Generation of Arc and Within-plate Chemical Signatures in Collision Zone Magmatism: Quaternary Lavas from Kurdistan Province, Iran
Generation of Arc and Within-plate Chemical Signatures in Collision Zone Magmatism: Quaternary Lavas from Kurdistan Province, Iran
复制标题
碰撞区岩浆作用中电弧和板内化学特征的生成：伊朗库尔德斯坦省第四纪熔岩
DOI：
10.1093/petrology/egs090
复制
发表时间：
2013
影响因子：
3.9
通讯作者：
Allen M
中科院分区：
文献类型：
--
作者：
Allen M
新的全岩和Sr-Nd同位素分析的第四纪熔岩从库尔德斯坦省，伊朗西部，揭示了造山高原岩浆作用的性质在大陆碰撞和副矿物在地幔部分熔融在这个构造环境中的可能作用。采样的熔岩来自阿拉伯-欧亚碰撞带内的土耳其-伊朗高原。典型的成分是碧玄岩、夏威夷岩和碱性玄武岩，还有少量流纹岩。Qorveh-Bijar地区的大多数基本样品具有高丰度的大离子亲石元素（LILE）和轻稀土元素（LREE）（例如76 ppm < La < 165 ppm），具有陡峭的REE模式：45 < La/Yb < 101。研究区北部塔卡卜的两个岩流的K2 O/Na 2 O和Rb值高于Qorveh-Bijar样品，而轻稀土和Ba值低于Qorveh-Bijar样品。所有基性样品的Sr-Nd同位素值都接近块状硅酸盐土，143 Nd/144 Nd在0·51263和0·51276之间，87 Sr/86 Sr在0·70467和0·70600之间;这与伊朗-土耳其边界到西北部的第四纪碱性玄武岩相似，但与同一碰撞带其他地方更贫化的源熔融不同;例如，在阿拉拉特山和卡尔斯高原（土耳其）。地壳混染似乎不是影响岩浆成分的重要因素。化学特征的范围表明至少有两个不同来源的不同熔化。一个推断的来源产生的熔体与La/Nb范围从1.35到1.12，这是不寻常的火山岩，否则是同时代的。我们解释这种变化的结果耗尽的K-锂霞石和金红石轴承源熔化过程中的石榴石稳定场。这一结果的重要性是，负Nb异常和分馏的LILE的大小可能取决于源矿物学中的K-里希特石和金红石，而不仅仅是在源区不相容的微量元素的大量丰度。我们推断金云母的存在下，在第二个地幔源，熔融产生更多的钾质熔岩从塔卡卜。在研究区域，岩石圈分层或板块断裂机制引发熔融是有问题的，因为据报道岩石圈厚达150-200公里。晚新生代的伸展作用还没有被认识到，因此伸展作用不太可能是熔融的原因。西北-东南对齐的火山中心，平行于区域结构颗粒，并暗示结构控制，至少在最后的喷发现场。欧亚大陆地幔岩石圈可能受到中生代-新生代早期俯冲和碰撞早期流体的交代作用。最近的会聚有可能导致再受精岩石圈的进一步流动和熔融，沿着造山带沿着的横向运动帮助岩浆快速上升。角闪石橄榄岩固相线的负dT/dP截面也可能是碰撞带岩石圈增厚的结果（即压缩熔融而不是减压熔融）。副相的耗尽也可能有助于解释造山带中从弧到板内化学的大规模转变，如古近纪的阿拉伯-欧亚体系，以及中国东部的中新生代岩浆活动。
New whole-rock and Sr–Nd isotopic analyses of Quaternary lavas from Kurdistan Province, western Iran, shed light on the nature of orogenic plateau magmatism during continental collision and the possible role of accessory minerals during mantle partial melting in this tectonic setting. The sampled lavas are from the Turkish–Iranian plateau within the Arabia–Eurasia collision zone. Compositions are typically basanite, hawaiite and alkali basalt, with minor rhyolite. Most of the basic samples from the Qorveh–Bijar region have elevated abundances of large ion lithophile elements (LILE) and light rare earth elements (LREE) (e.g. 76 ppm < La < 165 ppm), with steep REE patterns: 45 < La/Yb < 101. Two flows from Takab in the north of the study area have higher K2O/Na2O and Rb than the Qorveh–Bijar samples, but lower LREE and Ba. Sr–Nd isotope values for all the basic samples plot close to Bulk Silicate Earth, with143Nd/144Nd between 0·51263 and 0·51276, and87Sr/86Sr between 0·70467 and 0·70600; this is similar to Quaternary alkali basalts from the Iran–Turkey borderlands to the NW, but distinct from a more depleted source melting elsewhere in the same collision zone; for example, at Mount Ararat and the Kars plateau (Turkey). Crustal