华北克拉通南缘中-新元古代沉积演化:以豫西地区黄连垛组和董家组为例

华北克拉通(华北)南缘中元古代早期熊耳群火山活动之后,在渑池-确山地区发育了一套中-新元古代沉积(汝阳群、洛峪群、黄连垛组、董家组以及罗圈组和东坡组),记录了该时期沉积-构造演化过程。通过该区碎屑锆石和洛峪群顶部凝灰岩年龄的约束,将汝阳群-洛峪群的沉积时代基本限定于约1750～1600Ma,导致洛峪群由中元古界上部或新元古界下划到中元古界长城系。因此,在现有的地层年代格架下,需要重新对该区中-新元古代沉积演化进行讨论。本文通过对洛峪口组上覆黄连垛组和董家组沉积环境和物源分析,同时借助古生界辛集组源区分析的约束,揭示华北南缘中-新元古代沉积-构造演化。沉积环境分析显示,黄连垛组沉积初期发育了河口湾沉积环境。伴随海侵扩大,在下汤地区沉积了潮上带长石石英砂岩与泥质粉砂岩,而叶县地区发育了潮间带泥晶白云岩。晚期下汤和叶县地区发育潮下带泥晶白云岩与含硅质条带白云岩。董家组与下伏黄连垛组为平行不整合接触,董家组沉积初期为陆源碎屑物质供给充分的滨海相,在下汤和叶县地区沉积底部细砾岩及长石石英砂岩。随后,两个地区发育潮坪相长石石英砂岩与泥质粉砂岩,在顶部沉积了局限台地钙质泥岩。黄连垛组在豫西下汤和叶县地区沉积于河口湾-潮坪沉积环境,整体表现为自南向北的海进序列,而董家组总体上沉积于局限海盆的滨浅海-潮坪环境。由于下伏汝阳群-洛峪群分别沉积在河流-滨海-潮坪和浅海-滨海-潮坪环境,黄连垛组和董家组指示其沉积时期盆地产生收缩。碎屑锆石定年结果显示,黄连垛组和董家组碎屑锆石年龄主要峰值为1800Ma、2250Ma、2350Ma、2650Ma,两者物源均为华北克拉通。但下汤地区早古生界辛集组碎屑锆石显示主要峰值年龄为1850Ma、2500Ma、2200Ma、2700Ma,其次为1200Ma。结合华北克拉通发育大量的中元古代末期到新元古代碎屑锆石以及南缘中元古界官道口群和新元古界栾川群沉积特征,黄连垛组和董家组代表的局限盆地(海盆)沉积可能构成了该时期盆地的边缘相,期间伴随的抬升和盆地中心迁移可能与同期大地构造演化密切相关。

Meso-Neoproterozoic sedimentary evolution of the southern margin of the North China Craton: Evidence from the Huanglianduo and Dongjia formations in the western Henan

The Meso-Neoproterozoic sequences (the Ruyang, Luoyu, Huanglianduo, Dongjia, Luoquan and Dongpo groups/formations) deposited in the Mianchi-Queshan area after the Xiong''er volcanic-sedimentary succession within the southern margin of the North China Craton (NCC) recorded the tectono-sedimentary histories of this region. Based on the new age constrains from detrital and magmatic zircon, the Ruyang and Luoyu groups belong to the Early Mesoproterozoic, i.e., the Changcheng Period (1750~1600Ma). As the Luoyu Group was thought to be deposited in the Late Mesoproterozoic to Neoproterozoic previously, it is necessary to study the Meso-Neoproterozoic sedimentary and tectonic evolution in the southern margin of NCC. The Huanglianduo Formation was deposited in a river estuary in the early stage. Following a transgression from the south to the north, feldspar-quartz sandstones and pelitic siltstones in a supratidal zone deposited in the Xiatang area, and dolomicrites in a intertidal zone occurred in the Yexian area. Siliceous banded dolomites and dolomicrites in a subtidal zone developed in the upper unit within the Xiatang and Yexian areas. The overlying Dongjia Formation consists of sediments in a coastal environment in the bottom unit. Fine-grained conglomerates and feldspar-quartz sandstones developed first in the Xiatang and Yexian areas. Then, feldspar-quartz sandstones and pelitic siltstones in the tidal flat facies, and the calcareous argillites of the restricted platform occurred in the upper unit of the Dongjia Formation. Therefore,the Huanglianduo Formation include the river estuary and tidal flat environments in the Xiatang area and tidal flat facies in the Yexian area, respectively. The Dongjia Formation was deposited in the littoral and tidal flat facies within a restricted marine basin as a whole. Comparing with the underlying sediments developed in the fluvial-coastal-tide flat facies (Ruyang Group) and littoral to tidal flat facies(Luoyu Group), both Huanglianduo and Dongjia formations show that restricted marine basin sequences occurred in the southern margin of NCC. Evident depositional breaks and strong depocenter migration (from Mianchi-Queshan and Songji area to Lushi-Luanchuan area) developed in the Late Mesoproterozoic. Detrital zircons were taken from the Huanglianduo, Dongjia and the Early Paleozoic Xinji formations within the NCC to track the changes in their provenances. The analyzed detrital zircon grains from the Huanglianduo and Dongjia formations display four dominant age peaks at ca. 1800Ma, 2250Ma, 2350Ma and 2650Ma, respectively, which suggest that their provenances were derived from the NCC. However, four major age peaks at ca. 1850Ma, 2200Ma, 2500Ma and 2700Ma, and one minor peak at ca. 1200Ma are found in detrital zircon ages of the Xinji Formation. In combination with the Mesoproterozoic Guandaokou and Neoproterozoic Luanchuan sequences and the widely occurred detrital zircon ages from the Late Mesoproterozoic to Neoproterozoic, the Huanglianduo and Dongjia formations could be deoposited in the basin margin. It is likely that the changes in the sedimentary environments and sources of the Huanglianduo, Dongjia formations and the overlying depositions, accompanied with the migration of the depocenter of the sedimentary basin and the uplifts of the basement, are related to the tectonic evolution during the Late Mesoproterozoic to Neoproterozoic.