ti等元素的特点,类似于北山南部其它早古生代钾长花岗岩。它们的岩浆均起源于北山南部古老地壳基底的部分熔融,金塔钾长花岗岩可能还有幔源岩浆或新生下地壳的贡献。这同时也暗示了北山南部石板山地块与敦煌地块具有显著不同的地壳基底组成。结合敦煌地块早古生代高压麻粒岩的研究结果,我们认为北山南部早古生代岩浆活动可能与敦煌地块向北山南部石板山地块的碰撞、俯冲作用有关,反映了中亚造山带南缘的北山造山带在早古生代经历了造山带中微陆块与周缘克拉通碰撞拼贴的造山事件。 相似文献
11.
In the Gyirong and Nyalam areas, a massive amount of augen gneisses are extensively exposed in the middle Himalayan orogen. They consist of quartz, K-feldspar, plagioclase, biotite and minor muscovite. Zircons from augen gneisses have magmatic rims indicated by concentric oscillatory zoning. LA-ICP-MS zircon U-Pb dating gave weighted mean ages of (488.5±1.1) Ma (MSWD=0.6)、(475.1±0.7) Ma (MSWD=1.5) and (468.1±2.5) Ma (MSWD=4.2), hinting early Paleozoic magmatism in the Greater Himalayan Crystalline complex (GHC). The data in this study and other published geochronological results of Cambrian-Ordovician magmatites demonstrated that early Paleozoic orogenesis existed in the Himalayas. Early Paleozoic tectonic events preserved in Himalayas are well compared with the contemporaneous ones in the Lhasa terrane, Qiangtang terrane, Baoshan terrane and Tengchong terrane located in the south and southeast of Tibet Plateau. Integrating previous studies, we suggested an Andean-type orogeny corresponding to dynamic adjusting of the plates by subduction of the Proto-Tethys Ocean lithosphere along the northern margin of Gondwana, instead of Pan-African orogeny that was characterized by the continent-continent collisions during Gondwana assembly. 相似文献
12.
The Askot crystallines form a doubly plunging synformal belt and occurs as a detached crystalline belt or klippen in the vast
sedimentary terrain lying between Central crystallines towards north and the Almora crystallines to the south. It is dominated
by granite gneiss and augen gneiss, and also comprise of metapelites, migmatites and basic intrusives. In this paper, the
geochemical studies of the granite gneiss and augen gneiss from the Askot crystallines, Kumaun Himalaya were carried out in
order to understand their origin and evolution.
The granite gneiss is generally foliated, with less foliated and porphyritic variety seen in the core part. The K-feldspar
shows Carlsbad twinning, while plagioclases show complex twinning. They show euhedral zircon and apatite along with titanite
as accessory minerals. The granite gneiss is moderately evolved (Mg# ∼50) and has granodiorite composition with metaluminous,
calc-alkaline trends. They show higher concentration of Ti, Ca, Mg and low abundance of ∑REE (∼165 ppm) in comparison to augen
gneiss. They show volcanic arc signatures and compare well with Lateorogenic granites of Proterozoic times distributed world
wide. These calc-alkaline granites appear derived from a Paleoproterozoic mafic/intermediate lower-crust reservoir probably
involving arc magma underplating. Granite gneiss is also peraluminous with molar A/CNK>1.1, and the heterogeneity of granite
gneiss can be explained with the precursor melts, experiencing assimilation during up-rise through crust or contamination
of source itself involving sediments from the subduction zone. 相似文献
13.
A combined U–Pb zircon geochronological and whole-rock isotopic and geochemical study has been carried out on high-grade orthogneiss, meta-basite, and meta-sediments from the Erzgebirge. The results indicate multiple pulses of Ediacaran–Ordovician magmatism in a transitional volcanic-arc to rift-basin setting. Orthogneiss from high-pressure nappes exhibit a step-like pattern of inherited zircon ages and emplacement ages of 500–475 Ma. In contrast, granite gneiss from the medium-pressure core of the Erzgebirge is characterised by three pulses of magmatism in the Early Cambrian, Late Cambrian, and Early Ordovician. A trend of decreasing Th/U ratios in zircon is observed to c.500 Ma, after which significant increases in the trend and variability of the data is inferred to mark the transition from arc-related to rift-related magmatism. Sediments deposited in the Early Cambrian have continental island arc affinity. Major detrital peaks in the Ediacaran and subordinate Tonian, Palaeoproterozoic, and Neoarchaean data are consistent with an Avalonian-Cadomian Arc and West African Craton derivation. The Early Cambrian sediments were locally reworked by a thermal event in the Ordovician resulting in leucocratic banding and recorded in Ordovician zircon rims characterised by systematically lower Th/U ratios. Ptygmatically folded leucocratic bands containing Ordovician zircon rims, associated with low Th/U ratios, are further observed in the granite gneiss core of the Erzgebirge. Variscan ages are rare, except in a fine-grained high-pressure micaschist, which contains exclusively small, structure-less, zircon with a weighted mean age of 350 ± 2 Ma. These data, along with a re-evaluation of previously published data, have been interpreted as the product of flattening subduction during the Early Cambrian; followed by the opening of slab windows in the Late Cambrian; and finally delamination in the Early Ordovician. Delamination of the orphaned slab led to asthenospheric upwellings triggering extension, bimodal magmatic pulses, recycling of fertile crust, high-temperature metamorphism, and cratonisation of relatively young crust. 相似文献
14.
