Detrital zircon ages in Buller and Takaka terranes, New Zealand: constraints on early Zealandia history

Detrital zircon ages are presented for 34 early Palaeozoic sandstones from Buller and Takaka terranes, New Zealand, and formerly adjacent parts of Australia–Antarctica. The Buller–Takaka datasets always have two major groups: Ordovician–late Neoproterozoic, 444–700 Ma (but mainly 540–700 Ma), termed ‘Gondwana Assembly’ (GA), and early Neoproterozoic–Mesoproterozoic, 700–1600 Ma (but mainly 900–1200 Ma), termed ‘Rodinia Assembly’ (RA). In both terranes, significant age components within these groups are strikingly similar and also have RA/GA ratios, 0.6–1.8. The Cambrian volcanic arc of the Takaka Terrane has contributed little to the zircon patterns. Proportions of Late Cambrian–Early Ordovician zircons, characteristic of granitoid sources in the Ross–Delamerian Orogen are low. The zircons are predominantly reworked with contemporary zircons only evident in a few Buller datasets. The zircon patterns suggest that two major sources (late Mesoproterozoic and late Neoproterozoic), enduring over 120 Ma, were widely distributed and it is postulated they form Precambrian basement beneath southern Zealandia.

本文报道了新西兰布尔尔（Buller）地体与塔卡卡（Takaka）地体，以及曾与之毗邻的澳大利亚-南极洲区域的34件早古生代砂岩的碎屑锆石年龄数据。布尔尔-塔卡卡数据集始终包含两大主要锆石年龄组：其一为奥陶纪-新元古代晚期（444~700 Ma，主体集中于540~700 Ma），命名为冈瓦纳拼合体（Gondwana Assembly, GA）；其二为新元古代早期-中元古代（700~1600 Ma，主体集中于900~1200 Ma），命名为罗迪尼亚拼合体（Rodinia Assembly, RA）。两个地体的上述年龄组内的显著年龄组分极为相似，且二者的RA/GA比值介于0.6~1.8之间。塔卡卡地体的寒武纪火山弧对锆石谱系的贡献甚微，具有罗斯-德拉梅里亚造山带花岗岩质源区特征的晚寒武世-早奥陶世锆石占比偏低。绝大多数锆石均为再循环锆石，仅在少量布尔尔地体的数据集样本中可见同世代锆石。锆石谱系表明，两大持续时长超120 Ma的主要物源区（中元古代晚期与新元古代晚期）分布广泛，据此推测二者构成了西兰大陆南部下方的前寒武纪基底。