【作者】 曾雯；

【导师】 钟增球；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2010， 博士

【摘要】 华夏地块位于华南地块东南部,其北东段的闽西北地区零星的出露基底变质岩系,自古元古代形成以来,至晚古生代遭受强烈的变质变形,经历高角闪岩相—混合岩化作用。本论文主要运用详细的野外地质观察、系统的采样、岩相学研究、全岩地球化学、锆石U-Pb和Lu-Hf同位素、微量元素、角闪石和黑云母40Ar/39Ar定年以及矿物化学成分测定等研究方法,旨在揭示闽西北地区混合岩中新成体、长英质副变质岩以及基性变质岩的年代学特征和存在的相互关系,从而讨论本区变质岩系演化过程及其在前寒武纪Rodinia超大陆重建中的响应。获得主要认识如下：1.根据变质程度和变形特征,华夏地块闽西北地区变质岩系可分为两种类型,(1)经历中高级变质作用且发生流变的岩石和(2)经历过中级变质作用且发生韧性变形的岩石。本次研究所得的新La-ICPMS锆石U-Pb年龄数据以及前人的年代学研究表明,由于早-中古生代(～473-～423 Ma)的构造-热事件对闽西北地区变质岩产生的强烈再造作用,使其成为复杂的变质变形地质体,应采用“杂岩体”对其命名,代替原先所使用的如“群”、“组”等岩石地层学分类命名方法。2.华夏地块副变质岩原岩中锆石U-Pb年龄图谱中,位于～1800 Ma处明显的峰值表明其与北美基底物质存在一定联系,而不同于东印度和东南极年龄图谱。尽管在西澳大利亚的锆石年龄图谱中也存在～1800 Ma的峰值,然而其176Hf/177Hf比值(0.280706-0.281510)显然低于华夏地块南西段的比值(0.281515-0.282098)和此次对华夏北东段研究结果(0.281232-0.282213)。另外,碎屑锆石的Hf同位素研究结果表明华夏地块和扬子地块西北部在古-中古元古代时期存在存在显著的新生地壳物质,这一特征完全不同于西澳大利亚。这些证据表明,华夏地块同北美大陆存在着相似性,从而佐证Li et al.(2008)的Rodinia超大陆重建方案,即在晚中元古代Rodinia超大陆聚合之前以及聚合过程中,华夏地块同西Laurentia大陆相邻。3.闽西北地区长英质副片麻岩的原岩为不成熟沉积物,包括硬砂岩、长石砂岩以及岩屑砂岩等。沉积物源主要来自于发生在新元古代(820±6 Ma,780±6 Ma,776±6 Ma,758±3 Ma,740±8 Ma和722±9 Ma)的几次岩浆事件,其沉积时间上限可能不早于中新元古代(～680 Ma)。大量变质岩中含有0.99-0.72 Ga的碎屑岩浆锆石,说明这些构造-热事件的记录可能与新元古代Rodinia超大陆的聚合与裂解相关。4.在闽西北地区测得的La-ICPMS锆石U-Pb深熔年龄新数据表明,该区存在强烈而广泛的早古生代构造-热事件,并可能与造山运动相关。此次造山运动起始于中寒武纪,持续至中泥盆纪,其间存在三个主要期次(～473 Ma、～445 Ma、～423 Ma),并且其主要造山事件(包括同造山和后造山熔融)在华夏地块北东段发生于～473-～407 Ma,在其南西段则发生于-468.415 Ma。华夏地块古生代年龄图谱中存在的峰值(约488、471、455、440和415 Ma)处于秦岭-桐柏-大别在早-中古生代(512-406 Ma)发生的造山事件时限内。这说明当时两个造山事件之间存在着某种联系或相互作用。5.闽西北地区“加里东”造山事件的延续时间不短于～50 Myr,始于～473 Ma(早奥陶纪)或更早,完成于～423 Ma(中志留纪)或更晚。华夏地块的“加里东”造山事件的起因更可能是陆内碰撞而非洋壳俯冲或弧陆碰撞。闽西北地区天井坪杂岩体、交溪和麻源杂岩体不均一的冷却曲线,以及华夏地块不同区域发生深熔和岩浆事件的时限存在的差异性,暗示了“加里东”构造-热事件在华夏地块造山带的不均一性。更多还原

