Generation of a potassic to ultrapotassic alkaline complex in a syn-collisional setting through flat subduction: Constraints on magma sources and processes (Otjimbingwe alkaline complex, Damara orogen, Namibia)
Generation of a potassic to ultrapotassic alkaline complex in a syn-collisional setting through flat subduction: Constraints on magma sources and processes (Otjimbingwe alkaline complex, Damara orogen, Namibia)
复制标题
通过浅俯冲在同碰撞环境中生成钾至超钾碱性络合物：对岩浆来源和过程的限制（奥金宾韦碱性络合物，达马拉造山带，纳米比亚）
DOI：
10.1016/j.gr.2020.01.004
复制
发表时间：
2020
影响因子：
6.1
通讯作者：
Berndt
中科院分区：
文献类型：
--
作者：
Berndt
约545 Ma的同碰撞期Otjimbingwe碱性杂岩体由含辉石-角闪石-黑云母、中性霞石规范-石英规范的岩石组成，岩石成分从二长辉长岩到二长岩、正长岩和花岗岩。碱性岩石具有中等到高的SiO2（50.5-73.0重量%）和Na 2 O + K2 O（5.1-11.5重量%）以及中等到低的MgO（6.6-0.2重量%）浓度。所有样品都具有高的大离子亲石元素（LILE：Ba高达4600 ppm）和高场强元素含量（HFSE：Zr：155-1328 ppm; Nb：16-110 ppm; Ta：1.4-7.1 ppm和Hf：4-24 ppm），并具有强烈分馏的LREE模式（（La/Yb）N= 14-51）。最原始的成员缺乏显着的负Eu异常。地幔标准化多元素图解显示Ba、Rb、Nb（Ta）、P和Ti亏损。碱性岩具有中等放射成因的87 Sr/86 Sr比值（0.7061-0.7087）和非放射成因的87 Nd初始值（-3.9至-6.1）。这种同位素的签名，与高LREE/HFSE比值表明，父母的熔体中产生的富集部分的浅岩石圈地幔，这可能是以前的俯冲带过程的影响。此外，Sr和Nd同位素之间的相关性表明，其中一些变化是由地壳同化和分离结晶（AFC）过程相结合。提出了一种新的平面俯冲模式，解释了达马拉造山带造山演化中大部分未解决的问题，即（i）没有具有明显俯冲带背景的早期侵入岩，（ii）没有蓝片岩和榴辉岩等高压岩石，（iii）火成岩的分布不寻常，以花岗岩及花岗闪长岩明显占优势;及（iv）在经典俯冲过程中需要软流圈窗口来解释覆盖板块中的高T/中等P麻粒岩相条件。
The ~545 Ma-old syn-collisional Otjimbingwe alkaline complex is composed of pyroxene-amphibole-biotite-bearing, mildly nepheline-normative to quartz-normative rocks ranging in composition from monzogabbro to monzonite, syenite and granite. The alkaline rocks have moderate to high SiO2(50.5–73.0 wt%) and Na2O + K2O (5.1–11.5 wt%) and moderate to low MgO (6.6–0.2 wt%) concentrations. All samples have high large ion lithophile element (LILE: Ba up to 4600 ppm) and high-field-strength element contents (HFSE; Zr: 155–1328 ppm; Nb: 16–110 ppm; Ta: 1.4–7.1 ppm and Hf: 4–24 ppm) and have strongly fractionated LREE patterns ((La/Yb)N= 14–51). The most primitive members lack significant negative Eu anomalies. Mantle-normalized multi-element diagrams show depletion in Ba, Rb, Nb (Ta), P and Ti. The alkaline rocks have moderate radiogenic initial87Sr/86Sr ratios (0.7061–0.7087) and unradiogenic initial ɛNd values (−3.9 to −6.1). This isotope signature, associated with high LREE/HFSE ratios indicates that the parental melts were generated in enriched portions of the shallow lithospheric mantle, which was probably affected by previous subduction zone processes. In addition, correlations between Sr and Nd isotopes indicate that some of these variations result from combined crustal assimilation and fractional crystallization (AFC) processes. A new model of flat subduction is presented that explains most of the unsolved problems in the orogenic evolution of the Damara orogen, namely (i) the absence of early intrusive rocks with a clear subduction zone setting, (ii) the absence of high-pressure rocks such as blueschists and eclogites, (iii) the unusual distribution of igneous rocks with a clear predominance of granite and granodiorite and (iv) the need for a asthenospheric window during a classical subduction to explain the high T/moderate P granulite facies conditions in the overriding plate.
登录
查看更多内容
高T/低P麻粒岩地体（纳米比亚达马拉带）的变质岩石学——来自伪剖面建模和高精度Lu-Hf石榴石全岩测年的约束
影响因子：
3.4
作者：
Stefan Jung;S. Brandt;R. Bast;E. Scherer;J. Berndt
通讯作者：
J. Berndt
影响因子：
3.5
作者：
L. Schwark;Stefan Jung;F. Hauff;D. Garbe‐Schönberg;J. Berndt
通讯作者：
L. Schwark;Stefan Jung;F. Hauff;D. Garbe‐Schönberg;J. Berndt
影响因子：
3.1
作者：
Whitney, Donna L.;Evans, Bernard W.
通讯作者：
Evans, Bernard W.
幼年镁铁质对中地壳的深熔 – 闪长岩对花岗岩的主量元素和微量元素以及 SR、ND、PB 同位素的约束（纳米比亚达马拉造山带）
DOI：
--
发表时间：
2014
期刊：
影响因子：
--
作者：
Stefan Jung;J. Berndt;A. Stracke;F. Hauff;N. Kastek
通讯作者：
N. Kastek
达马拉带（纳米比亚）与剪切带相关的正长岩：地壳污染和来源成分的作用
影响因子：
3.5
作者：
Stefan Jung;K. Mezger;S. Hoernes
通讯作者：
S. Hoernes