青藏高原拉萨地块西部念青唐古拉岩群的地球化学特征及构造意义 总被引：1，自引：0，他引：1
拉萨地块西部呈断块状沿狮泉河-申扎-嘉黎蛇绿混杂岩带附近分布的念青唐古拉岩群被认为是前寒武纪变质基底。本文对念青唐古拉岩群进行了系统的岩石学、地球化学、同位素年代学及构造地质学研究。研究结果表明片岩-片麻岩-变粒岩含十字石、石榴子石等特征变质矿物,遵循粒度分异规律,其原岩可能为来自冈瓦纳古陆核北缘中新元古代弧盆体系的活动大陆边缘浊积岩。斜长角闪岩具低硅、高铁镁、富钙的基性岩特征,其原岩为岛弧型基性火山岩。念青唐古拉岩群中的花岗伟晶岩锆石LA-ICPMS U-Pb年龄为1150±13Ma,具过铝质S型花岗岩地球化学特征,可能为中元古代(1150±13 Ma)以前就开始沉积的念青唐古拉岩群基底岩石通过部分熔融形成。与花岗伟晶岩渐变过渡接触的二云斜长片麻岩第一组变质重结晶锆石U-Pb年龄为701±15 Ma,结合十字石特征变质矿物,暗示了该地区中温高压变质作用的峰期变质,变质程度达角闪岩相;第二组热液流体锆石UPb年龄为301±8.4 Ma,可能与冈瓦纳大陆北缘古特提斯洋演化过程中的岩浆热液作用有关。 相似文献
15.
中亚-蒙古造山带东段的锡林郭勒杂岩：早华力西期造山作用的产物而非古老陆块？ —— 锆石SHRIMP U-Pb年代学证据 总被引：17，自引：10，他引：7
锡林郭勒杂岩是华北板块北缘古生代褶皱带内出露面积最大的变质岩系,以前多被当着前寒武纪的古老地块.本文通过对该杂岩中副片麻岩和正片麻岩的锆石SHRIMP U-Pb年代学研究发现,副片麻岩中的锆石多为岩浆锆石,其206Pb/238U加权平均年龄为406±7Ma,指示它们的原岩主要是由近同期(略早些)的岩浆岩风化后就近沉积的产物,该年龄应代表源区(岛弧型?)花岗岩的形成时间,同时也是副片麻岩原岩沉积的下限年龄.正片麻岩中岩浆锆石的206Pb/238U加权平均年龄为382±2Ma,代表花岗片麻岩原岩的侵位年龄.岩石中锆石的变质增生边的形成年龄为337±6Ma,代表锡林郭勒杂岩发生变质和变形的时间,该变质事件可能与贺根山缝合带内所发生的一次主要的碰撞造山作用有关.这些年龄资料充分说明,锡林郭勒杂岩并非古老地块,而是华力西早期岩浆作用、沉积作用和变质作用事件的产物.整个事件是在较短的时间范围内(～70Ma)完成的,推测该杂岩发育在碰撞造山带的弧前环境.中亚-蒙古造山带东南部(内蒙古的中、东部)碰撞前的构造格局可能不是典型的多岛洋体制,由于缺少古老的陆块,造山过程更多的表现为大洋的大陆化过程,即洋内俯冲形成岛弧,岛弧在被动大陆边缘拼贴聚合转化为新的大陆. 相似文献
16.
