Temporal and spatial variations in magmatism and transpression in a Cretaceous arc, Median Batholith, Fiordland, New Zealand
Temporal and spatial variations in magmatism and transpression in a Cretaceous arc, Median Batholith, Fiordland, New Zealand
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DOI：
10.1130/l1073.1
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发表时间：
2019-10
期刊：
影响因子：
2.4
通讯作者：
Luisa F. Buritica;J. Schwartz;K. Klepeis;E. Miranda;A. Tulloch;M. Coble;A. Kylander‐Clark
中科院分区：
文献类型：
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作者：
Luisa F. Buritica;J. Schwartz;K. Klepeis;E. Miranda;A. Tulloch;M. Coble;A. Kylander‐Clark
我们研究了变形与岩体侵位的相互作用，目的是为了深入了解挤压作用和弧岩浆作用在大陆弧壳形成和改造中的作用。本文利用39个新的激光烧蚀裂流电感耦合等离子体质谱（LASS-ICP-MS）和次级离子质谱（SIMS） 206Pb/238U锆石和钛矿日期，以及来自新西兰中生代中位基下部和中部地壳的钛矿地球化学和温度，来(1)约束分离点组白垩纪弧岩浆活动的时间，(2)记录低应变和高应变变形结构中钛矿生长的时间。(3)将岩石圈尺度的反扭剪切带发育的时空格局与白垩纪弧爆发事件联系起来。锆石结果表明，在峡湾东部和中部的中地壳中，分离点套件的成岩作用持续了约129 ~ 110 Ma。在此期间，变形集中在一个20公里宽的弧形平行变形区，其中包括以前未报道的复杂剪切带的片段，我们称之为Grebe剪切带。在约129 ~ 125 Ma的早期变形中，Grebe剪切带发育浅倾矿物拉伸线理的低应变组构。这些岩石中的钛矿是自面体，通常与弱亚固体结构排列，岩石平均温度在675°C到700°C之间。我们将它们解释为在低应变织物发育之前生长的残余岩浆钛矿。相比之下，约125至116 Ma的变形涉及沿亚垂直糜棱质剪切带的运动，其中有中等至陡峭的矿物拉伸线。这些剪切带中的钛矿是斜面体颗粒/聚集体，排列在糜棱质织物中，岩石平均温度范围为~ 610°C至700°C。这些钛矿最符合角闪岩相变质过程中变形和（或）变质反应的（再）结晶。在造山带尺度上，分离点套件爆发始于中地壳低应变变形时期（约129 ~ 125 Ma），在高应变、跨震变形时期（约125 ~ 116 Ma）达到峰值，此时岩浆弧轴线加宽至70 km以上。我们认为，弧爆发事件期间的挤压变形是连接熔体储存区域和控制中地壳水平岩体分布和几何形状的重要过程。
We investigated the interplay between deformation and pluton emplacement with the goal of providing insights into the role of transpression and arc magmatism in forming and modifying continental arc crust. We present 39 new laser-ablation–split-stream–inductively coupled plasma–mass spectrometry (LASS-ICP-MS) and secondary ion mass spectrometry (SIMS) 206Pb/238U zircon and titanite dates, together with titanite geochemistry and temperatures from the lower and middle crust of the Mesozoic Median Batholith, New Zealand, to (1) constrain the timing of Cretaceous arc magmatism in the Separation Point Suite, (2) document the timing of titanite growth in low- and high-strain deformational fabrics, and (3) link spatial and temporal patterns of lithospheric-scale transpressional shear zone development to the Cretaceous arc flare-up event. Our zircon results reveal that Separation Point Suite plutonism lasted from ca. 129 Ma to ca. 110 Ma in the middle crust of eastern and central Fiordland. Deformation during this time was focused into a 20-km-wide, arc-parallel zone of deformation that includes previously unreported segments of a complex shear zone that we term the Grebe shear zone. Early deformation in the Grebe shear zone involved development of low-strain fabrics with shallowly plunging mineral stretching lineations from ca. 129 to 125 Ma. Titanites in these rocks are euhedral, are generally aligned with weak subsolidus fabrics, and give rock-average temperatures ranging from 675 °C to 700 °C. We interpret them as relict magmatic titanites that grew prior to low-strain fabric development. In contrast, deformation from ca. 125 to 116 Ma involved movement along subvertical, mylonitic shear zones with moderately to steeply plunging mineral stretching lineations. Titanites in these shear zones are anhedral grains/aggregates that are aligned within mylonitic fabrics and have rock-average temperatures ranging from ∼610 °C to 700 °C. These titanites are most consistent with (re)crystallization in response to deformation and/or metamorphic reactions during amphibolite-facies metamorphism. At the orogen scale, spatial and temporal patterns indicate that the Separation Point Suite flare-up commenced during low-strain deformation in the middle crust (ca. 129–125 Ma) and peaked during high-strain, transpressional deformation (ca. 125–116 Ma), during which time the magmatic arc axis widened to 70 km or more. We suggest that transpressional deformation during the arc flare-up event was an important process in linking melt storage regions and controlling the distribution and geometry of plutons at mid-crustal levels.