Trace element and isotope (Sr, Nd) geochemistry of porphyry- and skarn-mineralising Late Cretaceous intrusions from Banat, western South Carpathians, Romania
Trace element and isotope (Sr, Nd) geochemistry of porphyry- and skarn-mineralising Late Cretaceous intrusions from Banat, western South Carpathians, Romania
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罗马尼亚南喀尔巴阡山脉西部巴纳特晚白垩世斑岩和矽卡岩矿化侵入体的微量元素和同位素（Sr、Nd）地球化学
DOI：
10.1007/s00126-002-0274-7
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发表时间：
2002
影响因子：
4.8
通讯作者：
T. Berza
中科院分区：
文献类型：
--
作者：
A. Dupont;J. Vander Auwera;C. Pin;Ştefan Marincea;T. Berza
摘要。从罗马尼亚南喀尔巴阡山脉7个晚白垩世矽卡岩（Tincova, boc<e:1>, Ocna de Fier - Dognecea）和斑岩型铜钼/矽卡岩矿床（Oraviţa, Ciclova， Sasca和Moldova nouu）的24个样品中获得了地球化学和同位素（锶、钕）数据。这些侵入体在巴纳特成矿省切割了超实层推覆体，形成了一条长100公里、北北东—南西向的构造线。样品的组成范围从辉长岩到花岗闪长岩，并在主微量元素变化图中确定了钙碱性到高钾钙碱性的趋势，SiO2含量为50% ~ 67%。它们是富LILE/LREE、贫Nb、Ta、Zr的含磁铁矿型花岗岩，是与俯冲带有关的岩浆的共同特征。缺乏累积结构和阳性铕异常似乎表明样品代表液体成分。因此，观察到的趋势近似于由主元素和微量元素组成相似的母岩浆的分数结晶而产生的液体下降线。初始锶同位素比值（Sri）在0.7042 ~ 0.7058之间，εNd(t)在+3.9 ~ -0.2之间。Sri和εNd(t)值随SiO2的变化表现出轻微的地壳同化作用。εNd(t)值普遍为正，且Sri适中，表明母岩浆是由富铷贫稀土源（如非均质岩石圈地幔或由此衍生的年轻基性下地壳）的部分熔融形成的。根据TDM模型年龄（约600 Ma），选择性铷富集可能发生在早白垩世或更早的俯冲事件中，由上覆地幔楔的交代作用引起。Cu-Mo（-Pb-Zn-Fe）矿床与侵入体密切相关，Banat（罗马尼亚）地区可划分为两个成矿带。巴纳特北部以Fe-Cu-Pb-Zn矽卡岩为主，南部以斑岩型铜钼矿床为主。这些差异是由以下几个参数共同造成的：(1)岩浆组成，其中富铜和钼矿床往往与钙碱性组成有关；(2)巴纳特北部存在大型等粒状岩体，巴纳特南部存在与斑岩式矿化有关的斑岩冲天炉和斑岩状斑岩，表明现代侵蚀水平从南到北呈上升趋势；(3)寄主岩的性质，矽卡岩在钙质寄主岩中优先发育；(4)控制流体入渗和矿石沉淀条件的局部变化。
Abstract. Geochemical and isotopic (strontium, neodymium) data have been obtained from 24 samples of seven Late Cretaceous intrusions associated with skarn (Tincova, Bocşa, Ocna de Fier – Dognecea) and porphyry copper-molybdenum/skarn deposits (Oraviţa, Ciclova, Sasca and Moldova Nouă) in the South Carpathians of Romania. The intrusions cut the Supragetic-Getic nappes and form a 100-km-long, NNE-SSW-trending lineament in the Banat metallogenic province. The samples range in composition from gabbro to granodiorite and define, in major and trace element variation diagrams, a calc-alkaline to high-potassium calc-alkaline trend ranging from 50 to 67% SiO2. They are magnetite-bearing, I-type granitoids enriched in LILE/LREE and depleted in Nb, Ta and Zr, common features for magmas associated with subduction zones. The lack of cumulate textures and of positive europium anomalies seems to indicate that the samples represent liquid compositions. The observed trend thus approximates a liquid line of descent resulting from fractional crystallisation of parental magmas with similar major and trace element compositions. Initial strontium isotopic ratios (Sri) vary from 0.7042 to 0.7058 and εNd(t) values range from +3.9 to –0.2. Variations of Sri and εNd(t) values with SiO2 show minor crustal assimilation. The generally positive εNd(t) values, together with moderate Sri, indicate that the parental magmas result from partial melting of a rubidium-enriched and LREE-depleted source, such as a heterogeneous lithospheric mantle or a young mafic lower crust derived from it. Selective rubidium enrichment probably occurred during a previous subduction event by metasomatism of the overlying mantle wedge, either in the Early Cretaceous or earlier, as suggested by TDM model ages (ca. 600 Ma). The Cu-Mo(-Pb-Zn-Fe) deposits are intimately associated with the intrusions, and the Banat (Romania) region can be subdivided in two metallogenic zones. In northern Banat, Fe-Cu-Pb-Zn skarns occur whereas in southern Banat, porphyry-style copper and molybdenum deposits predominate. These differences result from a combination of several parameters: (1) magma composition, whereby copper- and molybdenum-rich deposits tend to be associated with calc-alkaline compositions; (2) an increase of the present-day erosion level, from south to north, as indicated by the presence of large equigranular plutons in northern Banat, and of porphyritic cupolas and apophyses associated with porphyry-style mineralisation in southern Banat; (3) the nature of the host rocks, with skarns preferentially developed in calcareous host rocks; and (4) local variations of conditions controlling the infiltration of fluids and the precipitation of ore minerals.