Petrogenesis of Gympie Group volcanics: evidence for remnants of an early Permian volcanic arc in eastern Australia
Petrogenesis of Gympie Group volcanics: evidence for remnants of an early Permian volcanic arc in eastern Australia
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DOI：
10.1016/0024-4937(88)90012-6
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发表时间：
1988-02
期刊：
影响因子：
3.5
通讯作者：
W. Sivell;J. B. Waterhouse
中科院分区：
文献类型：
--
作者：
W. Sivell;J. B. Waterhouse
富含镁铁质蛇绿晶玄武岩到玄武质安山岩凝灰岩-凝灰岩、凝灰岩和次级熔岩，与稀疏的石英和斜长英安质凝灰岩和玻璃流一起，构成了昆士兰东南部金皮群下二叠世构造形态异常的海底火山岩序列。地球化学数据表明，主要火山岩系列经历了三个不同的结晶阶段。它们是：(1)初始橄榄石(±铬尖晶石)+单斜辉石的剥离，导致上升地幔岩浆中的镁、钙、镍和铬的快速亏损；(2)广泛的单斜辉石主导的橄榄石+单斜辉石+斜长石的分馏作用，导致玄武岩-玄武岩系列中拉斑玄武岩FeO2、TiO2、Al2O3、P2O5、Zr和Y的富集；(3)斜长石(主要)+辉石+磁铁矿+磷灰石结晶，导致英安岩中Al2O3、TiO2、FeO1、P2O5、V、Nb和Sr的含量降低。玄武岩和英安岩的稀土元素(REE)分馏程度相同，表明它们是同源岩浆，排除了角闪石对其成岩作用的重大影响。岛弧拉斑玄武岩具有较低的镁含量(镁1)、镍、铬、稀土元素和高场强阳离子(HFSC)丰度，以及较低的ZY、TiY和Nb-Zr比值。金皮岩套代表了一个不成熟的海底拉斑玄武岩阶段，它代表了与冈瓦那接壤的一部分主要洋内弧的发展阶段，但由于塔斯曼海的开放而支离破碎。粗大的单斜辉石-斑状英安岩的存在，以及高度分异的英安岩，可能与冈瓦那边缘早二叠世演化期间对岩浆供应和体积喷发速率产生重要控制的走滑构造阶段有关。
Mafic ohenocryst-rich basalt to basaltic andesite tuff-breccias, agglomerates and subordinate lavas, together with sparsely quartz-and plagiophyric dacitic tuffs and glassy flows, comprise the tectonomorphically anomalous lower Permian submarine volcanic sequence of the Gympie Group, southeast Queensland. Geochemical data imply three distinct crystallisation stages for the main volcanic series. These are (1) initial olivine (±Cr-spinel)+ clinopyroxene removal that caused rapid MgO, CaO, Ni and Cr depletion in the ascending mantle-derived magma;(2) extensive clinopyroxene-dominated olivine+ clinopyroxene+ plagioclase fractionation that gave rise to tholeiitic FeO 1, TiO 2, Al 2 O 3, P 2 O 5, Zr and Y enrichment in the basalt-basaltic andesite range; and (3) plagioclase (dominant)+ augite+ magnetite+ apatite crystallisation that resulted in decreasing Al 2 O 3, TiO 2, FeO 1, P 2 O 5, V, Nb and Sr levels in the dacites. Identical degrees of rare-earth element (REE) fractionation for the basalts and dacites suggest their comagmatic origin and preclude significant amphibole involvement in their petrogenesis. Low Mg-numbers (Mg 1), Ni, Cr, REE and high-field-strength cation (HFSC) abundances in the Gympie basalts, along with low Zr Y, Ti Y and Nb Zr ratios, are features typical of island arc tholeiites. The Gympie suite represents an immature submarine tholeiitic stage of development of a portion of a major intra-oceanic arc that bordered Gondwana, but was fragmented by opening of the Tasman Sea. The presence of coarse clinopyroxene-phyric ankaramites, together with highly differentiated dacites, may relate to a phase of strike-slip tectonics that exerted important control on magma supply and volumetric eruptive rates during the early Permian evolution of the Gondwana margin.