【Abstract】 This thesis focuses on the Paleoproterozoic to Late Paleozoic basement evolution of the metamorphic rocks scattered in the NW Fujian Province, the NE Cathaysia Block the southeastern area of South China. Field observation, systematic sampling and petrographic investigation combined with of whole rock geochemistry, zircon U-Pb, Lu-Hf isotopes, trace elements, amphibole and biotite 40Ar/39Ar analyses and mineral chemistry study were applied in this project to determine the nature, ages and relations of the leucosomes, felsic paragneiss and mafic metamorphic rocks in study area and their implications to the reconstruction of the Precambrian Rodina Supercontinent.Following conclusions are made:1. Based on this study, according to their metamorphism and deformation characteristics, the metamorphic rock series in the study area can be divided into two types, moderately to strongly metamorphosed rock series that experienced ductile deformation and moderately metamorphosed rock series that have experienced ductile deformations. New La-ICPMS U-Pb zircon ages presented here and in previous study suggest that the original litho-stratigraphy should be abandoned and the terminology "Complex" should be used instead of "Group" and "Formation" for the high grade metamorphic rock series in northwestern Fujian, where the protoliths were strongly reworked by Early Paleozoic tectono-thermal events.2. Obvious zircon U-Pb age peaks of～1800 Ma suggest that the protoliths of the Cathaysia Block be comparable to the basements of North America rather than those of Eastern India and East Antarctica. Although the peaks of～1800 Ma are also present in Western Australia, their 176Hf/177Hf ratios (0.280706-0.281510) are apparently lower than those of zircons from SW Cathaysia (0.281515-0.282098) and from this study (0.281232-0.282213, NE Cathaysia). Besides, detrital zircons in Cathaysia and NW Yangtze indicate significant juvenile input during Paleo-to Mesoproterozoic according to the zircon Hf isotopes, which are distinctly different from Western Australia. These evidences suggest that the basement of the Cathaysia share similarities with that of North America, lending support for the Rodinia configuration proposed by Li et al. (2008), in which Cathaysia was next to western Laurentia before and during the late Mesoproterozoic assembly of Rodinia.3. The protoliths of the felsic paragneiss in the NW Fujian area are immature sediments, consisting of greywacke, arkose and lithic arenite compositions. The significant input of the paragneiss protolith was dominantly formed by several magmatic events during Neoproterozoic (820±6 Ma,780±6 Ma,776±6 Ma,758±3 Ma,740±8 Ma and 722±9 Ma), probably deposited not early than middle Neoproterozoic (-680 Ma). Many metamorphic rocks contain 0.99-0.72 Ga detrital magmatic zircons, which are interpreted as reflecting the tectono-thermal events related to the assembly and break-up of the Rodinia supercontinent during the Neoproterozoic.4. In this study, new La-ICPMS U-Pb anatectic zircon data from the NW Fujian area suggest that the strong and widespread tectono-thermal events were related to the orogeny probably having started during the Middle Cambrian and lasted until the Middle Devonian, consisting of at least three main episodes (～473 Ma,～445 Ma,～423 Ma), with major orogeny events (including syn-to post-orogenic melting) constrained between～473 Ma and～407 Ma in the NE Cathaysia, and between～468 Ma and～415 Ma in the SW Cathaysia. The age peaks in the Cathaysia Block (ca. 488,471,455,440 and 415 Ma) are within the age range of the Qinling-Tongbai-Dabie orogen during 512-406 Ma. This suggests a possible linkage or interaction of the two orogens.5. The duration of the "Caledonian" orogeny in the NW Fujian area was no shorter than～50 Myr, starting at～473 Ma (～Early Ordovician) or earlier, and terminating at～423 Ma (～Middle Silurian) or later. The "Caledonian" orogenic event in the Cathaysia Block was likely due to an intracontinental collision rather than the subduction of oceanic crust or arc-continental collision. Considering the inhomogeneous cooling paths for the Tianjingping, the Jiaoxi and Mayuan complexes, and different time restraint of the widespread anatectic and magmatic events occurred in different places, the "Caledonian" tectono-thermal events in the Cathaysia Block might vary between different segments of the orogen.更多还原