关于拉斯曼丘陵泛非期高级变质作用时代的限定

就目前认识,拉斯曼丘陵地区的所有基底和盖层岩石都卷入到了格林威尔期和泛非期高级变质和变形作用。泛非期高峰变质的时代大致在550—530 Ma,其造山晚期的花岗质岩浆作用遍及全区。我们观察到,中山站区石榴黑云斜长片麻岩固相变质作用过程,主要是对早期锆石的重启、改造,例如,对早期岩浆锆石环带的模糊化,对锆石棱、角的溶蚀,甚至同位素体系的重启等,难以形成变质锆石(边),退变或重启年龄平均值为522.7±6.6 Ma。峰期变质之后侵位的花岗岩结晶年龄为545±9 Ma,意味着峰期变质应不晚于该年龄。泛非期的变形、变质作用及花岗岩可对早期"干"岩石进行某种程度的退变质改造,从而造成高级变质岩变质结构的复杂性。这种变质作用及有关的花岗岩活动似乎缘于陆块内部的活化,而不是不同陆块间的碰撞所致。     

东南极新元古代晚期–早古生代(泛非期)花岗岩类的对比研究

东南极内部发育毛德和普里兹两条新元古代晚期-早古生代(泛非期)造山带,这两条造山带中均发育大量同-后构造花岗岩类。本文系统总结了以往东南极泛非期花岗岩类的岩石学、地球化学和年代学方面的研究成果,对不同地区岩体的岩石类型、岩浆源区及形成的构造环境进行了对比研究。结果表明：除南龙达讷山为I型花岗岩外,大部分花岗岩类表现出与碰撞造山作用相关的A型(或S型)花岗岩的特征。泛非期岩浆作用与区域高级变质作用的时代吻合(600-500 Ma)。两条造山带中泛非期岩浆作用与碰撞后岩石圈减薄、岩浆底侵以及上地壳的伸展垮塌相联系,均具有碰撞造山带的构造演化特点。所以,冈瓦纳超大陆的形成很可能是通过西冈瓦纳、印度－南极陆块和澳大利亚－南极陆块等三个陆块沿着两条造山带(毛德造山带和普里兹造山带)近于同期发生拼合碰撞的结果。     

东南极新元古代晚期-早古生代(泛非期)花岗岩类研究综述

东南极内部发育毛德和普里兹两条新元古代晚期-早古生代(泛非期)造山带,这两条造山带中均发育大量同-后构造花岗岩类。本文系统总结了以往东南极泛非期花岗岩类的岩石学、地球化学和年代学方面的研究成果,对不同地区岩体的岩石类型、岩浆源区及形成的构造环境进行了对比研究。结果表明:除南龙达讷山为I型花岗岩外,大部分花岗岩类表现出与碰撞造山作用相关的A型(或S型)花岗岩的特征。泛非期岩浆作用与区域高级变质作用的时代吻合(600—500Ma)。两条造山带中泛非期岩浆作用与碰撞后岩石圈减薄、岩浆底侵以及上地壳的伸展垮塌相联系,均具有碰撞造山带的构造演化特点。所以,冈瓦纳超大陆的形成很可能是通过西冈瓦纳、印度-南极陆块和澳大利亚-南极陆块等3个陆块沿着两条造山带(毛德造山带和普里兹造山带)近于同期发生拼合碰撞的结果。     

东南极格罗夫山地区冰碛石碎石带中高压麻粒岩和正片麻岩的锆石年代学研究及其构造意义

东南极的格罗夫山是普里兹造山带向南极内陆的延伸部分。对格罗夫山不同碎石带中收集的高压麻粒岩和正片麻岩进行锆石U-Pb年代学研究。四个高压麻粒岩的锆石多数为变质新生锆石,仅少数保留有继承核,其年龄为2633—2502 Ma。在变质锆石中获得~570 Ma和~555—545 Ma两个阶段变质年龄,锆石微量元素特征显示为重稀土亏损,结合前人研究结果,推测这两阶段年龄分别代表了变质作用过程中的进变质和高压峰期变质年龄。两个正片麻岩的锆石普遍发育核-边结构,由一个发育振荡环带的岩浆核和均匀无环带的变质边组成。正片麻岩的原岩年龄存在差异,在样品GR14-3-4的锆石核部获得了1060±40 Ma的上交点年龄,其原岩可能来自格罗夫山东南部的冰下高地,而在样品GR14-5-4的锆石核部获得的原岩年龄为917±4 Ma,与格罗夫山基岩中的基性麻粒岩和正片麻岩的原岩年龄一致。在锆石边部获得的变质年龄较为一致,为~530 Ma,与以前在高压麻粒岩中获得的退变质年龄相当。本次研究确认了高压麻粒岩在格罗夫山地区不同碎石带中分布的广泛性,表明其可能普遍存在于格罗夫山冰下高地之中。同时也进一步证明格罗夫山冰下高地并没有受到格林维尔期构造热事件的影响,而是只经历了泛非期的单相变质构造旋回。     

