Palaeoproterozoic and Archaean gneiss complexes in northern Greenland: Palaeoproterozoic terrane assembly in the High Arctic
Palaeoproterozoic and Archaean gneiss complexes in northern Greenland: Palaeoproterozoic terrane assembly in the High Arctic
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格陵兰岛北部的古元古代和太古宙片麻岩杂岩：高北极的古元古代地体组合
DOI：
10.1016/j.precamres.2007.09.006
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发表时间：
2008
影响因子：
3.8
通讯作者：
M. Hamilton
中科院分区：
文献类型：
--
作者：
A. Nutman;P. Dawes;F. Kalsbeek;M. Hamilton
利用SHRIMP U-Pb锆石定年法，结合丹麦和格陵兰地质调查局的测绘和全岩Nd同位素研究，对格陵兰北部的前寒武纪盾构进行了14种正长石和花岗岩类以及5种变质沉积物的测年研究。英格菲尔德活动带是英格菲尔德地和北普拉德霍地下部的古元古代沉积、深部成矿、多期变形和高变质作用带。在南缘78°30′n，东西向的Sunrise Pynt Straight belt是一个构造较晚的高等级剪切带，两侧地质对比明显。约1980年，在日出品直带以南，闪长岩和调性岩被安置在更古老的正长岩和变质沉积层中。两个变质石英岩（沉积于太古宙基底？）的碎屑锆石的年龄谱在3250Ma ~ 2350Ma之间，以2600 ~ 2450ma颗粒为主。伴生云母片岩，低Th/U，锆石日期1923±8Ma，高变质作用。与先前公布的同位素数据一致，所调查的最南部正正交（77°45'N）是新太古代（约2600Ma）。在北纬79°10′的日出品直带以北，有一角闪岩-麻粒岩相杂岩，其中含有大量泥质-沙质副长岩，是已知最古老的岩石。2个沙质副岩产出未圆角锆石，单峰碎屑年龄群集中在2000 - 1980 - ma。它们的来源可能是大约1980年左右来自日出品特直带以南的正地层，或者来自格陵兰东北部加里东褶皱带的基底内层。变质沉积层主要为年代期为1949±13Ma和1943±11Ma的闪长岩和闪长岩，年代期为1924±29Ma ~ 1915±19Ma的花岗岩类（不含锆石）。在1920Ma左右，变质沉积层发育低Th/U锆石过度生长，与花岗岩类同期发育。其他花岗岩年龄在1783±22Ma ~ 1741±15Ma之间，部分局部转化为片麻岩。后者的继承锆石年龄高达2650Ma。花岗岩岩脉锆石年龄为1783Ma， tdm值为2981Ma，强烈负的nda值为1.78Ga，表明太古宙地壳熔融或改造形成。因此，到1800Ma，这个幼年的古元古代地体可能已经被太古宙成分覆盖在地壳上。在英格尔菲尔德北部，前寒武纪的结晶岩直到维多利亚峡湾（北纬81°30）才被遮蔽。从那里获得的一个正长石勘测样本含有约3400毫安的振荡带锆石，这些锆石可能是岩石的年代，而不是年轻岩石中的异晶成分。因此，从北到南是太古宙、古元古代和太古宙至早古元古代片麻岩地体的组合。英格尔菲尔德活动带主要发育古元古代幼弧壳，夹在两个年龄对比不相关的太古宙壳块之间。这次碰撞发生在约1920ma，可能是一个古元古代的弧在一个南部太古代前陆上的逆冲，时间由变质锆石确定。新的同位素结果巩固了巴芬湾北部的太古宙和古元古代复合体的区域地图，这些复合体显示了从加拿大到格陵兰岛的连续性，没有跨越纳尔斯海峡的位移。
The Precambrian shield of northern Greenland has been investigated by SHRIMP U–Pb zircon dating of 14 orthogneisses and granitoids plus 5 metasediments, integrated with mapping by the Geological Survey of Denmark and Greenland and whole-rock Nd isotopic studies. The Inglefield Mobile Belt is a tract of Palaeoproterozoic sedimentation, plutonism, polyphase deformation and high-grade metamorphism that underlies Inglefield Land and northern Prudhoe Land. In the southern part of the belt at 78°30′N, the E–W-trending Sunrise Pynt Straight Belt is a high-grade, but structurally late, shear zone with contrasts in the geology on either side. South of the Sunrise Pynt Straight Belt, ca. 1980Ma diorites and tonalites were emplaced into older orthogneisses and metasediments. Detrital zircons from two metaquartzites (deposited on Archaean basement?) yielded complex age spectra from ca. 3250Ma to 2350Ma, with 2600–2450Ma grains dominant. In associated mica schist, low Th/U, 1923±8Ma zircons date high-grade metamorphism. The most southern orthogneiss investigated (77°45′N) is Neoarchaean (ca. 2600Ma), in agreement with previously published isotopic data. North of the Sunrise Pynt Straight Belt to 79°10′N an amphibolite–granulite-facies complex with extensive pelitic to psammitic paragneisses are the oldest rocks recognised. Two psammitic paragneisses yielded unrounded zircons with a unimodal detrital age population centred on 2000–1980Ma. Their source could be ca. 1980Ma orthogneisses from south of the Sunrise Pynt Straight Belt, or from basement inliers in the North-East Greenland Caledonian fold belt. The metasediments were intruded by tonalites and diorites with dates of 1949±13Ma and 1943±11Ma, and then by granitoids (free of zircon inherited from older rocks) with ages of 1924±29Ma to 1915±19Ma. The metasediments show development of low Th/U zircon overgrowths at ca. 1920Ma, coeval with the granitoids. Finally, other granites, some locally transformed into gneisses, have ages of 1783±22Ma to 1741±15Ma. Inherited zircons in the latter are up to 2650Ma old. A granite dyke with a zircon age of 1783Ma has an TDMage of 2981Ma and a strongly negative ɛNdat 1.78Ga, indicating derivation by melting or reworking of Archaean crust. Thus, by 1800Ma this juvenile Palaeoproterozoic terrane had probably overridden crust with Archaean components. North of Inglefield Land, Precambrian crystalline rocks are obscured until Victoria Fjord (81°30′N). One reconnaissance orthogneiss sample from there contains ca. 3400Ma oscillatory-zoned zircons, which probably date the rock, rather than being a xenocrystic component in a younger rock. Thus, from north to south there is an assemblage of Archaean, Palaeoproterozoic and Archaean to early Palaeoproterozoic gneiss terranes. The Inglefield Mobile Belt is dominated by juvenile Palaeoproterozoic arc crust trapped between two unrelated blocks of Archaean crust of contrasting age. The collision, and probably thrusting of a Palaeoproterozoic arc over a southern Archaean foreland, occurred at ca. 1920Ma—dated by metamorphic zircon. The new isotopic results consolidate the regional mapping of Archaean and Palaeoproterozoic complexes across northern Baffin Bay that show continuity from Canada into Greenland, without displacement across the Nares Strait.