Detrital zircon ages from a Lower Ordovician quartzite of the İstanbul exotic terrane (NW Turkey): evidence for Amazonian affinity
Detrital zircon ages from a Lower Ordovician quartzite of the İstanbul exotic terrane (NW Turkey): evidence for Amazonian affinity
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伊斯坦布尔奇异地体（土耳其西北部）下奥陶统石英岩的碎屑锆石年龄：亚马逊亲和力的证据
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发表时间：
2011
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通讯作者：
G. Zulauf
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作者：
P. A. Ustaömer;T. Ustaömer;A. Gerdes;G. Zulauf
土耳其西北部是几个大陆和海洋单元的马赛克，它们是由碰撞和走滑构造合并而成的。大陆单元之一为İstanbul地体，其古生代地层包括早奥陶世至早石炭世海侵沉积层序。博鲁地块暴露出古生代演替的基底，以晚新元古代（约575 Ma）长英质岩浆侵入的厚变质火山单元为代表。该变质火成岩基底被认为是卡多米亚岩浆弧的一个分支。不整合上覆早奥陶世地层始于红色河流碎屑（约3000 m），上覆浅海相石英岩（<250 m）。在与下伏红色河流碎屑接触处5 m处的奥陶系石英岩样品中分离出碎屑锆石。利用激光烧蚀扇形场-电感耦合等离子体质谱仪（LA-SF-ICP-MS）对99颗锆石进行了U-Pb测年。年龄在530 ~ 2550 Ma之间（97%一致，90%一致）。新元古代锆石年龄（约540,570,600 - 640和700-800 Ma）的优势（44粒）排除了İstanbul地体与波罗的海的任何联系。锆石种群中大量（40粒）的Grenvillian和中至古元古代（约1.0-1.2 Ga、1.3-1.6 Ga、1.7-1.8 Ga和1.9-2.1 Ga）的锆石进一步排除了与卡多米亚和米诺斯地体的联系，但表明了亚马逊河源区。新时代数据表明İstanbul地体为冈瓦纳大陆的近缘地体，位于冈瓦纳大陆西北边缘，靠近亚马逊河流域。这块地体在显生宙应该已经移动了很长一段距离。
NW Turkey is a mosaic of several continental and oceanic units, that were amalgamated by collisional and strike–slip tectonics. One of the continental units is the İstanbul terrane, the Palaeozoic strata of which comprise an Early Ordovician to Early Carboniferous transgressive sedimentary sequence. The basement to the Palaeozoic succession is exposed in the Bolu Massif and is represented by a thick meta-volcanic unit intruded by Late Neoproterozoic (ca. 575 Ma) felsic magma. This meta-igneous basement is considered to be a sliver of the Cadomian magmatic arc. Unconformably overlying Early Ordovician strata start with red fluvial clastics (ca. 3,000 m), overlain by shallow marine quartzites (<250 m). Detrital zircons were separated from an Ordovician quartzite sample located 5 m above the contact with the underlying red fluvial clastics. We have dated a total of 99 zircon grains by U–Pb method using laser ablation-sector field-inductively coupled plasma mass spectrometer (LA-SF-ICP-MS). The ages (97% are >90% concordant) range from 530 to 2550 Ma. The dominance (44 grains) of Neoproterozoic zircon ages (around 540, 570, 600–640 and 700–800 Ma) rules out any link of the İstanbul terrane with Baltica. The large amount (40 grains) of Grenvillian and Meso- to Palaeo-proterozoic ages (around 1.0–1.2, 1.3–1.6, 1.7–1.8, and 1.9–2.1 Ga) in the zircon population further rules out a link to Cadomian and Minoan terranes, but is indicative for Amazonian source areas. The new age data suggest the İstanbul terrane to be a peri-Gondwanan terrane that was located at the northwestern margin of Gondwana close to Amazonia. This terrane should have travelled a large distance in the Phanerozoic times.