东南极格罗夫山：普里兹造山带中一个典型的泛非期变质地体

提要：距我国中山站以南约400 km的格罗夫山是普里兹造山带向南极内陆的延伸部分,其基底地体由约在920?910 Ma期间侵入的镁铁质－长英质火成岩和少量中元古代的沉积岩构成,这些岩石仅在泛非期（约570?500 Ma）经历了单相变质－构造旋回,因此是一个典型的泛非期变质地体。泛非期高峰变质作用并不象前人所认为的那样仅为中低压麻粒岩相,而是高达770?840?C、1.18?1.40 GPa,并在随后经历了近等温减压（约0.6 GPa）的P-T演化过程。大规模的A型紫苏花岗岩和花岗岩在同造山－后造山阶段侵位,并造成了麻粒岩地体近等压降温的P-T轨迹。这些花岗质岩石是由长期富集地幔的底侵物质（碱性玄武质岩石）经部分溶融而形成的。结合相邻地质体的研究资料,我们认为普里兹造山带可能发育在太古宙－格林维尔期基底地体之上,这些基底地体可能与新元古代（？）盖层卷入到了统一的泛非期造山作用过程。在泛非期造山作用过程中,地壳曾被增厚约达40?50 km,而后又经历了厚约20 km的地壳伸展垮塌和剥蚀。所以,普里兹造山带应代表东冈瓦纳陆块内部由板块缝合作用所形成的一条泛非期碰撞造山带。     

陕西商洛秦岭群斜长角闪岩年代学研究

秦岭造山带一直是近些年来的热点研究地区。本文以北秦岭的主体秦岭群为重点研究对象,采集了位于陕西商洛一带斜长角闪岩样品Q18,在岩相学和岩石地球化学研究的基础上,对其锆石进行了U-Pb年龄测定。结果显示,锆石多成浑圆状,内部结构单调均一,原有的岩浆环带基本消失,为强烈变质改造锆石,其年龄集中在376Ma左右,指示秦岭群遭受了加里东期造山作用强烈改造。     

中国东南极地质考察20年进展与展望

在1998—2017年期间,我国组织了14次东南极地质考察,将考察的范围从中山站所在的拉斯曼丘陵向外扩展了约400 km,主要包括格罗夫山、埃默里冰架东缘-西南普里兹湾、北查尔斯王子山、布朗山、赖于尔群岛和西福尔丘陵等露岩区。通过大、中比例尺的地质编图和多学科综合研究,取得如下重要进展:(1)确定格罗夫山冰下高地为泛非期(~570—500 Ma)单相变质地体,发现镁铁质和泥质高压麻粒岩并刻画了泛非期造山的精细过程,为普里兹造山带的碰撞造山成因以及冈瓦纳超大陆的多陆块汇聚模型提供了岩石学支撑;(2)论证在印度克拉通与东南极陆块之间存在一个延长2 000 km的中元古代长寿命大陆岛弧,岛弧岩浆作用从~1 500 Ma一直持续到~1 000 Ma,提出雷纳造山带格林维尔期(~1 000—900 Ma)的构造演化可能经历了从弧陆碰撞到陆陆碰撞的过程;(3)在赖于尔群岛超高温变泥质岩中识别出早期蓝晶石的残留,确定了超高温变质作用顺时针演化的精细P-T轨迹;(4)在西福尔丘陵西南部基性岩墙群中发现了格林维尔期(~960—940 Ma)不均匀麻粒岩化,变质条件达820—870℃、0.84—0.97 GPa,认为西福尔陆块也卷入到印度克拉通与东南极陆块的碰撞造山过程;(5)在西福尔丘陵东南部浅变质冰川漂砾和松散砂中获得~3.5—3.3 Ga的古老锆石U-Pb年龄,推测在西福尔丘陵东南方向存在一个从前未知的古太古代冰下陆块。建议今后在东南极面向印度洋构造域的地质考察要进一步扩展到南查尔斯王子山、内皮尔杂岩和登曼冰川,研究工作的重点仍聚焦在南极大陆如何响应地质历史时期里超级大陆的聚散过程这一关键科学问题上,并可在以下几个方面展开:(1)太古宙古老地壳及陆核的识别与全球对比;(2)格林维尔期造山记录与罗迪尼亚超大陆汇聚;(3)泛非期造山记录与冈瓦纳超大陆汇聚;(4)显生宙冈瓦纳超大陆裂解及陆块分离。通过这些考察和研究工作,可以促使我国对南极地质科学的研究达到国际先进水平。     

