Late- and post-orogenic Neoproterozoic intrusions of Jordan: implications for crustal growth in the northernmost segment of the East African Orogen
Late- and post-orogenic Neoproterozoic intrusions of Jordan: implications for crustal growth in the northernmost segment of the East African Orogen
复制标题
约旦新元古代晚期和造山后侵入：对东非造山带最北段地壳生长的影响
DOI：
10.1016/s0301-9268(03)00073-1
复制
发表时间：
2003
影响因子：
3.8
通讯作者：
H. Al
中科院分区：
文献类型：
--
作者：
G. Jarrar;R. Stern;G. Saffarini;H. Al
约旦南部大约90%的上地壳由新元古代晚期的侵入岩组成，分为两个主要的分区：亚喀巴（600- 640 Ma）和阿拉巴（560- 600 Ma）杂岩。亚喀巴复合体由几个岩套组成，其成分范围从辉长岩到高硅花岗岩（SiO2含量为45-80%），并遵循高钾钙碱性趋势。这一阶段始于640 - 600 Ma之间Duheila Hornblendic Suite的侵位，代表了约旦西南部的主要地壳形成阶段。阿拉巴杂岩是一个双峰碱钙碱性火成岩套后，区域不整合和沉积的Saramuj砾岩的发展。亚喀巴杂岩的基性岩段Duheila Hornblendic岩套相对于HFSE富集LILE，并适度富集REE [（La/Lu）n=5-11]，具有典型的弧玄武岩特征。地球化学模拟表明，可能在俯冲带上方，含角闪石的尖晶石二辉橄榄岩熔融了10-15%。亚喀巴杂岩体中的花岗岩类具有高Ba、Sr和LREE，低Y和陡稀土配分模式[（La/Lu）n=20-25]的特征。它们具有较低的初始87 Sr/86 Sr（0.70305）和较高的ε Nd值（+2.3 ~+5.0）。这些可能是由俯冲洋壳的高度部分熔融（10-30%）产生的，有或没有一小部分海洋沉积物。阿拉巴杂岩的基性和中间端部成员，阿拉巴基性至中间岩套（SiO2含量48-65%）包括石英闪长岩、石英二长闪长岩、二长闪长岩和二长辉长岩。与Duheila Hornblendic岩套相比，该岩套的基性端元富集LILE，但其原始组成具有相似的REE模式[（La/Lu）n=5-15]，侵位于板内构造环境。地球化学建模支持形成的阿拉巴镁铁质到中间套件的金云母含尖晶石二辉橄榄岩的10%的部分熔融。低的初始87 Sr/86 Sr（0.7035）和高的ε Nd值（+2.4 ~+4.2）支持了这一假设。阿拉巴杂岩的长英质端员Humrat-Feinan岩套（SiO_2 68-80%）具有轻稀土元素（La/Sm）n_（10）~（12），重稀土元素（Gd/Lu）n_（10）~（11），Eu负异常（Eu/Eu_（10）= 0.07 - 0.53）的特征。这些花岗岩具有典型的A型花岗岩的地球化学特征，可由阿拉巴镁铁质至中间岩套的极端分离结晶（> 80%）形成。低初始87 Sr/86 Sr（0.7048）、高ε Nd值（+2.5 ~+4.8）以及与阿拉巴镁铁质岩套的时空联系支持了这一模式。最北端的阿拉伯努比亚地盾的地壳演化发生在东西冈瓦纳大陆碰撞的末期，岩浆来自幔源熔体。这些熔体发生了显着变化，在碰撞的时间，从一个单峰套件的收敛边缘岩浆的特点是深（石榴石控制）分馏，双峰套件的裂谷相关的岩浆的特点是浅（辉长岩控制）分馏。
Approximately 90% of the upper crust exposed in southern Jordan is composed of intrusive rocks of latest Neoproterozoic age, grouped into two major subdivisions: the Aqaba (600–640Ma) and the Araba (560–600Ma) complexes. The Aqaba complex comprises several suites that range in composition from gabbro to high silica granite (45–80% SiO2) and follow a high-K calc-alkaline trend. This phase, which started with the emplacement of the Duheila Hornblendic Suite between 640 and 600Ma, represents the main crust-forming stage in southwest Jordan. The Araba complex is a bimodal alkali-calcic to alkali igneous suite generated after development of a regional unconformity and deposition of the Saramuj Conglomerate. Mafic members of the Aqaba complex, the Duheila Hornblendic Suite, are enriched in LILE relative to the HFSE and are moderately enriched in REE [(La/Lu)n=5–11], traits typical of arc basalts. Geochemical modeling suggests derivation by 10–15% melting of amphibole-bearing spinel lherzolite, possibly above a subduction zone. The granitoids of the Aqaba complex are high in Ba, Sr and LREE, have low Y and have steep REE patterns [(La/Lu)n=20–25]. They have low initial87Sr /86Sr (∼0.70305) and high εNdvalues (+2.3 to +5.0). These may have been generated by high degrees of partial melting (10–30%) of subducted oceanic crust, with or without a small proportion of ocean sediments. The mafic and intermediate end members of the Araba complex, the Araba Mafic to Intermediate Suite (48–65% SiO2) comprises quartz-diorites, quartz-monzodiorites, monzodiorites and monzogabbros. The mafic end member of this suite is enriched in LILE compared to the Duheila Hornblendic Suite, although its primitive compositions have similar REE patterns [(La/Lu)n=5–15]; and has been emplaced in a within-plate tectonic environment. Geochemical modeling supports formation of the Araba Mafic to Intermediate Suite by 10% partial melting of phlogopite-bearing spinel lherzolite. This hypothesis is supported by low initial87Sr /86Sr (∼0.7035) and high εNdvalues (+2.4 to +4.2). The felsic end member of the Araba complex, the Humrat–Feinan Suite (68–80% SiO2), is characterized by moderate enrichments in LREE (La/Sm)n∼2, flat HREE patterns (Gd/Lu)n∼1, and strong negative Eu anomalies (Eu/Eu∗=∼0.07 –0.53). These granites have geochemical features typical of A-type granite and can be derived by extreme fractional crystallization (∼80%) of the Araba Mafic to Intermediate Suite. The low initial87Sr /86Sr (∼0.7048), high εNdvalues (+2.5 to +4.8), and spatial and temporal association with the Araba Mafic Suite support this model. Crustal evolution in the northernmost Arabian Nubian Shield occurred about the time of terminal collision between east and west Gondwanaland by the addition of magmas derived from mantle-derived melts. These melts changed markedly at about the time of collision, from a unimodal suite of convergent margin magmas characterized by deep (garnet-controlled) fractionation, to a bimodal suite of rift-related magmas characterized by shallow (feldspar-controlled) fractionation.