此外，由沿剖面變化甚小之 RSCM 峰值變質溫度，顯示退變質掘升過程中晚期正斷層構造變形廣泛但錯距不顯著。西部脊樑山脈板岩帶可見向西脫離底部加積區域導致的約 70 °C 之RSCM 峰值變質溫度連續遞減，遞減過程小幅溫度波動可能受控於底部加積作用推覆體疊加。並且，主要觀察到之兩期以上主葉理面皆形成於達最大構造深埋峰值變質之前。
綜合以上結果並結合前人低溫熱年代學數據，本研究推論本研究區岩石約於 5 Ma 達到最大構造深埋，並建構脊樑山脈南段由南海隱沒與弧陸碰撞造山至今之構造運動學演化歷史，最終進一步探討整個脊樑山脈之變質基盤與沉積蓋層構造邊界關係南北向空間演化。;The Taiwan Backbone Range is primarily composed of the pre-Tertiary metamorphic basement (Tailuko Belt) and its overlying Miocene sedimentary cover (Backbone Range Slate Belt). Together， these two tectonic units subducted into the Manila Trench along with the South China Sea oceanic crust and experienced regional metamorphism driven by the arc-continent oblique collision during the Penglai Orogeny.
In order to delve into the spatial evolution of the tectonic boundary between these two structural units from south to north along the strike of the Backbone Range， this study focuses on a key structural transition zone named the Sandimen-Zhiben transect in the southern Backbone Range， which is located in the transition zone from the initial to the mature stage of arc-continent collision. Combining the field geological surveys， microscopic observations and the quantitative constraints from 36 peak metamorphic temperature measurements with high resolution obtained through Raman spectroscopy of carbonaceous material (RSCM) at a roughly kilometer spacing along the transect， this research conducts the discussion below.
The RSCM peak metamorphic temperatures in the core regions of the study area are significantly lower by approximately 150°C compared to those in the core regions of the Southern and Central Cross-Island Highway transects to the north. Based on lithological variations and the nearly constant peak temperatures along the transect， this area exhibits structural stacking and deep burial metamorphism driven by basal accretion during the early stages of collision. Furthermore， the metamorphic basement and sedimentary cover are not separated by a single， distinct boundary. Instead， the newly exhuming basement and the overlying sedimentary cover appear alternately in their exposure， a pattern that is strongly controlled by significant topographic relief and other factors.
Moreover， the relatively flat RSCM peak temperature profile along the transect indicates that late-stage normal faulting during retrograde exhumation was widespread but with insignificant displacement. In the western BRSB， a continuous westward decrease in RSCM peak temperatures of approximately 70°C is observed， resulting from the increasing distance from the main basal accretion zone. The minor fluctuations during the decrease of temperatures are attributed to the nappe stacking caused by basal accretion. Additionally， the two or more generations of main foliations were entirely formed prior to reaching maximum structural burial and subsequent peak metamorphism.
By integrating the results above along with previously published low-temperature thermochronological data， this study proposes that rocks in the study area reached their maximum structural burial at approximately 5 Ma， and establishes a kinematic and tectonic evolution model for the southern Backbone Range spanning from the South China Sea subduction and arc-continent collision to the present. Ultimately， this study further explores the spatial evolution of the tectonic boundary between the metamorphic basement and sedimentary cover along the entire north-south extent of the Backbone Range.