对张三沟岩组SHRIMP锆石U-Pb年代学的研究

出露于华北陆块东北缘的张三沟岩组为一套变质火山—沉积岩系,前人根据变质程度和地层对比将其划归古元古代。本文通过SHRIMP锆石U—Pb年代学研究,获得2517±9Ma、2518±7Ma和2534±26Ma原岩年龄,2439±24Ma、2464±73Ma和2433±71Ma变质年龄。     

内蒙古北部阿仁绍布二长花岗岩形成时代、岩石地球化学特征及成因探讨

本文系统地报道了内蒙古北部乌日尼图地区阿仁绍布二长花岗岩的主量元素、微量元素和稀土元素特征,重点讨论了阿仁绍布二长花岗岩体的岩石成因特征及其地质意义。研究结果表明,阿仁绍布二长花岗岩体SiO2含量(wt%)较高,反映原始岩浆具幔源原生玄武岩浆特征,在上升过程中经历的结晶分异程度较低。U-Pb锆石年龄测定结果为308±2Ma,代表了阿仁绍布二长花岗岩体的结晶年龄,为晚石炭世。计算出石英结晶平均温度为999℃;斜长石结晶温度平均为1020℃;岩浆冷凝矿物共结晶时的深度约在3.3km-20km,其结晶条件代表岩体侵位时的物理环境,是在较深的岩浆房中结晶的,形成花岗岩的岩浆经历了高度的结晶分异作用。阿仁绍布二长花岗岩属准铝—过铝岩石,Rb/Sr平均比值为3.08,远高于整个陆壳的平均值。其物质来源于地壳物质的重熔,具有大陆边缘弧的地球化学特征,可能反映在岩浆形成之前,地幔源区发生了俯冲交代富集作用。     

东南极格罗夫山萨哈罗夫岭漂砾暴露年龄初探

首次对格罗夫山地区漂砾的暴露年龄进行的研究表明,萨哈罗夫岭冰原岛峰的两块漂砾样品的 Be最小暴露年龄分别为1．24±0．11Ma和1．37±0．12Ma, 。A1最小暴露年龄分别为0．90 4-0．12Ma和0．44±0．04Ma。萨哈罗夫岭附近冰面上的漂砾样品的 Be和 A1最小暴露年龄分别是0．47±0．3Ma和0．44±0．04Ma。考虑到误差,萨哈罗夫岭三块漂砾的最小暴露年龄与相近高程的基岩样品的最小暴露年龄基本一致。因此,在利用原地生成宇宙成因核素测年技术对东南极内陆格罗夫山地区的冰川消涨历史进行研究时,基岩和漂砾暴露年龄所反映出的冰川演化历史是明显吻合的。     

Additional Rb-Sr and single-grain zircon datings of Caledonian granitoid rocks from Albert I Land, northwest Spitsbergen

Previous K-Ar and Rb-Sr datings of the metamorphic and granitic rocks from the northwestern basement region of Spitsbergen mainly show the cooling time of the rocks, except for a Rb-Sr isochron age of the Hornemantoppen granitoid. New samples were collected during several years of geological mapping in the area and the Rb-Sr whole rock isochron and single-grain zircon evaporation methods were applied to the Hornemantoppen granitoids and the grey granites. A dioritic dyke was also dated by the latter method. The bulk rock chemistry study shows that most of both granitic rocks are of the S-type and probably post orogenic, with distinctive incorporation of crustal materials. The isotopic data also support this interpretation. The results of the Rb-Sr isotope analyses, 412 ± 4.8 Ma and the zircon Pb evaporation age of 424 ± 56 Ma, confirm the previous age of the Hornemantoppen granitoid, 414 ± 10 Ma. An older zircon age of 547 ± 19 Ma is considered to be the minimum age of inherited zircon. Zircons from the grey granites suggest an age of ca. 420 Ma with a large error. Field relations demonstrate that the grey granites are older than the Hornemantoppen granitoids. A minimum inherited zircon age, 952 ± 20 Ma, has been obtained from the grey granites. Three multi-grain Pb ages, 423 ± 22 Ma (2 grains), 461 ± 42 Ma and 561 ± 93 Ma (the last two 3 grains) were considered to be mixed ages. Although no definitive evidence for the presence of Grenvillian granites in this area has been obtained in the present study, preliminary results from the multi-grain zircon evaporation method, carried out in the Russian laboratory at Apatity, infer Paleo- and Mesoproterozoic protoliths for the metamorphic rocks of northwestern Spitsbergen.     