We present the first evidence of an early Paleozoic terrane in the southern Yanbian region, NE China. We used LA-ICP-MS zircon U–Pb and Hf isotope techniques to analyze one plagioclase gneiss and two garnet-bearing two-mica quartz schists from the early Paleozoic Jiangyu Group, as well as two tonalites that intruded the Jiangyu Group. The tonalites yield weighted mean 206Pb/238U zircon crystallization ages of 423 and 422 Ma. Zircons from the Jiangyu Group gneiss and two schist samples yield maximum depositional ages of 439 ± 4, 443 ± 2, and 443 ± 5 Ma, respectively. These constraints, together with the age of the tonalite intrusion, indicate that the Jiangyu Group was deposited between 443 and 423 Ma (i.e., Silurian). In addition, detrital zircon age spectra of the three Jiangyu Group samples exhibit prominent age peaks at 442, 473, 513, 565, 600, 635, 671, 740, 1000, and 1162 Ma, as well as secondary peaks between 1344 and 3329 Ma. The occurrence of the prominent Meso- and Neoproterozoic detrital zircon age populations for the Jiangyu Group, combined with the corresponding zircon Hf isotopic data, reveals that the Jiangyu Terrane has a tectonic affinity with northeastern Gondwana. The early Paleozoic magmatism, as suggested by the medium-K calc-alkaline I-type tonalite intrusion and Jiangyu Group detrital zircon age spectra, corresponds to coeval subduction–accretion events along the southern margin of the eastern Central Asian Orogenic Belt (CAOB). Accordingly, we propose that the Jiangyu Group is part of an exotic terrane that rifted from northeastern Gondwana, drifted northward, and ultimately became involved in the early Paleozoic tectonic evolution of the southern margin of the eastern CAOB after the Early Cambrian. 相似文献
17.
Geochronology and Petrogenesis for the Protolith of Biotite Plagioclase Gneiss at Lianghe, Western Yunnan 总被引：5，自引：0，他引：5
CONG Feng LIN Shiliang ZOU Guangfu XIE Tao LI Zaihui TANG Fawei PENG Zhimin 《《地质学报》英文版》2011,85(4):870-880
In this paper,we report an integrated study of U-Pb age and Hf isotope compositions of zircons from biotite plagioclase gneiss at Lianghe in western Yunnan.The zircons preserved inherited core and rim texture.Igneous zircon grains and rims yielded a weighted mean ~(206)Pb/~(238)U age of 120.4±1.7 Ma,theirε_(Hf)(120 Ma)values were mainly negative ranging from-13.9 to-10.7,with Hf model ages between 1.9 Ga and 2.0 Ga,some zircons had positiveε_(Hf)(120 Ma)values ranging from 0.2 to 2.1.The inherited cores ... 相似文献
18.
The central–south domain of the Tibet Plateau represents an important part of the northern segment of Gondwana during the early Paleozoic. Here we present zircon U–Pb, Lu–Hf isotope, and whole–rock geochemical data from a suite of early Paleozoic magmatic rocks from the central Tibet Plateau, with a view to gain insights into the nature and geotectonic evolution of the northern margin of Gondwana. Zircon grains in four granitic rocks yielded ages of 532−496 Ma with negative εHf(t) values (−13.7 to −0.6). Zircon grains in meta–basalt and mafic gneiss yielded ages of 512 ± 5 Ma and 496 ± 6 Ma, respectively. Geochemically, the granitic rocks belong to high–K calc–alkaline and shoshonitic S–type granite suite, with the protolith derived from the partial melting of ancient crustal components. The mafic gneiss and meta–basalt geochemically resemble OIB (Oceanic Island Basalt) and E–MORB (Enriched Mid–Ocean Ridge Basalt), respectively. They were derived from low degree (∼5–10%) partial melting of an enriched mantle (garnet and spinel lherzolite) that was contaminated by upper crustal components. The parental magmas experienced orthopyroxene–dominated fractional crystallization. Sedimentological features of the Cambrian–Ordovician formations indicate that the depositional cycle transformed from marine regression to transgression leading to the formation of parallel/angular unconformities between the Cambrian and Ordovician strata. The hiatus associated with these unconformities are coupled with the peak of the early Paleozoic magmatism in Tibet Plateau, indicating a tectonic control. We conclude that the Cambrian–Ordovician magmatic suite and sedimentary rocks formed in an extensional setting, and we correlate this with the post–peak stage of the Pan–African orogeny. The post–collision setting associated with delamination, orogenic collapse or lithospheric extension along the northern margin of Gondwana, can account for the Cambrian–Ordovician magmatism and sedimentation, rather than oceanic subduction along the external margin. We thus infer a passive margin setting for the northern Gondwana during the Early Paleozoic. 相似文献
19.
