PETROGENESIS AND TECTONO-MAGMATIC SIGNIFICANCE OF THE ALBANIDE - HELLENIDE SUBPELAGONIAN OPHIOLITES
PETROGENESIS AND TECTONO-MAGMATIC SIGNIFICANCE OF THE ALBANIDE - HELLENIDE SUBPELAGONIAN OPHIOLITES
复制标题
DOI：
10.4454/ofioliti.v29i1.207
复制
发表时间：
2004-01
期刊：
影响因子：
1.3
通讯作者：
E. Saccani;L. Beccaluva;M. Coltorti;F. Siena
中科院分区：
文献类型：
--
作者：
E. Saccani;L. Beccaluva;M. Coltorti;F. Siena
阿尔Albanide-Hellenide造山带的mirdata - subpelagonian蛇绿岩是从前南斯拉夫延伸到希腊的连续带的一部分，具有共同的地质、岩石地层、地球化学和成矿特征。在阿尔巴尼亚板块，可以清楚地识别出两条截然不同的蛇绿岩带：西带主要由洋中脊（MORB）蛇绿岩组成，东带以超俯冲带（SSZ）蛇绿岩为特征，主要有岛弧拉斑岩（IAT）和轻微的波长岩亲和力。在西带的最东端（中密地塔），还发育有MORB/IAT中间玄武岩和白质岩脉的过渡带。在希腊段，不能明确区分为两个蛇绿岩带，morb型蛇绿岩（西部型）是从属的，仅以Pindos地块的侵入和下火山层序为代表。SSZ-蛇绿岩（东部型）以Vourinos地块的IAT和博美岩层序以及Pindos火山层序上部的MORB/IAT中玄武-安山岩套和博美岩层序为主要代表。岩石学和地球化学模拟表明，不同的阿氏-希腊氏蛇绿岩序列起源于明显不同的母岩浆，是由于地幔源的部分熔融而逐渐被先前的熔体萃取耗尽。MORB可能来源于未枯竭的伊热橄榄岩源10 - 20%的部分熔融，而MORB/IAT中间玄武岩可能是由之前经历过MORB提取的cpx-贫伊热橄榄岩的约10%的h2o辅助部分熔融产生的。IAT岩浆和boninites可能依次来自同一来源的10 - 20%和约30%的部分熔融，并被俯冲衍生的流体和相关的不相容元素不同程度地富集。有利于Albanide-Hellenide蛇绿岩成因的构造-岩浆模式表明：1)在原始MORB岩石圈内的洋内俯冲，导致具有IAT亲和力的SSZ岩浆活动，并通过几乎开放系统的未分化玄武岩（片状脉杂岩）供应产生新生弧；2)板块的递进沉陷与地幔底辟作用相结合，并由弧轴向弧前区延伸，由枯竭弧下源区生成博宁质和（或）极低钛的拉斑岩，留下高度枯竭的哈兹伯尔质残余；(3)由于MORB源底辟岩与俯冲上地幔源的干扰，导致IAT/MORB中间玄武岩扩张轴同生；4)辐合过程导致大而相对完整的SSZ蛇绿岩岩石圈剖面向Pelagonian大陆边缘逆冲，经常伴有变质底的穿插。后者具有普遍的MORB亲和性，是由仍热的蛇绿岩板块逆冲的原始MORB岩石圈遗迹。
The Mirdita-Subpelagonian ophiolites of the Albanide-Hellenide orogen are parts of a continuous belt extending from the former Yugoslavia to Greece, and share common geological, litho-stratigraphical, geochemical, and metallogenic features. In the Albanian sector, two distinct ophiolitic belts can be clearly identified: the Western Belt, mainly composed of mid-ocean ridge (MORB) ophiolites, and the Eastern Belt characterized by supra-subduction zone (SSZ) ophiolites with prevalent island arc tholeiitic (IAT) and minor boninitic affinity. In the easternmost border of the Western Belt (Central Mirdita), a transitional zone with MORB/IAT intermediate basalts and boninitic dykes also occur. In the Greek sector, a definite distinction into two ophiolitic belts cannot be made, and MORB-type ophiolites (western type) are subordinate, being represented only by the intrusive and lower volcanic sequences of the Pindos Massif. By contrast, SSZ- ophiolites (eastern type) are predominant and well-represented by the IAT and boninitic sequences of the Vourinos Massif, as well as by MORB/IAT intermediate basaltic-andesitic suites and boninites of the upper part of the Pindos volcanic sequence. Petrological and geochemical modelling suggest that the different Albanide -Hellenide ophiolitic sequences originated from distinctly different parental magmas by partial melting of mantle sources progressively depleted by previous melt extractions. MORB may have derived from 10 - 20% partial melting of an undepleted lherzolitic source, while MORB/IAT intermediate basalts may have generated by ca. 10% of H2O-assisted partial melting of a cpx-poor lherzolite that had previously experienced MORB extraction. IAT magmas and boninites may, in turn, have derived from 10 – 20 % and ca. 30% partial melting of the same source, variably enriched by subduction-derived fluids and related incompatible elements. The favoured tectono-magmatic model for the genesis of the Albanide-Hellenide ophiolites implies a low plate-convergence velocity with: 1) intra-oceanic subduction within a pristine MORB lithosphere, resulting in SSZ magmatism with IAT affinity, and generation of a nascent arc by nearly open-system supply of undifferentiated basalts (sheeted dyke complexes); 2) progressive slab sinking and retreat coupled with mantle diapirism and extension from the arc axis to the forearc region, with generation of boninites and/or very low-Ti tholeiites from depleted sub-arc sources, leaving highly depleted harzburgitic residua; 3) contemporaneous generation at the spreading axis of IAT/MORB intermediate basalts resulting from the interference of MORB-source diapirs with suprasubduction mantle sources; 4) convergence processes leading to obduction of large and relatively intact lithospheric sections of SSZ ophiolites onto the Pelagonian continental margin, often with the interposition of metamorphic soles. The latter have prevalent MORB affinity and represent relics of the pristine MORB lithosphere overthrust by the still hot ophiolitic slab.