Grenvillian single-grain zircon Pb age of a granitic rock from the southern island of Hesteskoholmen, Liefdefjorden, northwestern Spitsbergen, Svalbard

A N-S trending, narrow zone of crystalline basement occurs from Biscayarhalvøya to Holtedahlfonna in northwestern Spitsbergen and is composed of various metasedimentary and igneous rocks, including granites. Previous isotopic age determinations on these rocks are by the K-Ar. Rb-Sr, ⁴⁰Ar/³⁹Ar and conventional zircon U-Pb method and yielded the Caledonian and Grenvillian ages. The single-grain zircon Pb evaporation method has recently been applied to solve complex problems and this is the first report by the method.
A granitic rock, syntectonically intruded into the phyllitic metasediments of the Biscayarhuken formation, which is the uppermost lithotectonic unit in the metamorphic rocks of the zone, was dated on four zircon grains, yielding a narrow age range from 955 ± 4 to 968 ± 9 Ma in average. This age of ca. 960 Ma is considered to be the age of intrusion, based on the occurrence and zircon morphology, which is roughly simultaneous with the formation of the phyllitic cleavages of the surrounding metasediments. The data obtained imply that the Caledonian events did not reset the Pb isotope system of zircon and major metamorphism occurred during the Grenvillian time in the Biscayarhuken formation, accordingly, the protolith age of the metasediments is Mesoproterozoic.     

Thermal history of the Cretaceous Sindong Group, Gyeongsang Basin, Korea based on fission track analysis

ABSTRACT Apatite and zircon fission track (FT) analyses were carried out to reconstruct the thermal history of the Lower Cretaceous Sindong Group, which is the lowermost stratal unit of the Gyeongsang Basin, Korea. Zircon FT central ages show a wide range from 83 ± 5 to 157 ± 18 Ma, and single-grain age spectra have multiple age populations, whereas all apatites have very consistent FT ages of c . 60 Ma, suggesting a totally reset cooling age. Co-existence of both older and younger ages compared with the depositional age and relatively short mean track length indicate that the Sindong zircons were partially annealed. The Sindong Group was heated into the zircon partial annealing zone (ZPAZ) around 80 Ma, and cooled below the apatite closure temperature at c . 60 Ma. Based on the zircon FT results combined with vitrinite reflectance data, the maximum palaeotemperature to which the Sindong Group had been subjected can be inferred to be about 260 °C. Zircon FT data from a granite body that is in contact with the Sindong Group and sandstones close to the granite body indicate that thermal influence caused by Upper Cretaceous intrusive rocks was limited in close vicinity of the intrusion and that the major heat source of the Sindong Group was burial. The thickness of uplifted and eroded section is estimated to be about 7 km.     

Geology of Gjelsvikfjella and western Mühlig-Hofmannfjella, Dronning Maud Land, east Antarctica

As a part of the Norwegian Antarctic Research Expedition 1984/85, geological mapping was performed in Gjelsvikfjella and western Mühlig-Hofmannfjella, Dronning Maud Land. The northern part of Gjelsvikfjella is dominated by the Jutulsessen metasupracrustals which have been intruded by a major gabbroic body and several generations of dykes. To the south the metasupracrustals gradually transform into the Risemedet migmatites. In western Mühlig-Hofmannfjella the bedrock is dominated by the large Svarthamaren Charnockite batholith. The batholith is bordered by the Snøtoa metamorphic complex outcropping to the south and west in Mühlig-Hofmannfjella and it is characterized by a high content of partly assimilated country rock inclusions. Mineral paragenesis and geothermometry/geobarometry suggest a two-stage tectonothermal-igneous history with an initial intermediate pressure, upper amphibolite to granulite facies metamorphism followed by high temperature transformations related to the charnockite intrusion. The age of the initial tectonothermal event is probably about 1,100 Ma. Geochronological work in the present study (Rb/Sr whole rock) gave an age of 500 ± 24 Ma for the Svarthamaren Charnockite, interpreted to record the age of crystallization. Late brittle faulting and undeformed dolerite dykes outcropping in Jutulsessen are believed to be related to Mesozoic crustal stretching in the Jutulstraumen-Pencksøkket Rift Zone to the west.     