U–Pb detrital zircon geochronology from Lower Devonian quartz arenites of the northwestern margin of the Yangtze block yields dominant early Neoproterozoic (0.85–1.0 Ga), Pan-African (0.5–0.65 Ga) and middle Neoproterozoic (0.68–0.8 Ga) age populations and minor Mesoproterozoic to middle Mesoarchean (1.0–3.0 Ga) ages. Middle Mesoarchean to Mesoproterozoic rocks, however, are widespread in the South China block. Although Hf isotopic compositions show both juvenile crustal growth and crustal reworking for all the age groupings, the crust growth, essentially mantle-derived, occurred mainly around 3.1 Ga, 1.9 Ga and 1.0 Ga, respectively. Zircon typology and youngest grain ages indicate that this suite of quartz arenites was the product of multiphase reworking. Abundant magmatic zircon detritus with concordant U–Pb Grenvillian and Pan-African ages, together with accompanying various εHf(t) values, indicate an exotic provenance for the quartz arenite external to the South China block. Qualitative comparisons of age spectra for the late Neoproterozoic sediments of the Cathaysian Block, early Paleozoic sediments of pre-rift Tethyan Himalaya sequence in North India and lower Paleozoic sandstone from the Perth Basin in West Australia, show that they all have two the largest age clusters representing Grenvillian and Pan-African orogenic episodes. The resemblance of these age spectra and zircon typology suggests that the most likely source for the Lower Devonian quartz arenites of the South China block was the East African Orogen and Kuunga Orogen for their early Grenvillian and Pan-African populations, whereas the Hannan–Panxi arc, Jiangnan orogen, and the Yangtze block basements might have contributed to the detrital zircon grains of the Neoproterozoic and Pre-Grenvillian ages. Hf isotopic data indicate that the crustal evolution of the drainage area matches well with the episodic crust generation of Gondwana. These results imply that the previously suggested position of the SCB in Gondwana should be re-evaluated, and the South China block should be linked with North India and West Australia as a part of East Gondwana during the assembly of Gondwana, rather than a discrete continent block in the paleo-Pacific. 相似文献
20.
Re–Os and U–Pb Geochronology of Porphyry and Skarn Types Copper Deposits in Jilin Province,NE China 
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下载免费PDF全文 Yong Zhang Shu–Wen Xing Quan–Heng Song Yan Wang Zheng–Tao Yu Xiao–Hui Du Yu–Bo Ma Zeng–Jie Zhang 《Resource Geology》2015,65(4):394-404
Jilin Province in NE China lies on the eastern edge of the Xing–Meng Orogenic Belt. Mineral exploration in this area has resulted in the discovery of numerous large, medium, and small sized Cu, Mo, Au, and Co deposits. To better understand the formation and distribution of both the porphyry and skarn types Cu deposits of the region, we examined the geological characteristics of the deposits and applied zircon U–Pb and molybdenite Re–Os isotope dating to constrain the age of the mineralization. The Binghugou Cu deposit yields a zircon U–Pb age for quartz diorite of 128.1 ± 1.6 Ma; the Chang'anpu Cu deposit yields a zircon U–Pb age for granite porphyry of 117.0 ± 1.4 Ma; the Ermi Cu deposit yields a zircon U–Pb age for granite porphyry of 96.8 ± 1.1 Ma; the Tongshan Cu deposit yields molybdenite Re–Os model ages of 128.7 to 130.2 Ma, an isochron age of 129.0 ± 1.6 Ma, and a weighted mean model age of 129.2 ± 0.7 Ma; and the Tianhexing Cu deposit yields molybdenite Re–Os model ages of 113.9 to 115.2 Ma, an isochron age of 114.7 ± 1.2 Ma, and a weighted mean model age of 114.7 ± 0.7 Ma. The new ages, combined with existing geochronology data, show that intense porphyry and skarn types Cu mineralization was coeval with Cretaceous magmatism. The geotectonic processes responsible for the genesis of the Cu mineralization were probably related to lithospheric thinning. By analyzing the accumulated molybdenite Re–Os, zircon U–Pb, and Ar–Ar ages for NE China, it is concluded that the Cu deposits formed during multiple events coinciding with periods of magmatic activity. We have identified five phases of mineralization: early Paleozoic (~476 Ma), late Paleozoic (286.5–273.6 Ma), early Mesozoic (~228.7 Ma), Jurassic (194.8–137.1 Ma), and Cretaceous (131.2–96.8 Ma). Although Cu deposits formed during each phase, most of the Cu mineralization occurred during the Cretaceous. 相似文献