contamination does not appear to be an important factor affecting magma composition. The range of chemical signatures suggests variable melting of at least two distinct sources. One inferred source produced melts with La/Nb ranging from ∼3·5 to ∼1·2, which is unusual for volcanic rocks that are otherwise coeval. We interpret this variation as the result of depletion of a K-richterite- and rutile-bearing source during melting in the garnet stability field. The importance of this result is that the size of the negative Nb anomaly and fractionation of LILE may depend on K-richterite and rutile in the source mineralogy, rather than simply the bulk abundances of incompatible trace elements in the source region. We infer the presence of phlogopite in a second mantle source, the melting of which produced the more potassic lavas from Takab. Lithosphere delamination or slab break-off mechanisms for triggering melting are problematic in the study area, as the lithosphere is reportedly ∼150–200 km thick. Late Cenozoic extension has not been recognized, and so extension is unlikely as a cause of melting. The NW–SE alignment of volcanic centres, parallel to the regional structural grain, does imply a structural control, at least on the final eruption site. Eurasian mantle lithosphere was probably metasomatized by fluids derived from Mesozoic–early Cenozoic subduction and the early stages of collision. More recent convergence has had the potential to cause further fluxing and melting of the re-fertilized lithosphere, with rapid magma ascent assisted by transcurrent motion along the orogen. It is also possible that the negative dT/dPsection of the amphibole peridotite solidus was crossed as a result of lithospheric thickening in the collision zone (i.e. compression melting rather than decompression melting). Exhaustion of accessory phases may also help explain larger-scale transitions from arc to within-plate chemistry in orogens, such as the Paleogene Arabia–Eurasia system, and the Mesozoic–Cenozoic magmatism of eastern China.
登录
查看更多内容
第四纪碰撞后火山作用的岩石成因模型：安纳托利亚中部和东部的案例研究
影响因子：
2.3
作者：
P. Şen;A. Temel;A. Gourgaud
通讯作者：
A. Gourgaud
影响因子：
3
作者：
G. Ahmadzadeh;A. Jahangiri;D. Lentz;M. Mojtahedi
通讯作者：
G. Ahmadzadeh;A. Jahangiri;D. Lentz;M. Mojtahedi
影响因子：
3.9
作者：
M. Kirchenbaur;C. Münker;S. Schuth;D. Garbe‐Schönberg;P. Marchev
通讯作者：
M. Kirchenbaur;C. Münker;S. Schuth;D. Garbe‐Schönberg;P. Marchev
影响因子：
2.1
作者：
M. Lustrino;M. Keskin;M. Mattioli;V. Lebedev;A. Chugaev;E. Sharkov;O. Kavak
通讯作者：
M. Lustrino;M. Keskin;M. Mattioli;V. Lebedev;A. Chugaev;E. Sharkov;O. Kavak
扎格罗斯带/伊朗高原的隆起时间和晚新生代阿拉伯-欧亚大陆辐合的调节
影响因子：
2.3
作者：
F. Mouthereau
通讯作者：
F. Mouthereau