U–Pb zircon and 40Ar–39Ar K-feldspar dating of syn-sedimentary volcanism of the Neoproterozoic Maricá Formation: constraining the age of foreland basin inception and inversion in the Camaquã Basin of southern Brazil

New U–Pb zircon and ⁴⁰Ar–³⁹Ar K-feldspar data are presented for syn-sedimentary volcanogenic rocks from the Neoproterozoic Maricá Formation, located in the southern Brazilian shield. Seven (of nine) U–Pb sensitive high-resolution ion microprobe analyses of zircons from pyroclastic cobbles yield an age of 630.2±3.4 Ma (2σ), interpreted as the age of syn-sedimentary volcanism, and thus of the deposition itself. This result indicates that the Maricá Formation was deposited during the main collisional phase (640–620 Ma) of the Brasiliano II orogenic system, probably as a forebulge or back-bulge, craton-derived foreland succession. Thus, this unit is possibly correlative of younger portions of the Porongos, Brusque, Passo Feio, Abapã (Itaiacoca) and Lavalleja (Fuente del Puma) metamorphic complexes. Well-defined, step-heating ⁴⁰Ar–³⁹Ar K-feldspar plateau ages obtained from volcanogenic beds and pyroclastic cobbles of the lower and upper successions of the Maricá Formation yielded 507.3±1.8 Ma and 506.7±1.4 Ma (2σ), respectively. These data are interpreted to reflect total isotopic resetting during deep burial and thermal effects related to magmatic events. Late Middle Cambrian cooling below ca . 200 °C, probably related to uplift, is tentatively associated with intraplate effects of the Rio Doce and/or Pampean orogenies (Brasiliano III system). In the southern Brazilian shield, these intraplate stresses are possibly related to the dominantly extensional opening of a rift or a pull-apart basin, where sedimentary rocks of the Camaquã Group (Santa Bárbara and Guaritas Formations) accumulated.     

东南极拉斯曼丘陵石榴斜长角闪岩中角闪石的~(40)Ar-~(39)Ar年龄及其地质意义

本文对东南极拉斯曼丘陵出露的石榴斜长角闪岩中的角闪石进行了４０Ａｒ－３９Ａｒ年龄测定,分别得到角闪石视年龄１５８６Ｍａ、１０１１～１０８０Ｍａ、７６１Ｍａ和５２９～５８２Ｍａ,角闪石坪年龄１０３６Ｍａ和５５４Ｍａ,角闪石Ａｒ－Ａｒ等时线年龄１０１０Ｍａ,这些同位素年龄证据,首次完整地记录了该区所经历的几乎所有构造变质热事件,为近几年国内外地质学家关于该区构造变质热事件争论的焦点问题,即晚元古代的１０００Ｍａ格林维尔事件（Ｇｒｅｎｖｉｌｉａｎ）与早古生代的５００Ｍａ泛非事件（Ｐａｎ－Ａｆｒｉｃａｎ）孰轻孰重以及前者是否存在,提供了答案。角闪石的４０Ａｒ－３９Ａｒ年龄测定结果表明,拉斯曼丘陵地区经历了复杂的多期变质演化历史,其原岩可能形成于早－中元古代,占主导地位的应该是晚元古代的１０００Ｍａ格林维尔事件,而５００Ｍａ泛非事件则是晚期较强烈的变质热事件。     

Metamorphism of the Mullerneset Formation, St. Jonsfjorden, Svalbard

The metamorphism of upper greenschist facies metasediments exposed in the extreme southwestern portion of St. Jonsjorden, Svalbard, is described. The rocks form part of the Mullerneset Formation of the late Precambrian age Kongsvegen Group and constitute a portion of the central-western Spitsbergen Cale-donides. Four deformations (D, -D4) and two metamorphic episodes (Mi and M2) have affected the rocks of the Mullerneset area. Mi was a prograde event which was initiated prior to the onset of the Di and continued through this deformation. Pre-Dt metamorphism reached biotite grade whereas garnet grade was attained syn-Di. M2 was a lower-middle greenschist facies metamorphism associated with D2. The results of quantitative geothermometry in the pelitic rocks show that peak Mi metamorphic temperatures decrease southwards across the field area from about 540°C to 510°C. Geobarometry and estimates of depth of burial indicate that Mi pressures were in the range of 5–7 kb. The data are consistent with geothermal gradients in the range of 21 ± 4°C/km to 24 ± 5°C/km. M2 metamorphic conditions are not precisely determinable but temperatures and pressures were probably less than those attained during Mi. It is suggested that the rocks of central-western Spitsbergen were originally deposited in an aulacogen before the initiation of Caledonian diastrophism.